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Pet Peeve Peavey (GPS 3500)
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Old 6th March 2017, 02:59 PM   #11
Peter S is offline Peter S  Canada
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First sign that this party is 'going south'; Outputs have been changed
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Old 6th March 2017, 03:06 PM   #12
Peter S is offline Peter S  Canada
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I will check all the outputs with my fluke meter, asap, obviously this will be telling.
The outputs which have been replaced are Q 113, 115, 117, 119, and 121.
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Old 6th March 2017, 03:12 PM   #13
Peter S is offline Peter S  Canada
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Dumb question: (one of likely many!)
The previously replaced outputs were the complete low rail B- side of channel A...But why does there seem to be a ground symbol on what I would think is the speaker output?
Thanks again, Peter, Hillsdale, Canada
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Old 6th March 2017, 06:14 PM   #14
indianajo is offline indianajo  United States
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Peavey does things to make the amps easily bridgeable. So you connect the two sides together without damage, as long as inputs are identical.
My PV-1.3k had "flying speaker ground" . Looks like this might have flying power supply rail. Like the rail was connected to the speaker. I'd need to see more of the schematic to tell.
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Old 6th March 2017, 06:21 PM   #15
indianajo is offline indianajo  United States
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Quote:
Originally Posted by Peter S View Post
I will check all the outputs with my fluke meter, asap, obviously this will be telling.
The outputs which have been replaced are Q 113, 115, 117, 119, and 121.
If you want the amp to work properly at high wattage, all the output transistors need to be from the same production run. Same part number helps, but there are revisions that happen that change characteristics. After you buy those, you need to match them and discard some. I use the Vce test at gain of 10, collector resistor 10 ohms, Vcc 12 v.
This is so at all temperatures, the transistors share current, none of them hog it and heat up too much.
If you don't need the wattage, leave the orphans out. Off the board.
Or buy a new set of OT's from Peavey. They will do the matching for you. I bet the fans they sell are better than the ones you can get at distributors, too.
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Old 7th March 2017, 08:47 PM   #16
Peter S is offline Peter S  Canada
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Thanks Indianajo;
Here is the full schematic, but I had to reduce it due to file size limitation. I will try to PM you the original.
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Old 7th March 2017, 09:04 PM   #17
Peter S is offline Peter S  Canada
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Thanks also for the in-depth info regarding matching outputs. I have always heard about this, but to be honest, I've just 'hoped for the best' in the past. I am now doing this for the learning experience, as well as getting the amp working.
Would it be possible to show me a schematic of a test jig to compare outputs? Also, what kind of tolerance would you suggest?

Yet another dumb question; If all the (PNP) outputs are matched when replaced, how should they be matched to the (NPN) outputs in the B+ bank? Am I correct in assuming that matching B+ and B- banks is a distortion issue rather than current sharing?
Thanks again, I bet you're sorry you hooked into this!
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Old 7th March 2017, 10:24 PM   #18
Enzo is online now Enzo  United States
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You don't match the pos to the neg side transistors.
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Old 7th March 2017, 11:55 PM   #19
indianajo is offline indianajo  United States
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I like BS ing about what I know. Sometimes I'm right.
I just take some clip leads and connect + of 12v battery charger (no electronics just transfomer rectifier filter cap) to a 10 ohm resistor then to the case of the npn. I connect a 100 ohm resistor from + charger clip to base. Emitter goes to - of battery charger. I put mine on a heat sink because I'm inexperienced. Voltmeter goes from case to emitter. Measure each at about the same time on because they self heat.
I had two .11 v, a lot of .12 and several .13 v. I put the two .11 v in the parts bin although they were "better" gain. Lucky since I only bought two extras.
Use opposite polarity of 12 v supply for the PNP ones. Turned out my pnp and npn were actually matched at .12 and .13 v.
Enzo is the world's expert on PA amp repair when he has time for us. He's retired now. hope he is traveling the world or persuing some really fun hobby.
As a jpg file the schematic once downloaded can be blown up and is readable. Will take a close look later.
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Old 8th March 2017, 12:39 AM   #20
indianajo is offline indianajo  United States
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Okay, if I rotate the schematic 3 times it is right side up.

If you look at the speakon diagrams at the bottom, there is a Channel A+ out on pin 1 and Channel A- out on pin 3. Grounds are 2 & 4.
The A+ derives from J102 pin WJ10. The ground derives from J103 WJ10. I can't spot where those come from but there are +mirl A connected to one set of collectors and -mirl A connected to another set of collectors. So if they drove the two sets of transistors with opposite phases, and the emitters were grounded, then the voltage between A out + and Aout- on the speakons would be double what either would be alone to ground.
Whoa, one high power amp.
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