Cathode stripping - an urban legend?

Posted by Ray Moth (A) on December 5, 2006 at 19:04:36

In Reply to: I didn't read the whole post but.... posted by Russ57 on December 5, 2006 at 12:00:46:

Some people worry about it, others don't; some say it's only a problem above 1,000v; some say it only happens with certain types of cathode material; some say there is a danger of bombarding the cathode with positive ions from the plate. Without deliberate destruction testing by some one, we'll probably never know the whole truth but I prefer to err on the side of caution.

An SS bridge rectifier, with its zero voltage drop, followed by a filter that includes a TV damper diode in series (giving 30 second warm-up, soft start and low voltage drop ~10v), seems like good medicine. It delays B+ until the tubes in the amp are good and ready - about 30 seconds or so. In addition, because the voltage through a therminoic diode ramps up slowly, it avoids the severe inrush that you can get with SS rectifiers due to sudden charging of filter caps. Got to be good for the caps, right?

Putting a damper in series with an SS bridge is one way of using it. A better way, which incurs a bit more of a voltage drop, is to use two dampers together with two SS diodes in a hybrid bridge. This has the added advantage of suppressing any switching noise the SS diodes might produce.

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Follow Ups Full Thread

Topic - quick question: is it OK to delay B+ by delaying switching on of rectifier... - radiance 10:41:48 12/04/06 (13)

Re: quick question: is it OK to delay B+ by delaying switching on of rectifier... - lipmanl 17:31:04 12/04/06 (0)

This problem has been solved in its time. - sser2 13:03:10 12/04/06 (11)

thanks guys, but this is a little different......... - radiance 21:55:31 12/04/06 (10)

Amperite relay reliability - sser2 12:27:49 12/05/06 (1)

the voice of experience, very good to know. thanks! (nt) - radiance 20:02:03 12/05/06 (0)

Re: thanks guys, but this is a little different......... - Ray Moth 05:58:41 12/05/06 (7)

Thanks, Ray, I didn't realize the rectifier tube.... - radiance 11:23:49 12/05/06 (6)

5V4 vs 5AR4 and cathode stripping... - Steve O 18:42:52 12/05/06 (0)

I didn't read the whole post but.... - Russ57 12:00:46 12/05/06 (4)

Cathode stripping - an urban legend? - Ray Moth 19:04:36 12/05/06 (3)

Re: Cathode stripping - an urban legend? - radiance 19:31:57 12/05/06 (2)

It has long since been settled - Russ57 09:55:17 12/06/06 (1)

OK, if that's true, then you're right. First time I've heard it. (nt) - radiance 10:01:53 12/06/06 (0)

Follow Ups

Cathode stripping - an urban legend? - Ray Moth 19:04:36 12/05/06 (3)

Re: Cathode stripping - an urban legend? - radiance 19:31:57 12/05/06 (2)

It has long since been settled - Russ57 09:55:17 12/06/06 (1)

OK, if that's true, then you're right. First time I've heard it. (nt) - radiance 10:01:53 12/06/06 (0)

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