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In Reply to: Re: "Glad you made up your mind... posted by John Chleapas on March 2, 2007 at 22:32:04:
IIRC, the 40k hour tube life is specified for the 300V plate, 60mA (57mA?) operating point; a classic operating point I believe, which is little used in these times of maximising power. Higher operating points (as in the DRD) will decrease tube life, relative to lower.Cheers
Raymond
Ultra-consumers: Spending money they do not have to buy things they do not need to impress people they do not like.
Follow Ups:
The WE data sheet says: "The life of the tube at maximum operating conditions will be shorter than at the recommended conditions." That data sheet (at least the copy I have) does not specify "maximum" or "recommended" conditions, except for the maximum plate voltage (450v), plate dissipation (40 watts), and maximum current (70mA fixed bias, 100mA cathode bias).I have also some scans of the STC 4300B (CV1452 Special) data sheets - the British specs for the same tube, which mark all the operating conditions as "maximum" where the plate voltage is 450v. 400v or less is not so marked, and the maximum plate dissipation in the unmarked conditions is 32 watts (400v at 80mA). I have always taken that to mean the life at no more than 32 watts, no more than 400v, and no more than the maximum plate current, would be the widely quoted 40,000 hours.
I believe I've read somewhere the expected life at 40 watts dissipation and/or 450v would be half, i.e. 20,000 hours.
I've never seen an authoritative WE-published expected lifetime number for this tube, though the above numbers are widely quoted. If anyone has an authoritative reference, I'd be delighted to learn of it!
Ron has written that the ss rectified DRD amps are a bit harder on the output tubes. He admits the ss rectifed versions put more stress on the output tubes at the initial start up Vs. the tube rectified versions. I wonder if converting my ss 300b DRD amps to tube rectified would cure this problem? This is because they do not have the soft start feature the tube rectified versions have. I would like to find out how hard it will be to turn my ss rectified 300b into a tube rectified version? While Ron states in writing he prefers the sound from the ss rectified version I was amazed at how much better sounding my tube rectified 45 DRD amps became when I swapped in a GZ37 replacing the Sovtek rectifier it came with stock. My only amplifier that I used prior to the Welborne DRD ss rectified ones are my Klimo push pull EL34 mono amps. They sound simply amazing to my ears. But for bang for the buck sound quality it is very hard to beat the Welborne DRD amplifiers. John
Ron has developed and his DRD amps; he has his preferences. Well experienced others prefer tube rectification for the DRD-type topologies, despite the advertised advantages of the SS approach.As for conversion, I think this has been posted previously, but not sure which forum. I am surprised a slow start-up facility has not been integrated into the amplifiers original design.
Regards
Raymond
Ultra-consumers: Spending money they do not have to buy things they do not need to impress people they do not like.
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