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previous: Mike T cathode volts/cathode resister ohms... -- 12/25/1997 10:34 AM

Re: Cathode Bias Idling Current

1/2/1998 5:07 PM
Mike T	Re: Cathode Bias Idling Current I removed the rectifier tube and replaced it with a 12AX7 for a long-tailed driver which installed OK. I replaced the rectifier circuit with 6 1N4007s and tied off the 5V filament leads. The amp works...BUT...I get 0 volts on the cathode. It's cathode biased with a 250 ohm 5 watt resister bypassed by a 25@25 cap. The polarity is correct on the cap. I get 300 volts at the plates and 250 volts at the screen grid (pin 4). All other pins read 0 VDC. The tubes get real hot, I had to turn it off. Both tubes share the rK and cap. Why am I not getting any bias? Mike T

1/2/1998 5:07 PM

Mike T

Re: Cathode Bias Idling Current

I removed the rectifier tube and replaced it with a 12AX7 for a long-tailed driver which installed OK. I replaced the rectifier circuit with 6 1N4007s and tied off the 5V filament leads. The amp works...BUT...I get 0 volts on the cathode. It's cathode biased with a 250 ohm 5 watt resister bypassed by a 25@25 cap. The polarity is correct on the cap. I get 300 volts at the plates and 250 volts at the screen grid (pin 4). All other pins read 0 VDC. The tubes get real hot, I had to turn it off. Both tubes share the rK and cap. Why am I not getting any bias?

Mike T

Replies:

stephen 250 Ohm Rk bypassed by 25/25 cap. <... -- 1/2/1998 11:05 PM