Re: RM503 - The story continues.


Denton, Adam (Exchange)
 

Aaah, you are in the same boat as i was. My 564B's 3.3kV supply
was leaking to ground thru the CRT filament supply also.
On the 564 the filly is driven from the (giant) main power
transformer so replacing the whole thing seemed dubious.

To make a long story short, I unwound the secondary of an
(ancient) radio shack 6.3V transformer, carefully put 2
layers of electrical tape on it and everywhere, and re-wound
it. Worked. *but* in 2 weeks guess what, broke down.
I think it is the plastic part where the leads go.
I repeated the operation but this time it broke down in a day,
again confirming it's the plastic part, not the tape.
The tape I verified by just seeing if the unloaded supply
would arc thru it. It didn't.

So I'm planning another rewind, but i am in need of a core
where the sec is totally isolated from the primary -- i
have a few 'formers like that but they are big 2A types
and i'd rather not waste them. The problem is, it's a
major hassle to re-wind a 'former because getting the E's
and I's apart is a MAJOR headache! The actual rewinding
operation only took about 2 hours including taping,
but disassembling the 'former the 1st time is a dangerous
and un-fun operation. That resin-like stuff that glues
the former is very tough, and you can't use the obvious
(propane torch) since that would melt the plastic form.
Came down to a sharp chisel and tapping with a hammer,
one layer at a time.

But it can be done. Leave NO part of the secondary
uncovered with tape, and there must be no gaps in the
tape either.

Another option would be to heist the core of an old
TV flyback (or vertical pincushion).
These cores are easy to take apart, trivial to wind
(no plastic needed). The problem is they're useless
at 50/60 Hz so you have to build a driver to power
them at e.g. 1-10kHz.

Another option is to junk the scope. I am considering
that option too :-( [it is only 10 MHz]

(funny, out the 1,000 resistors/caps/diodes/transisitors/tubes
in the beast, maybe there are only 2 or 3 components
that are impossible or prohibitively expensive to replace.
(CRT, main power 'former, and HV 'former. No hybrids!)
SO, Murphy's law applies and thus it one of the 2 or 3
dilly-parts that breaks! Figures!!)

----
2) Rewind the 6.3v winding on the transformer. It appears to be outside
winding on the device, so it should not be that hard.
3) Install a separate 6.3v transformer to supply the CRT heater voltage.


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