That sounds typical of some of thr Russian triodes too...I read somewhere a
few yrs ago of a conversion to GI7B`s in a MLA-2500 . The guy had a ac hum
on the audio as well as when keyed with no drive. They corrected the problem
by transposing heater voltage from the outside of one tube to the inside
connection of the other tube,and opposite wiring for the other fil leg.They
were feeding filament voltage thru a conventional bifilar filament choke
with .01 across both fil legs/cathode for rf drive, filament trans ct for
negative return. I found the same hum problem as Terry suggests with a
single GS-35b and cured it as he did with the yc-156.Jim.
----- Original Message -----
To: <firstname.lastname@example.org>; <email@example.com>
Sent: Thursday, September 08, 2005 7:24 PM
Subject: Re: [Amps] YC-156 Triode
> In a message dated 9/8/2005 5:56:31 P.M. Pacific Daylight Time,
> firstname.lastname@example.org writes:
> My filament transformer didn't have a center-tap
> so I improvised a B- by using an artificial centertap made of diodes
> to each leg of the filament's secondary.
> This tube is NOT a directly heated cathode. It has a indirectly heated
> cathode ... connection to the cathode is the outside heater connection.
> where you connect the B- through a RF choke to the tube. I found that any
> B- connection to this tube will induce hum in the transmitted signal do
> the AC heater current ending up in series with the cathode B-.
> Terry W6RU
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