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In Reply to: RE: Using fixed bias on a 6J5G posted by Paul Joppa on November 04, 2016 at 13:41:58
Hi Paul, do you have a favorite that you would care to share with me? thank you
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We (i.e. Bottlehead) use the HLMP-6000 which is "standard red," i.e. one of the earliest chemical formulations. It has an unusually low ESR, and at one time was known to be quieter than most others. Runs about 1.55v drop per diode. I suspect that the inefficient formulation produces less ESR, but I have not yet learned enough to defend that notion.
Some people use Schottky diodes, but they will have a very low voltage drop per diode, unless you get the high voltage silicon carbide diodes.
Don't use Zeners - they are much noisier because they operate in reverse-breakdown mode. To reduce that you need a huge bypass cap, in which case one might as well use a resistor and get the DC feedback stabilization.
I have a bunch of red, blue, green, yellow and white or clear. The red ones i have are bullet shaped with one lead shorter than the other and the base having a flat side associated with the shorter lead. right now with my resistor of 380 ohms, i am getting about 3.8vdc on the cathode with a plate voltage of 360 and a plate resistor of 100k. Plus there is a plate to plate feedback resistor of 100k(from plate of power tube to plate of 6j5).
So, for the 6j5 i would use it on the tube's cathode. with cathode of the LED grounded? I would find it informative to see if using a LED is of significant difference to the sound. How many LEDs do i need per tube? regards, Dak
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