Need help with my ST70, decrease in one channel

[JayH3]

I am having a problem with my ST-70 build which consists of the following: DIYtube driver board, tube rectified power supply board and transformers from Triode Electronics, 12ax7, 12au7, and e34l's.

The problem is that the volume is greatly diminished in the left channel. It started about two weeks ago when everything would play fine for about an hour then the channel would cut out. Since then it has gotten worse and worse until now when the left channel is immediatly quieter than the right.

What I have checked:
changed all driver tubes,
Biased and Moved power tubes around,
tightened tube sockets,
checked all wiring,
shorted terminals on volume pot,
Compared DC resistance of left OPT to right OPT
Compared resistance of resistors on driver board between channels.

I am sortof new to this stuff so I am out of ideas. What else would be a good idea to check. Is there any way to check capacitors without a capacitor meter?

Thanks.

[HollowState]

The next logical step is to make comparative voltage measurements between channels. (Amp powered on, speakers connected and no input)