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Testing and matching power tubes




 
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Author Topic: Testing and matching power tubes  (Read 457 times)
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K8DI
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« on: November 19, 2021, 08:30:08 AM »

So, given a box of four 4-400A tubes hat came from an RCA transmitter, and having that transmitter in working order, a dummy load, and standard test gear, how can I judge these tubes to be good or weak?  How important that pairs match in either push pull or parallel operation? Given a second box from a second (not now but supposedly formerly working condition) transmitter, can I mix and match brands?  One set is Eimac, the other Amperex, and those are graphite.

Ed
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Ed, K8DI, warming the air with RF, and working on lighting the shack with thoriated tungsten and mercury vapor...
w4bfs
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« Reply #1 on: November 19, 2021, 01:24:12 PM »

hi Ed. .... this question keeps coming up and needs a 'library card' for checkout ... a tube tends to lose vacuum with time passing ... either air seeps in around seals or is ungettered from metals in the tube .... so a long storage time tube needs to be  tested under controlled condx to determine state of internal vacuum.

this test can be done in an amplifier if a means is made to control available power .... how many hams have plugged in a 'good' tube, hit the switch and heard bang and smelled smoke ?  

so either make a  tube tester or adapt means (ballasts, variacs,  etc) In the power supplies to keep it  in check  Cheesy
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Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
K8DI
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« Reply #2 on: November 19, 2021, 02:30:02 PM »

Let me add that the four tubes are in the TX and it makes power and modulates. But the cathode currents are uneven in the finals and require different amounts of bias in the modulators to be made even. Due to saggy AC I haven’t tried to modulate to 100% yet, but the new #6 240 feed goes in this weekend.  What I really want to know is do they need to match and if so, how do I match them, and, secondly is there any way to tell how “good” they are?

Ed
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Jim, W5JO
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« Reply #3 on: November 19, 2021, 04:02:32 PM »

I have used these people before to check some tubes and you might  see if they will do the 4-400.  I could not find a listing for that tube but they did at one time.

It is a cost that  might save you a lot of grief.

https://www.ebay.com/itm/282206834823?hash=item41b4d69087:g:-KYAAOSw4shX86xe
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W7TFO
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« Reply #4 on: November 19, 2021, 10:58:46 PM »

Well, shucks!

I'll do 'em for return postage. Wink

73DG
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KL7OF
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« Reply #5 on: November 20, 2021, 09:54:31 AM »

these tubes are working, you are able to adjust the bias individually, If the cathode currents are not wildly different, run them..You may be overthinking this......  Good Luck
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KD6VXI
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« Reply #6 on: November 20, 2021, 03:26:10 PM »

Make sure you put the one with the best emissions in a socket that gives you higher positive peaks 😂😊

--Shane
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Patrick J. / KD5OEI
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« Reply #7 on: November 21, 2021, 09:13:25 AM »

Where can I get one of those sockets?
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« Reply #8 on: November 22, 2021, 02:52:02 PM »

patrick made a funny  Cheesy
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Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
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