Late 90's Peavey Transtube Supreme repair (power transistor questions)...

[tube power]

Tough first day of kindergarten.
All readings are around this range.
Readings look ok I guess, anyone think my transistors are not the problem, or am I reading this wrong?

Thanks...

[J M Fahey]

Fine. So far so good.
You are testing DC Gain/Beta, it shows around 20 which is normal for a power transistor.
Please set it to "short" and see what happens.
Or you can recheck with a modern multimeter in the diode check position.
You test continuity between 2 legs at a time:

You should have:

Red to Collector, Black to Emitter: open/over 1999 (no conduction)
Inverting :still no conduction.

Red to Base, Black to Collector *or* to Emitter: in both cases, around 600.
Inverting, in both cases open/no conduction.

Sorry but I'm not familiar with that transistor tester, find the Digital Multimeter more reliable.
Good luck.

[Enzo]

The tester checks for basic transistor function - does it "transist" or not. But the tester does not put real world conditions on it. Will that transistor still work when we try to drag 10 amps through it? Will it still be OK when it has 100v knocking on the door? Note that the tester has no adjustments for voltage or current. It tests that high powr transistor the same way it tests a little 2N3906.

Like most component testers, if it tells you the part is bad, it probably is. But if it tells you a part is good, it only is telling part of the story.

When the tester says "in circuit" that generally just means it uses enough testing voltage to turn on a semiconductor junction.

[tube power]

If this is correct for both pnp and npn...


Then here's what I get...
PNP

NPN

[Steve Conner]

OK, those transistors are f**!?d for sure. Even if you got the pinout wrong, a good transistor shouldn't give a zero reading for any combination of legs.

[J M Fahey]

Congratulations, now you are getting the hang of it..
On each left picture you are measuring a dead short (0.003 ohms is the resistance of the wires), from collector to emitter. That (irreversible) short is what blows fuses and burns speakers.
On both right pictures, you are measuring Base to Collector (watch the pinout); those "diodes" seem to be good, (forward voltage 0.403V; reverse over 3.000V , meaning no conduction) but it's irrelevant because already you have a short among other pins.
Now it's transistor exchange time, Baby.
Please somebody post the power amp schematic, because you probably have bad drivers or other components to check, plus some voltages.

[Gtr_tech]

From your pix there you have it connected wrong. The collector is normally the case connection on to-3s. You have the emitter lead to the case. I don't care for those jobs that make you identify the basing. I use the B&K 520b that doesn't care how you connect the leads.....there's just a 6 position switch that IDs it for you. Sure speeds things up. I use it so much for to-3s I made up a socket assy that plugs into the tranny checker. So I just shove the thing into the socket and flip a switch to check leakage if it checks good. Takes all of 5 seconds.

[tube power]

http://www.joeradachi.com/bansch.pdf

[tube power]

From your pix there you have it connected wrong. The collector is normally the case connection on to-3s. You have the emitter lead to the case. I don't care for those jobs that make you identify the basing. I use the B&K 520b that doesn't care how you connect the leads.....there's just a 6 position switch that IDs it for you. Sure speeds things up. I use it so much for to-3s I made up a socket assy that plugs into the tranny checker. So I just shove the thing into the socket and flip a switch to check leakage if it checks good. Takes all of 5 seconds.

I have the multimeter connected wrong?

[Gtr_tech]

I was referring to the transistor checker. Wasn't following this thread too closely.....looks like you got that straightened out already.

[J M Fahey]

Hi tubepower, thanks for the schematic.
You have already tested Q11 and Q13 as dead.
You already know you'll have to replace both.
As I told you before, I also suspect the drivers, Q9 and Q14.
Diode test them, all 6 possibilities (EC-BE-BC both ways).
For now, do not even pull them from the board, we want to know if any of them shows a "0" as you have already learnt to recognize.
We are taking a slow but sure path here, you need to be patient and will win.
*Probably* you'll need to change one of them too (or both).
Cost is nil, the only problem is time.
Also check the resistance of R105 and R115, they *might* be open, the correct value is 0.33 ohms, maybe your ohmeter will not show that exact value because the wire resistance alters such low measurements, but you should be in the ballpark.
Good luck.

[tube power]

No combination gives a zero on Q9 or Q14, typically .545 and 1.1710 and climbs, or .900 and climbs.
I left them on the board.

R105 and R115 both read 1.2
I left them on the board also.

[J M Fahey]

Good. Maybe you got lucky and only the output transistors shorted.
When are you getting your replacements?
*If* you have not ordered them yet (I mean, from a reputable supplier), then add a couple driver transistors too, just in case.
If not, well, assume they are fine and just replace the output ones.
Search the Forum and get the Peavey transistor equivalence chart, to know the commercial names , the ones you have come with "Peavey" names.
Also build a series lamp bulb limiter, nothing more frustrating than replacing something and see it go up in smoke, just because you did notice a 10 cent part which also needed replacement.
Search the Forum too for this.

[tube power]

I don't ever remember anyone describing me as lucky
I feel compelled to doubt myself, but I guess the meter is saying all else is well.
I like this person's limiter design...
Light Bulb Current Limiter

You guys have been very kind helping someone as challenged as me.
I can't wait to get this done so I can let you know how it goes.
I'm ordering from Mouser also so I guess it will be sometime late next week.
When the fake ones come it will be fun to open them up for a look inside.
I also gathered up a few basic books to study so I can educate myself further.
This seems like a great hobby for me since it also makes sense to know how to check my own gear.

Thanks to everyone who responded.

[tube power]

Here's an original with it's lid flipped...