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Peavey PA-200 Powerup With Dim Bulb Tester and Variac
Peavey PA-200 Powerup With Dim Bulb Tester and Variac
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Old 30th November 2020, 01:27 AM   #31
JMFahey is offline JMFahey  Argentina
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What indianajo and wgski said.
When you replace caps and transistors, remeasure (noload, still with dim bulbI) and post results.

As of :
Quote:
Interestingly, the dead parts are not from the same pairs (a resistor from dead transistor is ok, and vice versa).
probably dead resistors opened fast and worked as fuses, protecting "their" transistors, and viceversa.
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Old 30th November 2020, 02:34 AM   #32
wg_ski is online now wg_ski  United States
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And if you still have one working pair of output transistors, you can use them to make sure everything else is ok while you wait on new ones to arrive. Parallel pairs are only needed to handle a heavy load. A single in each side will work to check everything else, once dead diodes and resistors are replaced. The voltage on the hot side of the output cap should still center, and the amp should pass a signal into a light load (say 100 ohms). The light bulb limiter will prevent any other damage if there is still something that was missed, and it would be better to find it now before putting in new 15024s.
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Old 5th December 2020, 09:23 PM   #33
Cheeto333 is offline Cheeto333
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Hi all, I am installing my parts from Digikey and wanted to confirm the pinout of my transistors (datasheet here). The datasheet is not entirely clear which pin is the base and which is the emitter; the picture seems to show an arbitrary orientation. Do I have it correct in the picture below?

In addition, I'm a bit confused about the electrical connection of the case (red wire). The cases of the transistors aren't connected electrically to the middle pins of the transistor sockets, so what exactly is the purpose of the red wires?

Thanks again for the help.
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Old 5th December 2020, 10:19 PM   #34
indianajo is online now indianajo  United States
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For TO3 pin identification see post 25. I think this picture is looking from the long direction at the pins, but if not, other way.
I didn't take it apart so I don't know where the red wire goes. Possibly to one of the collectors but you have to get the right one. Each has an individual wire. Two of the collectors go to the centerline, the + of the speaker capacitor. Two of the collectors go to the +74 supply. Peavey later used the screws on the ends of the transistors to connect to a PCB; I don't know if they were doing it in 197? The screws must be insulated from the aluminum plate since all 4 transistors are mounted on it.
If this was disassembled and abandoned by a previous owner, you'll have to trace the base & emitter leads and compare to the schematic diagram to figure out which pair of output transistors is which. Then install red wire for the +74 and some other color (I use orange) for the centerline.
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Last edited by indianajo; 5th December 2020 at 10:23 PM.
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Old 5th December 2020, 11:15 PM   #35
JMFahey is offline JMFahey  Argentina
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Those cases ARE connected to the middle strip by the mounting screws.
And you got E and B right, at least on the last picture.
Your 45 degree angle is somewhat confusing, a 90 degree picture would be much better, then there is no doubt whatsoever about E-B-C pinout.
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Old 6th December 2020, 01:40 AM   #36
Cheeto333 is offline Cheeto333
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Good point about the screws; I had to clean up the head to make good contact with the case. That makes sense now.

To be 100% sure, the attached picture is accurate, correct?
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Old 6th December 2020, 03:35 AM   #37
JMFahey is offline JMFahey  Argentina
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Yes.

Now itīs easier to see that E and B pins are not halfway between mounting screws but shifted towards one end.

Your labelling is fine.
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Old 6th December 2020, 03:44 AM   #38
indianajo is online now indianajo  United States
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If all output transistor collectors are shorted together by the heat bar, then the schematic of post #12 is not accurate.
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Old 6th December 2020, 03:57 AM   #39
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The collectors are not shorted together by the chassis, I was mistaken.

Should I power up with the variac or just the dim bulb tester?
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Old 6th December 2020, 04:10 AM   #40
indianajo is online now indianajo  United States
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I don't own a variac, and I get by. 60 W bulb for amps to 100 W/ch, a 6 ohm room heater element on 650 W/ch amps (because the 100 W bulb did not allow the op amps to work on that big amp.)
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