My idea about loading the circuit came from the thought
that the multiplier input would see a peak-detected DC
voltage that had to see some load to discharge. Nonsense,
of course. My excuse is that it was at 7am this morning
and I had been working all day and night (not on this
problem).
Just pulled Q1201. Cathode voltage goes down to far below
2KV so Q1206, Q1214 and associated circuitry could well be
ok. Looking at the circuitry driving Q1201 now (R1245
etc). R1245B could be open but I can't easily measure
24.5Mohm.
Next would be the Grid Bias circuitry.
Cathode filament is not open (2 Ohm across P1275 pins 1,
2).
--- In TekScopes@...,
David wrote:
>
> I will not say that is impossible but if I designed
it, the cathode
> voltage regulation would function correctly with or
without the high
> voltage multiplier attached. I think the load on the
6.3 volt AC
> heater supply which also comes from T1225 would
overwhelm any effect
> from the high voltage multiplier load.
>
> You might want to check that the CRT heater is not
open. I think you
> said earlier it is not shorted to the cathode.
>
> The error amplifier design Tektronix used seems
rather unwieldy to me.
> I wish they had marked the typical operating voltages
on the schematic
> but maybe there was too much variation for that to be
useful.
>
> The 7613 and 7623 use the same basic design while the
7623A and 7633
> use a single ended oscillator driving the transformer
instead of a
> push-pull oscillator. I looked over the schematics
for all four of
> those and none provided any insight into the typical
operating values.
>
> On Wed, 24 Apr 2013 17:11:45 -0000,
"raymonddompfrank"
> wrote:
>
> >David,
> >I thought that the multiplier was needed to allow
regulation to work, so -4KV would be reasonable without
any load.
> >Of course, load by a healthy multiplier and CRT
would be minimal, so you maybe right, also re. destruction
of the multiplier as a consequence of the -4KV.
> >I will take a look at the feedback/regulation
circuit.
> >
> >Thanks for helping me on my way.
> >
> >With regard to encapsulating the discrete HV
components: What you describe is what I had in mind once
the circuit would work "supended in the air", plus thanks
for reminding me to get rid of air bubbles.
> >
> >Raymond
> >
> >--- In TekScopes@...,
David wrote:
> >>
> >> Concerning your point 4, with the presumably
bad high voltage
> >> multiplier disconnected, shouldn't the high
voltage test point settle
> >> at -2975 volts?
> >>
> >> That makes me think something failed in the
regulation circuit built
> >> around Q1201, Q1206, and Q1214 including
feedback divider R1245.
> >>
> >> If the high voltage regulator ran away then
maybe it damaged the high
> >> voltage multiplier instead of the reverse.
> >>
> >> As to building one with discrete parts, that
is what I would do. The
> >> esoteric thing that comes to mind other than
standard high voltage
> >> construction methods is the use of a vacuum
to remove air from any
> >> potting mixture. I would build the circuit
supported in air by its
> >> three external connections without using
perforated board and then pot
> >> it.
>
