H
Henry Kolesnik
Guest
What the easiest ways to measure the output impedance of a push pull
tube amplifier?
Thanks
Hank
tube amplifier?
Thanks
Hank
E
Engineer
Guest
On Nov 1, 9:24 pm, "Henry Kolesnik" <koles...@nojunksbcglobal.net>
wrote:
"near voltage" source, i.e. very low indeed, less than, say, 0.5 ohm?
Or do you mean what is the nominal speaker impedance that it is set up
for, e.g. 4, 8 or 16 ohms?
Cheers,
Roger
wrote:
Henry, do you mean the true Thevenin O/P impedance of the unit as a
"near voltage" source, i.e. very low indeed, less than, say, 0.5 ohm?
Or do you mean what is the nominal speaker impedance that it is set up
for, e.g. 4, 8 or 16 ohms?
Cheers,
Roger
H
Henry Kolesnik
Guest
normal speaker impedance
"Engineer" <junk2007@rogers.com> wrote in message
news:aaae8a3f-744b-41a2-9f82-a7f0ebe0061f@d36g2000prf.googlegroups.com...
On Nov 1, 9:24 pm, "Henry Kolesnik" <koles...@nojunksbcglobal.net>
wrote:
"near voltage" source, i.e. very low indeed, less than, say, 0.5 ohm?
Or do you mean what is the nominal speaker impedance that it is set up
for, e.g. 4, 8 or 16 ohms?
Cheers,
Roger
"Engineer" <junk2007@rogers.com> wrote in message
news:aaae8a3f-744b-41a2-9f82-a7f0ebe0061f@d36g2000prf.googlegroups.com...
On Nov 1, 9:24 pm, "Henry Kolesnik" <koles...@nojunksbcglobal.net>
wrote:
Henry, do you mean the true Thevenin O/P impedance of the unit as a
"near voltage" source, i.e. very low indeed, less than, say, 0.5 ohm?
Or do you mean what is the nominal speaker impedance that it is set up
for, e.g. 4, 8 or 16 ohms?
Cheers,
Roger
M
Michael A. Terrell
Guest
Henry Kolesnik wrote:
A low, known AC voltage is applied to the secondary winding, and the
voltage is measured across the other. Be careful, because the voltage on
the primary winding will be high enough to shock you.
The voltage on the primary over the applied voltage gives you the
turns ratio. Square that number and you have the impedance ratio from
primary to secondary. Since the transformer is in a push-pull
application, the primary impedance is 'Plate to plate'.
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There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.
A low, known AC voltage is applied to the secondary winding, and the
voltage is measured across the other. Be careful, because the voltage on
the primary winding will be high enough to shock you.
The voltage on the primary over the applied voltage gives you the
turns ratio. Square that number and you have the impedance ratio from
primary to secondary. Since the transformer is in a push-pull
application, the primary impedance is 'Plate to plate'.
--
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listed, or I will not see your messages.
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your account: http://www.usenettools.net/ISP.htm
There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.
H
Henry Kolesnik
Guest
This is in an old military radio which I suspect is not 3.2 ohms but
somewhat higher like maybe 600. It's kind of hard to get to the
primary. I guess I should have stated that at the beginning. I kind of
recall some way of measuring the open circuit voltage from a tone and
then with a pot connected across the output, set the pot to where the
voltage is 1/2 and then measure the pot. Do I have that correct?
Hank
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:b76dnReObKz5UZDUnZ2dnUVZ_tbinZ2d@earthlink.com...
somewhat higher like maybe 600. It's kind of hard to get to the
primary. I guess I should have stated that at the beginning. I kind of
recall some way of measuring the open circuit voltage from a tone and
then with a pot connected across the output, set the pot to where the
voltage is 1/2 and then measure the pot. Do I have that correct?
Hank
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:b76dnReObKz5UZDUnZ2dnUVZ_tbinZ2d@earthlink.com...
N
N_Cook
Guest
Henry Kolesnik <kolesnik@nojunksbcglobal.net> wrote in message
news:6elPk.6605$be.4177@nlpi061.nbdc.sbc.com...
AC volts, with amp set at low output.
If on some set of resistors of total value of R , the o/p voltage is greater
than with value R+d and R-d , where d is about R/4 then R is the output
impedance. If highest at R-d then go down, in steps, till it peaks, if R+d
is highest then go higher for peak value
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/
news:6elPk.6605$be.4177@nlpi061.nbdc.sbc.com...
I would go for a set of watty resistors in series, tone source and a DVM on
AC volts, with amp set at low output.
If on some set of resistors of total value of R , the o/p voltage is greater
than with value R+d and R-d , where d is about R/4 then R is the output
impedance. If highest at R-d then go down, in steps, till it peaks, if R+d
is highest then go higher for peak value
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/
C
Charles
Guest
"Henry Kolesnik" <kolesnik@nojunksbcglobal.net> wrote in message
news:Kj7Pk.6569$be.3512@nlpi061.nbdc.sbc.com...
voltage drops to 1/2 of the no-load voltage, the resistor can be removed and
measured with an ohmmeter.
news:Kj7Pk.6569$be.3512@nlpi061.nbdc.sbc.com...
Load the amplifier with an adjustable resistor. When the loaded output
voltage drops to 1/2 of the no-load voltage, the resistor can be removed and
measured with an ohmmeter.
I
Ian Jackson
Guest
In message <gelalc$gda$1@registered.motzarella.org>, Charles
<charlesschuler@comcast.net> writes
less severe - but measurable - drop in output voltage (say by 10 or
20%). Then do a simple 'pot-down' calculation to get the output
impedance.
--
Ian
<charlesschuler@comcast.net> writes
be better to load the output with a resistor low enough to produce a
less severe - but measurable - drop in output voltage (say by 10 or
20%). Then do a simple 'pot-down' calculation to get the output
impedance.
--
Ian
M
Michael A. Terrell
Guest
Henry Kolesnik wrote:
That is how we measured the input impedance on the PRC77 The input
was fed a 1 kHz tone, and a series resistance was added, till the
modulation dropped to half.
If it is an old military radio it is likely 600 ohms. What is the
brand and model, or the military ID number?
--
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listed, or I will not see your messages.
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your account: http://www.usenettools.net/ISP.htm
There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.
That is how we measured the input impedance on the PRC77 The input
was fed a 1 kHz tone, and a series resistance was added, till the
modulation dropped to half.
If it is an old military radio it is likely 600 ohms. What is the
brand and model, or the military ID number?
--
http://improve-usenet.org/index.html
aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.
If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm
There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.
H
Henry Kolesnik
Guest
It's a BC-794 but I think it's been modified and if not something else
is kaput.
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:vMKdnUYtEoDp_5PUnZ2dnUVZ_o3inZ2d@earthlink.com...
is kaput.
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:vMKdnUYtEoDp_5PUnZ2dnUVZ_o3inZ2d@earthlink.com...
E
Engineer
Guest
On Nov 2, 5:47 pm, "Charles" <charlesschu...@comcast.net> wrote:
i.e. equivalent generator source impedance (see Thevenin), and it will
be very low - no use in selecting speakers. You need the O/P
transformer (OPT) ratio. Make sure the receiver/amplifier is OFF. Use
a filament transformer run off a variac to energise the OPT secondary
(use the speaker terminals) - keep it low, say 2 to 4 VAC. Measure
the OPT primary and secondary voltages at a few levels. Calculate
each ratio and average them. Figure out the correct plate load for
the O/P tube (not covered here) - it will likely be in the range 4
Kohms to 8 Kohms, call it Rp. Then the correct speaker load will be
Rp/OPT ratio squared. Ex: Rp = 5000 ohms, OPT ratio found to be
36:1. Then, speaker should be 5000/(36)^2 = 5000/1296 = 3.86 ohms.
So use a 4 ohm speaker.
Cheers,
Roger
Sorry, not so. This will only give you what I originally mentioned,
i.e. equivalent generator source impedance (see Thevenin), and it will
be very low - no use in selecting speakers. You need the O/P
transformer (OPT) ratio. Make sure the receiver/amplifier is OFF. Use
a filament transformer run off a variac to energise the OPT secondary
(use the speaker terminals) - keep it low, say 2 to 4 VAC. Measure
the OPT primary and secondary voltages at a few levels. Calculate
each ratio and average them. Figure out the correct plate load for
the O/P tube (not covered here) - it will likely be in the range 4
Kohms to 8 Kohms, call it Rp. Then the correct speaker load will be
Rp/OPT ratio squared. Ex: Rp = 5000 ohms, OPT ratio found to be
36:1. Then, speaker should be 5000/(36)^2 = 5000/1296 = 3.86 ohms.
So use a 4 ohm speaker.
Cheers,
Roger
I
Ian Jackson
Guest
In message
<32b2cc1a-3eee-47a1-ba86-eb96907cd648@e1g2000pra.googlegroups.com>,
Engineer <junk2007@rogers.com> writes
to an earlier amplifier stage) do to the output impedance?
--
Ian
<32b2cc1a-3eee-47a1-ba86-eb96907cd648@e1g2000pra.googlegroups.com>,
Engineer <junk2007@rogers.com> writes
Surely this IS the output impedance?
But what does the invariable negative feedback (from the OPT secondary
to an earlier amplifier stage) do to the output impedance?
--
Ian
H
Henry Kolesnik
Guest
Roger
50 years ago I wound and rewound many a transformer with great success.
But today I'm older, more patient and lazy and looking for an easy way
out that may not be totally accurate.
But I kind of recall reading an excellent article with a trick that I
thought was pretty ingenious but I never saved it. It may have been a
ham mag, or Howard Sams booklet or maybe Rufus Turner. Maybe someone
will remember.
Hank
"Engineer" <junk2007@rogers.com> wrote in message
news:32b2cc1a-3eee-47a1-ba86-eb96907cd648@e1g2000pra.googlegroups.com...
On Nov 2, 5:47 pm, "Charles" <charlesschu...@comcast.net> wrote:
i.e. equivalent generator source impedance (see Thevenin), and it will
be very low - no use in selecting speakers. You need the O/P
transformer (OPT) ratio. Make sure the receiver/amplifier is OFF. Use
a filament transformer run off a variac to energise the OPT secondary
(use the speaker terminals) - keep it low, say 2 to 4 VAC. Measure
the OPT primary and secondary voltages at a few levels. Calculate
each ratio and average them. Figure out the correct plate load for
the O/P tube (not covered here) - it will likely be in the range 4
Kohms to 8 Kohms, call it Rp. Then the correct speaker load will be
Rp/OPT ratio squared. Ex: Rp = 5000 ohms, OPT ratio found to be
36:1. Then, speaker should be 5000/(36)^2 = 5000/1296 = 3.86 ohms.
So use a 4 ohm speaker.
Cheers,
Roger
50 years ago I wound and rewound many a transformer with great success.
But today I'm older, more patient and lazy and looking for an easy way
out that may not be totally accurate.
But I kind of recall reading an excellent article with a trick that I
thought was pretty ingenious but I never saved it. It may have been a
ham mag, or Howard Sams booklet or maybe Rufus Turner. Maybe someone
will remember.
Hank
"Engineer" <junk2007@rogers.com> wrote in message
news:32b2cc1a-3eee-47a1-ba86-eb96907cd648@e1g2000pra.googlegroups.com...
On Nov 2, 5:47 pm, "Charles" <charlesschu...@comcast.net> wrote:
Sorry, not so. This will only give you what I originally mentioned,
i.e. equivalent generator source impedance (see Thevenin), and it will
be very low - no use in selecting speakers. You need the O/P
transformer (OPT) ratio. Make sure the receiver/amplifier is OFF. Use
a filament transformer run off a variac to energise the OPT secondary
(use the speaker terminals) - keep it low, say 2 to 4 VAC. Measure
the OPT primary and secondary voltages at a few levels. Calculate
each ratio and average them. Figure out the correct plate load for
the O/P tube (not covered here) - it will likely be in the range 4
Kohms to 8 Kohms, call it Rp. Then the correct speaker load will be
Rp/OPT ratio squared. Ex: Rp = 5000 ohms, OPT ratio found to be
36:1. Then, speaker should be 5000/(36)^2 = 5000/1296 = 3.86 ohms.
So use a 4 ohm speaker.
Cheers,
Roger
H
Henry Kolesnik
Guest
I just recalled I have an old GR 583-A Output Power Meter and if it
still works it'll tell me. It's been wasting gravity for years, Google
it and you'll see one on Sphere. Thanks to all for the comments, and
I'd like to know any tricks?
Hank
"Henry Kolesnik" <kolesnik@nojunksbcglobal.net> wrote in message
news
tNPk.5508$x%.851@nlpi070.nbdc.sbc.com...
still works it'll tell me. It's been wasting gravity for years, Google
it and you'll see one on Sphere. Thanks to all for the comments, and
I'd like to know any tricks?
Hank
"Henry Kolesnik" <kolesnik@nojunksbcglobal.net> wrote in message
news
tNPk.5508$x%.851@nlpi070.nbdc.sbc.com...
E
Engineer
Guest
On Nov 3, 6:12 pm, Ian Jackson
<ianREMOVETHISjack...@g3ohx.demon.co.uk> wrote:
voltage generator (increasing the damping factor) but does not affect
the speaker impedance to be used. The speaker impedance determines
the O/P tube plate (anode) load via the OPT ratio.
Cheers,
Roger
<ianREMOVETHISjack...@g3ohx.demon.co.uk> wrote:
(snip)
Ian, it reduces the source output impedance of the amplifier as a
voltage generator (increasing the damping factor) but does not affect
the speaker impedance to be used. The speaker impedance determines
the O/P tube plate (anode) load via the OPT ratio.
Cheers,
Roger
I
Ian Jackson
Guest
In message
<5ad1401b-583e-40e1-a58d-d48c8590af23@u29g2000pro.googlegroups.com>,
Engineer <junk2007@rogers.com> writes
output impedance of a push pull tube amplifier?" It didn't mention
loudspeakers.
--
Ian
<5ad1401b-583e-40e1-a58d-d48c8590af23@u29g2000pro.googlegroups.com>,
Engineer <junk2007@rogers.com> writes
But the original question was "What the easiest ways to measure the
output impedance of a push pull tube amplifier?" It didn't mention
loudspeakers.
--
Ian
E
Engineer
Guest
On Nov 4, 4:49 am, Ian Jackson
<ianREMOVETHISjack...@g3ohx.demon.co.uk> wrote:
don't know any with P-P output...) I have a BC348 and the OPT (from a
single 6K6 O/P tube) is designed for 'phones only, both "high" and
"low" impedance. The "low" impedance 'phone O/P is 300 ohms so using
a regular LS is not possible. I put a typical radio OPT in this radio
(I left the original 'phones OPT in place so it could be restored to
original sometime in the next 100 years!) The new OPT and the nominal
8 ohms LS used puts a reasonably correct plate load on the 6K6, about
7K. Volume is quite good - I'd guess about 2 watts output (but not
measured.)
There is no NFB in the original radio but there is a little bit now as
I routed the Rk decoupling cap to the top of the OPT secondary as a
token NFB (properly phased.) Of course, invariably there is a lot of
NFB on P-P audio amplifiers and, as noted above, it reduces the true
output impedance of the amplifier as a voltage source, but it does NOT
change the correct LS impedance as the latter defines the O/P tubes'
plate-to-plate load.
I don't know why Henry first asked about a "PP amplifier then "morphed
to a "military radio" but it doesn't matter - it's all the same
physics!
Cheers,
Roger
<ianREMOVETHISjack...@g3ohx.demon.co.uk> wrote:
Henry mentioned a miltary radio with a high output impedance (but I
don't know any with P-P output...) I have a BC348 and the OPT (from a
single 6K6 O/P tube) is designed for 'phones only, both "high" and
"low" impedance. The "low" impedance 'phone O/P is 300 ohms so using
a regular LS is not possible. I put a typical radio OPT in this radio
(I left the original 'phones OPT in place so it could be restored to
original sometime in the next 100 years!) The new OPT and the nominal
8 ohms LS used puts a reasonably correct plate load on the 6K6, about
7K. Volume is quite good - I'd guess about 2 watts output (but not
measured.)
There is no NFB in the original radio but there is a little bit now as
I routed the Rk decoupling cap to the top of the OPT secondary as a
token NFB (properly phased.) Of course, invariably there is a lot of
NFB on P-P audio amplifiers and, as noted above, it reduces the true
output impedance of the amplifier as a voltage source, but it does NOT
change the correct LS impedance as the latter defines the O/P tubes'
plate-to-plate load.
I don't know why Henry first asked about a "PP amplifier then "morphed
to a "military radio" but it doesn't matter - it's all the same
physics!
Cheers,
Roger
H
Henry Kolesnik
Guest
Neil Sutcliffe was kind enough to send me a manual on his GR 783A which
is a more recent version of my GR 583A Output Impedance Meter. The o/p
xfrmr on my Hmmarlund Super Pro 210X Type O is 10 ohms and I looked
inside and saw no evidence that it was changed. I confirmed that the
meter works by the same technique on my Ten Tec SP 325 which is 600 ohms
and it measured 600 ohms. The GR 583A is a neat piece of gear, easy as
pie to use.
--
Thanks & 73
Hank WD5JFR
"Henry Kolesnik" <kolesnik@nojunksbcglobal.net> wrote in message
news:GpOPk.5519$x%.257@nlpi070.nbdc.sbc.com...
is a more recent version of my GR 583A Output Impedance Meter. The o/p
xfrmr on my Hmmarlund Super Pro 210X Type O is 10 ohms and I looked
inside and saw no evidence that it was changed. I confirmed that the
meter works by the same technique on my Ten Tec SP 325 which is 600 ohms
and it measured 600 ohms. The GR 583A is a neat piece of gear, easy as
pie to use.
--
Thanks & 73
Hank WD5JFR
"Henry Kolesnik" <kolesnik@nojunksbcglobal.net> wrote in message
news:GpOPk.5519$x%.257@nlpi070.nbdc.sbc.com...
I just recalled I have an old GR 583-A Output Power Meter and if it
still works it'll tell me. It's been wasting gravity for years, Google
it and you'll see one on Sphere. Thanks to all for the comments, and
I'd like to know any tricks?
Hank
"Henry Kolesnik" <kolesnik@nojunksbcglobal.net> wrote in message
news
Roger
50 years ago I wound and rewound many a transformer with great
success. But today I'm older, more patient and lazy and looking for
an easy way out that may not be totally accurate.
But I kind of recall reading an excellent article with a trick that I
thought was pretty ingenious but I never saved it. It may have been a
ham mag, or Howard Sams booklet or maybe Rufus Turner. Maybe someone
will remember.
Hank
"Engineer" <junk2007@rogers.com> wrote in message
news:32b2cc1a-3eee-47a1-ba86-eb96907cd648@e1g2000pra.googlegroups.com...
On Nov 2, 5:47 pm, "Charles" <charlesschu...@comcast.net> wrote:
"Henry Kolesnik" <koles...@nojunksbcglobal.net> wrote in message
news:Kj7Pk.6569$be.3512@nlpi061.nbdc.sbc.com...
What the easiest ways to measure the output impedance of a push
pull tube
amplifier?
Load the amplifier with an adjustable resistor. When the loaded
output
voltage drops to 1/2 of the no-load voltage, the resistor can be
removed and
measured with an ohmmeter.
Sorry, not so. This will only give you what I originally mentioned,
i.e. equivalent generator source impedance (see Thevenin), and it
will
be very low - no use in selecting speakers. You need the O/P
transformer (OPT) ratio. Make sure the receiver/amplifier is OFF.
Use
a filament transformer run off a variac to energise the OPT secondary
(use the speaker terminals) - keep it low, say 2 to 4 VAC. Measure
the OPT primary and secondary voltages at a few levels. Calculate
each ratio and average them. Figure out the correct plate load for
the O/P tube (not covered here) - it will likely be in the range 4
Kohms to 8 Kohms, call it Rp. Then the correct speaker load will be
Rp/OPT ratio squared. Ex: Rp = 5000 ohms, OPT ratio found to be
36:1. Then, speaker should be 5000/(36)^2 = 5000/1296 = 3.86 ohms.
So use a 4 ohm speaker.
Cheers,
Roger
D
Dave Plowman (News)
Guest
In article <NmMRk.4472$W06.1336@flpi148.ffdc.sbc.com>,
Henry Kolesnik <kolesnik@nojunksbcglobal.net> wrote:
and was never designed to feed a speaker. 600 ohms is the old line driving
impedance and headphones are available that will work fine from this at
line level.
--
*Why do we say something is out of whack? What is a whack?
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
Henry Kolesnik <kolesnik@nojunksbcglobal.net> wrote:
If the output really is 600 ohms it sounds like it uses a cathode follower
and was never designed to feed a speaker. 600 ohms is the old line driving
impedance and headphones are available that will work fine from this at
line level.
--
*Why do we say something is out of whack? What is a whack?
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
H
Henry Kolesnik
Guest
Dave
The SP 310X has a pair of 6F6 triode connected driving a pushpull
transformer with output of 15 watts. It was mainly a military Rx BC 794
etc butmine is a civilian model.
No cathode follower.
Any headphones work fine at 10 ohms.
--
Thanks & 73
Hank WD5JFR
"Dave Plowman (News)" <dave@davenoise.co.uk> wrote in message
news:4ffbf9448fdave@davenoise.co.uk...
The SP 310X has a pair of 6F6 triode connected driving a pushpull
transformer with output of 15 watts. It was mainly a military Rx BC 794
etc butmine is a civilian model.
No cathode follower.
Any headphones work fine at 10 ohms.
--
Thanks & 73
Hank WD5JFR
"Dave Plowman (News)" <dave@davenoise.co.uk> wrote in message
news:4ffbf9448fdave@davenoise.co.uk...