Transformers for Germanium transistors

[moonbird]

Hello all -

I want to play around with making a small practice guitar amp with 50s-70s Germanium transistors. Getting the transistors is fairly easy - but knowing what interstage and output transformers to obtain is beyond my grasp (like the ones used in old transistor radios). Can't seem to find much about this topic anywhere. Does anyone have any clues?? Can you point me to info about selecting the right transformers? thx much.

[Bone]

Why do you need transformers. You can make a Germanium amplifier without them. What power do you want? Would 10 watts be enough?

How about this one? 10 Watts into 3 ohms. I don't know where it came from but I've made a few. I think it was originally an amplifier for an organ but works well on guitar with a suitable preamp.

Tony.

[moonbird]

Hey Bone --

Thanks much for the post -- from what I know (not much) this looks to be single ended OC35 OTL amp that is directly coupled (no interstage xformer required). Right? Can't read all the transistors -- could you help out there? How did the overdrive sound? Very interesting. thx again.

[Bone]

Yes you're right Moonbird. First and second transistors, are OC75 or NKT (Newmarket) 213, upper driver (PNP) OC81 or NKT271. Lower driver (NPN) AC127 or NKT717. Outputs can be any of these OC35, OC36, OC28, OC29 or NKT404. There are also many other alternatives which can be used. Never tried overdriving it, we were after clean then - before fuzz etc.

Tony

[moonbird]

Well .. the only real quantities of Germanium transistors these days are -- Russian seems like (same as vac tubes). Does anyone out there have a handy equivalent chart for Russian germanium transistors???? thx.

[wahab]

AD161/162 TO66 complementary pair as output devices where very
good in their times..
Enough for a 5 to 10w rms/8r amplifier of great quality...


http://www.datasheetarchive.com/AD161-datasheet.html

[kenpeter]

PNP germaniums can still be had fairly easy.
Tanner Electronics in Dallas has a boatload
in all crazy shapes and sizes for cheap...

Unfortunately NPN are not so easy to find.
You might end up wanting for a transformer
after all? 600:600 telephone type might be
the ticket. Bandwidth just about right for
guitar.

[moonbird]

Originally Posted by kenpeter

... 600:600 telephone type might be the ticket. Bandwidth just about right for guitar.

Thanks for the post Ken. Are you referring to the driver transformer here?? For which transistor? Sorry for the noob questions.

I gotta bunch of the attached laying around (See the B2136). Would these work -- if not what the heck in the instrument amp world *could* they be used for . What would be a good source for the proper transformer. thx again.

[wg_ski]

Which circuit configuration are you trying to build - the "classic" push-pull with a center tapped driver and output transformer? Mouser has some of those - but they are limited to about 400mW. For higher power, you could use a standard 60Hz 12-24VCT secondary as a center tapped autotransformer (take speaker output off the collectors - leave the 120V "primary" open unless you want to step it down). For the driver, just drive the 120V winding and use an appropriate ratio -- maybe a 48V trafo - you won't need a lot of VA.

For a totem pole driver you need a dual secondary. A 600:600 dual secondary telecom trafo seems like a good idea, but you really need about 30 ohms to drive the bases. Again, in the absence of the "right" trafo I might look at 60 Hz stuff if you just don't need great HF response.

[moonbird]

wg_ski - this is exactly the type of "ball-park" suggestions I needed especially about the low VA comment. I have some EIs and toroids in the range to play with. Would have figgered it out eventually -- but this gets me close enough to start breadboarding. I am looking PP to start but would like to try SE too. My preamp will be a two-stager using the 12AU7. It is called the VALVECASTER on da Web. Given all this, what Ge transistors would you recommend I start playing with for the outputs -- if I could get along without the driver tranny so much the better to start. Looking small to learn - 1w output. thx again.