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previous: R.G. (1) did you get the pinout right? -- 6/5/2000 3:26 AM

Re: Runaway Bias

6/5/2000 4:21 AM
Casey4s	Re: Runaway Bias RG, Thanks for the speedy reply. (1) Yes, I double checked all the pinouts. (2) Yes, I can read neg voltage on the "tube side" of the sockets. (3) I read the voltages,thru my bias probe so the sockets are good all the way thru. (4) Yes, I can get from -38.5 to -41.6 by turning the 25k pot. (5) The tubes are good, NOS, TV-7 tested, but I put a known good used pair of 6L6's in ther just to be sure, they biased at around 160 ma ( (6) Not sure here...The screens have 534v and the plates have 535v. The original drawing calls for 475v on the plates and 470v on the screens, BUT, that was for a pair of 6L6GC's. The screens could be a "little" high but not really that much. I should still be able to get the bias in the ball park I would think. This has almost got to be some stupid oversite someplace. Let me make sure I have my head on strait here... if I INCREASE the neg voltage to the grids, this should drive the bias reading (ma) down right? or is my head up my @$$? A simple resistor change and I can get the base neg voltage up or down. Somthin' just ain't kosher. Thanks again RG, Any more suggestions? Casey4s

6/5/2000 4:21 AM

Casey4s

Re: Runaway Bias

RG,

Thanks for the speedy reply.

(1) Yes, I double checked all the pinouts.

(2) Yes, I can read neg voltage on the "tube side" of the sockets.

(3) I read the voltages,thru my bias probe so the sockets are good all the way thru.

(4) Yes, I can get from -38.5 to -41.6 by turning the 25k pot.

(5) The tubes are good, NOS, TV-7 tested, but I put a known good used pair of 6L6's in ther just to be sure, they biased at around 160 ma

(

(6) Not sure here...The screens have 534v and the plates have 535v. The original drawing calls for 475v on the plates and 470v on the screens, BUT, that was for a pair of 6L6GC's. The screens could be a "little" high but not really that much. I should still be able to get the bias in the ball park I would think.

This has almost got to be some stupid oversite someplace.

Let me make sure I have my head on strait here... if I INCREASE the neg voltage to the grids, this should drive the bias reading (ma) down right? or is my head up my @$$? A simple resistor change and I can get the base neg voltage up or down. Somthin' just ain't kosher.

Thanks again RG,

Any more suggestions?

Casey4s

Replies:

Bryan James are you grounding out your bias som... -- 6/5/2000 5:47 AM
Bruce Beam forming tubes don't seem to ne... -- 6/5/2000 7:36 AM
Gil Ayan q{(4) Yes, I can get from -38.5 to ... -- 6/5/2000 3:25 PM