03-31-2009, 08:17 PM
Howdy all:
Just finished with my bro-in-law's brother's 46-1203. Replaced a few tubes, and did minor clean up (remove mud-dawber nests). Audio was fine from phono side, but radio inop. Grid-dipper showed dip from RF tuning LC. Started checking caps, and came to one measuring about 200k. Now, here's the kicker - this cap doesn't show on the Rider schematic, and was a .05 paper connected between 7A8 and 7C7 filaments. End result? Both tubes would get warm, but neither got enough voltage to reach operating temp, therefore no IF osc and no RF amp. Removing the cap solved the issue. Now, I can tell the cap was factory installed, and understand that changes happen mid-course, but what is the purpose of a .05 shunting two adjacent filaments? RF bypass? Needles to say, some secrets of the ac/dc age are still a secret to me.
Just finished with my bro-in-law's brother's 46-1203. Replaced a few tubes, and did minor clean up (remove mud-dawber nests). Audio was fine from phono side, but radio inop. Grid-dipper showed dip from RF tuning LC. Started checking caps, and came to one measuring about 200k. Now, here's the kicker - this cap doesn't show on the Rider schematic, and was a .05 paper connected between 7A8 and 7C7 filaments. End result? Both tubes would get warm, but neither got enough voltage to reach operating temp, therefore no IF osc and no RF amp. Removing the cap solved the issue. Now, I can tell the cap was factory installed, and understand that changes happen mid-course, but what is the purpose of a .05 shunting two adjacent filaments? RF bypass? Needles to say, some secrets of the ac/dc age are still a secret to me.
Until next time,
Stirling KC0NXM.
