Thanks A LOT for all your useful efforts to help DIYers   :dbtu: :dbtu: :dbtu:

Thanks.
Looks like Jordan was quite the pioneer, this amp has the basic structure of a Polytone amplifier.
Amazing.

Thanks.
INCREDIBLY advanced (for 1970) :Op Amp preamp, variable damping output, Op Amp driven power amp, green fluo panel paint illuminted by a UV tube (now I know where did Trace Elliot get the idea from), etc.

That said, power stage is operated pure Class B and has no provision for biasing, so crossover distortion is inevitable.

Which played LOUD in a live situation is almost undetected; big problem at bedroom levels though.

Use as is and don´t get fancy 
And not sure about actual function of that jack, it might be a supply jack for an externally connected device or even to feed the desk lamp or anything.
You (we)  can´t advance until you draw a proper schematic.
Not sure you´ll want to though.

Just look at older Galaxiex posts, who buys old "orphan" SS amps and draws the schematics himself.
Plenty of examples.

Probably a custom build or small run production focused on travelling salesmen and such.
Besides the front panel, they don´t seem to have invested much time in it: cheesy power supply built on perfboard with two transformers in parallel (were they on sale?), using a store bought prebuilt amp module , minimal passive input circuitry built on tagboards, this amp didn´t even deserve its own PCBs.
Anything else, only a local guy would know.

Excellent work.Please sharevthe schematic when you have it.
I´m specially intrigued by the damping control.
I have my own, but there´s many ways to skin a cat

Excellent book.

But if you want to design, start with this:  http://www.rason.org/Projects/bipolamp/bipolamp.htm

You can´t use 2 or 3 transistore until you learn how to use one
Go step by step.

Cool  :dbtu: :dbtu:
Good to know, nd thanks for the post, it´s useful to remind people that not all problems are just "bad parts"  but very often what I call "mechanicals"  for lack of a better word: dirty/cracked pots; dirty/weak/worn jacks/switches/connectors/fuse holders, riveted ground lugs, cracked tracks, etc.

One modern very common pest is cracked led free solder  :grr :grr :grr , sometimes very difficult to detect.
Later I will edit this post and show an "impossible to see" solder crack a colleague found in a Fender amp .... of course can happen on any other brand 

And casually it caused lots of crackling 

QuoteSometimes Enzo you can be a real PITA.  In spite of your electrical genius.

Ihope you choke on that statement.

QuoteI have 6 amps floating around here and I don't need the 3210 right away.

Which means?

QuoteAnd yes I will replace known components that have a history of failure.

Not in your amp.
Hey, you might take some Diabetes medications because panchreas have a history of failures.
And some heart medicines too, those are *known*  to fail.
CDC statistics can´t be wrong 
What about Parkinson medicines ...or Alzheimer .... or ... or ... or ....
There´s thousands of *common problems*  in Human bodies. 

QuoteBefore I even use them.  Like the brakes on my 1990 Ford Ranger I bought used and had dropped off at my mechanic and had them overhauled right away.

Here is the main fallacy in your reasoning: mechanical parts wear out, tubes wear out, solid components (active or passive) do not ... they either work or die, unless abused and that kills them in a short time, often with visible results ... not the case here or at least you are not reporting that.

QuoteI don't like catastrophes.

Nobody does, and I don´t see any caused by "parts wear" either.
Only parts where some of that might apply are electrolytic caps, and even so I´d try to detect some problem first, such as increased ripple.
You have checked nothing yet.

Quote
So I will replace the output MOSFETs

Why? they do not wear; they either work as in the first day or die, which is very unlikely.
But ... but .... I read about of them blowing!!!! 
True enough, but they didn´t "die" , they were "killed", not the same by a country mile. Hope you see the difference.
The Guitar Amp World is abusive on amplifiers and that´s an understatement; amps DO get used at full power for long hours, horrible shorted/cracked plug/stepped on/yanked/poorly plugged cables are *routinely* used to plug them into cabinets, users often get (cabinet)  trigger happy and connect any odd box they find laying around, never check impedance (what???  xP ) , THAT is the "common problem"  behind 95% of published failures.

Quote
and then run the 3210 at 4 ohms and see what happens.

Then there is a reasonably high possibility that you will blow them 
new or old have exact same specs, will use exact same heatsink, both are just as capable of driving a 4 ohm load (or not) , so replacing Hitachi by Exicons will not improve your amp a bit.
As I said, there is not a "wear" factor involved, but a specs/rating one.

Since this is not a rant against you, but in any case a "get real"  one, now I´ll try to help you with your amp, but let´s address the real problem instead of imagined ones :
in my opinion, that is an excellent amp, with just one problem: the output devices are simply not enough for a 4 ohm load.
They are electrically too close to maximum specs (so rating same spec fresh ones will not help) and I *guess* they are poorly cooled.
Can you please post a couple pictures showing the heatsink and how are the transistors mounted?
If possible, from both sides (fins and inside the chassis) plus a somewhat farther away one showing its general position inside the cabinet, also showing the back perforated panel.
The idea is to check whether you can add an extra pair of power devices or if physically impossible, replace them by "double die" Exicons (essentially 2 chips each inside same TO3 case) and/or add a small PC type fan *somewhere*  to improve cooling.

As said before, the idea is to avoid killing them, they are not dying on their own .

On the same token, make/get a *good*  pair of speaker cables, keep a spare nearby just in case, make a point of always checking connections (valid for *any* amp) and you will have a reliable amp for the next 30 years (or more )

Funny and sadly not unusual: one of the filament wires was wrapped around a 6V6 socket leg *and*  heatshrinked ... but never soldered 

What is somewhat unusual is that apparently the 7812 regulator was running too hot and being the plastic insulated back type, self-turned OFF thermally.
Weird because I don´t think Crate who are experienced builders would specify a regulator (or any power device) *too*  close to maximum rating.

Guess there is a first time for everything  xP

Agree and add: study how Operational Amplifiers work, since they are a MAJOR building block there´s tons of books and articles explaining them; which also explain NFB since that´s the tool to make them do what you want.
And of course the differential amplifier is explained, since it constitutes the input stage of an Op Amp.

Once you understand this, modern SS Power Amps are simple: they *are* an Op Amp !!!!!! ... just a beefy kind, able to drive speakers with high power.,

Agree and add

QuoteI figured they are both solid state could I get the fender distortion sound from the yamaha?

Hey !!! they are both cute, have 4 legs, tail, paws, whiskers, glow in the dark eyes,  they are both felines!!!!

I think I will get inside that cage, ... after all ..... what could go wrong?  :loco :duh


Short answer: get a *good* distortion pedal ... or two if you feel particularly wicked  8| , and plug them into your loud killer Yamaha.

In the old days they often underbiased everything so thermistors or diodes only had to track ambient temperature, now once you set the proper current the transistors start dissipating even if you do not drive them, so things become critical.
Yes, glue thermistor to one heatsink (or clamp it with a small strip of aluminum or even a piece of thick copper wire) so it *really*  tracks it , add a 100 ohm trimmer and start raising bias until crossover notch (which is visible at *low* power) just disappears.
Doublecheck by measuring current, you may measure voltage drop across emitter resistors, once you get them passing, say, 10mA they are beyond the crossover area.
Play at good volume for a few minutes, so heatsinks get warm to the touch, and measure idle current again.
If same or lower, you are fine; if higher the system is not stable and yu should bias it colder.

FWIW most old transistor amps, specially those transformer driven such as VOX or Standel *did* have crossover distortion ... or else.

Part of the early rejection of transistor amps, at least this one problem was real.

Well they say so themselves
Just ground the purple wire, but first doublecheck it has no continuity against *any* other wire.
Voltage and VA is fine, as Enzo said.

Quote from: galaxiex on April 05, 2017, 11:31:00 PMPlugged it in today and something is not right...

Very "fizzy" sounding distortion follows all notes but more noticeable on Bass notes,
especially noticeable if you just pick a single note and let it decay.
As the note decays the "Fizz" becomes very obvious and also seems to modulate, or pulse.

Crossover distortion.
That said, bias is not adjustable and even if it were, you might risk thermal escalation and eventual transistor burnout, doubly so because those are Germaniums.
Small consolation: amp probably works the same as when it left Factory in the 60´s 

You *might* add a 100 ohm trimmer in series with 200 ohm bias resistor , put out low power 1 or 2 V RMS into a load, scope it, and increase bias slightly until crossover notch/kink disappears but tou´d better epoxy thermistor to one heatsink so it tracks temperature better.

**Personally** I´d replace power amp with a single supply LM3886 ; sound will not change at all, butvreliability will improve 1000% .
Same supply, in/out capacitors and gain of course.

OR mod that amp to a Silicon version using same PCB and 90% of current components and add the proper biasing network.

Again this would not change sound, SS power amps in general are just "large OpAmps"  and by definition "all sound the same".

QuoteFor a quick check I put a scope on the output and got a "kinda sorta" normal waveform,
so I scoped the DC power supply.

The audio is modulating the DC power supply.

Where there should be a nice flat line of DC, the audio shows up on the power supply as a very distorted waveform.
Also, when not playing any notes, the DC shows a saw-tooth waveform.

Perfectly normal.
I bet you increased Scope gain a lot just to see that, we are tlking  few hundred mV at most (on the powe rail), a couple V ripple when full blast.

Quote
All voltages look normal when checked with a DVM.

o no problem there.

QuoteWhere should I start to look?
All caps are new and this amp was working fine a couple weeks ago.

Bad bridge diodes? Something else?

You probably only *noticed* it now ... unless a speaker is scratching which is something else.
Try it with another known good speaker.