Re: Tek 464 CRT tube presenting "double-peaking" - Is rejuvenation recommended

Fabio Trevisan

Hi David,
Thanks for sharing your "shocking" story too!
From a perspective, it's good that you were on an aluminum ladder...
With 1000V on hundreds of uF, would this jig be on your bench instead, and
would have you done
anything as stupid as I did (your hands instead of your finger)... and we
wouldn't be having this conversation!
Falling from the ladder assured you didn't get stuck to the thing!

More comments from me next to your last replies...

2016-10-14 22:52 GMT-03:00 David @DWH [TekScopes] <

I do not think anything exotic is required. Or at least nothing
exotic was required for the 7834 when I did it.
It's the last week countdown for the transformer...
My Brother in Law is coming down to Brazil next Saturday.
Meanwhile, I am putting all the H.V. components back after proper cleaning
of H.V. dust and replacement of most carbon compound resistors by modern
H.V. grade film resistors.
Capacitors have all tested Good under 3.2kV and heat gun so, I will keep

Next in line is performing the storage calibrations and then start some
plan for the
CRT rejuvenation.

I do not have any experience with this so I made the suggestion before
searching back through the archives and I am now thinking that raising
the heater temperature temporarily will not be enough to make a useful

Ed Breya posted back in February that he had excellent results
rejuvenating two 576 CRTs using several cycles of "clean-balance" mode
from a B&K 470. On the second tube, he had to use the "remove shorts"
function between rejuvenation cycles.
I understand your change of mind regarding the possible (in)effectiveness in
achieving any useful rejuvenation using the scope's own bias but you know
I think I`ll try it anyway!
It's easy to implement (a variable heater supply) and at the very least I
to be able to assess if there's anything to be gained with going further.
If by just raising the heater I can see improvements in Focus / Focus
then I will be more even more driven to take the next steps.

Whatever the outcome of the test, I don't plan to keep the heater over
driven anyway.

Oh, that is a good call. I missed those parts marked on the schematic
and the theory section does not say what the heater voltage is. There
was a past discussion here about heater voltages which I will not have
to find now.
I`m glad that I`m being able to bring some contribution...After all, it's
my project
and still, you're the one usually coming with the ideas!

I have a similar story also involving a flashlamp power supply.
When I was about the same age and in high school, I picked up a small
xenon strobe light at a garage sale and decided that I wanted to build
a more powerful one. So I got some big strobe tubes but needed a DC
power supply. I had this transformer from some tube era consumer gear
(TV?) with a 700 volt AC secondary so I used a full wave bridge and
capacitor filter to get 1000 volts DC.
I got the capacitors from the same place, Orvac Electronics on
Orangethorpe avenue in Fullerton, California, that I got the big
strobe tubes. Now I knew that I needed to put three 450 volt
capacitors in series to get a high enough voltage rating but I did
*not* know that the capacitors should be as small as possible for
safety reasons. So I got 6 of the largest 450 volt capacitors they
had and used them in parallel and series. The total capacitance was
hundreds of microfarads. The strobe circuit itself used a current
limiting resistor and smaller capacitor to limit the energy per
discharge. I thought that later I might use the same power supply for
multiple strobes.
So the whole thing worked and I was adjusting its position up in the
garage rafters for Halloween while standing on an aluminum step ladder
when I managed to shock myself between my index finger and elbow
knocking me completely off of the ladder and onto the cement floor. My
arm hurt for a week and I had two little burn marks on my finger.

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