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Old 10-14-2015, 01:32 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 15,473
Update:
Replaced C1,C9,C10 since those were open, leaky and leaky respectively.
B+ increased from 85V to 100V with the cap change, and reception range has improved. If I feed it's output through my SKL tube TV band RF amp the range is comparable to a Blonder Tongue BAVMZ series.
Decided to measure the fine tuning control on the modulator and discovered it is not a pot, but rather a 50pF trimmer cap. Up dated schematic below. It works great, but after about half an hour prominent hum started leaking into the signal so I may end up recapping it further and nixing the seleniums. Here is a pic of the test set up running a Monty Python VHS as the signal source.
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