Peavey Renown

[Hawk]

Thanks Enzo. I'm now getting 23.95 volts on all collectors at 77 volts from the variac.

Peavey sent me the wrong parts. They are going to send me the correct ones with no extra charge.

The original transistors in the amp only came with a shim per transistor and nothing else. Somehow,  the screws through the heat sink were not touching the heat sink when this amp was  built but when I replaced the transistors I was having a hell of a time getting them not to short against the chassis In fact, just as a quick fix, I've used electrical tape on the screw to see if that would work and it has. Crude yeah, but I was determined to see if that was the problem--it's been a rough ride!!

The shims appear to be in good shape.

The amp is unloaded.

So, wouldn't plastic screws be a good solution for these output transistors??

Thanks for all your help everyone. Is it too early to say I might be getting somewhere?

[Enzo]

There should be ample clearance for the screws through the holes.  No, you cannot use plastic screws.  The screws are what connects the collector - which is the transistor case - to the circuit board.  Also, as the parts get hot, the screws will soften and get weak.

Unless the heat sink is somehow detached from the circuit board, the holes should align.

really, what voltages you get at 77v on the variac are not meaningful, other than to tell us they are not shorted out.  I am hoping you get that 23v only on the upper side output transistors, remember the lower side ones have their EMITTERS connected to V-.  The collectors of the lower ones are connected to the output bus - the speakers.

See, I knew Peavey would want to make it right.  I have been running a pro shop the last 29 years, and PV has always been at the top of my list for customer friendly companies.

[Hawk]

The amp will function with a transistor missing on each side.  I wouldn't expect it to go to full power, but you can play it at reasonable volume.  I also wouldn't play it for extended periods that way.

But the value of doing that is you have the opportunity to find out if other parts are bad that were not discovered while the amp was blowing fuses.  We don't want to order our one part only to find one more part reveals itself after we get the first new one.  You may find you need a few parts, and that helps put together a good order.

This was Enzo's response earlier on in this thread.  So remembering this and, after making sure the collectors weren't shorting to the heat sink: I ran the amp with variac at 49 volts, at low volume, light bulb not lighting up, and two less output transistors (still waiting for the correct transistors to arrive), plugged my guitar into the amp and: Sound!!! Yes, sound!!! So this looks very good. I remembered Enzo saying that these transistors turn on at lower voltages so that we can troubleshoot the amp to find out if anything else needs replacing.
Will follow up once I insert the new transistors! Fingers crossed!  :tu:

[Hawk]

Okay so Peavey sends me the new transistors and they are NPN but the woman on the phone had to do a lot of cross-referencing and I'm concerned that what she gave me may be incorrect...again!

Tested on my Peak Atlas DCA55:

Old Transistors (Ic 2.5ma test current), Hfe-27 VBe-.58 (Test current Ib-4.83mA, Leakage Current Ic=0
New Transistor (same test currents) Hfe=59!!! VBe-.62 everything else the same.

What am I doing with transistors with current gain of 59? Can these be used, or will the extra current cause problems?

[Enzo]

I've never bothered to measure them, they are current amps.  Try measuring them with 3 or 4 amps running through.

WHAT transistors did they send you?  The originals were sj6392.  Those were generically replaced by either 2N3055A or MJ15015.  The order number was 70483100.  They have since changed some numbers to I think 304xxxx format.  Frankly I just use MJ15003 and am done with it.  If you don't tell us what you got, we cvan't tell you if they are right.

[Hawk]

They sent me 70484200/MJ15024G.  I have the Peavey cross reference chart which shows the replacement info you've given me.

On the phone, when I re-ordered 2x, I told them it's SJ6392. I also told them the replacement I see on my chart which is all over the internet and matches your info, and they say that this has been changed and they read a bunch of engineer's notes on the computer telling them to send me something else. I think I need to speak to a supervisor when I re-order for the 3rd time. Friendly, but confused.
If I can't get satisfaction from Peavey maybe I should follow your advice and pick up two MJ15003's--do they have to be a matched pair if only one transistor is shorted? Will one do the job?

[Hawk]

2N3055's. My local electronics supply shop has these in stock....hmmm

[g1]

  Those will be fine.  They are equivalent to MJ15015 but with a higher voltage spec.
For Peavey, it means one less part to stock, as they can use them for both MJ15015 and MJ15024 applications.
  You can consider it an upgrade, or "beefier" part. 

[Hawk]

By "those" you mean MJ15024G? Just need to make sure! Thanks for your help!! Appreciated!

[Enzo]

MJ15024 is a perfectly fine sub for the MJ15015.  I often refer to the 15024 as universal replacements.  They have heftier specs than the smaller ones.  I stock both those and the MJ15003, mainly because there are a lot of other amps that use MJ15003.  Were that not the case, I would stock only the MJ15024 as it will cover the lesser ones.

I can tell you all the same engineering stuff too, but I will just say from experience, the MJ15024 will work fine.

There are variations on 2N3055, and the 2N3055A they used would have been tested for 100v, are the local ones thus tested?  Also, the 2N3055 as a commodity part of old is often counterfeited.   I only buy my parts from trusted suppliers.

[J M Fahey]

2N3055's. My local electronics supply shop has these in stock....hmmm

Sadly, any shop bought 2N3055 must be considered fake or at least unable to service old guitar amps.

There's 2 kinds:

1) FAKE FAKES , crap of the worst kind, with doubtful dies, no internal copper heat spreader, the works.
I have tested some which stood 48Vce or less (original spec is 60/70V), even have a couple which measures 24V  :trouble

2) real ones but barely meeting old manual specs, forget surpassing them.

Prices have plummeted: an old RCA would cost $5 to $7 today while I can buy all the 2N3055E I want, very good ST brand , for 67 cents each in closed Factory cartons, with all papers ... but they explode in my old amps.
And I can't complain, they (just) meet all datasheet specs.

Very good for 40W/ch home Hi Fi amps with, say, +/- 28V rails.

[Hawk]

Great info! Since only one is shorted can I replace just that one or should I replace both--i ask this because Peavey sells this particular transistor as a "matched pair" so I bought two....

[Enzo]

Often as not, these old peaveys kill a single transistor, and that is all it takes to fix it, but you now have a spare at least.

[Hawk]

Okay, this amp works!!! Thanks Fahey, Enzo, and G1 for sticking with me on this. Learned a ton! Couldn't have done it without everyone's help. :tu: :tu:

[Hawk]

Anyone know the pin out configurations for the foot pedal that comes with the amp? It has an xlr end. Has a red, green, black and ground wire. Wires were ripped off the terminals and I'm not sure how to reconnect.

Thanks.