uncontroversial? floating of the filiment...

[Chadwick]

I don't know if this one will make people angy.. I didn't find it from Torres. I learned it from a guy that used to work at Antique Electronic Tube Supply [Bruce Thorp] who deciphered it from a variation in a sovtek mig 50... And I'm sure that somebody did it forever ago before I was born.

Just take the center tap of the filiment supply and and put 25 volts or so on it and it quiets the filiment supply a whole bunch lifting it away from audio ground. Maybe more usufull for high gain but I think extremely usefull and noticeable in all circuits.

Here is an example. Great for hum chasers and a lot easier than recitifying filiment for DC operation.

[Enzo]

That is not floating the heaters, that is elevating them DC. FLoating would be no reference at all to anything else - wires from the transformer to the heater pins on the sockets and nothing else. But I am being fussy.

Raising the heaters is an old trick, in fact we have a thread about it on here going on right now somewhere around.

In cathode biased amps, one easy way was to conntect the heater CT to the power tube cathodes.

WHile dividing off the screen rail strikes me as odd, I see no reason it wouldn't work as well as any other source of offsetting voltage.

Quoting RCA - page 83 in RC28 -
"Much lower hum levels can be achieved when...the center tap of the heater supply is grounded, or preferably, connected to a positive bias source of 15 to 80 volts DC..."

[Chadwick]

sweet

so thats where it came from.. cool. works great.

[Arthur B.]

It's been discussed to death on AX84. Search the archives there for more information.