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In Reply to: Re: Filament voltage ? posted by Laudanum on August 26, 2004 at 22:21:00:
Filament voltage update:I changed out a resistor (R21) and now measure 6.2 volts on the heaters.
Just listened to three hours of great LP music. I definitely have increased gain in my phono stage now since I need to turn down the volume on my preamp to maintain similar spl. Overall there is a greater weight to the music and better balance top to bottom. The RIAA function may be more accurate with the gain tubes functioning near their rated heater voltage. My phono stage is delivering much better “punch” to the music (for lack of a better word, you know what I mean).Now I'll start experimenting with various cartridge loading resistor values...
-S
Follow Ups:
Thanks for the update.
The RIAA is defintely more accurate at spec'd filament volatge of 6.3 volts, this according to Jim himself.
My cornet runs to a hybrid 100 wpc integrated with much more power than I need so I didn't look for a change in the volume knob position when I knew my voltages were down compared to up as it always seems to be situated between 1/4 and 1/3 of the way up and 1/3 is definitely past moderate levels in the small room. I'm sure that gain would go up some as well. I have to admit though, I can't hear any difference between when the voltages are up at 6.3 (120V line voltage) or down around 5.7 (115V line voltage).You were using the Hammond 370 though, yes? What was R21's original value in your Cornet?
Yes, I'm using the 370BX now since my 270BX smoked and died.
I had only changed out the tranny and was enjoying the music daily, when I finally got around to measuring the voltage at various points in the circuit. (Cornet Classic)R21 was 2.4 ohms which yielded 5.77v. It is now 1.8 ohms and yields 6.15v.
Next I plan to change out R2 to get the B+ back up to spec. Jim's comments in the AudioCircle dated 8-23-03 indicate dropping R2 from 6.8K to 3.9K when using the 370BX. I will buy several resistors from 3.3K to 4.7K so I can experiment.
Another evening of spinning vinyl has confirmed my original sense of greater dynamics. The proof is in the position of the volume knob.
Later last evening I put a 10K in parallel with R14 to yield about 8.3K cartridge loading. So far I like the sound. I plan to further reduce R14 and discover the best value for my situation. I'm using a medium output moving coil cartridge, Benz ACE.
Regards,
S
Good deal. R21 value was supposed to be dropped as well with the 370 so you've taken care of that and should be right on spec when you take care of the B+ with R2.Regards
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