filmosound 202 conversion to GA17RVT minus RV

[filmdiary]

The journey continues with an oddball filmosound - this time a 202 with a ton of superfluous circuitry that was designed to record audio to a very slim magnetic track applied to the film after it was printed. I have cleaned up the 2 x 9 pin miniature sockets and left the plate and screen connections at the 6AQ5 sockets. I've mounted the PT on top of the chassis (it was normally connected through an 11 pin umbilical plug) and have confirmed good voltages at the secondary windings.

The schematic below was very loosely adapted from a GA17RVT Scout where I've subbed 12AX7's in place of the 6EU7's, subbed the 6CA4 for the 5Y3 that came with the 202, deleted the reverb circuit and the tone components between the first input triode and the volume pot. The PT was originally spec'd for 2x5879's, 2x12AX7's, and 3x6AQ5's and is pretty massive relative to the size of the chassis! This conversion is clearly an experiment to see what kind of tone the PT and OT will produce so I'm open to whatever advice this community can provide.

Thanks!!!

[acheld]

Off topic, but . . .

Does that large braided insulator contain asbestos?     Many decades ago, while aboard my beloved tender USS Hector, we had a bunch of cables looking just like that that were indeed asbestos containing. If so, you don't want the dust in your house . . .   

[filmdiary]

For reference here is a shot of the power supply side of the chassis. Trying to help out someone that is trying to identify secondary pairs of the power transformer. I sold this amp a while ago but recall that the black pair is the primary side. As I'm sure most techs know it's easy to id windings by measuring resistances between all of the wires. Those with some continuity belong to the same winding - unless there is a short! The high voltage pair will have the highest resistance value (the centre tap will have roughly equal resistance from each of the ends), the 6.3V and 5V lines will have much less. I'm pretty sure the 6.3V winding on these PT's came with a CT so once you identify the high voltage tap the other collection of 3 wires with resistance between them will be the filament supply. To be sure I normally apply 120VAC to the primary with a variac - with all leads taped down / secured so they wont make unwanted contact - and measure the AC voltage at the secondaries.

Basic testing no doubt and a bit of a pain in the ass but the best way to make sure the PT is not shorted out before installing!

[filmdiary]

Here is a photo of the completed build...