Here the B+ and B- wiring harness is fabricated, and installed inside the
braid. (which will have heat shrink tubing installed over top).
Also shown is the dual / staggered Alden B+ / B- HV connectors plus HV
interlock assy. GTO-15 kv AC rated HV wire used.
RVS connected diodes installed between B- and chassis. Each assy consists
of 3 x 10A10 diodes in parallel, to create a 1200 amp surge rating. (6 x
diodes in total). That keeps the B- within +/- .7vdc of chassis potential
at all times, and does not affect the plate or grid current metering.
I had to redesign the HV metering circuit. The new version uses a single
100 megohm / 1% tolerance, 20 kv rated resistor, 5 watt axial type. Then
the 100 ua multimeter will read 0-10 kvdc. A 100 K @ 3 watt mof resistor
is wired in series with the 100 megohms, and is in parallel with the 100 ua
meter. The multimeter consists of a dual wafer rotary switch...which also
is used to read fil V and also used to read the 12 vdc and 24 vdc
supplies. When the multimeter is switched to any other position, other
than HV, we don't want full B+ appearing on the now un-used contact of
wafer #1. The 100k ensures that the max vdc across the un used wafer
contacts is no more than 10 vdc if 10 kv applied...and in this amp, normal
unloaded B+ is 7.5 kv..... so no more than 7.5 vdc can appear across the
wafers of the rotary switch. 100K resistor only dissipates .0005
watts...and that's only when the multimeter is in any other position than
HV.
The 100K will not affect the HV meter reading. The 100 megohm resistor
only dissipates .5625 watts.
A spst NC temp sensor switch will also be installed (rated at 35 C / 95F)
which will ensure total shutdown of the amp (except blower) in case the
room ambient air temp gets too high.
One more item to be installed is a single 250 vac rated neon (with a 20k
resistor in series) which gets wired across the + and - of the last HV
lytic (at the cold end). Under normal operation, the 375 vdc V drop across
the last cap will turn on the red neon. That's just an extra layer of
safety, and alerts the user that B+ is present....and can be easily seen
from 50' away.
I used that method on a 6700 vdc supply that I built years ago....except
that I used 2 x 120 vac neon's in series. Works superb as a visual
indicator.
More work to be done before the new 7500 vdc B+ supply can be tested.
It's coming along nicely.
https://www.youtube.com/watch?v=bxnG07-PaHw&t=10s
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