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Author Topic: Peavey Filter Caps  (Read 1410 times)

Jazz P Bass

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Re: Peavey Filter Caps
« Reply #15 on: November 30, 2018, 12:38:03 AM »

"Well fellas, as I practiced putting filter caps In a second Peavey amp head I bought to tinker"

Which model amp are you now working on?
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Tennerondack

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Re: Peavey Filter Caps
« Reply #16 on: November 30, 2018, 06:38:54 AM »

I have a second identical head which works fine, and I tested around and compared things just to get familiar and everything tested very similarly.
I still have the same weak distorted output.


This is from the post previous to yours. Sorry that wasn't clear in the one you quoted. Here is a schematic too.
Thanks for your help.
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phatt

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Re: Peavey Filter Caps
« Reply #17 on: November 30, 2018, 07:17:32 AM »

Well go check you have +/-15 vdc at that pa header block.
Also check the preamp supply is outputting same voltages, at C28 and C29.
Phil.
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Tennerondack

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Re: Peavey Filter Caps
« Reply #18 on: November 30, 2018, 12:16:16 PM »

Wrong schematic. Waiting on PV. Meanwhile, a pic or two
Can you point me in the right direction what to test ?
« Last Edit: November 30, 2018, 12:30:03 PM by Tennerondack »
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Tennerondack

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Re: Peavey Filter Caps
« Reply #19 on: December 01, 2018, 06:35:44 PM »

Quite sure this is it.

I have no voltage to preamp pins .
« Last Edit: December 01, 2018, 06:51:27 PM by Tennerondack »
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phatt

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Re: Peavey Filter Caps
« Reply #20 on: December 01, 2018, 11:18:23 PM »

I doubt the schematics posted are even close to the pictures shown.

Best I can do is ask Q's and a couple of observations;

Your Amp pictured has no opamps on the PCB poweramp board which tells us the schematic is different from the board shown.

I assume the 3 pins on the top left corner are where the preamp plugs into this board?(Please verify *Where* on the board you are taking measurements)
If so one will be preamp signal input, one circuit ground/common and the other will be power for the preamp.
If there are no opamps on the preamp PCB then likely the preamp runs on single supply which would run TO92 type BJT's or similar.

Also how many wires come from the main power Tx? (I can only make out 3?)
Phil.
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Tennerondack

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Re: Peavey Filter Caps
« Reply #21 on: December 02, 2018, 08:52:40 AM »

Thanks Phil,
There are three wires coming from the transformers, two red , one each to the the + - rails, and one yellow to the filter caps.
The connector for the pre amp cable is on upper left hand part of board. Pins are power, ground, and signal top to bottom.
I have include a couple of new pics of that section of the board, there are two transistors I believe are what I understand you to be describing.
« Last Edit: December 02, 2018, 08:56:38 AM by Tennerondack »
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Enzo

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Re: Peavey Filter Caps
« Reply #22 on: December 02, 2018, 11:40:46 AM »

I have lost track of what we are fixing.

Your three wires to the preamp are indeed ground, signal, and power.  Power is 40v or so?   That goes onto the preamp where it is stepped down to lower voltages for the transistor circuits.   If nothing is working there, see if it has lost that lower voltage.
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Tennerondack

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Re: Peavey Filter Caps
« Reply #23 on: December 02, 2018, 03:14:25 PM »

We are fixing an early PV Standard 260, ca. 1972.
I'll get back with more, not home @ moment. Thanks Enzo.
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Tennerondack

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Re: Peavey Filter Caps
« Reply #24 on: December 02, 2018, 05:33:33 PM »

I have zero voltage on the pa pin.
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g1

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Re: Peavey Filter Caps
« Reply #25 on: December 02, 2018, 08:48:17 PM »

Not sure where the naming of that pin as 'pa' is coming from?  Maybe it is marked on the board like that?
Anyway, I think it would be better to call it the 'preamp power supply' pin to avoid confusion.

So there is 0V coming out of the power supply/power amp board at the pin that feeds the preamp?
We need to find the correct power amp schematic for this amp.
There is probably a resistor that knocks down the main +V supply a bit before it gets sent to the preamp.
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g1

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Re: Peavey Filter Caps
« Reply #26 on: December 02, 2018, 08:50:54 PM »

Also, in one of the pictures you can see through the board that there are ground traces that rely on the mounting screws to connect the ground to the chassis.  If the boards are not mounted with the screws, they probably will not work right.
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Tennerondack

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Re: Peavey Filter Caps
« Reply #27 on: December 03, 2018, 05:05:32 AM »

Thanks g1
I can't find a proper schematic anywhere.
I took the "pa" cue from PV schematics of later revisions.
I'll take your suggestion for "preamp power supply" thanks.
The board is labeled  " 130W Power" on the solder side. I've searched high and low as well as contacting PV is and come up dry.

I will remount the board, I'm pretty sure the pin was showing 0 voltage before I removed it.

Thanks, T

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phatt

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Re: Peavey Filter Caps
« Reply #28 on: December 03, 2018, 06:10:57 AM »

It looks like that larger 2 Watt resistor at top right corner (Brown-Black-Brown-silver = 100 Ohms) is connected to the top power pin (the hollow one)

Again I'm guessing but the other side of that resistor is connected to what looks like the positive supply track which runs across the top edge.

So if you have full supply voltage on one side of that resistor and little or none on the power pin side then that resistor is likely dead.

Easy to check with power off,, read the Ohms across that resistor it should be around 100R.
Phil.
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phatt

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Re: Peavey Filter Caps
« Reply #29 on: December 03, 2018, 06:22:31 AM »

Thanks Phil,
There are three wires coming from the transformers, two red , one each to the the + - rails, and one yellow to the filter caps.
The connector for the pre amp cable is on upper left hand part of board. Pins are power, ground, and signal top to bottom.
I have include a couple of new pics of that section of the board, there are two transistors I believe are what I understand you to be describing.

Regards the preamp and TO92 transistors.
TO92 is the case type,, there are many types.
Your big power transistors are TO3 type.
Your preamp likely has many small signal transistors and a fair bet most will be similar types.
Just google to92 transistor and you will get a page full of many. ;)
Phil.
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