Hello, I have read many of the threads relating to this tuner chassis, but have concerns regarding the one I own (Model 690-T, Serial 33680D) which is installed in a 1964 Ambassador console. I have used this console for many years but now need to update out of spec components. My questions relate to the mismatch between the schematics for the 690-T listed in the 1964 Ambassador A-69 Service Manual, the Sam's Photofact 977, and the tuner itself. First, the MPX unit is the #65 (3 12AX7 Tubes), which matches that listed in Sam's schematic but not that in the A-69 Service Manual. However the Sam's schematic does not match the rest of the tuner. My 690-T more closely matches the Model 680-T tuner schematic serials 10001 to 19999 inclusive, listed in the Ambassador V Service Manual A-68. However my 690-T includes a number of modifications which because of the consistent use of ROE(derstein) branded capacitors appear to be original. Past posts stated that Fisher mismatched chassis depending on available inventory, etc. My question is whether an accurate schematic is actually available or is it best to simply replace electrolytics and out of spec resistors as they are in the tuner or revert to the closely matching 680-T schematic? I have included an image of a portion of the 680-T schematic with a variation from my tuner shown in red (the 680-T is the only chassis I found which uses a pair of 820K resistors (R82-83) near the MPX as in my 690-T).
This is only one of several variations which I have found. If more information is required, let me know, Thanks. Terry.
This is only one of several variations which I have found. If more information is required, let me know, Thanks. Terry.