Also, charity type thrift stores or youth drop-in centres would probably appreciate it.

That reminds me what Enzo used to always say, 'a tube tester can only tell you a tube is bad'.  I think that applies to most test equipment, and not just for tubes.
You can measure a part and find out it's either bad, or 'may be good'.
Real testing in actual use will tell you if it really is good in it's end application.

When you reverse that speaker that has wrong polarity, you should notice better bottom end/bass response.

Quote from: saturated on May 02, 2023, 10:55:03 AMI have read that yellow and red are pos
and blue and black are neg...
but i can not find any markings on the speakers or terminal

You are correct, that is the colour coding Peavey uses.  The red dots on the speaker baskets are the + terminal.  (that means one spkr in pic is wired wrong polarity)

I have a '77 K15 GMC, also with 4 spd.
The hood is in the same condition as yours, that's why it caught my eye. 

Might be a bit of an uncommon amp module?
Most of the guitar amp manufacturers using those kind of modules have a split +/- aux. supply to run the preamps.
For example, the ICE power modules often have +/-25V aux output.

Nice truck.   

Ok.  Set-up looks correct.  I guess you meant you had one meter probe at each end of resistor.
I thought you had meant you checked from each end to ground.  My mistake.

A 1K load on the 8V line only tests at 8mA which is still pretty low current.  It's probably alright, but could still be bad.
100R resistor would test at 80mA which would be a better test, as the part should be able to deliver 1A of current, though that much would require heatsinking.

Quote from: saturated on April 15, 2023, 12:00:41 PM...hooked everything up..put my multimeter on each side of the resistor...8.05v....dang it 

One end of the resistor needs to go to ground and would measure 0 volts.

It can put out the proper 8V unloaded in your test circuit, yet the voltage could collapse with a load on it.
In your test circuit, put a resistor from the output to ground.  Something in the 100 to 470 ohm range should do the trick.

Quote from: saturated on April 11, 2023, 08:45:27 PMglad to see you recommend using mouser or digikey....was tempted to go elsewhere.
if there is anything else I should get from there let me know I hate to spend $7.99 on a $3 order.

Any kind of shop supplies or tools you might need.  Solder, solder wick, heatshrink, test clips, pliers, cutters, etc.

Quote from: saturated on April 11, 2023, 09:30:54 PMresistance across C58 about 3.5kohm

No shorts or excess load on the +9V rail indicated.  Might have been that just the regulator went bad.

The 3A rating of your power supply is the max. it is capable of delivering.  It will only put that much current out if the load demands it.

While you have the regulator removed, measure resistance across C58.
UA7808CKCT are cheap and readily available at places like mouser or digikey.

I suppose a 7805 and a 3.9V zener would work also.

Quote from: FleshOnGear on April 09, 2023, 03:21:56 PMUsing simulations, I've figured that I can get roughly 10x as much wattage at 5kHz if the output impedance of the power amp is about 12 ohms, which is about twice as loud as with pure voltage feedback.

I'm not sure what you are comparing to here, 10x more power than what?