Heater Elevation, how high?

alexmoose · 22nd March 2007, 04:40 PM

Hello!

I just changed chassis for my simple 5687 preamp to an amazing new box, The future plan is to put in a phono stage, so there was a transition to DC heaters. With the transition to DC the heaters need to be elevated even higher to get rid of noise ( there is still a little bit in there, possibly from the shift from 6.3v to 12.6v heaters). The heater supply is Regulated, ripple less than 1mv (scope confirmed).

My question to the DIY community is how high can I elevate the heaters? I want to raise them to something like 90-95v above ground, this would put the heaters way above the noise floor. are there any consiquences I should consider?

Thanks a bunch.

-Moose

rdf · 22nd March 2007, 04:49 PM

Stay within the heater-cathode voltage ratings from the spec sheet. If your heater supply is DC it shouldn't be contributing any hum though. In any case, a Tung-Sol paper from the Thirties had a graph showing about 35 volts positive between heater and cathode pretty much reached maximum benefit. I aim for 30-40 volts above maximum positive cathode AC signal voltage within the limits of the tube ratings.

alexmoose · 22nd March 2007, 06:25 PM

I had it around 36v when I posted, since I boosted it to 70ivsh, and the noise is gone completly.

rdf · 22nd March 2007, 07:30 PM

What kind of noise was it?

alexmoose · 22nd March 2007, 08:27 PM

Before the heaters were rased at all, it was pretty horrible, volume controll did nothing to it, I raised the Heaters to ~35v and the hum was gone when the pot was bast 3 O'clock, it wasn't very loud at all, but I have fixed the exact same problem elevating the heaters before hand as well. At ~75 Volts it sounds stunning My SACD of Layla really likes it

Wavebourn · 22nd March 2007, 08:40 PM

Hmmm....
Probably the hum gone because you had to lift the supply from the ground so removed heater's current through ground wires? 1mv ripple voltage on heaters can't be audible.

Salectric · 23rd March 2007, 04:05 AM

Moose, did you change the filter cap in the heater bias supply when you raised the voltage? If so you may be hearing the effect of changing this cap as well as the change in voltage. I have found that this filter cap has a definite effect on sound quality. Try different types without changing the voltage and you hear the effects of the cap alone.

David Davenport · 23rd March 2007, 02:04 PM

Quote:

Originally posted by Salectric
I have found that this filter cap has a definite effect on sound quality.