04-06-2023, 06:15 PM
(This post was last modified: 04-06-2023, 06:29 PM by Mike Watterson.)
I only heard mush on SW today, but it was on a short vertical.
The 4uF (or similar) is + to chassis on the FM detector?* It does respond a bit slower than AM (typically 0.1uF and it is on the AGC line), though sounds unusually slow. The FM likely has no AGC.
I'd check the HT on scope, not just the DVM and maybe measure the AC current on Electrolytic. The Selenium rectifiers can pass AC without getting too hot.
Yes, I usually put 1KV or 2KV XY ceramics for "tone corrector" (really a snubber) as the voltage is AC out on top of HT and any noise spikes can be huge due to cut off of current causing big volts from inductance of transformer.
[* I've forgotten why it's that way, but obviously the magic eye needs 0V for no signal and increasingly negative for stronger signals. Also the FM Voltage can be -20V or more, so often a DC attenuator on FM vs AM mode to the Magic Eye]
The 4uF (or similar) is + to chassis on the FM detector?* It does respond a bit slower than AM (typically 0.1uF and it is on the AGC line), though sounds unusually slow. The FM likely has no AGC.
I'd check the HT on scope, not just the DVM and maybe measure the AC current on Electrolytic. The Selenium rectifiers can pass AC without getting too hot.
Yes, I usually put 1KV or 2KV XY ceramics for "tone corrector" (really a snubber) as the voltage is AC out on top of HT and any noise spikes can be huge due to cut off of current causing big volts from inductance of transformer.
[* I've forgotten why it's that way, but obviously the magic eye needs 0V for no signal and increasingly negative for stronger signals. Also the FM Voltage can be -20V or more, so often a DC attenuator on FM vs AM mode to the Magic Eye]
