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Make SURE you size your TX / Rx relay correctly.




 
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Author Topic: Make SURE you size your TX / Rx relay correctly.  (Read 489 times)
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KD6VXI
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« on: January 19, 2023, 06:39:17 PM »

Friend send some pics.  Thought I'd share.

He runs legal limit AM Smiley


Size your gigavac right.  This was NOT a cheap fix.

--Shane
WP2ASS / ex KD6VXI


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KD6VXI
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« Reply #1 on: January 19, 2023, 06:42:00 PM »

Yes.  The first pic of the inside of the relay, that's Cload next to it.  Sized appropriately.....  Peak currents are in the range above 75 amps on that cap.



--Shane
WP2ASS / ex KD6VXI

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KD1SH
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« Reply #2 on: January 19, 2023, 07:58:31 PM »

Is he sure it wasn't a sequencing issue - hot switched it?
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KD1SH
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« Reply #3 on: January 19, 2023, 08:16:00 PM »

I'm using a Greenstone VC-2 in my 8877 two-holer; specs say 50 amps. It's enclosed in a Budd die-cast box, so at least the shrapnel will be contained.
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W3SLK
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« Reply #4 on: January 20, 2023, 11:21:01 AM »

I'll bet that will keep your panfish down! Wink
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Mike(y)/W3SLK
Invisible airwaves crackle with life, bright antenna bristle with the energy. Emotional feedback, on timeless wavelength, bearing a gift beyond lights, almost free.... Spirit of Radio/Rush
KD6VXI
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« Reply #5 on: January 20, 2023, 09:07:54 PM »

Is he sure it wasn't a sequencing issue - hot switched it?

He uses a foot pedal for the amp and a microphone for the radio.  I do believe his amps are sequenced, I know there is more than one stage but I only saw one foot pedal.....  Didn't get into it that close / behind the scenes, other than the amplification room.

I wondered about balanced currents in the configuration used.  I would have preferred symmetric but that's a tall order for 4 vac relays that large.

--Shane
WP2ASS / ex KD6VXI
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KD1SH
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« Reply #6 on: January 21, 2023, 09:21:18 AM »

Probably almost impossible to ensure balanced current through multiple relays; even less possible to ensure perfectly simultaneous closing/opening. I'm only using a single vac-relay for the output switching,  but I designed my sequencer to be almost painfully slow to make sure that everything is settled down before the final application of operating bias brings the tubes out of cutoff.
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« Reply #7 on: January 24, 2023, 01:22:25 AM »

Handles noted.
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« Reply #8 on: January 25, 2023, 04:34:40 AM »

Handles noted.

8 handles.

4 pairs.


--Shane
WP2ASS / ex KD6VXI
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