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Peavey "Vintage" Guitar Amp-What Transistor?
Peavey "Vintage" Guitar Amp-What Transistor?
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Old 18th May 2018, 11:55 PM   #1
ampexperts is offline ampexperts  United States
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Default Peavey "Vintage" Guitar Amp-What Transistor?

I have a Peavey Vintage amp in the shop that's not making any positive peaks. The output tubes are driven by solid state plastic transistors.

They have a house number on them, making identification difficult.

Cannot find schematic online.

This is a hybrid SS/Tube amp.

The transistor in question has the following markings:

G4278
GRRCA427

Can anyone identify the transistor?
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Old 19th May 2018, 02:47 AM   #2
llwhtt is offline llwhtt  United States
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64278 = MJE3439 There's a Peavey transistor cross reference on the interwebs, just Google.

Any luck on those SAE relays?

Craig

Last edited by llwhtt; 19th May 2018 at 03:00 AM.
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Old 19th May 2018, 03:35 AM   #3
steveu is offline steveu  United States
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I found these:
hybrid amps
Music Man Amps Discussion Forum: JE1692 Substitutes
Note the transistors are TO-220 NPN driving the 6L6 cathodes. The 6L6 grid bias is 30V so the cathode voltage will be about 50V and a 6L6 plate current should never be more than 300mA, so the transistor needs to be heat sunk for about 15 Watts.
So look for a fast TO-220 NPN that only need to handle half to 2 Amps.
http://www.onsemi.com/pub/Collateral/MJE3439-D.PDF
is a little short on current and power and the 350V is not necessary. If B+ voltage gets to the transistor, it's more likely to survive if it avalanches.
Be sure the op-amp and coupling caps are good.
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Old 19th May 2018, 03:46 AM   #4
steveu is offline steveu  United States
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www.thetubestore.com - Peavey Amp Schematics

http://www.thetubestore.com/lib/thet...-Schematic.pdf
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Old 19th May 2018, 04:18 PM   #5
llwhtt is offline llwhtt  United States
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I have a Musicman in the shop now that has cathode drive, some versions were "normal" with grid drive and a tube. It's been a while since I've seen a Peavey with cathode drive but I think the mechanics are wrong for a TO-220 style xsistor. The OP mentioned plastic but that could be either TO-126 or 220.

Craig
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Old 19th May 2018, 04:56 PM   #6
JMFahey is offline JMFahey  Argentina
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Peavey schematic identifies tube drivers as "5884" and peavey official replacement guide says:

Quote:
ORIGINAL IN-HOUSE NUMBER : SJ-5884
ALTERNATE IN-HOUSE NUMBER: MJE-15030
FIELD REPLACEMENT NUMBER MJE-15028
CASE: TO-220
ORDER NUMBER: 70405884
NOTES: TUBE DRIVER, REPLACE PAIR
EDIT: notice that there are two DIFFERENT ways Peavey uses to drive power tubes, with completely different needs, both are NOT interchangeable.

1) there are *cathode driven* amps, in which case you should use the MJE-15030 I suggested above, based on schematic.
You do not need that much high voltage rating, 100 Vce is enough, I have used TIP31C in a pinch and they worked very well, both in peavey and Music Man amps, and they can pass all the current 2 or 4 6L6 can need, think almost 1A peaks.
TO220 case.

2) there are *grid driven* amps, where you have to handle way lower current, only a couple mA, but high voltage, hence the 350V rating, transistors are used like a conventional Long Tail Phase Inverter, replacing the typical 12A*7 used there.

BOTH TRANSISTORS ARE INCOMPATIBLE so please check *how* are the 6L6 driven: through cathode current or in the conventional, grid voltage way.

EDIT2: your transistor labelling suggests itīs the grid voltage driven one, BUT maybe a former Tech (or the Musician himself) replaced it with the wrong type, because he looked at the PV list and grabbed the first one he saw, BOTH are labelled "Tube Drivers" but are very different.
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Last edited by JMFahey; 19th May 2018 at 05:11 PM.
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Old 19th May 2018, 05:22 PM   #7
llwhtt is offline llwhtt  United States
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We need to know what model of Peavey amp it is, there are three listings for tube drivers in the Peavey cross reference. We're all just guessing now.

Craig
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Old 19th May 2018, 07:51 PM   #8
mozz is offline mozz  United States
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I thought Peavey was very good as responding to schematic requests? Send them a email asking for the schematic.
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Old 21st May 2018, 04:14 AM   #9
Enzo is offline Enzo  United States
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"Vintage" is a Peavey model. Best to call them on the phone, but they will always provide drawings if they have them.
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Old 23rd May 2018, 04:21 PM   #10
ampexperts is offline ampexperts  United States
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Quote:
Originally Posted by llwhtt View Post
64278 = MJE3439 There's a Peavey transistor cross reference on the interwebs, just Google.

Any luck on those SAE relays?

Craig
Thanks Craig, that was a big help!

Turned out both transistors test okay on the curve tracer. Problem was a bad capacitor, which was taken care of by recapping the entire board.

I found a workable substitute for the SAE.. the part number is similar but ending in 210. It's double throw, so two pins must be cut in order to install in PCB, but it works. Same coil specs.
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