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Air gap protection on plate modulator and HV Choke




 
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Author Topic: Air gap protection on plate modulator and HV Choke  (Read 1060 times)
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VE2VMS
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« on: February 26, 2018, 07:29:33 PM »

Does anyone knows how to adjust the air gap.  Tubes are. Pairs of 4-440 on a RCA BTA 1R2


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W3RSW
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Rick & "Roosevelt"


« Reply #1 on: February 27, 2018, 04:41:26 PM »

They look pretty clean, unmolested and may be fine as they are unless you've already experimented with them. Are they a  A 1.5 mm gap or so?
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RICK  *W3RSW*
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« Reply #2 on: March 01, 2018, 03:06:50 PM »

This link may help you?

It worked for me Grin Grin I usually use a match book cover thickness and if that gap results in a continuous arc, I double the matchbook by a factor of two where MX2= gap...(non scientific formula)  

https://sciencing.com/calculate-voltage-spark-gaps-8776030.html
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K1JJ
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« Reply #3 on: March 01, 2018, 06:43:00 PM »

Does anyone knows how to adjust the air gap.  Tubes are. Pairs of 4-440 on a RCA BTA 1R2

I have spark gaps on my 4-1000A plate modulated rig.  They are on the Heising reactor and both sides of the mod xfmr. This was how the iron came stock.

I use a seat-of-the-pants method to set the gaps as taught to me by the Tron. Basically you set them closer and closer until they begin to arc during normal voice speech. Then back them off until they arc only when there is an unusual problem, like an audio pop or transient. You also watch the T/R key-up and un-key sequence to see that they arc only occasionally.

Keying transients are another subject, so if you have an arcing un-key problem, don't set the gaps too far apart to compensate. Fix the arcing the best you can.  A 100-200 watt 5K power resistor across the mod iron during un-key using a vacuum relay will quench and dissipate most collapsing magnetic fields. I use the scheme here.

The gaps are really a failsafe device to keep the high voltages from arcing over the mod iron windings. Occasional gap arcing will not hurt a good transformer, though excessive arcing can put a load stress on it, just like a low resistance short.

Bottom line is that you want to hear the gaps arc only occasionally during robust operation -  and for good reason.

T
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« Reply #4 on: March 01, 2018, 07:10:18 PM »

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They are on the heisting reactor and both sides of the mod xfmr. This was how the iron came stock.

Interesting! Tron gave me a 5 KW mod transformer and a 5 KW mod reactor. The mod transformer is made by RCA and it has spark gaps on the mod transformer secondary but none on the primary. The reactor is made by Electro Engineering and it has no spark gaps on it. Maybe they were inside the 5 KW transmitter? I will install spark gaps on it if I ever get it going again? I also have a 17 kva three phase power transformer on it that he also gave me. What a guy! Believe it or not, I can actually by changing taps on the plate transformer, get it down to the so called legal limit.
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WD8BIL
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« Reply #5 on: March 02, 2018, 10:21:31 AM »

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I can actually by changing taps on the plate transformer, get it down to the so called legal limit.

Why would you want to do that? Cool
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