Bootstrapping a Tube...

On a sunny day (Sun, 25 Sep 2022 13:45:38 -0700) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<u1f1jh5qhhu1nkhuf672fhktf90q97vi9g@4ax.com>:

An R-L-C goes to unity gain at low frequencies, which suggests Q=1 by
the simple voltage multiplier formula, for any R.

Or Q goes to zero if the L is the grounded part.

Q is a crude way to collapse the actual impedances. I use it to select
parts for LC oscillators, where it does correlate to spectral purity
and jitter.
Click to expand...

I have used parallel resistors in about 30 MHz circuits (TV IF etc) to reduce Q and
increase bandwidth.

As Q is also w.L / R there is room to play and think about things.
Staggered tuning is an other way to increase bandwidth, bandfilters is an interesting playground.
For an LC I keep C at 220 pF between about .5 MHz and 50 MHz.
For lower frequencies bigger C, for higher smaller.
Always works
Remember old AM radios with 500 pF tuning capacitors?
Those often had longwave and shortwave too.
For FM radio, about 100 MHz, there was a separate section on the tuning capacitor with less capacitance,
For TV UHF tuners even smaller tuning capacitors and some sort of cavities with striplines.

Designed and build all that myself...
becomes sort of a second nature, even TV IF, color circuits, etc.


Coaxial ceramic resonators get into the thousands, 10\'s of thousands
sometimes, but are not well suited to my oscillators; equivalent
txline impedances are too low.
Click to expand...

Crystal filters is an other interesting thing , 9 MHz SSB crystal filters were common in projects.
in the sixties....
Nowadays with software defined radio.... RTL-SDR sticks...
world has changed, in a way got simpler (if you can code)
But when nukes hit and no more chips for whatever reason, that old knowledge can become very handy to sent and receive SOS
or \'we are still alive here\'.

Good old RSGB Ham radio handbook from the sixties recommended!

The guy is working with tubes after all!

But a reality check on precision in Q measurements is indeed a good idea
Anything 10% or less is probably good,
 
On 9/25/2022 10:49 PM, John Larkin wrote:
On Sun, 25 Sep 2022 21:37:54 -0500, amdx <amdx@knology.net> wrote:

On 9/25/2022 3:22 PM, John Larkin wrote:
On Fri, 23 Sep 2022 18:33:05 -0500, amdx <amdx@knology.net> wrote:

 On one of the groups I monitor, it was ask if the tube circuit shown
below could be bootstrapped to raise the input impedance,
especially at the higher frequencies where it drops pretty low. (purpose
is to reduce loading on the LC being measured--Q meter)
 Can you give a little detail on how you would implement it? And what
happens to gain and frequency response?
When was bootstrapping introduced, the word started in the 1880s, but
when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it didn\'t use a
100M? grid resistor, Is that a detriment to adding bootstrapping?
 I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100M?, does
bootstrapping help that?
 Might be barking up the wrong tree.

https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0


                            Thanks, Mikek
Here\'s a High-Q resonator we created at lunch today:

https://www.dropbox.com/s/eeocp4rvgaz2dis/Hi-Q_resonator.MOV?dl=0

entirely by accident. There may be a gain mechanism involved.

Air currents from the fan sloshing around in the bowl adding gain?

I had comments on another group about bootstrapping the tube.

\"The V301 valve in the Boonton Q meter is NOT a cathode follower
but an \" infinite impedance detector\" due to the capacitor C302.
So you cannot bootstrap at AC.\"

 That\'s beyond my level.
The triode is acting like a rectifier into C201 so it can drive a DC
meter.

But a little grid capacitance can be, probably already is, calibrated
out of the circuit.

A triode grid has a resistive component that reduces Q a bit. I don\'t
know the magnitude of that.
Click to expand...
 Here\'s the graph of how the input resistance drops from almost 100MΩ
at 50kHz to 57kΩ at 50MHz.
> https://www.dropbox.com/s/5wc0htizojcp4xu/Boonton%20Input%20impedance%20vs%20Frequency.jpg?dl=0

                                      Mikek
 
On Mon, 26 Sep 2022 06:24:15 -0500, amdx <amdx@knology.net> wrote:

On 9/25/2022 10:49 PM, John Larkin wrote:
On Sun, 25 Sep 2022 21:37:54 -0500, amdx <amdx@knology.net> wrote:

On 9/25/2022 3:22 PM, John Larkin wrote:
On Fri, 23 Sep 2022 18:33:05 -0500, amdx <amdx@knology.net> wrote:

 On one of the groups I monitor, it was ask if the tube circuit shown
below could be bootstrapped to raise the input impedance,
especially at the higher frequencies where it drops pretty low. (purpose
is to reduce loading on the LC being measured--Q meter)
 Can you give a little detail on how you would implement it? And what
happens to gain and frequency response?
When was bootstrapping introduced, the word started in the 1880s, but
when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it didn\'t use a
100M? grid resistor, Is that a detriment to adding bootstrapping?
 I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100M?, does
bootstrapping help that?
 Might be barking up the wrong tree.

https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0


                            Thanks, Mikek
Here\'s a High-Q resonator we created at lunch today:

https://www.dropbox.com/s/eeocp4rvgaz2dis/Hi-Q_resonator.MOV?dl=0

entirely by accident. There may be a gain mechanism involved.

Air currents from the fan sloshing around in the bowl adding gain?

I had comments on another group about bootstrapping the tube.

\"The V301 valve in the Boonton Q meter is NOT a cathode follower
but an \" infinite impedance detector\" due to the capacitor C302.
So you cannot bootstrap at AC.\"

 That\'s beyond my level.
The triode is acting like a rectifier into C201 so it can drive a DC
meter.

But a little grid capacitance can be, probably already is, calibrated
out of the circuit.

A triode grid has a resistive component that reduces Q a bit. I don\'t
know the magnitude of that.

 Here\'s the graph of how the input resistance drops from almost 100M?
at 50kHz to 57k? at 50MHz.
https://www.dropbox.com/s/5wc0htizojcp4xu/Boonton%20Input%20impedance%20vs%20Frequency.jpg?dl=0

                                      Mikek
Click to expand...

The 260A design was early 1950s. Big parts, hand wired, lots of
switches, lots of skin loss.
 
On Monday, September 26, 2022 at 7:24:26 AM UTC-4, amdx wrote:
On 9/25/2022 10:49 PM, John Larkin wrote:
On Sun, 25 Sep 2022 21:37:54 -0500, amdx <am...@knology.net> wrote:

On 9/25/2022 3:22 PM, John Larkin wrote:
On Fri, 23 Sep 2022 18:33:05 -0500, amdx <am...@knology.net> wrote:

On one of the groups I monitor, it was ask if the tube circuit shown
below could be bootstrapped to raise the input impedance,
especially at the higher frequencies where it drops pretty low. (purpose
is to reduce loading on the LC being measured--Q meter)
Can you give a little detail on how you would implement it? And what
happens to gain and frequency response?
When was bootstrapping introduced, the word started in the 1880s, but
when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it didn\'t use a
100M? grid resistor, Is that a detriment to adding bootstrapping?
I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100M?, does
bootstrapping help that?
Might be barking up the wrong tree.

https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0


Thanks, Mikek
Here\'s a High-Q resonator we created at lunch today:

https://www.dropbox.com/s/eeocp4rvgaz2dis/Hi-Q_resonator.MOV?dl=0

entirely by accident. There may be a gain mechanism involved.

Air currents from the fan sloshing around in the bowl adding gain?

I had comments on another group about bootstrapping the tube.

\"The V301 valve in the Boonton Q meter is NOT a cathode follower
but an \" infinite impedance detector\" due to the capacitor C302.
So you cannot bootstrap at AC.\"

That\'s beyond my level.
The triode is acting like a rectifier into C201 so it can drive a DC
meter.

But a little grid capacitance can be, probably already is, calibrated
out of the circuit.

A triode grid has a resistive component that reduces Q a bit. I don\'t
know the magnitude of that.

Here\'s the graph of how the input resistance drops from almost 100MΩ
at 50kHz to 57kΩ at 50MHz.
https://www.dropbox.com/s/5wc0htizojcp4xu/Boonton%20Input%20impedance%20vs%20Frequency.jpg?dl=0

Mikek
Click to expand...

Don\'t you think C201A and C201B have something to do with that?

How are they adjusted? Is this like the trim capacitance in a scope probe? But it is in the wrong place.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209
 
On 26/09/2022 19:47, Ricky wrote:
On Monday, September 26, 2022 at 7:24:26 AM UTC-4, amdx wrote:
On 9/25/2022 10:49 PM, John Larkin wrote:
On Sun, 25 Sep 2022 21:37:54 -0500, amdx <am...@knology.net> wrote:

On 9/25/2022 3:22 PM, John Larkin wrote:
On Fri, 23 Sep 2022 18:33:05 -0500, amdx <am...@knology.net> wrote:

On one of the groups I monitor, it was ask if the tube circuit shown
below could be bootstrapped to raise the input impedance,
especially at the higher frequencies where it drops pretty low. (purpose
is to reduce loading on the LC being measured--Q meter)
Can you give a little detail on how you would implement it? And what
happens to gain and frequency response?
When was bootstrapping introduced, the word started in the 1880s, but
when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it didn\'t use a
100M? grid resistor, Is that a detriment to adding bootstrapping?
I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100M?, does
bootstrapping help that?
Might be barking up the wrong tree.

https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0


Thanks, Mikek
Here\'s a High-Q resonator we created at lunch today:

https://www.dropbox.com/s/eeocp4rvgaz2dis/Hi-Q_resonator.MOV?dl=0

entirely by accident. There may be a gain mechanism involved.

Air currents from the fan sloshing around in the bowl adding gain?

I had comments on another group about bootstrapping the tube.

\"The V301 valve in the Boonton Q meter is NOT a cathode follower
but an \" infinite impedance detector\" due to the capacitor C302.
So you cannot bootstrap at AC.\"

That\'s beyond my level.
The triode is acting like a rectifier into C201 so it can drive a DC
meter.

But a little grid capacitance can be, probably already is, calibrated
out of the circuit.

A triode grid has a resistive component that reduces Q a bit. I don\'t
know the magnitude of that.

Here\'s the graph of how the input resistance drops from almost 100MΩ
at 50kHz to 57kΩ at 50MHz.
https://www.dropbox.com/s/5wc0htizojcp4xu/Boonton%20Input%20impedance%20vs%20Frequency.jpg?dl=0

Mikek

Don\'t you think C201A and C201B have something to do with that?

How are they adjusted? Is this like the trim capacitance in a scope probe? But it is in the wrong place.
Click to expand...

C201 is part of the resonant tuned circuit, they will be big solid parts
(probably silver plated) with very low loss and high Q. The drop of
input impedance is due to the tube transit delay as discussed up thread.

57kohm loading at 50MHz is amazingly good for 70 years ago and pretty
respectable still.

piglet
 
On 24/09/2022 13:44, amdx wrote:
On 9/24/2022 6:47 AM, piglet wrote:
On 24/09/2022 11:58, amdx wrote:
On 9/24/2022 1:11 AM, piglet wrote:
On 24/09/2022 00:33, amdx wrote:
  On one of the groups I monitor, it was ask if the tube circuit
shown below could be bootstrapped to raise the input impedance,
especially at the higher frequencies where it drops pretty low.
(purpose is to reduce loading on the LC being measured--Q meter)
  Can you give a little detail on how you would implement it? And
what happens to gain and frequency response?
When was bootstrapping introduced, the word started in the 1880s,
but when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it didn\'t use
a 100MΩ grid resistor, Is that a detriment to adding bootstrapping?
  I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100MΩ, does
bootstrapping help that?
  Might be barking up the wrong tree.

 
https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0



                             Thanks, Mikek


Did you see the value of C302? I think V301 is being used in the so
called \"infinite impedance\" detector configuration. The cathode
voltage is not the buffered grid ac input but instead is a dc level
representing something between the peak and average ac input. So AC
bootstrapping that circuit not possible. I guess you could insert a
whole new hi-z buffer between tuned circuit under test and detector
but in practice it would be difficult to get it to be an improvement?

piglet


  I thought I\'d seen it referred to as an \"infinite impedance
detector\", but don\'t find it in the manual.
I do see this line in the manual and don\'t understand how transit
time loss in the voltmeter
tube causes a shunt resistance across the measuring circuit at High
Frequencies.
Can someone provide a simple explanation?

\"QVOLTMETERCONDUCTANCE.
Anotherinternalparameterwhich causestheindi-
catedQtodeviatefromeffectiveQ,atbothvery low
andveryhighfrequencies, is theinputconductanceof
theQvoltmeter circuit.Atvery low frequenciesthis
conductance consistsofa 100megohmgridleak resistor
inparallelwiththeinternallossesofthevacuum tube.
Atveryhighfrequenciesthetransittime lossinthevolt-
metertubeshuntstheresonatingcapacitorandintro-
duces ashuntresistance acrossthemeasuring circuit\"

Someone has developed a single fet circuit that does an OK job.
I always wanted to try this circuit,
https://www.dropbox.com/s/wvwkw2iapf4ufd7/High%20impedance%20input.jpg?dl=0

  But have not got to it yet, to much computer time and not enough
bench time.
                                       Mikek




The transit time part comes into it like this: due to the electron
travel time there is a short delay before grid voltage changes during
the positive peaks get to influence the cathode voltage. At very high
frequencies this increased loading at the peaks gets more significant.

The 535A tube is quite large and looks like it was built for low
inter-electrode capacity and low leakage. For VHF use a smaller tube
like an acorn device may have had shorter delay times.

Looks to me like that bootstrap all nodes fet buffer came straight out
of a late 1960s-early 70s NatSemi app note.

piglet

  Yes, it did, but, the question is will it work in place of the tube?
                                             Thanks, Mikek
Click to expand...

The touted capacitance of the bootstrapped fet is 0.25pF which at 50MHz
is reactance of 13kohm. If it were a good capacitance you could resonate
it away but it probably is very lossy and a lousy \"capacitor\" so that
fet buffer could be worse than just leaving the Boonton alone. Since
your main interest is around 1.5MHz you perhaps needn\'t worry a lot
about behavior at 50MHz?

piglet
 
On Tue, 27 Sep 2022 06:49:46 +0100, piglet <erichpwagner@hotmail.com>
wrote:

On 26/09/2022 19:47, Ricky wrote:
On Monday, September 26, 2022 at 7:24:26 AM UTC-4, amdx wrote:
On 9/25/2022 10:49 PM, John Larkin wrote:
On Sun, 25 Sep 2022 21:37:54 -0500, amdx <am...@knology.net> wrote:

On 9/25/2022 3:22 PM, John Larkin wrote:
On Fri, 23 Sep 2022 18:33:05 -0500, amdx <am...@knology.net> wrote:

On one of the groups I monitor, it was ask if the tube circuit shown
below could be bootstrapped to raise the input impedance,
especially at the higher frequencies where it drops pretty low. (purpose
is to reduce loading on the LC being measured--Q meter)
Can you give a little detail on how you would implement it? And what
happens to gain and frequency response?
When was bootstrapping introduced, the word started in the 1880s, but
when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it didn\'t use a
100M? grid resistor, Is that a detriment to adding bootstrapping?
I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100M?, does
bootstrapping help that?
Might be barking up the wrong tree.

https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0


Thanks, Mikek
Here\'s a High-Q resonator we created at lunch today:

https://www.dropbox.com/s/eeocp4rvgaz2dis/Hi-Q_resonator.MOV?dl=0

entirely by accident. There may be a gain mechanism involved.

Air currents from the fan sloshing around in the bowl adding gain?

I had comments on another group about bootstrapping the tube.

\"The V301 valve in the Boonton Q meter is NOT a cathode follower
but an \" infinite impedance detector\" due to the capacitor C302.
So you cannot bootstrap at AC.\"

That\'s beyond my level.
The triode is acting like a rectifier into C201 so it can drive a DC
meter.

But a little grid capacitance can be, probably already is, calibrated
out of the circuit.

A triode grid has a resistive component that reduces Q a bit. I don\'t
know the magnitude of that.

Here\'s the graph of how the input resistance drops from almost 100M?
at 50kHz to 57k? at 50MHz.
https://www.dropbox.com/s/5wc0htizojcp4xu/Boonton%20Input%20impedance%20vs%20Frequency.jpg?dl=0

Mikek

Don\'t you think C201A and C201B have something to do with that?

How are they adjusted? Is this like the trim capacitance in a scope probe? But it is in the wrong place.


C201 is part of the resonant tuned circuit, they will be big solid parts
(probably silver plated) with very low loss and high Q. The drop of
input impedance is due to the tube transit delay as discussed up thread.
Click to expand...

Most of the cycle, especially at high Q, the tube is in cutoff, so
there is no transit delay.

The tube likely has a minor effect on Q measurement.
 
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

All the usual definitions of Q and resonant frequency give the same
results at high Q, but not at low Q. You have to pay attention for Q <~
10.

Cheers

Phil Hobbs
Click to expand...

Q < 4

Radiotron Designer\'s Handbook
Chapter 9 Tuned Circuits
SECTION 2: DAMPED OSCILLATIONS

https://tinyurl.com/mvkhesey




--
MRM
 
On 9/26/2022 1:47 PM, Ricky wrote:
On Monday, September 26, 2022 at 7:24:26 AM UTC-4, amdx wrote:
On 9/25/2022 10:49 PM, John Larkin wrote:
On Sun, 25 Sep 2022 21:37:54 -0500, amdx <am...@knology.net> wrote:

On 9/25/2022 3:22 PM, John Larkin wrote:
On Fri, 23 Sep 2022 18:33:05 -0500, amdx <am...@knology.net> wrote:

On one of the groups I monitor, it was ask if the tube circuit shown
below could be bootstrapped to raise the input impedance,
especially at the higher frequencies where it drops pretty low. (purpose
is to reduce loading on the LC being measured--Q meter)
Can you give a little detail on how you would implement it? And what
happens to gain and frequency response?
When was bootstrapping introduced, the word started in the 1880s, but
when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it didn\'t use a
100M? grid resistor, Is that a detriment to adding bootstrapping?
I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100M?, does
bootstrapping help that?
Might be barking up the wrong tree.

https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0


Thanks, Mikek
Here\'s a High-Q resonator we created at lunch today:

https://www.dropbox.com/s/eeocp4rvgaz2dis/Hi-Q_resonator.MOV?dl=0

entirely by accident. There may be a gain mechanism involved.

Air currents from the fan sloshing around in the bowl adding gain?

I had comments on another group about bootstrapping the tube.

\"The V301 valve in the Boonton Q meter is NOT a cathode follower
but an \" infinite impedance detector\" due to the capacitor C302.
So you cannot bootstrap at AC.\"

That\'s beyond my level.
The triode is acting like a rectifier into C201 so it can drive a DC
meter.

But a little grid capacitance can be, probably already is, calibrated
out of the circuit.

A triode grid has a resistive component that reduces Q a bit. I don\'t
know the magnitude of that.

Here\'s the graph of how the input resistance drops from almost 100MΩ
at 50kHz to 57kΩ at 50MHz.
https://www.dropbox.com/s/5wc0htizojcp4xu/Boonton%20Input%20impedance%20vs%20Frequency.jpg?dl=0
Mikek
Don\'t you think C201A and C201B have something to do with that?

How are they adjusted? Is this like the trim capacitance in a scope probe? But it is in the wrong place.
Click to expand...
Those are the tuning caps to get resonance. The small one is a vernier
+/- 3pf.
 Yes, I\'m sure they add to the loss resistance, I read once the tuning
capacitor had a Q of 20,000, but no mention of
at what frequency or capacitance setting, so may have been the maximum.
                                Mikek
 
On 9/27/2022 3:59 AM, piglet wrote:
On 24/09/2022 13:44, amdx wrote:
On 9/24/2022 6:47 AM, piglet wrote:
On 24/09/2022 11:58, amdx wrote:
On 9/24/2022 1:11 AM, piglet wrote:
On 24/09/2022 00:33, amdx wrote:
  On one of the groups I monitor, it was ask if the tube circuit
shown below could be bootstrapped to raise the input impedance,
especially at the higher frequencies where it drops pretty low.
(purpose is to reduce loading on the LC being measured--Q meter)
  Can you give a little detail on how you would implement it? And
what happens to gain and frequency response?
When was bootstrapping introduced, the word started in the 1880s,
but when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it didn\'t
use a 100MΩ grid resistor, Is that a detriment to adding
bootstrapping?
  I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100MΩ, does
bootstrapping help that?
  Might be barking up the wrong tree.

 
https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0



                             Thanks, Mikek


Did you see the value of C302? I think V301 is being used in the
so called \"infinite impedance\" detector configuration. The cathode
voltage is not the buffered grid ac input but instead is a dc
level representing something between the peak and average ac
input. So AC bootstrapping that circuit not possible. I guess you
could insert a whole new hi-z buffer between tuned circuit under
test and detector but in practice it would be difficult to get it
to be an improvement?

piglet


  I thought I\'d seen it referred to as an \"infinite impedance
detector\", but don\'t find it in the manual.
I do see this line in the manual and don\'t understand how transit
time loss in the voltmeter
tube causes a shunt resistance across the measuring circuit at High
Frequencies.
Can someone provide a simple explanation?

\"QVOLTMETERCONDUCTANCE.
Anotherinternalparameterwhich causestheindi-
catedQtodeviatefromeffectiveQ,atbothvery low
andveryhighfrequencies, is theinputconductanceof
theQvoltmeter circuit.Atvery low frequenciesthis
conductance consistsofa 100megohmgridleak resistor
inparallelwiththeinternallossesofthevacuum tube.
Atveryhighfrequenciesthetransittime lossinthevolt-
metertubeshuntstheresonatingcapacitorandintro-
duces ashuntresistance acrossthemeasuring circuit\"

Someone has developed a single fet circuit that does an OK job.
I always wanted to try this circuit,
https://www.dropbox.com/s/wvwkw2iapf4ufd7/High%20impedance%20input.jpg?dl=0

  But have not got to it yet, to much computer time and not enough
bench time.
                                       Mikek




The transit time part comes into it like this: due to the electron
travel time there is a short delay before grid voltage changes
during the positive peaks get to influence the cathode voltage. At
very high frequencies this increased loading at the peaks gets more
significant.

The 535A tube is quite large and looks like it was built for low
inter-electrode capacity and low leakage. For VHF use a smaller tube
like an acorn device may have had shorter delay times.

Looks to me like that bootstrap all nodes fet buffer came straight
out of a late 1960s-early 70s NatSemi app note.

piglet

   Yes, it did, but, the question is will it work in place of the tube?
                                              Thanks, Mikek

The touted capacitance of the bootstrapped fet is 0.25pF which at
50MHz is reactance of 13kohm.
Click to expand...

 I would think any capacitance just adds to the resonating capacitance,
so just need to calculate in the loss of the capacitance, not the
capacitance.

Since your main interest is around 1.5MHz you perhaps needn\'t worry a
lot about behavior at 50MHz?
Click to expand...

 That is very true, but as the much maligned John Larkin said, \"this is
a discussion group\" so, I\'m having the topic discussed!

Mikek
 
On 27/09/2022 17:07, John Larkin wrote:
On Tue, 27 Sep 2022 06:49:46 +0100, piglet <erichpwagner@hotmail.com
wrote:

On 26/09/2022 19:47, Ricky wrote:
On Monday, September 26, 2022 at 7:24:26 AM UTC-4, amdx wrote:
On 9/25/2022 10:49 PM, John Larkin wrote:
On Sun, 25 Sep 2022 21:37:54 -0500, amdx <am...@knology.net> wrote:

On 9/25/2022 3:22 PM, John Larkin wrote:
On Fri, 23 Sep 2022 18:33:05 -0500, amdx <am...@knology.net> wrote:

On one of the groups I monitor, it was ask if the tube circuit shown
below could be bootstrapped to raise the input impedance,
especially at the higher frequencies where it drops pretty low. (purpose
is to reduce loading on the LC being measured--Q meter)
Can you give a little detail on how you would implement it? And what
happens to gain and frequency response?
When was bootstrapping introduced, the word started in the 1880s, but
when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it didn\'t use a
100M? grid resistor, Is that a detriment to adding bootstrapping?
I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100M?, does
bootstrapping help that?
Might be barking up the wrong tree.

https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0


Thanks, Mikek
Here\'s a High-Q resonator we created at lunch today:

https://www.dropbox.com/s/eeocp4rvgaz2dis/Hi-Q_resonator.MOV?dl=0

entirely by accident. There may be a gain mechanism involved.

Air currents from the fan sloshing around in the bowl adding gain?

I had comments on another group about bootstrapping the tube.

\"The V301 valve in the Boonton Q meter is NOT a cathode follower
but an \" infinite impedance detector\" due to the capacitor C302.
So you cannot bootstrap at AC.\"

That\'s beyond my level.
The triode is acting like a rectifier into C201 so it can drive a DC
meter.

But a little grid capacitance can be, probably already is, calibrated
out of the circuit.

A triode grid has a resistive component that reduces Q a bit. I don\'t
know the magnitude of that.

Here\'s the graph of how the input resistance drops from almost 100M?
at 50kHz to 57k? at 50MHz.
https://www.dropbox.com/s/5wc0htizojcp4xu/Boonton%20Input%20impedance%20vs%20Frequency.jpg?dl=0

Mikek

Don\'t you think C201A and C201B have something to do with that?

How are they adjusted? Is this like the trim capacitance in a scope probe? But it is in the wrong place.


C201 is part of the resonant tuned circuit, they will be big solid parts
(probably silver plated) with very low loss and high Q. The drop of
input impedance is due to the tube transit delay as discussed up thread.

Most of the cycle, especially at high Q, the tube is in cutoff, so
there is no transit delay.

The tube likely has a minor effect on Q measurement.
Click to expand...

100% agree!

piglet
 
amdx <amdx@knology.net> wrote:
On 9/27/2022 3:59 AM, piglet wrote:
On 24/09/2022 13:44, amdx wrote:
On 9/24/2022 6:47 AM, piglet wrote:
On 24/09/2022 11:58, amdx wrote:
On 9/24/2022 1:11 AM, piglet wrote:
On 24/09/2022 00:33, amdx wrote:
??On one of the groups I monitor, it was ask if the tube circuit
shown below could be bootstrapped to raise the input impedance,
especially at the higher frequencies where it drops pretty low.
(purpose is to reduce loading on the LC being measured--Q meter)
??Can you give a little detail on how you would implement it? And
what happens to gain and frequency response?
When was bootstrapping introduced, the word started in the 1880s,
but when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it didn\'t
use a 100M? grid resistor, Is that a detriment to adding
bootstrapping?
??I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100M?, does
bootstrapping help that?
??Might be barking up the wrong tree.

?
https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0



???????????????????????????? Thanks, Mikek


Did you see the value of C302? I think V301 is being used in the
so called \"infinite impedance\" detector configuration. The cathode
voltage is not the buffered grid ac input but instead is a dc
level representing something between the peak and average ac
input. So AC bootstrapping that circuit not possible. I guess you
could insert a whole new hi-z buffer between tuned circuit under
test and detector but in practice it would be difficult to get it
to be an improvement?

piglet


??I thought I\'d seen it referred to as an \"infinite impedance
detector\", but don\'t find it in the manual.
I do see this line in the manual and don\'t understand how transit
time loss in the voltmeter
tube causes a shunt resistance across the measuring circuit at High
Frequencies.
Can someone provide a simple explanation?

\"QVOLTMETERCONDUCTANCE.
Anotherinternalparameterwhich causestheindi-
catedQtodeviatefromeffectiveQ,atbothvery low
andveryhighfrequencies, is theinputconductanceof
theQvoltmeter circuit.Atvery low frequenciesthis
conductance consistsofa 100megohmgridleak resistor
inparallelwiththeinternallossesofthevacuum tube.
Atveryhighfrequenciesthetransittime lossinthevolt-
metertubeshuntstheresonatingcapacitorandintro-
duces ashuntresistance acrossthemeasuring circuit\"

Someone has developed a single fet circuit that does an OK job.
I always wanted to try this circuit,
https://www.dropbox.com/s/wvwkw2iapf4ufd7/High%20impedance%20input.jpg?dl=0

??But have not got to it yet, to much computer time and not enough
bench time.
?????????????????????????????????????? Mikek




The transit time part comes into it like this: due to the electron
travel time there is a short delay before grid voltage changes
during the positive peaks get to influence the cathode voltage. At
very high frequencies this increased loading at the peaks gets more
significant.

The 535A tube is quite large and looks like it was built for low
inter-electrode capacity and low leakage. For VHF use a smaller tube
like an acorn device may have had shorter delay times.

Looks to me like that bootstrap all nodes fet buffer came straight
out of a late 1960s-early 70s NatSemi app note.

piglet

?? Yes, it did, but, the question is will it work in place of the tube?
????????????????????????????????????????????? Thanks, Mikek

The touted capacitance of the bootstrapped fet is 0.25pF which at
50MHz is reactance of 13kohm.

?I would think any capacitance just adds to the resonating capacitance,
so just need to calculate in the loss of the capacitance, not the
capacitance.

Since your main interest is around 1.5MHz you perhaps needn\'t worry a
lot about behavior at 50MHz?

?That is very true, but as the much maligned John Larkin said, \"this is
a discussion group\" so, I\'m having the topic discussed!
Click to expand...

The sub-circuit you discuss is just a RF voltmeter. You want low
losses, that is high resistance. Having high resistance on RF side
is tricky and Boonton result looks good. It is not clear if
complicated RF circuit could better. OTOH, since voltages are
high I would try Silicon diode (say 1N4148 at first), with very
small load on rectified side something like 1M or 10M. To measure
this voltage you need a buffer amplifier, something like TL084 have
enough range and presents very small load. So with 10M resitor
load would be 10M + diode leakage + losses due to charge in
junction. 1N4148 has reverse recovery time of 4ns, this may be
better than tube. If 1N4148 works resonably well one could
search for better diodes.

--
Waldek Hebisch
 
On Tue, 27 Sep 2022 12:46:28 -0500, amdx <amdx@knology.net> wrote:

On 9/27/2022 3:59 AM, piglet wrote:
On 24/09/2022 13:44, amdx wrote:
On 9/24/2022 6:47 AM, piglet wrote:
On 24/09/2022 11:58, amdx wrote:
On 9/24/2022 1:11 AM, piglet wrote:
On 24/09/2022 00:33, amdx wrote:
  On one of the groups I monitor, it was ask if the tube circuit
shown below could be bootstrapped to raise the input impedance,
especially at the higher frequencies where it drops pretty low.
(purpose is to reduce loading on the LC being measured--Q meter)
  Can you give a little detail on how you would implement it? And
what happens to gain and frequency response?
When was bootstrapping introduced, the word started in the 1880s,
but when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it didn\'t
use a 100M? grid resistor, Is that a detriment to adding
bootstrapping?
  I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100M?, does
bootstrapping help that?
  Might be barking up the wrong tree.

 
https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0



                             Thanks, Mikek


Did you see the value of C302? I think V301 is being used in the
so called \"infinite impedance\" detector configuration. The cathode
voltage is not the buffered grid ac input but instead is a dc
level representing something between the peak and average ac
input. So AC bootstrapping that circuit not possible. I guess you
could insert a whole new hi-z buffer between tuned circuit under
test and detector but in practice it would be difficult to get it
to be an improvement?

piglet


  I thought I\'d seen it referred to as an \"infinite impedance
detector\", but don\'t find it in the manual.
I do see this line in the manual and don\'t understand how transit
time loss in the voltmeter
tube causes a shunt resistance across the measuring circuit at High
Frequencies.
Can someone provide a simple explanation?

\"QVOLTMETERCONDUCTANCE.
Anotherinternalparameterwhich causestheindi-
catedQtodeviatefromeffectiveQ,atbothvery low
andveryhighfrequencies, is theinputconductanceof
theQvoltmeter circuit.Atvery low frequenciesthis
conductance consistsofa 100megohmgridleak resistor
inparallelwiththeinternallossesofthevacuum tube.
Atveryhighfrequenciesthetransittime lossinthevolt-
metertubeshuntstheresonatingcapacitorandintro-
duces ashuntresistance acrossthemeasuring circuit\"

Someone has developed a single fet circuit that does an OK job.
I always wanted to try this circuit,
https://www.dropbox.com/s/wvwkw2iapf4ufd7/High%20impedance%20input.jpg?dl=0

  But have not got to it yet, to much computer time and not enough
bench time.
                                       Mikek




The transit time part comes into it like this: due to the electron
travel time there is a short delay before grid voltage changes
during the positive peaks get to influence the cathode voltage. At
very high frequencies this increased loading at the peaks gets more
significant.

The 535A tube is quite large and looks like it was built for low
inter-electrode capacity and low leakage. For VHF use a smaller tube
like an acorn device may have had shorter delay times.

Looks to me like that bootstrap all nodes fet buffer came straight
out of a late 1960s-early 70s NatSemi app note.

piglet

   Yes, it did, but, the question is will it work in place of the tube?
                                              Thanks, Mikek

The touted capacitance of the bootstrapped fet is 0.25pF which at
50MHz is reactance of 13kohm.

 I would think any capacitance just adds to the resonating capacitance,
so just need to calculate in the loss of the capacitance, not the
capacitance.

Since your main interest is around 1.5MHz you perhaps needn\'t worry a
lot about behavior at 50MHz?

 That is very true, but as the much maligned John Larkin said, \"this is
a discussion group\" so, I\'m having the topic discussed!

Mikek
Click to expand...

I\'m not maligned by anybody that matters. That\'s by definition.
 
On 9/29/2022 5:42 PM, John Larkin wrote:
On Tue, 27 Sep 2022 12:46:28 -0500, amdx <amdx@knology.net> wrote:

On 9/27/2022 3:59 AM, piglet wrote:
On 24/09/2022 13:44, amdx wrote:
On 9/24/2022 6:47 AM, piglet wrote:
On 24/09/2022 11:58, amdx wrote:
On 9/24/2022 1:11 AM, piglet wrote:
On 24/09/2022 00:33, amdx wrote:
  On one of the groups I monitor, it was ask if the tube circuit
shown below could be bootstrapped to raise the input impedance,
especially at the higher frequencies where it drops pretty low.
(purpose is to reduce loading on the LC being measured--Q meter)
  Can you give a little detail on how you would implement it? And
what happens to gain and frequency response?
When was bootstrapping introduced, the word started in the 1880s,
but when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it didn\'t
use a 100M? grid resistor, Is that a detriment to adding
bootstrapping?
  I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100M?, does
bootstrapping help that?
  Might be barking up the wrong tree.

 
https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0



                             Thanks, Mikek

Did you see the value of C302? I think V301 is being used in the
so called \"infinite impedance\" detector configuration. The cathode
voltage is not the buffered grid ac input but instead is a dc
level representing something between the peak and average ac
input. So AC bootstrapping that circuit not possible. I guess you
could insert a whole new hi-z buffer between tuned circuit under
test and detector but in practice it would be difficult to get it
to be an improvement?

piglet

  I thought I\'d seen it referred to as an \"infinite impedance
detector\", but don\'t find it in the manual.
I do see this line in the manual and don\'t understand how transit
time loss in the voltmeter
tube causes a shunt resistance across the measuring circuit at High
Frequencies.
Can someone provide a simple explanation?

\"QVOLTMETERCONDUCTANCE.
Anotherinternalparameterwhich causestheindi-
catedQtodeviatefromeffectiveQ,atbothvery low
andveryhighfrequencies, is theinputconductanceof
theQvoltmeter circuit.Atvery low frequenciesthis
conductance consistsofa 100megohmgridleak resistor
inparallelwiththeinternallossesofthevacuum tube.
Atveryhighfrequenciesthetransittime lossinthevolt-
metertubeshuntstheresonatingcapacitorandintro-
duces ashuntresistance acrossthemeasuring circuit\"

Someone has developed a single fet circuit that does an OK job.
I always wanted to try this circuit,
https://www.dropbox.com/s/wvwkw2iapf4ufd7/High%20impedance%20input.jpg?dl=0

  But have not got to it yet, to much computer time and not enough
bench time.
                                       Mikek



The transit time part comes into it like this: due to the electron
travel time there is a short delay before grid voltage changes
during the positive peaks get to influence the cathode voltage. At
very high frequencies this increased loading at the peaks gets more
significant.

The 535A tube is quite large and looks like it was built for low
inter-electrode capacity and low leakage. For VHF use a smaller tube
like an acorn device may have had shorter delay times.

Looks to me like that bootstrap all nodes fet buffer came straight
out of a late 1960s-early 70s NatSemi app note.

piglet

   Yes, it did, but, the question is will it work in place of the tube?
                                              Thanks, Mikek
The touted capacitance of the bootstrapped fet is 0.25pF which at
50MHz is reactance of 13kohm.
 I would think any capacitance just adds to the resonating capacitance,
so just need to calculate in the loss of the capacitance, not the
capacitance.

Since your main interest is around 1.5MHz you perhaps needn\'t worry a
lot about behavior at 50MHz?
 That is very true, but as the much maligned John Larkin said, \"this is
a discussion group\" so, I\'m having the topic discussed!

Mikek
I\'m not maligned by anybody that matters. That\'s by definition.

 Agreed and, I looked it up before I used it, I thought it fit well.
Click to expand...

\"If you describe someone or something as much-maligned,
you mean that *they are often criticized by people,
but you think the criticism is unfair or exaggerated because they have
good qualities too*.\"

  The people that criticize you have a political opinion and they have
to go after you personally
rather than argue their point. That don\'t like it when you have a good
point, so they malign you.
                                             Mikek
 
On Thu, 29 Sep 2022 23:23:18 -0500, amdx <amdx@knology.net> wrote:

On 9/29/2022 5:42 PM, John Larkin wrote:
On Tue, 27 Sep 2022 12:46:28 -0500, amdx <amdx@knology.net> wrote:

On 9/27/2022 3:59 AM, piglet wrote:
On 24/09/2022 13:44, amdx wrote:
On 9/24/2022 6:47 AM, piglet wrote:
On 24/09/2022 11:58, amdx wrote:
On 9/24/2022 1:11 AM, piglet wrote:
On 24/09/2022 00:33, amdx wrote:
  On one of the groups I monitor, it was ask if the tube circuit
shown below could be bootstrapped to raise the input impedance,
especially at the higher frequencies where it drops pretty low.
(purpose is to reduce loading on the LC being measured--Q meter)
  Can you give a little detail on how you would implement it? And
what happens to gain and frequency response?
When was bootstrapping introduced, the word started in the 1880s,
but when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it didn\'t
use a 100M? grid resistor, Is that a detriment to adding
bootstrapping?
  I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100M?, does
bootstrapping help that?
  Might be barking up the wrong tree.

 
https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0



                             Thanks, Mikek

Did you see the value of C302? I think V301 is being used in the
so called \"infinite impedance\" detector configuration. The cathode
voltage is not the buffered grid ac input but instead is a dc
level representing something between the peak and average ac
input. So AC bootstrapping that circuit not possible. I guess you
could insert a whole new hi-z buffer between tuned circuit under
test and detector but in practice it would be difficult to get it
to be an improvement?

piglet

  I thought I\'d seen it referred to as an \"infinite impedance
detector\", but don\'t find it in the manual.
I do see this line in the manual and don\'t understand how transit
time loss in the voltmeter
tube causes a shunt resistance across the measuring circuit at High
Frequencies.
Can someone provide a simple explanation?

\"QVOLTMETERCONDUCTANCE.
Anotherinternalparameterwhich causestheindi-
catedQtodeviatefromeffectiveQ,atbothvery low
andveryhighfrequencies, is theinputconductanceof
theQvoltmeter circuit.Atvery low frequenciesthis
conductance consistsofa 100megohmgridleak resistor
inparallelwiththeinternallossesofthevacuum tube.
Atveryhighfrequenciesthetransittime lossinthevolt-
metertubeshuntstheresonatingcapacitorandintro-
duces ashuntresistance acrossthemeasuring circuit\"

Someone has developed a single fet circuit that does an OK job.
I always wanted to try this circuit,
https://www.dropbox.com/s/wvwkw2iapf4ufd7/High%20impedance%20input.jpg?dl=0

  But have not got to it yet, to much computer time and not enough
bench time.
                                       Mikek



The transit time part comes into it like this: due to the electron
travel time there is a short delay before grid voltage changes
during the positive peaks get to influence the cathode voltage. At
very high frequencies this increased loading at the peaks gets more
significant.

The 535A tube is quite large and looks like it was built for low
inter-electrode capacity and low leakage. For VHF use a smaller tube
like an acorn device may have had shorter delay times.

Looks to me like that bootstrap all nodes fet buffer came straight
out of a late 1960s-early 70s NatSemi app note.

piglet

   Yes, it did, but, the question is will it work in place of the tube?
                                              Thanks, Mikek
The touted capacitance of the bootstrapped fet is 0.25pF which at
50MHz is reactance of 13kohm.
 I would think any capacitance just adds to the resonating capacitance,
so just need to calculate in the loss of the capacitance, not the
capacitance.

Since your main interest is around 1.5MHz you perhaps needn\'t worry a
lot about behavior at 50MHz?
 That is very true, but as the much maligned John Larkin said, \"this is
a discussion group\" so, I\'m having the topic discussed!

Mikek
I\'m not maligned by anybody that matters. That\'s by definition.

 Agreed and, I looked it up before I used it, I thought it fit well.

\"If you describe someone or something as much-maligned,
you mean that *they are often criticized by people,
but you think the criticism is unfair or exaggerated because they have
good qualities too*.\"

  The people that criticize you have a political opinion and they have
to go after you personally
rather than argue their point. That don\'t like it when you have a good
point, so they malign you.
                                             Mikek
Click to expand...

Because they can\'t design electronics.
 
On 9/30/2022 12:01 AM, John Larkin wrote:
On Thu, 29 Sep 2022 23:23:18 -0500, amdx <amdx@knology.net> wrote:

On 9/29/2022 5:42 PM, John Larkin wrote:
On Tue, 27 Sep 2022 12:46:28 -0500, amdx <amdx@knology.net> wrote:

On 9/27/2022 3:59 AM, piglet wrote:
On 24/09/2022 13:44, amdx wrote:
On 9/24/2022 6:47 AM, piglet wrote:
On 24/09/2022 11:58, amdx wrote:
On 9/24/2022 1:11 AM, piglet wrote:
On 24/09/2022 00:33, amdx wrote:
  On one of the groups I monitor, it was ask if the tube circuit
shown below could be bootstrapped to raise the input impedance,
especially at the higher frequencies where it drops pretty low.
(purpose is to reduce loading on the LC being measured--Q meter)
  Can you give a little detail on how you would implement it? And
what happens to gain and frequency response?
When was bootstrapping introduced, the word started in the 1880s,
but when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it didn\'t
use a 100M? grid resistor, Is that a detriment to adding
bootstrapping?
  I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100M?, does
bootstrapping help that?
  Might be barking up the wrong tree.

 
https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0



                             Thanks, Mikek

Did you see the value of C302? I think V301 is being used in the
so called \"infinite impedance\" detector configuration. The cathode
voltage is not the buffered grid ac input but instead is a dc
level representing something between the peak and average ac
input. So AC bootstrapping that circuit not possible. I guess you
could insert a whole new hi-z buffer between tuned circuit under
test and detector but in practice it would be difficult to get it
to be an improvement?

piglet

  I thought I\'d seen it referred to as an \"infinite impedance
detector\", but don\'t find it in the manual.
I do see this line in the manual and don\'t understand how transit
time loss in the voltmeter
tube causes a shunt resistance across the measuring circuit at High
Frequencies.
Can someone provide a simple explanation?

\"QVOLTMETERCONDUCTANCE.
Anotherinternalparameterwhich causestheindi-
catedQtodeviatefromeffectiveQ,atbothvery low
andveryhighfrequencies, is theinputconductanceof
theQvoltmeter circuit.Atvery low frequenciesthis
conductance consistsofa 100megohmgridleak resistor
inparallelwiththeinternallossesofthevacuum tube.
Atveryhighfrequenciesthetransittime lossinthevolt-
metertubeshuntstheresonatingcapacitorandintro-
duces ashuntresistance acrossthemeasuring circuit\"

Someone has developed a single fet circuit that does an OK job.
I always wanted to try this circuit,
https://www.dropbox.com/s/wvwkw2iapf4ufd7/High%20impedance%20input.jpg?dl=0

  But have not got to it yet, to much computer time and not enough
bench time.
                                       Mikek



The transit time part comes into it like this: due to the electron
travel time there is a short delay before grid voltage changes
during the positive peaks get to influence the cathode voltage. At
very high frequencies this increased loading at the peaks gets more
significant.

The 535A tube is quite large and looks like it was built for low
inter-electrode capacity and low leakage. For VHF use a smaller tube
like an acorn device may have had shorter delay times.

Looks to me like that bootstrap all nodes fet buffer came straight
out of a late 1960s-early 70s NatSemi app note.

piglet

   Yes, it did, but, the question is will it work in place of the tube?
                                              Thanks, Mikek
The touted capacitance of the bootstrapped fet is 0.25pF which at
50MHz is reactance of 13kohm.
 I would think any capacitance just adds to the resonating capacitance,
so just need to calculate in the loss of the capacitance, not the
capacitance.

Since your main interest is around 1.5MHz you perhaps needn\'t worry a
lot about behavior at 50MHz?
 That is very true, but as the much maligned John Larkin said, \"this is
a discussion group\" so, I\'m having the topic discussed!

Mikek
I\'m not maligned by anybody that matters. That\'s by definition.

 Agreed and, I looked it up before I used it, I thought it fit well.

\"If you describe someone or something as much-maligned,
you mean that *they are often criticized by people,
but you think the criticism is unfair or exaggerated because they have
good qualities too*.\"

  The people that criticize you have a political opinion and they have
to go after you personally
rather than argue their point. That don\'t like it when you have a good
point, so they malign you.
                                             Mikek
Because they can\'t design electronics.

Neither can I, but I\'m not maligning you!
Click to expand...

 btw, I got the 1000 Hz bandpass to work, it was tuned to 1008 Hz.
I wanted it to use to set the focal point of a parabolic mic.
 I could not get a clean voltage measurement because of all the other
environmental sound. I added the 1008 Hz bandpass filter between my
preamp and amp, then, with an app on my phone that I put across the room,
I generated a 1008Hz sine wave, and had a very clean,
stable waveform on my scope. Easy peasy, I moved the mic about 3\"
further away from where I thought the focus was, and doubled the Voltage
output.
 4 hrs building the bandpass filter for a 3 minute adjustment!
 Also, I have never seen this on a parabolic mic, I put a small funnel
on the mic
this also increased my output voltage.

  I used a sensitive, low noise AOM-PU5024 mic,
> https://api.puiaudio.com/file/8a1a7f37-cd74-49b0-81f3-f74090655669.pdf

 A low noise TS-472 preamp,

> https://tinyurl.com/56zv2czx

and this \'very neat\' little headphone amp to drive the headphones. 3.7\"
x 2\" x 0.5\".

> https://www.amazon.com/dp/B07MHRBMBY?psc=1&ref=ppx_yo2ov_dt_b_product_details

Which I was able to tap into the power switch to drive the preamp.

 I used a $19 (slightly scratched, returned) squirrel baffle (16\") as
the parabolic reflector, I can always upgrade to
a $135 22\" parabolic dish, but no.
 Totally worthless project, but it was fun to figure out.

  Next up, a photochopper replacement for my HP3400A, I finally got a
schematic, it uses a DG403 and 555 for 90Hz drive signal.
                               Mikek
 
On Fri, 30 Sep 2022 08:29:07 -0500, amdx <amdx@knology.net> wrote:

On 9/30/2022 12:01 AM, John Larkin wrote:
On Thu, 29 Sep 2022 23:23:18 -0500, amdx <amdx@knology.net> wrote:

On 9/29/2022 5:42 PM, John Larkin wrote:
On Tue, 27 Sep 2022 12:46:28 -0500, amdx <amdx@knology.net> wrote:

On 9/27/2022 3:59 AM, piglet wrote:
On 24/09/2022 13:44, amdx wrote:
On 9/24/2022 6:47 AM, piglet wrote:
On 24/09/2022 11:58, amdx wrote:
On 9/24/2022 1:11 AM, piglet wrote:
On 24/09/2022 00:33, amdx wrote:
  On one of the groups I monitor, it was ask if the tube circuit
shown below could be bootstrapped to raise the input impedance,
especially at the higher frequencies where it drops pretty low.
(purpose is to reduce loading on the LC being measured--Q meter)
  Can you give a little detail on how you would implement it? And
what happens to gain and frequency response?
When was bootstrapping introduced, the word started in the 1880s,
but when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it didn\'t
use a 100M? grid resistor, Is that a detriment to adding
bootstrapping?
  I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100M?, does
bootstrapping help that?
  Might be barking up the wrong tree.

 
https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0



                             Thanks, Mikek

Did you see the value of C302? I think V301 is being used in the
so called \"infinite impedance\" detector configuration. The cathode
voltage is not the buffered grid ac input but instead is a dc
level representing something between the peak and average ac
input. So AC bootstrapping that circuit not possible. I guess you
could insert a whole new hi-z buffer between tuned circuit under
test and detector but in practice it would be difficult to get it
to be an improvement?

piglet

  I thought I\'d seen it referred to as an \"infinite impedance
detector\", but don\'t find it in the manual.
I do see this line in the manual and don\'t understand how transit
time loss in the voltmeter
tube causes a shunt resistance across the measuring circuit at High
Frequencies.
Can someone provide a simple explanation?

\"QVOLTMETERCONDUCTANCE.
Anotherinternalparameterwhich causestheindi-
catedQtodeviatefromeffectiveQ,atbothvery low
andveryhighfrequencies, is theinputconductanceof
theQvoltmeter circuit.Atvery low frequenciesthis
conductance consistsofa 100megohmgridleak resistor
inparallelwiththeinternallossesofthevacuum tube.
Atveryhighfrequenciesthetransittime lossinthevolt-
metertubeshuntstheresonatingcapacitorandintro-
duces ashuntresistance acrossthemeasuring circuit\"

Someone has developed a single fet circuit that does an OK job.
I always wanted to try this circuit,
https://www.dropbox.com/s/wvwkw2iapf4ufd7/High%20impedance%20input.jpg?dl=0

  But have not got to it yet, to much computer time and not enough
bench time.
                                       Mikek



The transit time part comes into it like this: due to the electron
travel time there is a short delay before grid voltage changes
during the positive peaks get to influence the cathode voltage. At
very high frequencies this increased loading at the peaks gets more
significant.

The 535A tube is quite large and looks like it was built for low
inter-electrode capacity and low leakage. For VHF use a smaller tube
like an acorn device may have had shorter delay times.

Looks to me like that bootstrap all nodes fet buffer came straight
out of a late 1960s-early 70s NatSemi app note.

piglet

   Yes, it did, but, the question is will it work in place of the tube?
                                              Thanks, Mikek
The touted capacitance of the bootstrapped fet is 0.25pF which at
50MHz is reactance of 13kohm.
 I would think any capacitance just adds to the resonating capacitance,
so just need to calculate in the loss of the capacitance, not the
capacitance.

Since your main interest is around 1.5MHz you perhaps needn\'t worry a
lot about behavior at 50MHz?
 That is very true, but as the much maligned John Larkin said, \"this is
a discussion group\" so, I\'m having the topic discussed!

Mikek
I\'m not maligned by anybody that matters. That\'s by definition.

 Agreed and, I looked it up before I used it, I thought it fit well.

\"If you describe someone or something as much-maligned,
you mean that *they are often criticized by people,
but you think the criticism is unfair or exaggerated because they have
good qualities too*.\"

  The people that criticize you have a political opinion and they have
to go after you personally
rather than argue their point. That don\'t like it when you have a good
point, so they malign you.
                                             Mikek
Because they can\'t design electronics.

Neither can I, but I\'m not maligning you!

 btw, I got the 1000 Hz bandpass to work, it was tuned to 1008 Hz.
I wanted it to use to set the focal point of a parabolic mic.
 I could not get a clean voltage measurement because of all the other
environmental sound. I added the 1008 Hz bandpass filter between my
preamp and amp, then, with an app on my phone that I put across the room,
I generated a 1008Hz sine wave, and had a very clean,
stable waveform on my scope. Easy peasy, I moved the mic about 3\"
further away from where I thought the focus was, and doubled the Voltage
output.
 4 hrs building the bandpass filter for a 3 minute adjustment!
 Also, I have never seen this on a parabolic mic, I put a small funnel
on the mic
this also increased my output voltage.

  I used a sensitive, low noise AOM-PU5024 mic,
https://api.puiaudio.com/file/8a1a7f37-cd74-49b0-81f3-f74090655669.pdf

 A low noise TS-472 preamp,

https://tinyurl.com/56zv2czx

and this \'very neat\' little headphone amp to drive the headphones. 3.7\"
x 2\" x 0.5\".

https://www.amazon.com/dp/B07MHRBMBY?psc=1&ref=ppx_yo2ov_dt_b_product_details

Which I was able to tap into the power switch to drive the preamp.

 I used a $19 (slightly scratched, returned) squirrel baffle (16\") as
the parabolic reflector, I can always upgrade to
a $135 22\" parabolic dish, but no.
 Totally worthless project, but it was fun to figure out.

  Next up, a photochopper replacement for my HP3400A, I finally got a
schematic, it uses a DG403 and 555 for 90Hz drive signal.
                               Mikek
Click to expand...

There are some great optocoupled solid-state relays around. The input
side is LEDs and the output is mosfets, zero offset voltage.
 
On Friday, September 30, 2022 at 8:42:58 AM UTC+10, John Larkin wrote:
On Tue, 27 Sep 2022 12:46:28 -0500, amdx <am...@knology.net> wrote:
On 9/27/2022 3:59 AM, piglet wrote:
On 24/09/2022 13:44, amdx wrote:
On 9/24/2022 6:47 AM, piglet wrote:
On 24/09/2022 11:58, amdx wrote:
On 9/24/2022 1:11 AM, piglet wrote:
On 24/09/2022 00:33, amdx wrote:

That is very true, but as the much maligned John Larkin said, \"this is
a discussion group\" so, I\'m having the topic discussed!

I\'m not maligned by anybody that matters. That\'s by definition.
Click to expand...

Nobody who won\'t flatter John Larkin matters to John Larkin.

The climate change denial propaganda lobby flatters everybody who is silly enough to read their output, so John Larkin takes them very seriously, and pointing this out is maligning him. He probably ought to re-work his definitions but he\'s much too addicted to getting flattered for this to be likely to happen.

--
Bill Sloman, Sydney
 
On 9/30/2022 11:06 AM, Anthony William Sloman wrote:
On Friday, September 30, 2022 at 8:42:58 AM UTC+10, John Larkin wrote:
On Tue, 27 Sep 2022 12:46:28 -0500, amdx <am...@knology.net> wrote:
On 9/27/2022 3:59 AM, piglet wrote:
On 24/09/2022 13:44, amdx wrote:
On 9/24/2022 6:47 AM, piglet wrote:
On 24/09/2022 11:58, amdx wrote:
On 9/24/2022 1:11 AM, piglet wrote:
On 24/09/2022 00:33, amdx wrote:
That is very true, but as the much maligned John Larkin said, \"this is
a discussion group\" so, I\'m having the topic discussed!
I\'m not maligned by anybody that matters. That\'s by definition.
Nobody who won\'t flatter John Larkin matters to John Larkin.

The climate change denial propaganda lobby flatters everybody who is silly enough to read their output, so John Larkin takes them very seriously, and pointing this out is maligning him. He probably ought to re-work his definitions but he\'s much too addicted to getting flattered for this to be likely to happen.
Click to expand...
 The lead antagonist chimes in with more personal attacks. Nothing
changes for the libs,
they hate conservatives, while conservatives just think the libs have it
wrong.
                             Mikek
 
On 9/30/2022 11:45 AM, amdx wrote:
On 9/30/2022 9:32 AM, John Larkin wrote:
On Fri, 30 Sep 2022 08:29:07 -0500, amdx <amdx@knology.net> wrote:

On 9/30/2022 12:01 AM, John Larkin wrote:
On Thu, 29 Sep 2022 23:23:18 -0500, amdx <amdx@knology.net> wrote:

On 9/29/2022 5:42 PM, John Larkin wrote:
On Tue, 27 Sep 2022 12:46:28 -0500, amdx <amdx@knology.net> wrote:

On 9/27/2022 3:59 AM, piglet wrote:
On 24/09/2022 13:44, amdx wrote:
On 9/24/2022 6:47 AM, piglet wrote:
On 24/09/2022 11:58, amdx wrote:
On 9/24/2022 1:11 AM, piglet wrote:
On 24/09/2022 00:33, amdx wrote:
     On one of the groups I monitor, it was ask if the
tube circuit
shown below could be bootstrapped to raise the input
impedance,
especially at the higher frequencies where it drops pretty
low.
(purpose is to reduce loading on the LC being measured--Q
meter)
     Can you give a little detail on how you would
implement it? And
what happens to gain and frequency response?
When was bootstrapping introduced, the word started in the
1880s,
but when was it first used in an electrical circuit?
I did manage to find a bootstrapped tube circuit, but it
didn\'t
use a 100M? grid resistor, Is that a detriment to adding
bootstrapping?
     I made my proposed idea on the right side.
Hmm, the problem is more the tube input than the 100M?, does
bootstrapping help that?
     Might be barking up the wrong tree.

    
https://www.dropbox.com/s/in6no3nvw0qnie7/Boonton%20260A%20Tube%20bootstrap%20question.jpg?dl=0




                                Thanks, Mikek

Did you see the value of C302? I think V301 is being used
in the
so called \"infinite impedance\" detector configuration. The
cathode
voltage is not the buffered grid ac input but instead is a dc
level representing something between the peak and average ac
input. So AC bootstrapping that circuit not possible. I
guess you
could insert a whole new hi-z buffer between tuned circuit
under
test and detector but in practice it would be difficult to
get it
to be an improvement?

piglet

     I thought I\'d seen it referred to as an \"infinite
impedance
detector\", but don\'t find it in the manual.
I do see this line in the manual and don\'t understand how
transit
time loss in the voltmeter
tube causes a shunt resistance across the measuring circuit
at High
Frequencies.
Can someone provide a simple explanation?

\"QVOLTMETERCONDUCTANCE.
Anotherinternalparameterwhich causestheindi-
catedQtodeviatefromeffectiveQ,atbothvery low
andveryhighfrequencies, is theinputconductanceof
theQvoltmeter circuit.Atvery low frequenciesthis
conductance consistsofa 100megohmgridleak resistor
inparallelwiththeinternallossesofthevacuum tube.
Atveryhighfrequenciesthetransittime lossinthevolt-
metertubeshuntstheresonatingcapacitorandintro-
duces ashuntresistance acrossthemeasuring circuit\"

Someone has developed a single fet circuit that does an OK job.
I always wanted to try this circuit,
https://www.dropbox.com/s/wvwkw2iapf4ufd7/High%20impedance%20input.jpg?dl=0


     But have not got to it yet, to much computer time and
not enough
bench time.
Mikek



The transit time part comes into it like this: due to the
electron
travel time there is a short delay before grid voltage changes
during the positive peaks get to influence the cathode
voltage. At
very high frequencies this increased loading at the peaks
gets more
significant.

The 535A tube is quite large and looks like it was built for low
inter-electrode capacity and low leakage. For VHF use a
smaller tube
like an acorn device may have had shorter delay times.

Looks to me like that bootstrap all nodes fet buffer came
straight
out of a late 1960s-early 70s NatSemi app note.

piglet

      Yes, it did, but, the question is will it work in place
of the tube?
Thanks, Mikek
The touted capacitance of the bootstrapped fet is 0.25pF which at
50MHz is reactance of 13kohm.
    I would think any capacitance just adds to the resonating
capacitance,
so just need to calculate in the loss of the capacitance, not the
capacitance.

Since your main interest is around 1.5MHz you perhaps needn\'t
worry a
lot about behavior at 50MHz?
    That is very true, but as the much maligned John Larkin
said, \"this is
a discussion group\" so, I\'m having the topic discussed!

Mikek
I\'m not maligned by anybody that matters. That\'s by definition.

   Agreed and, I looked it up before I used it, I thought it fit
well.

\"If you describe someone or something as much-maligned,
you mean that *they are often criticized by people,
but you think the criticism is unfair or exaggerated because they
have
good qualities too*.\"

    The people that criticize you have a political opinion and
they have
to go after you personally
rather than argue their point. That don\'t like it when you have a
good
point, so they malign you.
                                               Mikek
Because they can\'t design electronics.

Neither can I, but I\'m not maligning you!

  btw, I got the 1000 Hz bandpass to work, it was tuned to 1008 Hz.
I wanted it to use to set the focal point of a parabolic mic.
  I could not get a clean voltage measurement because of all the other
environmental sound. I added the 1008 Hz bandpass filter between my
preamp and amp, then, with an app on my phone that I put across the
room,
I generated a 1008Hz sine wave, and had a very clean,
stable waveform on my scope. Easy peasy, I moved the mic about 3\"
further away from where I thought the focus was, and doubled the
Voltage
output.
  4 hrs building the bandpass filter for a 3 minute adjustment!
  Also, I have never seen this on a parabolic mic, I put a small funnel
on the mic
this also increased my output voltage.

   I used a sensitive, low noise AOM-PU5024 mic,
https://api.puiaudio.com/file/8a1a7f37-cd74-49b0-81f3-f74090655669.pdf
  A low noise TS-472 preamp,

https://tinyurl.com/56zv2czx
and this \'very neat\' little headphone amp to drive the headphones. 3.7\"
x 2\" x 0.5\".

https://www.amazon.com/dp/B07MHRBMBY?psc=1&ref=ppx_yo2ov_dt_b_product_details

Which I was able to tap into the power switch to drive the preamp.

  I used a $19 (slightly scratched, returned) squirrel baffle (16\") as
the parabolic reflector, I can always upgrade to
a $135 22\" parabolic dish, but no.
  Totally worthless project, but it was fun to figure out.

   Next up, a photochopper replacement for my HP3400A, I finally got a
schematic, it uses a DG403 and 555 for 90Hz drive signal.
                                Mikek

There are some great optocoupled solid-state relays around. The input
side is LEDs and the output is mosfets, zero offset voltage.

  The H11F1M has been used, but I didn\'t get a schematic for it. I
don\'t expect much
in the way of a circuit required. I was disappointed it doesn\'t come
in a quad.
 If there is a second round I might try it.
                     Mikek
Click to expand...
 Also an AD7510D has been used for the switches.
                                    Mikek
 
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