Transformer coupled transistor bass amp question

[Brymus]

Hi, I have been trying to solve two issues with a Peavey TNT 100 bass amp.
The first is an oscillation at high volume,the other seems vibrational may be related.
I have been over the PCB with a magnifying glass and cant find any cracks ,ect.
I re-flowed anything even half suspect.
Of note the last NPN driver before the OT is supposed to be a TIP31c by the Peavey cross reference chart.
And the big filter caps were replaced with new 47,000uf caps last year and now one reads 22,000uf
It works great at practice volume but under heavy load sounds awful,oscillation.
If you whack it it will make a noise,but I am not sure thats the oscillation issue.
Any ideas ?
Thanks

[Brymus]

Bigger schematic
http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=44977&g2_serialNumber=1
Also the that last NPN before the OT that is supposed to be a TIP31c by the Peavey cross reference chart (also in my gallery under misc schematics)
Is instead replaced by CS2703 last year.If that helps at all.

[amptramp]

If a filter capacitor has dropped to less than half its original value in a year, it needs to be replaced.  If both of them are the same type, they may both need to be replaced.  A 50 volt cap on a 36 volt line is a bit marginal.  This cap takes all of the ripple current plus all of the current variation from the amplifier and capacitors that are not designed for the current will overheat internally and fail.  Do they get warm when the amplifier is at full power?  If so, the ESR (equivalent series resistance) is too high.  Replacements should be rated at 63 volts (a common standard value) or higher.  The closer you get to the rated value, the greater the failure rate.

I would also replace the 2 µF / 35 volt capacitor in the feedback path with a non-polarized electrolytic capacitor or use a film capacitor.  On any signals larger than whisper quiet, this capacitor will be reverse biased on the positive half of the output cycle and the combination of amplifier drive and speaker motion may drive the voltage well above the 35 volt rating even in the forward biased direction.  Expect his capacitor to become leaky and suffer reduced capacitance value.   A 2.2 µF film capacitor or a pair of 1 µF capacitors in parallel would be the best replacement here.  Use at least a 63 volt rating but if you can find 100 volt devices, use them.

[Brymus]

Thanks for the reply Amptramp 
The 2.2uf caps all appear original,the 100uf filter caps were replaced with 470uf caps but either a long time ago or at the factory.
The 47000uf are 50v so I will replace both.
First
I will pull it out and check for heat on that bad cap,and replace the one in the feedback path with two 1uf film caps.
thanks again