I'm overhauling a 52 yr old tube CB Knight Kit transceiver. Noise suddenly showed up. I began replacing electrolytic caps and diodes. It helped the overall background noise level but not the pulsed noise. The noise sounds like static bursts about 50 Hz & is loud enough to drown all but the strongest signals. Noise traced to internet router. ATT told me how to change settings in router but that didn't help yet noise disappears when router is turned off. It transmits the noise all over the house. They are currently stumped over the noise frequency and its transmission. I've put ferrites and RFI filters all over but nothing helps. The noise is present only when the antenna is plugged in. I can use help here.
Since I began replacing the old caps in the radio, I've noticed that I can have anywhere from 27 to 68 VAC from chassis to gnd. It varies when I change caps. Maybe the ones I'm swapping in are as bad as the originals. I don't know a good way to measure leakage. They seem pretty good when I try. I can't find any caps that may be leaking to gnd as the possible source of the chassis voltage. I don't know if the chassis voltage was always there or not as I'd never measured it. I replaced the 2 wire power cord with a 3 wire and that's when I noticed this voltage. It can also show up on my antenna when I transmit. It should be on the antenna via the coax shield but I once measured nothing unless I transmitted. That has me stumped. I need help here also.
One non-polarized electrolytic capacitor in the power supply has a value of 0.12 uF, 600 VAC. I was wondering why a big electrolytic paper cap would be used when a small ceramic cap can give 0.12 uF at 1KV & save space? What's the advantage of using electrolytic over ceramic. The radio runs fine with ceramics in its place.
In general, the tubes seem good though reception and transmission seem a bit weak. (I should be getting a transmission voltage of about 15 volts but with the chassis voltage as it is I can have 50 volts measured as my output.) I could use help adjusting the tuning range to match the manual dial. I'm attaching a copy of the schematic.
Since I began replacing the old caps in the radio, I've noticed that I can have anywhere from 27 to 68 VAC from chassis to gnd. It varies when I change caps. Maybe the ones I'm swapping in are as bad as the originals. I don't know a good way to measure leakage. They seem pretty good when I try. I can't find any caps that may be leaking to gnd as the possible source of the chassis voltage. I don't know if the chassis voltage was always there or not as I'd never measured it. I replaced the 2 wire power cord with a 3 wire and that's when I noticed this voltage. It can also show up on my antenna when I transmit. It should be on the antenna via the coax shield but I once measured nothing unless I transmitted. That has me stumped. I need help here also.
One non-polarized electrolytic capacitor in the power supply has a value of 0.12 uF, 600 VAC. I was wondering why a big electrolytic paper cap would be used when a small ceramic cap can give 0.12 uF at 1KV & save space? What's the advantage of using electrolytic over ceramic. The radio runs fine with ceramics in its place.
In general, the tubes seem good though reception and transmission seem a bit weak. (I should be getting a transmission voltage of about 15 volts but with the chassis voltage as it is I can have 50 volts measured as my output.) I could use help adjusting the tuning range to match the manual dial. I'm attaching a copy of the schematic.
Attachments
-
863.1 KB Views: 15