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Old 3rd October 2012, 09:19 PM   #11
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4 kt-88's would work...but check the Ip's of the tubes. There is a pretty wide varience of resulting bias current ranges deepnding on brands. Some tubes will never bias correctly in some amps with out circut mdification. one amp I have can use 10 el-34's/kt-90's/6550a's as long as their Ip's are in the 22 to 32 range. Can use KT-88's if they are in the 24 to 32 range. But I have a few dozen kt-88's and 6550's that are over 32 in Ip, some as high as 38, which the amp can't use...fuses blow and the bias will not fall into range. If I change the bias circut to support hi Ip tubes, it can't run low and med Ip ones. You'll catch this when powering it up if you bring it up using a variac and a bias probe. I bought a probe on ebay that has 4 sockets and a rotary switch....but I also have amps that use a bias resister along with a rotary switch that runs to normal meter sockets that let me check the bias of all the tubes pretty quickly by selecting them and using a meter.
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Old 4th October 2012, 03:41 AM   #12
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I have built amps before with a voltage divider in a multi-pole switch to allow for bias adjustment on differt tubes. I love the SEDs, but they are way "hotter" than other tubes typically. Much lower bias voltage.

Do you happen to know the Ip of the Sovtek KT88? That is the tube I plan to get things fired up on. Then maybe the KT120.

Thanks,

Blair
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