On Sun, 13 May 2007 21:09:52 GMT, Steve wrote:

On 13 May 2007 20:21:15 GMT, Jim Yanik wrote:
snipped


Makes me wonder if you don't have a HV multiplier problem.
If the rear socket is off,the geom and astig elements are unconnected,and
the 95V is not going to the CRT at all.Nor the negative cathode V,just the
12-16KV anode supply.

Or the anode connection inside the bad CRT has some sort of problem,drawing
too much current from the multiplier,and that is why the HV was loading.
I suspect this is the real problem.

Luckily I work at a cal lab so I can probably put it on the bench for
cheap. Unluckily, I will be the one calibrating it and this procedure
looks a bit lenghty. Oh well, good experience.

Thanks for your help,
Steve

Well,if you work at a cal lab,then you have all the proper cal equipment!
The procedure is not that hard.
You want hard,try a 7844 dual beam 7000 series mainframe,or a bistable
transfer storage scope like a 464/466. I HATED those 2 scopes.


The 30mA I was speaking of was just the difference in draw on the 32V
unreg supply with no tube in vs tube in, so really just an observation
I guess.

I've never tried those two scopes. We see a lot of the TDS scopes, I
love those. Usually received in great condition, cal takes about 20
minutes, can't complain about that. I used to hate cal'ing the analog
scopes when I started, I was spoiled with the easy DSO's. I'm
starting to come around though, the amount of engineering that went
into them is amazing and they're interesting to work on.

This has sparked my curiousity. When I pulled the jumper off the 95V
rail, it didn't fix the problem. If the schematic is correct, that
should have isolated everything on the 95V supply, leaving the other
items sharing the transformer to blame (tripler, cathode, etc). With
no tube in, everything worked fine, so I would figure the HV module
was ok (maybe a bad assumption). So it must be in the tube (again,
maybe a bad assumption). With just the anode connected, the supply is
loaded down. With just the rear plug connected, the supply is loaded
down. With another tube, it has no problem. If it was just a anode
lead problem, shouldn't the supply have come up with just the rear
plug on? I may be beating a dead horse here, I just like to learn.

I think I'm going to pull the bad tube out of the bad scope I put it
in and see if I can't find the problem. Would doing continuity
measurements show anything useful, or would the likely problem be too
high in resistance for say, a Fluke 87?

Thanks for all your help.
Steve

Well, not sure if it means anything at all, but I couldn't measure any
resistance with my meter between any pins. I know the meter puts out
small DC voltage, and things become a different story at kV, but I did
it anyway. Visual check of the tube looks fine.
I was going to hook up a little 8kV transformer I have lying around
between anode and cathode, put a couple volts on the filament and see
if I got a trace, but then I started thinking about XRays. Would
doing this out of the metal shield be a bad idea? Would this produce
XRays or radiation? I don't want to give myself cancer or cause
damage. Also, would this even produce a trace or am I just wasting my
time?

Thanks again,
Stev