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Ok, II'll compare those images to my IIa A question though: what is "larson" ? as in: "On lead mode, the reverb is attenuated to probably avoid Larsen effect ..." Maybe "feedback" ?? Thanks, -Dale

Any chance of posting a schematic of these changes? Or better diagrams of the grounding changes? Thanks! -Dale

My IIa super 60 has reverb, no eq. The rca jacks on mine go to/from the reverb tank. There is another 1/4 inch jack underneath for the reverb foot switch. Never used or even tried it. The schematic hints that this is (or can be) a stereo jack and the other signal can be for switching the...

Nice Pics! What are those extra gray wires and extra jacks and pot on the back? I'm guessing some kind of effects loop? Was that Mesa installed? Or...?

Is there any way to retrieve the images that were posted by mark2boogie? All I see is the word "Image" with no link.

Well I was reading this: https://mesa-boogie.imgix.net/media/User%20Manuals/Mark%20I%20Maint-Repair.pdf Specifically about the fetron: and So that explains my 62K plate resistors on v1!

So I'd really like to have a better effects loop in my IIa. From the schematics, it looks like I can convert it to a IIb style loop without too much difficulty. But I've heard the initial IIb loop had problems and there are fixes for it. Do the usual schematics for the IIb show the original...

So here are some other changes. Serial 3390. PC board is RP-6A. Both v1 plate resistors are 62K instead of 82K v1a grid resistor is 220K instead of 1M The 33K resistor by the 12ax7/fetron switch is 47K The slope resistor seems to be unchanged at 100K The 56K between v1b and the lead drive pot...

My 2/79 IIa "SSR" is also different from the schematic. I bought this in '81 from the original owner. 60 watts, reverb. No graphic eq. White tolex. Both plate resistors on V1 are 62K instead of the listed 82K. The 1M resistor from the grid of v1a to ground is 200K. The voltages on the...