Just and update, and a couple of questions ...
The 'henry' I picked up with a fault seems to work .. I finally got the
thing to come up and the blowers [ all 14 of them!] to come on ... and
putting it into 'tune' and applying a little drive showed power out of the
intermediate stage, but nothing out of the final stage ... a bit of tweaking
revealed some very 'odd' behaviour ... I could tweak the intermediate stage
for around 500W out and by tweaking the input side of the final stageI could
see that the two were connected OK and get a peak ... but almost 100%
reflection to the intermediate stage ... the air coming out of the 3cx1500
was warm the air coming out of the 3cx15000 was cold .. and no plate current
...
I pulled the heater connections off the 3cx15000 chassis .. o/c .. damn ...
maybe the valve is duff, I know they changed the valve and coudn't get it to
work afterwards (which is howcome I got it ..) ... pull the chassis .. and a
bit more investigation shows .. the valve isn't seated in its socket properly
;)) ... a firm shove soon cures that ... heater continuity is restored.
Firing the thing up I now get a nice match to the intermediate stage
amplifier, it peaks and I see power out of the main stage ... due to lack of
a suitably rated load, I've not pulled more than 5kw out if it yet ...
Now then .. questions :) ... the 3cx1500 is drawing about 280ma plate bias
current, I'm reading about 10mv as bias on the transformer CT ... but on the
3CX15000 I'm showing just a tiny bit of plate resting current ... and 39V on
the heater txfmr CT .... so its quite strongly biased off ... the manual says
the bias current shoudl be 0.5A ...so I susect the bias diode stack ... its
a few years since I played with these things, but that should look like a
load of diodes pointing to ground, pulling the grid a bit closer to Ov yes?
sounds like ones o/c maybe?
[fwiw, the bias stack seems to consist of about 20 stud diodes on a series of
aluminum heatsinks .. and 3 fans to keep it cool ;]
Now .. if I could find some 'LC' connectors I could run this thing up to full
power .. or an EIA glange water cooled load ...
--
RapidCut CNC Technology
CNC Plasma Cutter
http://www.rapidcut.co.uk/
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