Recent content by Jim55

FYI people, I've mentioned how the 12AQ5 audio output & modulator tube used to run hot back in the 60's. Back then I tried making heat radiator fins for it but I couldn't get good thermal contact. I tried a water jacket but it soon boiled. I tried an oil jacket but it smoked so I gave up...

@ everyone...I have good news. I'm going out on a limb here with my fingers crossed hoping I may have solved the problem. I was poking around V-1, pins 8 & 9. When I checked the operation, I noticed the frequency wasn't jumping any more. No matter how many times I Transmitted. In 60 years I've...

Brandon, You're right about the 3 meg resistor in parallel with the 470 meg. I was trying to solve some problem but the radio, and the problem, didn't seem to care much about this. And thanks for explaining what happens with the different resistances. I was planning to look for a few tubes...

@ Brandon...I redrew the mic contacts at least 50 years ago. I didn't know details of how the circuit worked, I was just trying to show how the mic mechanism might look in Tx mode. In Rx everything is grounded and connected to black & shield. So I figured, apparently wrongly, that in Tx the...

I measured no increase in temperature for PC-1 with a thermocouple. Here are the measured values of the 3 internal resistors: 100K = 86.5K; 68K = 60.6K; 1K = 1.8K. I tried to monitor voltages as the mic was keyed and saw nothing strange. I'll attach a table showing the mfgr's recommended...

I tried to measure PC-1 temp with a thermocouple but saw no change in Tx vs Rx. Here are measured values of the internal resistors: 100K = 86.5K; 68K = 60.6K and the 1K = 1.5K ohms. I don't have any answer for your question, but I'm attaching a table in which the instructions give the...

I'll try to watch for temperature changes on PC-1 and monitor the 100K resistor. I had to build one of these encapsulated PC's from scratch in the past. There isn't much inside PC-1 so I can do that if I have to. Thanks for giving me a new place to look.

I cleaned tube pin sockets and mic switch. The mic switch is enclosed so I can't see inside but it feels as smooth as always. The problems started as soon as I turned the radio on back in 2020. I didn't have any opportunity to key the mic. I replaced many caps. I never heard of equalizing...

Hello, I'm new here with an old radio. I am troubleshooting a 60-year-old Knight-Kit C-540 6 tube transceiver. It receives 23 channels, transmits on 1 (just have 1 crystal.) The radio now receives and transmits reasonably well, though it has seemed weak for many years, but I still have one...