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Hi, I have built a modified princeton (12ax7,6l6gc,5ar4). I have it up and running and it sounds great! It is running 445v (pin3) 404v on (pin4) 680ohm dropping 33.3 volts at the resistor, which would make my bias at .49ma,(if my math is correct). I used an old zenith P.T. for this project.
Despite sounding good I would like to know about the blue glow in the 6l6 tube? I have subistituted 3 different brands of 6l6gc tubes and all have a similar blue glow on the inside glass. I tired a 5y3gt rectifier to lower the voltage, but still the same blue glow. should I worry? I also noticed the same blue glow in my 71' twin reverb with 4-6l6gc black plates?
Do I need to install an 800 ohm bias resistor? I guess I don't know why every 6l6gc tube I install glows blue .Is it a design flaw on my part or voltage problem , P.T. problem ?
Thanks, Gerard
Despite sounding good I would like to know about the blue glow in the 6l6 tube? I have subistituted 3 different brands of 6l6gc tubes and all have a similar blue glow on the inside glass. I tired a 5y3gt rectifier to lower the voltage, but still the same blue glow. should I worry? I also noticed the same blue glow in my 71' twin reverb with 4-6l6gc black plates?
Do I need to install an 800 ohm bias resistor? I guess I don't know why every 6l6gc tube I install glows blue .Is it a design flaw on my part or voltage problem , P.T. problem ?
Thanks, Gerard
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