Tube Amp

[Dave.H]

Hi, I'm looking for plans for a 1 or 2 tube low voltage amplifier to
go with a regenerative radio. Does not have to be the best, but needs
to drive at least 250 mW speaker, preferably 1 watt or more.

Thanks, Dave
Australia

 

[Tim Wescott]

On Mon, 21 Apr 2008 09:12:56 -0700, Dave.H wrote:

Hi, I'm looking for plans for a 1 or 2 tube low voltage amplifier to go
with a regenerative radio. Does not have to be the best, but needs to
drive at least 250 mW speaker, preferably 1 watt or more.

Thanks, Dave
Australia

I don't know what's available in Oz, but some ARRL or RSGB handbooks from
the '40s, '50s or early '60s will give you tons of sample circuits.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

 

[Mike Silva]

On Apr 21, 12:12 pm, "Dave.H" <the19...@googlemail.com> wrote:

Hi, I'm looking for plans for a 1 or 2 tube low voltage amplifier to
go with a regenerative radio.  Does not have to be the best, but needs
to drive at least 250 mW speaker, preferably 1 watt or more.

Thanks, Dave
Australia

How low is low? Anything much under 100V gets tough to make any
power.

You'll get the most power at a low voltage by using a tube intended
for such use (kind of a DUH statement!). Look for a tube that has a
higher heater current, since low-voltage tubes need more cathode
emission to make decent power. That might be something like a 6CU5,
6W6, 6Y6, 6DB5, etc. Some of those are miniature tubes, others are
octals.

You'll probably only need one triode stage of AF amplification between
the detector and the output tube. Something like a 6C4, 6J5, etc. If
one stage isn't quite enough you could try a tube with higher
amplification factor like 6AV6 or 6SR7.

BTW, you can talk tube radio homebrew to your hearts content on the
glowbugs email list. Google should turn it up for you.

Mike

 

[Mike Silva]

On Apr 21, 12:12 pm, "Dave.H" <the19...@googlemail.com> wrote:

Hi, I'm looking for plans for a 1 or 2 tube low voltage amplifier to
go with a regenerative radio.  Does not have to be the best, but needs
to drive at least 250 mW speaker, preferably 1 watt or more.

Thanks, Dave
Australia

Hmm, I thought I hit SEND but who knows where it went. Anyway, I had
another idea so I'll reply again.

First, what kind of low voltage are you talking about? Anything much
under 100V is going to be very hard to make any power.

You'll want an output tube designed for low voltage operation
(typically around 110V). Look for a tube with high heater current,
typically 1.2A at 6.3V. That's because low voltage tubes need big
cathodes to produce enough current at low voltages to make decent
power. Examples would be 6CU5, 6W6, 6Y6, 6DB5, etc.

You'll probably only need one stage of AF amplification between
detector and output tube. Look at triodes such as 6C4 or 6J5. If you
need more gain look at a higher gain triode like 6AV6 or 6SR7.

I don't know what voltage source you have or are looking at, but I
like the Triad N68X isolation transformer for low (tube) voltage use.
You can get 150-160V out of a bridge rectifier and filter. You'll
need a separate heater transformer, but the combination usually still
ends up being cheaper and easier to obtain than a combined tube
transformer with both HV and heater windings.

BTW, if you want to learn about tube radio homebrew you'll want to
look into the glowbugs email list - best resource on the net that I
know of. Google should turn it up for you.

Mike

 

[Dave.H]

On Apr 22, 11:14 am, Tim Wescott <t...@seemywebsite.com> wrote:

On Mon, 21 Apr 2008 09:12:56 -0700, Dave.H wrote:
Hi, I'm looking for plans for a 1 or 2 tube low voltage amplifier to go
with a regenerative radio. Does not have to be the best, but needs to
drive at least 250 mW speaker, preferably 1 watt or more.

Thanks, Dave
Australia

I don't know what's available in Oz, but some ARRL or RSGB handbooks from
the '40s, '50s or early '60s will give you tons of sample circuits.

--
Tim Wescott
Control systems and communications consultinghttp://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes,http://www.wescottdesign.com/actfes/actfes.html

Found one at http://www.oldradios.co.nz/hikers/52octalhikersamp.jpg
Would P-T156 at www.tubesandmore.com work for the transformer

 

[Don Bowey]

On 4/22/08 8:54 AM, in article
90e54e91-01ec-4bc6-9e68-3662d7e70470@b64g2000hsa.googlegroups.com, "Dave.H"
<the1930s@googlemail.com> wrote:

On Apr 22, 2:12 am, "Dave.H" <the19...@googlemail.com> wrote:
Hi, I'm looking for plans for a 1 or 2 tube low voltage amplifier to
go with a regenerative radio. Does not have to be the best, but needs
to drive at least 250 mW speaker, preferably 1 watt or more.

Thanks, Dave
Australia

Going off topic a bit here, concerning the regen radio previously
mentioned, that I've yet to build, there are some connections I'm not
sure of, first is the A connection, this doesn't appear to be the
antenna connection,

The "A" on the top end of the coil is the antenna. The "A" terminal strip
is the 1.5V filament battery + connection.

second is the B+ 1 1/5 v connection. Do they mean
A+ 1 1/5, even though it's not connected to the + filament pin?

The schematic is incorrect, so it's hard to tell what's up without guessing.
Also, no tube type is shown.

The lower grid in the tube schematic is drawn out of place. It should be
drawn above the grid that is connected to the grid-leak R/C parts. The grid
with the grid-leak parts is called the control grid. The out of place grid
is, I' sure, a screen grid. A screen grid requires a positive voltage, and
in *most* circuits it is provided by a suitable resistor from B+. I don't
really understand what the "B+ 1 1/2 V" note is intended to mean, *unless*
it is the authors intention to denote it is 1.5V "B+" for the screen. In
any case it indicates you should use a 1.5 V battery, connecting the +
terminal to the screen grid, and necessarily connecting the - terminal to
the E/B-/A buss.

Link to the schematic http://www.oldradios.co.nz/hikers/51hikers11.jpg

Thanks, Dave
Australia

 

[Dave.H]

On Apr 22, 2:12 am, "Dave.H" <the19...@googlemail.com> wrote:

Hi, I'm looking for plans for a 1 or 2 tube low voltage amplifier to
go with a regenerative radio. Does not have to be the best, but needs
to drive at least 250 mW speaker, preferably 1 watt or more.

Thanks, Dave
Australia

Going off topic a bit here, concerning the regen radio previously
mentioned, that I've yet to build, there are some connections I'm not
sure of, first is the A connection, this doesn't appear to be the
antenna connection, second is the B+ 1 1/5 v connection. Do they mean
A+ 1 1/5, even though it's not connected to the + filament pin?

Link to the schematic http://www.oldradios.co.nz/hikers/51hikers11.jpg

Thanks, Dave
Australia

 

[Don Bowey]

On 4/22/08 10:40 AM, in article
4e96a299-af7d-419e-a6c8-e7053078c38e@c65g2000hsa.googlegroups.com, "Mike
Silva" <snarflemike@yahoo.com> wrote:

On Apr 22, 1:23 pm, Don Bowey <dbo...@comcast.net> wrote:
On 4/22/08 8:54 AM, in article
90e54e91-01ec-4bc6-9e68-3662d7e70...@b64g2000hsa.googlegroups.com, "Dave.H"

the19...@googlemail.com> wrote:
On Apr 22, 2:12 am, "Dave.H" <the19...@googlemail.com> wrote:
Hi, I'm looking for plans for a 1 or 2 tube low voltage amplifier to
go with a regenerative radio.  Does not have to be the best, but needs
to drive at least 250 mW speaker, preferably 1 watt or more.

Thanks, Dave
Australia

Going off topic a bit here, concerning the regen radio previously
mentioned, that I've yet to build, there are some connections I'm not
sure of, first is the A connection, this doesn't appear to be the
antenna connection,

The "A" on the top end of the coil is the antenna.  The "A" terminal strip
is the 1.5V filament battery + connection.

second is the B+ 1 1/5 v connection.  Do they mean
A+ 1 1/5, even though it's not connected to the + filament pin?

The schematic is incorrect, so it's hard to tell what's up without guessing.
Also, no tube type is shown.

The lower grid in the tube schematic is drawn out of place.  It should be
drawn above the grid that is connected to the grid-leak R/C parts.  The grid
with the grid-leak parts is called the control grid.  The out of place grid
is, I' sure, a screen grid.  A screen grid requires a positive voltage, and
in *most* circuits it is provided by a suitable resistor from B+.  I don't
really understand what the "B+ 1 1/2 V" note is intended to mean, *unless*
it is the authors intention to denote it is 1.5V "B+" for the screen.  In
any case it indicates you should use a 1.5 V battery, connecting the +
terminal to the screen grid, and necessarily connecting the - terminal to
the E/B-/A buss.

Actually the circuit is employing a trick that was sometimes used in
low voltage applications. The tube control grid is connected to a
small positive voltage to help accelerate the electrons towards the
plate to obtain reasonable plate current, and the tube screen grid is
then used as the circuit control grid. Unless you've run across that
trick you'd be justified in thinking "what the heck?!"

Mike

I had wondered about such a thing, but dismissed it. I need to try it and
compare the result with the more conventional use of the grids.

Thanks

Also, I should have caught the use of that extra 1.5V cell to boost the B+.

 

[Mike Silva]

On Apr 22, 11:54 am, "Dave.H" <the19...@googlemail.com> wrote:

On Apr 22, 2:12 am, "Dave.H" <the19...@googlemail.com> wrote:

Hi, I'm looking for plans for a 1 or 2 tube low voltage amplifier to
go with a regenerative radio.  Does not have to be the best, but needs
to drive at least 250 mW speaker, preferably 1 watt or more.

Thanks, Dave
Australia

Going off topic a bit here, concerning the regen radio previously
mentioned, that I've yet to build, there are some connections I'm not
sure of, first is the A connection, this doesn't appear to be the
antenna connection, second is the B+ 1 1/5 v connection.  Do they mean
A+ 1 1/5, even though it's not connected to the + filament pin?

Link to the schematichttp://www.oldradios.co.nz/hikers/51hikers11.jpg

"A" is the filament voltage, "B" is the plate voltage and "C" is the
grid bias voltage (which is not present in the schematic you show).
When you see things like B+1.5V and B+9V that's referring to taps on
the B+ battery (many of them were made with such taps). Of course for
B+1.5V you could also use a separate 1.5V battery. Here's a schematic
that shows such a separate battery.
http://www.schmarder.com/radios/tube/hikers1.htm

BTW, the amplifier you're looking at won't give anywhere near 250mW,
much less 1W. The specs for the tubes show that they just get to
250mW output at 90V B+. At the 18V given in the schematic you'll only
be in the tens of mW. And also, you'll need an output transformer to
connect the amplifier to a speaker.

Mike

 

[Dave.H]

On Apr 23, 3:00 am, Mike Silva <snarflem...@yahoo.com> wrote:

On Apr 22, 11:54 am, "Dave.H" <the19...@googlemail.com> wrote:



On Apr 22, 2:12 am, "Dave.H" <the19...@googlemail.com> wrote:

Hi, I'm looking for plans for a 1 or 2 tube low voltage amplifier to
go with a regenerative radio. Does not have to be the best, but needs
to drive at least 250 mW speaker, preferably 1 watt or more.

Thanks, Dave
Australia

Going off topic a bit here, concerning the regen radio previously
mentioned, that I've yet to build, there are some connections I'm not
sure of, first is the A connection, this doesn't appear to be the
antenna connection, second is the B+ 1 1/5 v connection. Do they mean
A+ 1 1/5, even though it's not connected to the + filament pin?

Link to the schematichttp://www.oldradios.co.nz/hikers/51hikers11.jpg

"A" is the filament voltage, "B" is the plate voltage and "C" is the
grid bias voltage (which is not present in the schematic you show).
When you see things like B+1.5V and B+9V that's referring to taps on
the B+ battery (many of them were made with such taps). Of course for
B+1.5V you could also use a separate 1.5V battery. Here's a schematic
that shows such a separate battery.http://www.schmarder.com/radios/tube/hikers1.htm

BTW, the amplifier you're looking at won't give anywhere near 250mW,
much less 1W. The specs for the tubes show that they just get to
250mW output at 90V B+. At the 18V given in the schematic you'll only
be in the tens of mW. And also, you'll need an output transformer to
connect the amplifier to a speaker.

Mike

I'll use the 2 watt IC amp I have sitting around, easiest option.

If I have this right, and usually I don't, I connect the plus end of
the filament battery to the terminal simply marked "A", and a separate
"C" battery to the B+ 1 1/5v connection. Why is there only one
connection for the bias battery?

Will I get good lifetime out of a 9 volt transistor battery? I intend
on using a "D" cell for the filament, as I do with my other regen
radio (which BTW, you will find on Dave Schmarder's web page, very
first radio on his tube radio page).

 

[Mike Silva]

On Apr 22, 1:23 pm, Don Bowey <dbo...@comcast.net> wrote:

On 4/22/08 8:54 AM, in article
90e54e91-01ec-4bc6-9e68-3662d7e70...@b64g2000hsa.googlegroups.com, "Dave.H"

the19...@googlemail.com> wrote:
On Apr 22, 2:12 am, "Dave.H" <the19...@googlemail.com> wrote:
Hi, I'm looking for plans for a 1 or 2 tube low voltage amplifier to
go with a regenerative radio.  Does not have to be the best, but needs
to drive at least 250 mW speaker, preferably 1 watt or more.

Thanks, Dave
Australia

Going off topic a bit here, concerning the regen radio previously
mentioned, that I've yet to build, there are some connections I'm not
sure of, first is the A connection, this doesn't appear to be the
antenna connection,

The "A" on the top end of the coil is the antenna.  The "A" terminal strip
is the 1.5V filament battery + connection.

second is the B+ 1 1/5 v connection.  Do they mean
A+ 1 1/5, even though it's not connected to the + filament pin?

The schematic is incorrect, so it's hard to tell what's up without guessing.
Also, no tube type is shown.

The lower grid in the tube schematic is drawn out of place.  It should be
drawn above the grid that is connected to the grid-leak R/C parts.  The grid
with the grid-leak parts is called the control grid.  The out of place grid
is, I' sure, a screen grid.  A screen grid requires a positive voltage, and
in *most* circuits it is provided by a suitable resistor from B+.  I don't
really understand what the "B+ 1 1/2 V" note is intended to mean, *unless*
it is the authors intention to denote it is 1.5V "B+" for the screen.  In
any case it indicates you should use a 1.5 V battery, connecting the +
terminal to the screen grid, and necessarily connecting the - terminal to
the E/B-/A buss.

Actually the circuit is employing a trick that was sometimes used in
low voltage applications. The tube control grid is connected to a
small positive voltage to help accelerate the electrons towards the
plate to obtain reasonable plate current, and the tube screen grid is
then used as the circuit control grid. Unless you've run across that
trick you'd be justified in thinking "what the heck?!"

Mike

 

[Dave.H]

On Apr 23, 3:23 am, Don Bowey <dbo...@comcast.net> wrote:

On 4/22/08 8:54 AM, in article
90e54e91-01ec-4bc6-9e68-3662d7e70...@b64g2000hsa.googlegroups.com, "Dave.H"

The schematic is incorrect, so it's hard to tell what's up without guessing.
Also, no tube type is shown.

I'm planning on using a 1C5GT tube.

 

[Mike Silva]

On Apr 22, 2:48 pm, "Dave.H" <the19...@googlemail.com> wrote:

On Apr 23, 3:23 am, Don Bowey <dbo...@comcast.net> wrote:

On 4/22/08 8:54 AM, in article
90e54e91-01ec-4bc6-9e68-3662d7e70...@b64g2000hsa.googlegroups.com, "Dave..H"
The schematic is incorrect, so it's hard to tell what's up without guessing.
Also, no tube type is shown.

I'm planning on using a 1C5GT tube.

Here's what I think. I don't claim it's the only way, or even the
best way, it's just what I would be inclined to do. Take the money
you would spend on the 1:3 interstage transformer and spend it instead
on a power transformer and build yourself a battery eliminator that
will give you 90-110V to run a power output stage. Tap it down to run
your other stage(s). If you want, add a low voltage regulated DC
output for filaments/heaters. Then just use RC coupling between the
detector and the AF stage.

That's unless you were planning to use the radio away from AC power,
in which case ignore everything I said.

Mike