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In Reply to: RE: Sure sounds like a bad power tube to me. posted by Ralph on July 21, 2014 at 09:00:10
Hi Ralph,
This is an MA-1 Deluxe with 12 tubes but was brought up to 3.1 spec by you a few years ago. It has two very big power transformers and has the large blue oil caps situated between. It may well be a bad tube as I could not leave well enough alone and replaced the "old" tubes on one amp with a bunch of NOS tubes I picked up and decided to try out to see the difference between the amps was noticeable. It wasn't. I then decided to keep playing the new tubes amd only noticed a problem when I tried,some days later to turn the amp on and the third LED,did not light. I conditioned the tubes for three days and all tubes were tested before insertion but who knows. I can try retesting the tubes but will certainly try what you recommend and see if it is the power supply. If a tube went bad during burn in will it show on the tester or is there a different criteria to see if a tube is likely to take out a fuse? The wires to the tube bases seemed intact but I'll have to check again. I suppose the new Chinese tubes are better than RCAs finest.
Follow Ups:
If the top LED won't light you have a blown fuse by the power cord.
Generally speaking we have had bad luck with the American power tubes, the exception being the Sylvanias.
If a tube does have a problem it will show up on a tester. I would do a visual examination first, see the link below.
I pulled the tubes and subbed the 7A fuse from the other amp to see if it was the power supply- it wasn't. I then checked the tubes and reinstalled them without the speaker cables and powered up. All three lights are good and strong. If it were a bad tube I think it would have taken out the fuse right away, but so far so good. I use a set of old Z-Transformers and was trying a different wiring which I believe shorted the amp and probably caused all my issues. I will see how it goes and report back if any issues but I think it was a case of fooling with something that should probably have been left alone.
Thanks,
Charles
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