What is important is the follwing 4 voltages.
+22Vdc
-22Vdc
+37Vdc
-37Vdc
These are the rectified dc voltages that the amp needs to function properly.
Please list them.

Here are the files.

https://reverb.com/item/78914907-peavey-705-18713-bandit-65-power-transformer

Your serial number indicates a manufacture date of June of 1975.
The schematics that you found are from 78 & 79.

I think your meter is trying to average the AC voltage on the two inner pins.
Try with the meter set to to Volts AC.

The rectifier is installed backwards.

It appears to be a power amp issue.

Yes.
Nice work!

Not to beat a dead horse but if the TIP 142/ 147 transistors are plastic enclosed at the collector then you do not need the mica. Just grease.
As a matter of fact, it may hinder the transfer of the heat.
It would be nice if you would indicate what you have as both the BDV & the TIP transistors come both ways.

Short answer: It depends.
 Some transistors have the collector tab totally encapsulated in plastic.
These do not need a mica insulator.
Just heat grease.
 If the collector tab is metal then, yes, it must be isolated from the heatsink IF the circuit calls for it.
 Some amplifier topologies use a grounded collector.

Run a patch cord from the FX in to FX out.
If the contacts are dirty you will get no sound without a patch cable.

I would start with checking the output transistors for a gross short.

Have you tried attempting to isolate the issue.
Do Any controls affect the ticking?
Try using the FX Send to another amplifier.
That is the preamp circuit.
Also, you can plug a guitar into the FX Return which is the power amplifier circuit.

Holy Moly.
What a rat's nest.
All because they didn't use a double-sided board.
I cannot find Any component designators that match that schematic.

Is there an issue with the amplifier?
The resistor in question may be a factory fact.
Please provide a schematic and a pic of the underside of the board.