[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[TCML] VTTC filament getting brighter



Hello Folks.

First thanks to all who advised concerning the staccato controller,
I am currently waiting for the parts I ordered.
But in the meantime some more beginners questions:

I just changed from self-rectified AC mode to a level shifter using
3 MO an a 2nF MMC caps in parallel and a MO diode, the level shifter
itself does not seem to be the problem, output increased significantly.
But at a price: After 2 seconds you can see the tube getting brighter,
I would say it is the filament getting brighter, but as I can only observe it
for a very short moment and cannot get my head too close to the tube I still might be
wrong. I use 47nF bypass caps, two from the filament connetions to ground and
one between the connections ( its a GU81 with center tapped filament ) directly on
the socket.
On the first occasion it happened I realized it to late and there was some kind of
sparkling/arking inside the tube for a second or so. However, with lower voltage
the tube still runs smooth and seems to be OK.

What could be the problem? Am I pushing things too hard? Of course  I am pushing
beyond factory values, but others have done that, too, without too much problems.
I would have expected a red plate, but I can't even run the thing long enough to get
to that point.

Further specs that might help in finding an answer:

Setup type: impromptu lashup ;-)
Tube: russian GU81M, new ( well, until this evening ;-) in triode configuration
Plate xformer is a MOT, 2.1KV feeding a doubler,
estimated plate voltage around 4 or 5 KV
L1 10inch, 21turns of 6sqmm ( about 9AWG ), tapped at 19 ( tank ) and 19 1/3 (
supply )
L2 7" by 15" wound with awg23, 20mH
Feedback coil below L1, 16turns awg17 / 1sqmm, tapped at 15 turns.

Any suggestions are welcome.

best regards

Christoph Bohr

_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla