Transformers for Germanium transistors

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moonbird

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#1
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.
 
#2
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.
 

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#3
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.
 
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#4
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 🙂
 
#5
Russian Germanium Transistor rosetta stone

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???? :hypno2: thx.
 
#7
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.
 
#8
More info

kenpeter said:
... 600:600 telephone type might be the ticket. Bandwidth just about right for guitar.
Click to expand...

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.
 

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#9
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.
 
#10
Thanks much for the Great tips!!

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.
 
#14
NTE has a group of Germs.

I have a small pile of them. I am going to try using them to build some preamps and small power amps with to see if they sound decent as they are made now.

i would like to use the old split coil driver transformer for the Vintage sound.

You can find a list of their Germ transistors here:

NTE Electronics, Inc. - Keyword Search

This is a list of just "The Germs"...

I last two years have repaired several old Vox and other transistor amps, all with the driver transformer, the Vox being great bass amps, and super simple to build.
 
#18
moonbird said:
tiefbassuebertr

Whoa what a link -- electronics and history -- my favorite things -- thanks much!!!!!! :wave2:
Click to expand...

have a look also to this topic:
http://www.diyaudio.com/forums/parts/167680-vintage-transistors.html#post2201610
here you will find some pics of vintage data book covers. For an ordering about your local library/bookstore (interlibrary loan - for the aim of copy) you need in all cases the exact book title (fuzzy search isn't possible there).
On the pics you will find all necessary informations for ordering or copy service.
Vintage semiconductor/transistor databooks from Japan I will also try to find.

Back to the actually topic:
By vintage solid state amplifier topologies I note, that there are four basicly kind of transformer use (if not quasi complementary OTL is in use):

1) both transformer for driving and output (phase matching for the lower half)
2) only transformer for driving (phase matching for the lower half)
3) only transformer for output (phase matching for the lower half)
4) only transformer for output (actually OTL, only 1:1 or 2:1, DC-prot., impedance matching)
about
http://www.diyaudio.com/forums/soli...id-state-audio-amplifier-components-want.html
and
http://www.diyaudio.com/forums/parts/167680-vintage-transistors.html#post2201610
you will find schematics about all.
Then there are two kinds of different transformer core requirements:
1) DC biased 2) not DC biased
Sanshine (Xiamen) Electronics Co.,Ltd
Suppliers for tube audio transformers there are a lot. But who knows suppliers and manufacturers for such transformers appropriate for not OTL solid state topologies?

Of course the easist way is the use of OTL. But you will get a complete other THD spectrum than by no OTL concepts, because the main source for not symmetric THD behaviour is the transformer itself (and by OTL the phase shifting stage). Independend of the THD Value itself most musicans (especially by E-guitar and E-piano/organ amp) don't like the THD spectrum from OTL versions cause much more high order THD components (not necessarily odd order - odd order if low order also ear friendly distortion). Therefore I can well understand, why solid state amp concepts with transformer much more popular than OTL, even by some home audio/hifi lovers. McIntosh e. g. still uses output transformers in their amplifier.
Here some advices for service maintenence and modification on exist amps:
http://www.geofex.com/article_folders/voxamp/voxprot.htm
 
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#19
Patent No 3142807 (3,142,807)

By searching of informations about TEC I have found this:

Biasing for transistorized ("Solid State") amplifiers with transformer for driving the output power devices (driver transformer) - patent No 3142807 (3,142,807) Transis-Tronics, a corporation of California, Filed June 4, 1962
Biasing means for transistorized amplifiers
perhaps of interest.

by post #80 about
http://www.diyaudio.com/forums/soli...-amplifier-components-want-8.html#post2206915
you will find more about TEC's T15/S15 from 1962 (maybe very first solid state HiFi/home audio amplifier).
 
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#20
Many mains powered germanium amps used a driver transformer with the two PNP's in series and the speaker connected from the centre point. Many amps using driver and output transformers were typically for 12V operation. For example, I recall seeing an application note for a 50 W PA which had two OC29 outputs and an OC29 driver stage. It probably was a Mullard publication.
Several companies offer NOS devices and the OC29 was a prime example device but for 50W series mode output you probably need the higher voltage OC28's.

Sowter Transformers in the UK may still be able to provide suitable driver and output transformers for either style.

Cheers
 
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