FM25K question

FM does it with frequency!
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Joe Friday
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FM25K question

Post by Joe Friday » Mon Oct 10, 2016 9:05 pm

I am working to get a FM25K back on the air. Last week, the ceramic feed through at the top of the cavity decided it was time for early retirement, and failed in a rather spectacular fashion. Part of the carnage damaged the RG213 coax used to bring the high B+ to the cavity from the base of the transmitter. I have been looking for replacement cable as the dielectric is dried out and very brittle, and it looks like this will be another point of failure in the near future.

The concern I have is that the spec on RG213 that I have found rates the cable at about 3800 volts. High B+ in this box is nearly 3X this rating. Just wondering what I am missing. RG213 has served this purpose in the transmitter for over 35 years. If the cable was that severely under rated, it seems like it would have failed long before now.

Thanks!

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Deep Thought
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Re: FM25K question

Post by Deep Thought » Mon Oct 10, 2016 9:37 pm

RG-213 is rated at 5 KV RMS AC (14 KV peak to peak) so that's where you are getting confused.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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Deep Thought
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Re: FM25K question

Post by Deep Thought » Mon Oct 10, 2016 9:42 pm

By the way, I have some assorted FM-25K parts like IPA modules, combiner and smaller transformers if you get desperate. 8)
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

ChuckG
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Re: FM25K question

Post by ChuckG » Mon Oct 10, 2016 10:18 pm

Deep Thought wrote:By the way, I have some assorted FM-25K parts like IPA modules, combiner and smaller transformers if you get desperate. 8)
If you have PA components like socket and blocker, I want to talk to you. Have one getting repaired for standby service soon.
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Chuck Gennaro
Central Wisconsin

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Deep Thought
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Re: FM25K question

Post by Deep Thought » Mon Oct 10, 2016 10:32 pm

Let me see what is in the boxes. If I don't have it, they may still have the PA socket assembly in Minnesota.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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