improving the Mcintosh C22

[Craig405]

Kmtang, you conncted heaters to the HT?
Interesting, how does this get rid of hum, does it raise the 6.3v ac component upon such a high DC level you somehow get less inteference from it?

I have run my heaters from DC and i can hear no hum at all
(after i replaced a regulator valve which was oscillating)
I only hear a small hiss through the cheapo amp i have just tested through on maximum volume no signal input.

You said you can still hear huma bit, this might be interesting for you
http://members.aol.com/sbench/humbal.html

Cheers
Craig

 

[anatech]

Hi Johnny & Craig,
Normally the heaters are run +30 ~ 50VDC above ground. Just off the final tap on the B+ line. This acts as a light bleeder. Many units have this as one resistor. Just calculate the voltage and replace the one resistor with two. Add a cap to ground at that junction and run to the heaters.

-Chris

 

[SY]

Kmtang, you conncted heaters to the HT?
Interesting, how does this get rid of hum, does it raise the 6.3v ac component upon such a high DC level you somehow get less inteference from it?

Sort of. If the heater is negative wrt the cathode, it can act as a cathode with the "real" cathode filling in the anode role. This unintentional diode can couple heater hum to the cathode.

By biasing the heater positive wrt the cathode, you "reverse bias" the unintentional diode.