[Amps] regulated screen supply

[Nils Petter Pedersen]

Hi !
You got some serious power there :-)
I do not think it is recommended to run that tube at full ratings at 144 Mhz. Tube parts will overheat ! I have never seen it used higher than VHF TV ch 2  around 50 Mhz. Output capacitance is also very high, so commercial constructions used cavity even at that frequency. I  still have an amplifier using this tube for 3-15 Mhz cw/ssb in my "attic museum". Class AB2 at 5000v / 1.3 amps CCS . That amplifier uses a heavy duty Zener stack as G2 supply. The stack has a noise filter at the output. If you wish I can look up the documentation and copy the G2 supply schematic for you. And the amp does show negative IG2 over a part of the operating range. Be aware that recommended tube position for full ratings is vertical, anode down.. (tube upside down). The blower in that thing is VERY big , so it must need a lot of air at high back pressure.
I tested that amp at full power into a dummy load, and it easily put out 4,5 KW or more....single tone. At dual tone
recommended drive it showed nice IMD specs and no noise-sidebands on spec-analyzer due to zener noise.
I can copy G2 schematic if you wish !
Peter
Original message:
Hello ,

I'm looking for ideas.... I am using a QBL5-3500 amplifier on 2m. Untill 
now , I have been using unregulated screen power supply with quite good 
success , but since I've moved to a new place , my mains voltage is higher 
than previously and my screen voltage went up to 1000v ( instead of 800v 
recommanded for that tube) . Off course , it is possible to use a small 
variac on the transformer primary , but a better idea would be to design 
and build a 800V screen regulator , if possible , an high performance 
design , like the one designed by GM3SEK in his famous " Tetrode Boards" , 
with the various protections needed..
But the tube is a little bit greedy ( or GRIDdy :0))

Screen voltage is 800V WG2 power is 100W maximum , so screen current can 
go up to 120ma during normal operation. There is nothing said in the tube 
data sheet about negative screen current , but there is no reason why it 
cannot occur.
So I am looking for a design able to statisfy my needs. Maybe the GM3SEK 
can be modified to run with that tube?

73 Dom/F6DRO