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Peavey output transistor substitution?

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  • Peavey output transistor substitution?

    I've got an old workhorse Peavey 6-channel powered head. The power board on back is a 400BH. I loaned it to a friend, and when I got it back, it blew a fuse the first time I plugged it in.
    I 'think' I've got it narrowed down to a bad output transister (labelled 8113). The rest of the TO-3 size transistors are labelled 8026. I'm trying to find a suitable replacement. Mouser lists an NTE 130MP as a replacement. Is this what I'm going for?
    Sorry for the stupidity, I'm an old tube guy, and working on this solid state stuff has me puzzled.
    Thanks in advance!

  • #2
    peavey 400bh output xistors

    I just looked through my Peavey T0-3 case style list & see nothing there with a designation even close to 8113 or 8026. I also cannot find the model number 800bh in the schematics either....are you certain of that model designation...Sorry I cannot help further ...glen


    • #3
      Thanks for the reply, Glenn. The mixer panel on front is a 600 series. The back panel, which houses the output section, is marked 400 BH. This unit is from the early 80's. I found a copy of the schematic on the web, and the output transistors aren't marked on the schematic... it just says Q4, Q5, etc.
      The full label on the transistor is: SJ6357

      I'm not sure how to test these, so I used the diode checker on my meter. They all registered except one, so I'm assuming that's the culprit.

      Thanks for checking!


      • #4
        Oh so many issues here.

        8027 and 8113 are date codes. SJ6357 is the house part number. The industry number for that is MJ15003. You can get the real parts right from PV, or buy the MJ numbers from Allied.

        DO NOT use the NTE crap, especially when it has to mix with other parts. Not only do the NTE parts cost a lot more, they are not real matches. Then when they are in parallel with other power transistors, they won't share current well, they won't track. That means that at high power, either they will try to hog the current and burn up, or they won't fully turn on and it will leave the work for the others.

        400BH is the power amp module, and was used in a number of models. SOunds like you have an XR600 of some sort. PV will send the drawings if you email a request. That will include the parts layout.

        My 400BH drawing shows the part numbers. It says "6357 (4)" between Q4 and Q5 and again between Q14 and Q15. Also on page 2, the parts layout, each power transistor says 6357 on it.

        The case of these large transistors is the COLLECTOR. It should not be shorted to either of its legs. The two legs should not be shorted together either, but in circuit, they are only separated by a 1 ohm resistor, so they have to come out to check. Usually the short is to collector. And if ever in doubt, pull the part from the board and retest it.

        Make sure the large rectifier diodes are not shorted while you are in there.
        Education is what you're left with after you have forgotten what you have learned.


        • #5
          Thanks, Glen and Enzo! I joined the Peavey forum, and I'll be ordering parts from them directly.
          It's funny... when I was a young lad, I was a JBL/EV snob, and wouldn't look twice at Peavey stuff. Like most working musicians, sooner or later you end up with a few pieces of Peavey gear almost by accident. As I got older, I finally figured out that this Peavey stuff does the job it's intended for, and is almost indestructable unless it's REALLY abused. We've got a trailer full of newer, high-priced gear, but we use that little 6-channel mixer all the time, and I really missed it when it went down. Now, as I see how well Peavey supports their products with parts and documentation, I have even more respect for the company. Integrity is a tough thing to find these days.
          Thanks again, guys!


          P.S... Enzo, you're still working on that book, right? 'Cause I'd sure buy a copy or two....


          • #6
            Quick update

            Peavey was helpful and prompt with the parts, and I got the old mixer up and running last night. No problems at all.
            Thanks, guys!