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Alpha 8410 tube replacement

May 14, 2020
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Greetings to all, I'm not sure if this has been covered before but.... has anyone ever replaced the tubes in an alpha 8410 linear amplifier? If so, what is the process? My 8410 has 2 eimac 4cx1000a tubes in it. My tubes have full output, I'm just wondering because I have some spare tubes I would like to try out in the linear. Thank you for any reply.
 

Yes, I know thank you. I have several spare 8168 tubes I would like to try. What is the procedure for changing the tubes? I heard you have to mess with the bias? And connect the amp to a computer?
 
8168 4CX1000A (pocnet.net)

Alpha 8410 - AE9K

Tubes used in the Alpha 8410 are supplied as a matched pair.
ALPHA 8410 (alpharfsystems.com)

Alpha 8410 – manual tune – Alpha RF Systems


I would say if those tubes were untested, and not spare "pulls" from that amp.
I would have them tested and make sure they are matched before usage.
I have checked around; the tube testing services for those tubes have disappeared since covid...
I have no idea who would do that anymore!!!!:(:confused:
All the Best
Gary/W9FNB
 
Thank you.. D & C electronics in Brooksville Florida is currently testing various tubes including the 4cx1000a. It costs about $100. Including shipping per 4cx1000a tube with documentation on what they tested. They have an ebay listing for that service.
 
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I would test the tubes first too. Placing a bad tetrode in a good amplifier, can be a fast way to make the amplifier match the tube.
 
A proper lab test should include heater current at rated voltage, and any indication that the vacuum is contaminated or has a short. What other parameters they measure is up to them.

I do wonder to they smack it around a little bit to check for intermittents? This is a famous way for 3-500Z tubes to fail. One lengthwise wire on the grid will come loose from its spot weld at one end. Only when it gets hot will it change shape and touch the surface of the cathode. Not sure if a loose grid wire can creep outwards enough to reach the anode. Would be a fireworks show if so.

Learned the hard way to check for this with both the 3-500Z and 3CX1200A.

73
 
Yeah, we built one of those from Rich's plans almost 20 years ago. Has been incredibly handy. His suggestion to test breakdown between grid and cathode is what we use for the 3-500Z, 4-400 and such.

Oddest thing I see doing that is the occasional relaxation oscillator. A loose grid wire will literally "sing" and make accoustic noise you can hear coming from the tube. And if a CB happens to be turned on in the room, you'll hear a buzz in the speaker from the arc inside the tube. The first wireless transmitters did use an arc as the RF source, after all.

Turns out the real value from that tester comes from taking the two HV secondary wires loose in a SB-220 amplifier and checking them for breakdown or leakage to chassis ground. Always better to warn the customer his HV transformer is on the edge of a cliff before big money gets spend on new HV filter caps and such.

Got tired of discovering a bad HV transformer after a few hundred bucks got spent on an amplifier.

Before is better.

The neon-sign transformer at the heart of his setup is becoming an extinct dinosaur, year by year. High-brightness LEDs largely replace neon in custom signs nowadays. And even the diehards who use neon tubes have solid-state switchmode power lighting them now. Might want to track down an old-school neon transformer before it's too late if you contemplate copying this design.

73
 
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