Tube Amp

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

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

On Apr 21, 12:12=A0pm, "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. =A0Does 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

On Apr 21, 12:12=A0pm, "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. =A0Does 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

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

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

On Apr 22, 11:54=A0am, "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. =A0Does 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. =A0Do 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

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).

On Apr 22, 1:14=A0pm, "Dave.H" <the19...@googlemail.com> wrote:

> I'll use the 2 watt IC amp I have sitting around, easiest option.
>
> =A0If 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. =A0Why 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.

Wire up the batteries exactly as shown on the schematic at the bottom
of the page I linked (http://www.schmarder.com/radios/tube/
hikers1.htm).  Yes, you should get good life out of your 9V battery.

Mike

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