Thursday, March 10, 2011
Drake R-4b Bias Filter R&R
Receiver would not fully mute, S-Meter would not go past S-9 when turning RF Gain Counter Clockwise. TP2 Voltages were not correct. Bias Voltage was good when circuit was 'unhooked' from the P/S board. Cap tested leaky compared to new one on the old Heathkit C-3 Cap checker. The new filter Cap from AES is a Sprauge Atom 10uf @ 500v which was a close as I could find to the original from Digi Key or AES at order time. The fit is a 'B' fit and required slight enlargement of the holes on the board which I did with the point of an exacto knife in just a min or two. Clearance is 'OK' if you fit it in close to the board. I added some heat shrink but it is probably not needed. After fitting the new Cap the AVC voltages all aligned up as per section 6.4.9 of the manual.
Pix of original Cap CDE 'Beaver' 8mfd @150V