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Post by cbraydio on Dec 31, 2020 1:07:28 GMT -5
Checked everything, all components check within 10% tolerance. Anyone have an idea what could be causing this. Just a slight dimming of the AM neon transmitter lamp when keying up. Is this normal behavior? Radio works great otherwise...thanks for your help/guidance. Everyone in CB Land have a Happy New Year!
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Post by sgtpepper on Dec 31, 2020 1:31:38 GMT -5
What is the voltage coming off of ZR-1, the zener diode? It should be close to 150VDC. It's also possible that you could be having a break down in the mode switch.
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Post by cbraydio on Dec 31, 2020 1:51:37 GMT -5
I know the mode switch deal, it looks to be clean as the day it was made. Zener diode is approximately 148 volts. Maybe the lamp has dimming all along. I just rearranged my shack and the radio is at eye level. Maybe it's my OCD, lol. I was just wondering if anyone else experiences a dimming of the neon AM transmitter lamp when keying up.
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Post by 2600 on Jan 1, 2021 23:34:54 GMT -5
Just on a hunch, I would check C61A, the section of the 3-section 'can' filter cap that has only one red wire attached to it.
It tends to fail first as a high series resistance. Shows normal B+ voltage and filtering on standby, but the B+ voltage falls when you key the mike. I'm accustomed to probing it with the 'scope. If it's failing, the ripple amplitude will be way beyond the normal 5 to 10 percent.
If the main B+ voltage drops far enough, the 150-Volt zener won't hold full voltage, and the neon lamps powered from it would dim.
Just a hunch. Never have figured out why that section of the factory 3-section filter tended to fail first.
73
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