Beer of the Bass Posted April 2, 2012 Posted April 2, 2012 I've got a late 60's Carlsbro CS100/8 PA head which I use for bass; it's a 100 watter using EL34s. I've been running Electro Harmonix 6CA7 valves as they were on special offer at the time I got the amp. I don't run the amp particularly hard, as the power stage stays clean, and I've always set the bias fairly conservatively. Everything in the amp is healthy, it's been re-capped and thoroughly checked over. I've just had a valve develop noise issues, for the second time in only about 12 gigs - the first one developed random crackling and sizzling noises and got replaced, now one has started producing microphonic jangle through the speakers. I have a spare to replace the offending valve, but the next time I re-valve, what's out there that might be more reliable? NOS are out of my price range, so I'm wondering which currently-made valves have been more reliable for people. Quote
Mr. Foxen Posted April 2, 2012 Posted April 2, 2012 Shuguang. What plate voltage is the amp running? Quote
Beer of the Bass Posted April 2, 2012 Author Posted April 2, 2012 [quote name='Mr. Foxen' timestamp='1333372507' post='1600680'] Shuguang. What plate voltage is the amp running? [/quote] Shuguang are one I hadn't thought of trying, but I guess if they withstand Doom they'll be fine for my usage. The plate voltage is at 500v, so it's on the high side but not outrageous. Space is a bit tight with the fat bottle 6CA7s, so possibly they're getting hotter than is ideal - though they've never red-plated. Quote
Mr. Foxen Posted April 2, 2012 Posted April 2, 2012 Maybe fitting a fan might help. Not sure where you'd tap the power from, but doable. Quote
3below Posted April 2, 2012 Posted April 2, 2012 500V should be ok. Remove power tubes, clean contacts, inspect closely, may be worth changing any suspicious valve bases. I have found JJ tubes pretty good. Then again my Sound City and Marshall still have original (as far as I know) Mullards in and are still good to go . Quote
pete.young Posted April 2, 2012 Posted April 2, 2012 I have JJ Tesla in my Burmans - KT77s rather than EL34s, though JJ make both. The KT77s are really good valves, might be worth giving them a try instead of the EL34s. Conventional shape rather than fat bottles. Quote
umph Posted April 2, 2012 Posted April 2, 2012 i like the shuguangs, not happy with jj's strange you had problems with the ehx 6ca7's been running the ones in my roost for about 3 years now Quote
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