[Boatanchors] NEED TUBE INFO

[Glen Zook]

In most sets one side of the filament/heater is
connected to ground.  If the filament of the rectifier
is connected in parallel with the rest of the tubes
then the rectified high voltage is going to be applied
to ground through the filaments before the rectifier
tube shorts out due to the ground connection from the
filament circuit.

Even if one side of the filament circuit is not
connected to ground the tubes still won't work because
in directly heated tubes (where the filament is the
cathode) you will be applying the positive voltage to
the cathode instead of a negative voltage.  In
indirectly heated tubes (which have a separate
cathode) the filaments can act as the plate (anode)
and will can burn out because of the electron flow
from the cathode to the heater.  It depends on the
actual tube but this is possible in certain cases.

That is why when directly heated rectifiers (which
most tube type rectifiers are directly heated) are
used they always have a separate winding on the power
transformer since the B+ comes off of the filament
(cathode).

Glen, K9STH


--- Brian A Clarke <brianclarke01 at optusnet.com.au>
wrote:

Would you please explain how having the filaments of
other than the rectifier at B+ shortens the life of
those other valves - especially if they are heaters?
Just as an aside, I regularly design and build valve
amplifiers with the heaters at quite high dc
potentials compared with their respective cathodes -
gets my hum-type noise down around -110 dB wrt the
output.









Glen, K9STH

Website:  http://k9sth.com


       
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