Sylvania 4-400's

[W2NBC]

Anyone had experience with Sylvania 4-400A's? Design is almost exactly Eimac- like in structure and glass envelope.  Recently purchased  a  "N.O.S." boxed pair.. The reason I ask is that I wasn't aware that Sylvania even produced them!

They are sitting in the transmitter, filaments on, and ready to be fired up in AB1 with 3600 volts as I write this..  

[WA5VGO]

Almost certainly produced by Eimac and simply branded Sylvania.

[w8khk]

They look nice, similar to the Eimac and Amperex 4-400/8438 tubes I have used.

I ran into difficulty with a couple 4-400s and a 250-TH at initial turn on when using full plate voltage.  Even though they are NOS, there is a possibility of gas via leakage at the seals. 

I found that in some cases a NOS tube would trip the HV PS breaker when first turned on if not de-gassed.  The plate on these tubes, when run at a dull to bright red dissipation level, functions as a getter, effectively de-gassing the tube.  So I always bring up the tube slowly after heating the filament for a while.  If there is any indication of blue in the tube, I will avoid bringing up the plate voltage, but instead reduce the negative grid bias to dissipate a significant amount of power to heat the plate, then slowly over time reduce the negative grid bias and increase the plate voltage until hopefully the gas is eradicated.  Hopefully your tubes do not have any noticeable gas, but if they do this procedure may be helpful.

GL OM

73, Rick

[w4bfs]

what Rick said ....

[W2NBC]

Thanks Rick and others for the replies.. The tubes work FB!  I always bring up "new" or unknown tubes as incrementally as possible with Variacs on the HV making that easy..

What is interesting is that these Sylvania branded tubes came in original boxes with serial numbers on both the box and etched on the grid shrouds.

Were they manufactured by Eimac?  Who cares, they work!

Thanks again,
Jeff

[n1zpy]

A little off topic but what is the best plate voltage to run in an amp with  a pair of 4-400 tubes?

[Opcom]

If not grounded grid, the max set of voltage specs in the data sheet. More volts less current burden on the filament.

3500-4000V on a pair in the data sheet says you can get 1650-1750W. 3KV gets you only 1300W. Those are the AB2 audio ratings but good enough for HF.

There is an Eimac appnote on grounded grid service somewhere on here giving recommendations. Can't go wrong using the recommended conditions.

Just opinions.. I never built a 4-400 amp so.. my opinion is worth what you paid for it!