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
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