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I recently acquired some Dumont Red Base 5692s which were said to be NOS in "new" condition. Oddly the seller gave no emission figure just that the tubes tested good.
They are in their original boxes have the RCA stop sign etching and clear distinct lettering on their bright red bases. Upon listening to them they sounded distorted and lacking definition. Really just bad.
Much worse than my Red Base RCA 5692s which claimed only that were well used. Tested good but just 20% above marginal.
Could these Dumonts need breaking in or was I duped and got bad tubes?
Follow Ups:
Sometimes tubes that sit unused for a long period will build up a contamination coating on the cathode. It's sometimes referred to as cathode poisoning. Until that burns off (from use), the tube won't perform at its best.
I will increase a 6.3 filament tube after warm-up to 10 volts on a tube tester for 30 seconds, then two minutes at 7.5 volts to burn off contaminates on oxide filaments. Data comes from a picture tube gun manufacture in Tucson, AZ 25 years ago.I would have some reservations at the higher 10 volt filament on some valuable tubes, however never lost one to date.
This works with most tubes such as 6SN7s, but IME, it will destory the transductance of other tubes like 45s. So be careful what tube you decide to try this trick with.
45s & other direct heated tubes do not have a cathode or specifically an oxide cathode. But your post is good as some would not know that.
I am going to get my first tester from a dealer who I have a lot of experiece with. He is selling a couple testers for private reasons I was told about. This particular one is a calibrated that he used on occasion etc.a Hickock 800. I don't know if it can test a 6SN7 or the separate triodes. I almost certain it can.
Yes this a "blind" e-pray purchase because I had not bought anything from this dealer previously. I really like the RCAs in my set up. They sound very euphonic which is actually what I desire for this system its for my wife. I was really hungry for the Dumonts because they supposed to be rebranded RCAs and these were "NOS" I got the for a lowish price. He sent a very elaborate reciept with his phone number and the name and address of his real business.
Just so you know I also have a detailed high power audiophile sound set up with a 6 tube pre and big monobockcs etc. That my wife forced me to put in the basement which is fine with me, she set it nicely with near field and long field listening positions. Carpet blah ,blah...
Mechans, hi. Have the tubes tested. I'll wager both sections on the tubes that sound distorted etc are way down on emission. Even in the first hour of service you should not have had the result you did. Did you buy these on e-bay? Caveat Emptor.
Yes, tubes break-in even after sitting in a box for 50 years unused. I never cared for the RCA 5692, but perhaps just my application.
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