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RCA BTA 1MX question




 
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Author Topic: RCA BTA 1MX question  (Read 2239 times)
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John K5PRO
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« on: January 11, 2007, 01:26:38 PM »

I picked up a manual for this on EPAY. I didn't realize that RCA also had made a quad 833 rig, although it isn't surprising since they made 833s in Lancaster PA plant. I wonder why they later switched to the 4-400s as in the BTA-1R series?
I guess they made just about everything, with several varieties of 250 watt, several 1 kW, linear amplifier versions, and the ill-fated solid state 5 kW in the 1970s.

This transmitter was pretty keen, being only 23 inches wide. They had a single holer final as well, with one 833 in it for 500 watt tops.

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WA3VJB
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« Reply #1 on: January 11, 2007, 02:27:58 PM »

Many of the big transmitter manufacturers went to 4-400s from earlier models with 833A because they're easier to drive and tube life was longer for similar service, according to BC engineers with vast experience in both.

Gates was one of the few that stayed with big triodes right into solid state, as with the BC-1 series recently discussed elsewhere on this page.

Collins went from the 300-G (810s) to the 300-J (4-125/250), and there was an 833A Collins that descended into the 20V series (4-400)

RCA went from the BTA-1M(X) (833A) to the BTA-1R and 1S (4-400).

Interesting transition, and these days it seems the 4-400 type transmitter is more popular among AMers on the ham bands simply because the tubes and tanks re-tune more easily to higher frequencies, in most cases.

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John K5PRO
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« Reply #2 on: January 11, 2007, 06:05:28 PM »

Yes, I suppose it makes sense that the socketed 4-400A type tubes with shorter cathode leads to the base would be able to play higher frequencies than big ol' Frankenstein socketless 833As. The BC1G does not have a high frequency layouy, so to speak. In addition, neutralization was done carefully on frequency with those rigs and I suppose that the 4-400A types  either didn't have it, or it was less critical with the tetrode. I added it to my DX100 and it made the 6146s tune a little smoother (Very little grid I fluctuation when plate is tuned).

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