In Reply to: that's great to know posted by aol908 on April 2, 2001 at 09:07:30:
Just because the bias is fixed on an 800 does NOT mean that you cannot adjust it. It just takes a bit more effort. If you can track him down, you should contact the Fisher Doc and score one of his re-build plans. The plans discuss the rectifier and shunt resistor for your particular iteration of the 800. VTV rebuild plans probably do the same.The Fisher doc recommends that the bias on these things be increased from about -18 v to -21 to -25 volts (this is from memory, I may be a few volts off). 7591s run fairly cool at that bias, hence the tubes are saved. But since we now have reasonably priced replacement tubes from EH, that may no longer be an issue. I say run em hot.
The point of all of this is that you need to check your bias and replace the bias rectifier if you are under-biased.
Good luck!
joe
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Follow Ups
- Whoa, daddy-o! - funkwrench 19:14:31 04/08/01 (0)