• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

JJ Kt77 Bias?

Yeah, I know...That's why I've ended up with 8 Small Pins for the price of 4...But they Still do Sound Good, and if I Red-Plate them...I'll look into Others...I still would like to know what a Good Bias is for a KT77....

Now, I've just Checked...For under $75 a Match Quad, they Really Sound Nice..For how long they Sound Nice, well I guess that's a Roll of the Dice..
 
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They are the later ones with the good pins - about 150-200 hours on them
and no issues at all.

How can you tell if they have the good pins or the bad pins? What is the difference? I have a quad and run them at respectable levels (475v) and have had no problems with them. I don't know why so many people complain about the JJ KT77; maybe I have just been lucky.
Daniel
 
It's been a few years now, but JJ had some quality control issues with their octal tubes. They had issues with undersized pins, weird misshapen "square" pins, and other problems with the build quality of their internals.

The first quad of KT77s that I put into my freshly-rebuild VTA-70 arced over the rectifier due to an internal short. The cathode had slid down, out of the mica rested on one of the straps below. I gave the tube a few good smacks in my palm, which slid the cathode back up. They worked fine after that, but AES exchanged them and even replaced the GZ34 that had arced as a result. The new set have been in there ever since and sound and work great. I think I bias them at 40mA.