![]() ![]() I will not further speculate why the one brand works and the other doesn't. I have since then acquired a set of new production Gold Lion KT88 tubes and they behave perfectly. ![]() It is possible that this is a situation with just the one brand of KT88s. By comparison the JJ 6L6GC tubes and JJ KT77 will balance within one mA and stay there. With current balance being an important consideration of the design this is not good. One or the other tube (not predictable which one) will start to conduct more than its fair share of the current. The circuit allows for adjustment of the bias (the 25 ohm variable resistor) but the EH tubes do not stay in sync. I suspect the reason is related to thermal problems and the use of common (joint) cathode bias. Additionally they don't behave well in this particular amp. The EH KT88 can deliver more power, but the sound is different from the KT77. Using the EH KT88 tubes has been a mixed situation. I tried the amp with Electro-Harmonix KT88 tubes. I initially used KT77 tubes as I was familiar with the sound and it would be a good starting point. has a good selection of these tubes - NOS and new productions. The Odd Blocks are rather similar only they are two separate amps and were planned up front to be able to use any of the power tubes that share the same pin arrangements (6L6GC, KT77, KT88, E元4, 6CA7 and all the variants). The previous project, the OddWatt 225 (6SL7 SRPP / KT77 Class-A Push-Pull Tube Amplifier) is in daily operation and (with JJ KT77 tubes) has a wonderful tube sound. ![]()
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