Help with mu-follower repair

[MPRCTCL]

I'm working on a Rogue 88 amp with a distortion problem that I cannot figure out. I found a schematic online, so I’m filling in the missing component values which I will share eventually. In the meantime, attached is a shot of the left channel.

I'm totally beside myself. I have decades of experience with solid state and a smattering of valve projects, but this repair has me stumped. I'm the second person attempting to fix it - the other gave up saying "I guess I know less than I thought about tubes."
I have a (measured) distortion problem on the left channel that I have localized to the non-inverted mu-follower stage. First I'll describe what I've observed, then what I've tested:

ALL RELATIVE TO THE WORKING RIGHT CHANNEL:
I get distortion in the output that increases with frequency.
The non-inverting 12AU7 circuit is roughly 36 degrees out of phase (measured at 10kHz) = delayed 9uS
The non-inverted 12AU7 circuit is lower in amplitude than the inverting side.

The obvious, easy step was to test as well as swap tubes between channels to see if the problem moved. It did not.
Fortunately, it is a capacitively coupled design, so it was simple to lift two caps (C3, C13) to isolate the second stage and A-B the working right channel and the left.

WITH THE mu-FOLLOWER STAGE ISOLATED FROM THE REST:
The inputs (pin 7) are identical in phase
The inputs (pins 7) are slightly different in amplitude with the "bad" channel being 0.2V higher.
The outputs (pin 3) are different:
   left channel is delayed by 9.2uS
   left channel is attenuated by 3.2 dB (37.4Vac, 25.8Vac) w/ 10kHz input. At 1KHz, the delay is the same but 1.5dB attenuation.

Another screen shot shows this.

When I turn the amp on, I can see a difference in how fast the DC voltage increases on the output. The left is slower in addition to being lower amplitude.   

A picture shows this.

I also noticed on the 'scope that when I turned off the amp, the two channels were very different as the caps discharged. A photo shows this too.

DC voltages are as follows:
PIN   ELECTRODE   LEFT (bad)   RIGHT (good)   
1   t2 PLATE           380         381   
2   t2 GRID          120         118.5   
3   t2 CATHODE     213         226   
4   heater         
5   heater         
6   t1 PLATE           163         175   
7   t1 GRID         
8   t1 CATHODE     8.3         8.6   
9   heater          

I measured the resistors in-circuit for values and compared to the working channel and most were spot-on, but some are different in-circuit between channels. Removing the tubes did not change the measured values. This is what has stumped me. I'll use the LEFT channel part references since I'm not showing the RIGHT side schematic.

DESIGNATOR - LEFT / RIGHT  - value from color-code
R7 - 585k / 740k   - 1M  (1M out of circuit)
R9 - 700K / 710K  - 1M  (1M out of circuit or with C5 removed)
R11 - 9.96K / 9.97K  - 10K
R27 - 100 / 100 - 100
R25 – 1M / 1M  - 1M
R23 - 4.3K / 4.3K - 4.3K
R21 - 21.4K / 21.4K - 21.5K
R17 - 100 / 100 - 100
R15 - 422K / 460K – 1M (1M out of circuit)
R19 - 4.3K / 4.3K - 4.3K


CAPACITORS

C9 - REPLACED (ELECTROLYTIC)
C11 - MEASURED AND SWAPPED BETWEEN CHANNELS no change
C7 - MEASURED AND SWAPPED BETWEEN CHANNELS no change
C5 - MEASURED

I have finally run out of ideas.  I don't understand the DC difference if the component values are the same. Typically, I would associate phase shift with a capacitor, but they seem fine, so is it the bias point?

HELP!

[shooter]

some easy stuff;


swap the PA tubes from left (bad) to right good
disconnect the NFB


I came from the Solid state land, in my world phase shift was probably the most important thing in my systems, here in tube world, phase shift really isn't a thing.  once you start to "see" all the phase shifts from the amp, the room, the guitar strings, etal, you'll just accept it 

[MPRCTCL]

some easy stuff;


swap the PA tubes from left (bad) to right good
disconnect the NFB


I came from the Solid state land, in my world phase shift was probably the most important thing in my systems, here in tube world, phase shift really isn't a thing.  once you start to "see" all the phase shifts from the amp, the room, the guitar strings, etal, you'll just accept it 

I swapped the tubes and even some caps from side to side with no difference. The NFB is disconnected, everything on both sides of the stage are... input is through C3 with the "upstream" side lifted and output is at pin seven with C13 lifted.  The phase shift is a problem because the non-inverting circuit is phase shifted from the inverting one...

[tubeswell]

My hunch is bad/wrong cap values. Check caps for DC leakage, and if they’re good, then try smaller capacitances.

[MPRCTCL]

My hunch is bad/wrong cap values. Check caps for DC leakage, and if they’re good, then try smaller capacitances.

Thanks.

I've tested them and swapped them between the "good" and "bad" channels, but the problem does not move.

[Merlin]

When I turn the amp on, I can see a difference in how fast the DC voltage increases on the output. The left is slower in addition to being lower amplitude.   

The difference in DC voltage charging makes me question the power supply itself. Do the power supply voltage nodes charge identically between L and R?

[MPRCTCL]

When I turn the amp on, I can see a difference in how fast the DC voltage increases on the output. The left is slower in addition to being lower amplitude.   

The difference in DC voltage charging makes me question the power supply itself. Do the power supply voltage nodes charge identically between L and R?

Yes. The pin 1(s) are all tied together and I confirmed with the 'scope that they are all indeed identical.

[jjasilli]

A quick internet search shows these amps to be prone to unusual problems.  Could even be such things as bad lead dress; oxidized tube pin sockets. 

[MPRCTCL]

A quick internet search shows these amps to be prone to unusual problems.  Could even be such things as bad lead dress; oxidized tube pin sockets.

Given all the hours I've logged sitting behind this thing, replacing a socket seems worth a shot!