I've had some recent NYC experience with my 500c.
First, I would NOT recommend taking anything to a place called SG Custom Sound in Queens. Without getting into details, that dude doesn't seem to know anything about working on Fishers- he screwed up my power supply when he replaced a bunch of caps to fix a little hum that had developed. He also incorrectly biased the NOS Sylvanias I had him install.
I've used Blackie for my guitar amps for years and he's great... but I've never taken him any hifi equipment.
I can vouch for "captailfantastic" in Brooklyn. He's the guy I originally bought my 500c from. He's pricey, but he knows his stuff. I took my 500c to him after the other guy screwed it up. He offers a "full restoration service" on eBay for $500, but I think that's kind of overkill. He "upgraded" some coupling caps for me, but I found that I preferred the sound of the original ones (especially in the phono section), so I put them back in. He got my Fisher working great again. Put in adjustable bias too. And fast turnaround. I should have taken it back to him in the first place. PM me if you want his number.
-Keith
Patrick; The Scorched "resistor" that I see in the last pic is CP4 below C10. CP4 is a PEC (Packaged Electronic Component) that contains a few resistors and capacitors to make the "HIGH FILTER" circuit or a RIAA (equalization) circuit for the Left side. The corresponding RIGHT SIDE PEC is isolated on a 7 terminal strip next to the front of the unit. These are un available, BUT! The schematic will show them in a dotted line box as CP3 and CP4. These can be built on a small perf board and soldered right to the terminals. Get the assembly manual and these are found in Stage 21 and Stage 22. The drawing of the PEC is from the X-101-B manual. All of the FISHER Integrateds in the X100/X101 series used this PEC (PC50187-2) so I copied it from the X-101-B manual.
Side corresponding to the last pic above. Note C-10 above CP-4. Lift C-10 away from CP 4 about 1/2". Or DeSolder C-10, and mount it on the other side of the terminal strip. The PEC is probably Ok tho.
View attachment 1081653
The same area on the other Channel.
View attachment 1081657
The PEC in the schematic. Values are: Caps-- 220pf (1), 100pf(2), Resistors 100K 1/4W (2).
View attachment 1081652
Larry
If it doesn't have a phase switch, look at the speaker switch. Give it a shot of DeOxit, and cycle it 30-40 times briskly. As the speaker switch seldom gets moved, it will tend to build up crud, which can cause the problem you have. Clean it and then lube with DeOxit Faderlube or CRC 626 Electronics Lubricant (Home Depot in Electrical Dept.). While you are in there doing the spkr switch, go ahead and do all the switches and pots.
From what you describe the problem is just with V10 and just that channel. I'll assume you've swapped the tube in V10 with the tube in the adjacent socket and flickering stays with the tube in the V10 position? If so, with the set on and playing, put your fingertip on V-10 and push it around in the socket to see if that affects the flickering/distortion. If not then I would suspect that there is a ground fault or a component failure with something connected to V10. With the unit playing, CAREFULLY trace back from V10 and with a non-conductive tool (I use a thin dowel) and carefully examine and tap every device and solder joint along the way. Also, check the intergrity of the transformer connections to the offending tube. See if that reveals anything. If not, post the voltages of V9 and V10 and post them, (clip NEG to chassis, positive probe to socket pin.)
With the problem related to V10 only, I can't see how it cannot be related to a connection/component involving that socket only. If you have a schematic, post a clipping of the V9/V10 tubes and related connections so we can see how V-10 is connected.