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Author Topic: 26Z5W Rectifiers filaments gone  (Read 2499 times)
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Posts: 4403

« on: October 27, 2016, 04:19:27 PM »

OK guys, I'm tracking down a problem with the KB3AHE memorial R390A. I found a 1K load resistor and .033uf plate bypass cap crapped out. This is in the AGC cathode follower circuit, V502 IIRC.

Got those changed and fired it up ....... still nothing!
Measured B+ rail ...... nothing. A quick look found the filaments in the rectumfinders not glowing. Sure enough ..... open filaments.

My question is; Is it not unusual that the filaments in BOTH tubes would go at the same time?

Resistance measurements on all the other decks are close enuf to spec not to suspect any further issues.

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Posts: 262

« Reply #1 on: October 27, 2016, 04:38:09 PM »

With out looking at the Y2K R3.

Power supply et all has three fuses, check those. Some of the R390/A have been converted to use a diode & resistor, leave tube socket MT.

Ck power tranny, they seldom fail.


Ham radio is now like the surprise in a box of "Cracker-Jacks". There is a new source of RFI every day.

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Posts: 2632

« Reply #2 on: October 27, 2016, 04:54:31 PM »

This would be a good question for Ted, K1QAR.  He's "Doctor R390"
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