ChopperChas
Super Member
I bought 8 "factory second" Teslovak KT88 tubes off of eBay, and got four that appear to work. I've got them in my tube amp now, burning them in at a low bias. (as low as my amp goes, which is between 0.19v and 0.43v, depending on the tube... with one running at 0.69v. Not socket dependent, the bias voltage follows the tube)
First, the questions about the working tubes.
1. Why does one have an idle bias voltage of 0.69v (or 69 ma, I guess, but my manual says to use a voltmeter to measure bias)
Now questions about the bad tubes:
2. Two have heaters that don't light up. What causes this? No orange glow, no nothing.
3. Two have perfectly working heaters, but I never get bias voltage across the test points. Always 0.000v. What is wrong with these two tubes?
Thanks!
Charles.
First, the questions about the working tubes.
1. Why does one have an idle bias voltage of 0.69v (or 69 ma, I guess, but my manual says to use a voltmeter to measure bias)
Now questions about the bad tubes:
2. Two have heaters that don't light up. What causes this? No orange glow, no nothing.
3. Two have perfectly working heaters, but I never get bias voltage across the test points. Always 0.000v. What is wrong with these two tubes?
Thanks!
Charles.