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Title: Testing and matching power tubes Post by: K8DI 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 Title: Re: Testing and matching power tubes Post by: w4bfs 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 :D Title: Re: Testing and matching power tubes Post by: K8DI 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 Title: Re: Testing and matching power tubes Post by: Jim, W5JO 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 Title: Re: Testing and matching power tubes Post by: W7TFO on November 19, 2021, 10:58:46 PM Well, shucks!
I'll do 'em for return postage. ;) 73DG Title: Re: Testing and matching power tubes Post by: KL7OF 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
Title: Re: Testing and matching power tubes Post by: KD6VXI 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 WP2ASS Title: Re: Testing and matching power tubes Post by: Opcom on November 21, 2021, 09:13:25 AM Where can I get one of those sockets?
Title: Re: Testing and matching power tubes Post by: w4bfs on November 22, 2021, 02:52:02 PM patrick made a funny :D AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
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