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previous: JCS I have a SFTR I just blackfaced and... -- 4/25/2000 4:17 AM

Re: No bias current ?

4/25/2000 7:24 PM
Ray Ivers	Re: No bias current ? JCS, If "all voltages are normal", then the only thing it could be are the output tube cathodes lifting, and even then I doubt that ALL voltages would be normal. Every single voltage on each pin of all the output tubes are normal? If you haven't checked them all, I would go back and check them, especially the screen grids (pin 4) - it sounds to me like during the replacement of the first (1K) resistor the screen grid supply voltage was lost, maybe due to a wire popping out as soon as the solder melted. The choke, first filter cap, the resistor, and the screen grids all are connected to this point - a lot of potential for soldering problems. If the tubes' cathodes are grounded and every voltage on the tube sockets reads normal (heaters too!) and you still have no current flow through the tube, and the measuring instrument is OK and connected correctly - then I honestly have no idea what's wrong with your amp; it sounds like 'one for the record books' (unless all your output tubes decided to quietly fail at once). Ray Ivers

4/25/2000 7:24 PM

Ray Ivers

Re: No bias current ?

JCS,

If "all voltages are normal", then the only thing it could be are the output tube cathodes lifting, and even then I doubt that ALL voltages would be normal. Every single voltage on each pin of all the output tubes are normal? If you haven't checked them all, I would go back and check them, especially the screen grids (pin 4) - it sounds to me like during the replacement of the first (1K) resistor the screen grid supply voltage was lost, maybe due to a wire popping out as soon as the solder melted. The choke, first filter cap, the resistor, and the screen grids all are connected to this point - a lot of potential for soldering problems.

If the tubes' cathodes are grounded and every voltage on the tube sockets reads normal (heaters too!) and you still have no current flow through the tube, and the measuring instrument is OK and connected correctly - then I honestly have no idea what's wrong with your amp; it sounds like 'one for the record books' (unless all your output tubes decided to quietly fail at once).

Ray Ivers

Replies:

JCS Thanks for the replies guys. OK her... -- 4/26/2000 2:25 AM