Tube Amp

On Apr 22, 1:23=A0pm, 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. =A0Does not have to be the best, but need=
s
> >> 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. =A0The "A" terminal str=
ip
> is the 1.5V filament battery + 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?
>
> The schematic is incorrect, so it's hard to tell what's up without guessin=
g.
> Also, no tube type is shown.
>
> The lower grid in the tube schematic is drawn out of place. =A0It should b=
e
> drawn above the grid that is connected to the grid-leak R/C parts. =A0The =
grid
> with the grid-leak parts is called the control grid. =A0The out of place g=
rid
> is, I' sure, a screen grid. =A0A screen grid requires a positive voltage, =
and
> in *most* circuits it is provided by a suitable resistor from B+. =A0I 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. =A0I=
n
> 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

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.

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&#4294967295;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. &#4294967295;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. &#4294967295;The "A" terminal strip
>> is the 1.5V filament battery + connection.
>> 
>>> second is the B+ 1 1/5 v connection. &#4294967295;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. &#4294967295;It should be
>> drawn above the grid that is connected to the grid-leak R/C parts. &#4294967295;The grid
>> with the grid-leak parts is called the control grid. &#4294967295;The out of place grid
>> is, I' sure, a screen grid. &#4294967295;A screen grid requires a positive voltage, and
>> in *most* circuits it is provided by a suitable resistor from B+. &#4294967295;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. &#4294967295;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+.

On Apr 22, 2:48=A0pm, "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 guess=
ing.
> > 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