Peavey PA-400

[nosaj]

Hi all I've got a Peavey PA-400 Had 30 something volts on the output. Tested the outputs and found one that was super leaky Rca 60142 . Replaced it with MJ15003 Fired it up now I'm getting -.385Vdc on the output. Looking at the schematics It seems like the only other possible reason for the voltage could be the diode on the -40v rail. Does that sound right? Also the diode part number is not listed.

Thanks,
nosaj

[nosaj]

Ok I see they are standard 1n400x diodes.
nosaj

[Enzo]

OK, the 6xxxx types are RCA as noted, while MJ15003 are Moto. Go read the page on mixing transistors in the PV semiconductor master guide. You want all the parallel guys to be the same, otherwise either the odd one will hog the current or it will not turn on, and so not carry its own weight.

You have 385mv on the output, marginal but not really a problem. Does it remain when a load is applied?

In my 30+ years as a PV authorized shop, I NEVER had to replace one of those diodes. Yes of course they can fail, but I seriously doubt they leak a third of a volt in reverse.

The schematic has a bunch of voltages on it, how do they compare.

[Dave H]

I'm getting -.385Vdc on the output. Looking at the schematics It seems like the only other possible reason for the voltage could be the diode on the -40v rail. Does that sound right?

It could be a leaky LTP transistor or a leaky 25/25 capacitor in series with the 2.7k feedback divider so check the voltages as Enzo said.

[nosaj]

OK, the 6xxxx types are RCA as noted, while MJ15003 are Moto. Go read the page on mixing transistors in the PV semiconductor master guide. You want all the parallel guys to be the same, otherwise either the odd one will hog the current or it will not turn on, and so not carry its own weight.

You have 385mv on the output, marginal but not really a problem. Does it remain when a load is applied?

In my 30+ years as a PV authorized shop, I NEVER had to replace one of those diodes. Yes of course they can fail, but I seriously doubt they leak a third of a volt in reverse.

The schematic has a bunch of voltages on it, how do they compare.

Ok I have a PV2000 I think I can cull enough transistors from 70474200 and 70484200 to make everything match.

nosaj

[Enzo]

You just need them to match on a side. Like you can have MJ15003 on the negative side and keep your 60142 on the positive or whatever. You just need all the parallel ones to be alike. So they work together. The positive and negative don't work together. You want all your hamburgers to be the same, and all your french fries to be the same, but your burgers don't have to match your fries, so to speak.

[nosaj]

You just need them to match on a side. Like you can have MJ15003 on the negative side and keep your 60142 on the positive or whatever. You just need all the parallel ones to be alike. So they work together. The positive and negative don't work together. You want all your hamburgers to be the same, and all your french fries to be the same, but your burgers don't have to match your fries, so to speak.

Yep gotcha on that . We like Burger King burgers and McDonalds French fries. a real PIA but you get your burger first and then the fries.
The PV-2000 I think has 16 transistors I only need 8. That Beast is heavy.

nosaj

[nosaj]

You know on this amp all the outputs are NPN . But I should be able to put all the 60412 on one rail and a match of others on the other rail.

also one other question on this amp are the 761 's what are considered the LTP transistors?

Thanks,
nosaj

[Enzo]

personally I wouldn't use the tem long tail pair on this circuit, but I get your drift. I'd call them the "differential pair". Or if you are a hipster like me, "diffy pair".

[nosaj]

DaveH mentioned it earlier in thread and I wasn't sure what he was referring to.
nosaj

[Enzo]

Dave is right, I just quibble over the words.

[nosaj]

On these old Peavy PA's What is the monitor jack for? Is it similar to a line out?

Thanks,
nosaj

[Enzo]

DArn similar, you might almost say they were the same thing....

[nosaj]

Right now it sounds pretty crappy. With only a monitor jack is there somewhere I can wire in a jack to insert to the power amp?
nosaj

[Enzo]

Wire in a jack? I'd just use clip wires. ANd on your schematic, how about at the point labelled INPUT?