Help identify another germanium

[skidmark]

You always should include the community here in issues like this. Have you posted a picture of the amp in question? I’m sure someone will know what amp it is or not. Either way we could have known this or not a few posts ago. But we need a schematic to really be of any use immediately. No schematic. Then get there with the camera and take pictures of the boards and things. Especially the output section. Interstage transformer? What resistors are we gonna have to adjust? These are the only important things at this moment. Without more information we are in the dark.

I would have provided a schematic in the beginning if I had one, or even the name of the amp, but I have nothing! I've spent a bit of this evening reverse engineering the amp and I'm pretty sure I've located the bias resistors. Right now I'm trying to convince myself
to crank up my schematic capture program and start record my discoveries. It's a cheap amp that a buddy of mine really wants to get going.

P.S. Please excuse my ignorance, but how do I include the community?

[DrGonz78]

P.S. Please excuse my ignorance, but how do I include the community?

By taking a picture of the amp and posting it for all to see. Perhaps someone might recognize it or have some feedback.

[R.G.]

Ok gents, I've decided to bite the bullet and convert to silicon. I've never done this before. I'm quite capable of doing it, but with any new thing there's always the possibility of some
gotcha's out there lurking. So with that said could any one of you educate me. You do not have to dumb it down too much, I HOPE. I've read enough to know that one of the things
is changing the bias from .2 I think, to .5 to .6 volts, but that is about as far as I know. So with that, class is in session if one of ya don't mind teaching.

Good call. I wrote up a procedure for doing this on the Thomas Vox series of amps that used germanium outputs. I can dig that out, but you're already on the right track; just change the bias so it can produce about 0.5 to 0.6V. A good trick is to use the emitter resistors to measure for idle current, get that close, then look for crossover, just like with complementary output stages.
If it's a transformer driver type, there is nearly always a resistor divider providing the idle bias, identical for positive-side and negative side. In this case, just increasing the base-emitter resistor does the trick.

[skidmark]

The elephant in the room. I apologize guys. I've had this small amp upside down for so long decomposing the circuit I forgot the amps name was on the other side. So I lied to all of ya.
Pictures attached.. Its an Audition amp.

Al

[skidmark]

Good call. I wrote up a procedure for doing this on the Thomas Vox series of amps that used germanium outputs. I can dig that out, but you're already on the right track; just change the bias so it can produce about 0.5 to 0.6V. A good trick is to use the emitter resistors to measure for idle current, get that close, then look for crossover, just like with complementary output stages.
If it's a transformer driver type, there is nearly always a resistor divider providing the idle bias, identical for positive-side and negative side. In this case, just increasing the base-emitter resistor does the trick.

Just keep your write up close in hand in case. I'm fairly confident I can pull this off, but just in case its nice to know I got some backup.
al

[mozz]

Teisco. Maybe one of these?

[DrGonz78]

Check this link out and see if it is a similar model Audition amp. Galaliex drew up a schematic.

[R.G.]

Yep, if it's like the CM-66 and CM- 88, the trick is to increase the small-value resistor in the two divider chains. Silicon will need about 2.5-3 times the resistor value, at a first guess.
These kinds of output stages have no, naught, zero, zip, nada DC connections to the drivers. All of the DC conditions on the output are done by biasing the output transistors and their idle current gain. The ones with an output cap are less prone to burning up speakers from mistakes in biasing and transistor matching.
It is also possible to convert them to NPN by rewiring the output stage. A 2N3055 would probably be great for that output stage if you're a glutton for punishment.

[skidmark]

Check this link out and see if it is a similar model Audition amp. Galaliex drew up a schematic.

Thanks a million DrGonz. I'll hopefully get a lot of millage out of these 2. Also, I went to the you listed. When I got there a note on the page suggest the picture were deleted.

[DrGonz78]

Yeah props to Galaiex for his time and hard work. He is a member here too. Not sure about the missing files but I will check it out. Glad to hear you are finding all the resources to make working on the amp easier.

[g1]

The missing files at the ssguitar link have been restored but only show up for members. Sign-up is free.

[skidmark]

I am signed up and signed in. Still see nothing except that image have been removed. However I did capture the images on this page.
Al

[J M Fahey]

Just thinking aloud and in no particular order:

1) I *usually* convert Germanium to Silicon but *here*, given the absolute lack of data , zero, zilch, plus the hard to read PTP on terminal strips construction, (a PCB would be much easier), etc. , I would take the shortest path, which would be to get a suitable TO3 PNP Germanium, anything standing 25V or better, 3 to 5A or larger, and put it where the dead one was.
anything available at one of the "good" suppliers,
Amp "should" start.

It is very low powered, main filter cap is rated only 15V, so supply must be a couple V less so amp is probaly some 4W RMS or so.

Enough for a student in any case.

2) again against usual procedure, even though amp is some 50-60 y.o. . for now I would refrain from replacing caps (un less visibly exploded, squirting liquid, etc.), focusing on making it start.

Only after making certain it works I would start polishing it.

I HATE adding new variables and unknowns to the ones I *already* have

Thanks Mozz, Galaxieex and all others whon shed light on this *obscure* subject.

[g1]

I am signed up and signed in. Still see nothing except that image have been removed.

That's strange. I get 8 photos at the bottom of the first post in that thread. I'm sure galaxiex would not have an issue with it being posted here but I'm not going to do it without his permission.
I will PM you his power amp drawing.

[glebert]

While I don't think it is electrically similar, the cosmetics (except color) on that amp look just like a Kay Vanguard 700.