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In Reply to: RE: phono noise floor posted by Michael Samra on February 24, 2015 at 10:39:14
I'll check that out, I have a friend that can lend me some 5751s to try. I don't seem to have too much gain, I have phono level around 80 and volume at 2:00 to get "loud". Certainly enough but at those levels the noise is an issue in quiet passages. I'll check out the 5751s, thanks.
Dave
Follow Ups:
Just out of curiosity, have you changed out the selenium rectifier on the DC heaters of the 12AX7 tubes and verified that the heater voltage across each heater is 5 volts as specified by the schematic? You might get a lot more noise if the heaters are off that spec which is a bit unusual for a 12AX7 (I guess Scott liked to starve the tubes for long life). If you still have the original selenium rectifier it may be putting out a whole lot less voltage now (perhaps down to 4 volts?)...and if someone updated it with a silicon bridge without a dropping resistor you might be closer to 7 volts....either of those scenarios might be contributory.
Not something I had considered, thanks. I did replace the bridge, but I'm not certain what the heater voltages are nor had I noticed that they should be so low. I'll check it out.
Dave
At the very least it will spare you from prematurely wearing out a set of TFK 12AX7's
By the way, if you have them, a set of 1950's Raytheon black plate tubes are sensational in the phono position.....even better than the TFK IMHO....and quieter.
David
If its at 12.0vdc or higher on the phono tubes especially,get it down to around 10.6vdc..With the heater voltage too high,this will cause rush because you are really pushing the tube hard.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
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