This is my first project of such magnitude since 1992, and you get out of practice over such a time. I welcome all suggestions about anything done so far, or anything else that should be done, while I have this unit on the bench. The original selenium bridge was replaced in 1977 with a Motorola MD980-2 silicon bridge (bridge checks out OK by meter), and voltage divider resistors were updated at that time. The bias supply is to be overhauled tomorrow. Retensioned several of the small sockets with a dental pick. Strip-cleaned chassis and spot-cleaned undersides of 7868 sockets (crud accumulation). Also replaced 820K AC-line-to-chassis reference resistor paralleling line cap. 01mf cap bypassing rectifier diode to ground. Replaced 1K output control grid "swamper" resistors.
Replaced 330K bias feed resistors with 270K's. These still check out OK, therefore left alone for time being.ġ2-ohm quarter-watt cathode resistors installed on output tubes (no 10-ohm resistors on hand).Īdded 200-ohm 1-watt screen resistors to output tubes. 1-630v units in 1977 (all paper caps updated at that point).
#Bias amp 2 version differences full#
Replaced decoupling resistors along B+ chains (several had drifted off value).Ĭhecked power transformer and remaining output transformer for damage (none found w/meter, full voltage tests pending).īypasses into output control grids had been replaced with. Verified B+ cap chains, replacing all softs but leaving those that showed no deterioration (including power factor check). Replaced power rectifier diodes with 1N5408's. It is a mid-thirty-thousands serial-number unit. It finally fouled out the left-channel output transformer (plate winding shorted to the core).
This receiver has been in everyday service since it was overhauled in 1977.
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