3 W Ge Transistors Power Amp

Fernando · Post by **Fernando** » 25 Nov 2009, 19:43

that TV amp looks great!

lolbou · Post by **lolbou** » 25 Nov 2009, 21:59

Here's the schem (the details of the first stage are missing but are basic)...

Must have the pcb layout somewhere, but can't find it... Just to have a trackside topology...

himister · Post by **himister** » 25 Nov 2009, 23:29

Thanks Laurent. This one looks also very interesting, tone control is almost same as in BMP. It would be nice if you find layout so we could do some redrawing and use that old-timer too.
Cheers.

Fernando · Post by **Fernando** » 26 Nov 2009, 00:24

interesting the tone control similarity!

Fernando · Post by **Fernando** » 26 Nov 2009, 13:06

Alessandro answered:

>
I've built this amp a couple of years ago, I believe that *any* germanium diode would work in this project, and 1N60 should be an easy-to-find candidate.
I've not tested it yet, but Schottky diodes should work as well, as long as they have a low voltage drop index (usually stated as "Vd" in component datasheet).
>

Fernando · Post by **Fernando** » 26 Nov 2009, 13:16

Now for the pre.

My plan is to implement a 12V tube pre using 12U7 or 12AU7 based on the examples around (Sopht amps, Valvecaster/Vibracaster, TubeTown overdrives, TubeCricket, etc.) This would be great since with the GE amp there's no output transformer needed, saving money and weight vs a 12V all-tube amp.
Also, a tremolo can be implemented as in the Vibracaster!

Another interesting option would be a JFET tube simulation: to use the pre section of ProfessorTweed, EnglishChannel, Matchbox... FetzerValve being the simplest. But they are designed for 9V... but I guess that with a correct BIAS adjust they would work OK at 12V???
(what do you think about running those JFET circuits at 12V?)
This would make easy to have an amp with two (or three!) channels! Say a Tweed and a Vox channels, switchable, into the GE amp! :P

A third option would be to design a GE transistor guitar pre with a similar topology of the classic amps (as in the JFET examples above) But I can't design circuits, only build them...

My plan is to be able to use it from both a 12V DC supply and a 12V battery

SPeter · Post by **SPeter** » 26 Nov 2009, 17:40

Fernando wrote:
Another interesting option would be a JFET tube simulation: to use the pre section of ProfessorTweed, EnglishChannel, Matchbox... FetzerValve being the simplest. But they are designed for 9V... but I guess that with a correct BIAS adjust they would work OK at 12V???
(what do you think about running those JFET circuits at 12V?)
This would make easy to have an amp with two (or three!) channels! Say a Tweed and a Vox channels, switchable, into the GE amp!

My plan is to be able to use it from both a 12V DC supply and a 12V battery

I had similar ideas but just with switchable R.O.G. Fetzer and MarshaValve in front of the circuit! Another option is a clean MosFet Preamp with good tonestack.

Cheers,

Peter

slim_blues_boy · Post by **slim_blues_boy** » 22 Jan 2011, 13:46

hi, can I change matched pair AC187K/AC188K with matched pair AC128/AC176?

RnFR · Post by **RnFR** » 23 Jan 2011, 04:45

not sure. but i finally pulled out my "matched" pair of 187/188 equivalents the other day, and they are hardly matched to say the least. one has a decent gain of about 100, and the other has a gain of something like 12

. anyone know if these will work for an output stage? maybe they were meant for something else?

slim_blues_boy · Post by **slim_blues_boy** » 23 Jan 2011, 19:34

how about the hfe of the transistors?
is it necessary to use transistors in certain hfe range? any specific gain?

Fernando · Post by **Fernando** » 18 Apr 2012, 14:52

Anyone built this amp yet?

Opinions, experiences...

best to all

Fernando