18 Jul
2010
18 Jul
'10
11:36 a.m.
Make sure neither valve has a heater to cathode
leakage. Insure the DC
It used to be common to run the rectifier heater off its own winding, and
tie one end of that (or the centre tap if there is one) to the rectifier
cathode. Then a bit of h-k leakage does little if any harm.
bus is clean
as a common old valve gear problem is dried up electrolytics. Try
grounding the other
side of the filament string or float the heater string (insure neither
side of the heater
The better power transformers have centre-tapped heater windings
(3.15-0-3.15V). Try earthing the tap (rather than one side).
winding on the power transformer is grounded.
I've also put a 100ohm 2W pot
across the heater winding and grounded the slider to be able to balance
the heater
Commonly called a 'humdinger' in the UK :-)
voltage against ground. If all else fails run the
heaters on DC.
Certainly for testing. RRun the heaters off a battery. If the hum goes
away, at least you know where it's coming from.
-tony