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Vintage threads from the first ten years

Sovtek reliability

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11/2/1999 2:57 AM
Paul Frischmann	Sovtek reliability I have been having a huge problem with pretty much all Sovtek tubes. After a couple of hours they just sort of die. Anybody else have problems? Thanks in advance, Paul F

11/2/1999 6:14 PM
Doc	How do they die? Do they not light up any more? Can you be a little more specific? Which tube numbers, and what kind of circuits? What voltages are used, including heater supply?

11/2/1999 6:20 PM
FredG.	Paul, I have experienced no problem whatsoever with Sovtek 5881's, El-34's, or 12AX7's. Sounds like you've got some other problem. As Doc asked previously - more info would help. Fred G.

11/2/1999 6:42 PM

All the other post-ers may be right. When you say "all Sovtek tubes", are you referring to power tubes, preamp tubes, rectifier tubes?

You should note that not all power tubes of a given nomenclature are spec'd at the same plate voltage ratings. E.g., 5881's are the preferred tube for tweed Bassman amps and are the original Tung-Sol's that came with it 40 years ago were spec'd to over 500 volts if I'm not mistaken. I bought an untubed tweed Bassman, bought some Chinese 5881's, and guess what - they lasted a few hours before glowing blue. I later found out that the Chinese tubes were not spec'd for the high plate voltage they were getting. I replaced them with unmatched Sovtek 6L6's, and haven't had a problem since.

If this describes your scenario, the problem is not the tubes, but the mismatch between tube and amp. Pity that one has to acquire so much knowledge just to avoid wasting money like this. The world would be a happier place if tubes and amps were coded for maximum plate voltage. Then you could just walk into a store and ask for a matched set of "A-category" power tubes, and avoid having to buy things 2 or 3 times.

11/2/1999 8:32 PM
anonymous	Mark, The original 5881 is only spec'd for 350v. on the plate. They will survive in an amp with plate voltages of 500v. and significantly longer than Chinese 6L6s. The "real" 5881 is equivilent to a 6L6WGB, if I'm not mistaken

11/2/1999 10:56 PM
Doc	You are correct about the 5881 electrical rating equivalence to the 6L6WGB. But the maximum plate & screen rating is 400v, not 350. These were conservative ratings (for extended service reliability in military equipment) and those tubes are known to hold up in a 500v environment.

11/3/1999 8:37 AM
Jeff	I have the same problem with the LPS. 2 hours then they're spent. Well, most of them. I have found 3 that still work. Jeff

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