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

Fabio Trevisan
 

Hello David,
Thanks for your valuable input so far.
For now, I`m mostly standing by, or doing some cosmetic cleaning here and
there, while the new transformer doesn't arrive from Canada.
See my replies next to your last answers...
Rgrds,
Fabio

2016-10-09 2:58 GMT-03:00 David @DWH [TekScopes] <
TekScopes@...>:

If doubling peaking is a problem, then it is usually pretty
unambiguous. Just having the trace bloom is not enough.
That the trace bloom is there is sure, as well as many other symptoms
described
here and there on the net as being associated to cathode poisoning and/or
wearing.
Since the trace is not that much dim and I can still get decent focus
(although with
some struggle and having to retouch it when I change Intensity), I have
hopes that
the damage is still recoverable to some good degree. We shall see.

Do not forget to do the storage calibrations.
I will, as soon as the transformer is installed and I can put it back
online again.
I didn't go through the procedure yet and I hope it doesn't involve exotic
test equipment,
as I don't have them.

The second one is what I was thinking of.

Increase the heater voltage slightly with intensity set to maximum and
the CRT defocused to prevent damage. The trace could be moved off of
the screen for added safety.

Do we know what the standard heater voltage is for a 464? You may
need to carefully measure this before starting.
I`m glad that you're actually thinking of the second option!
It gives me hopes that I will be able to improve matters without having to
resort
to more radical approaches. I fear hurting the CRT.

I tried to measure the heater voltage with my DMM (in AC) to no avail.
It can't measure AC to 50KHz... It's not True RMS.
I can still try to obtain a good reading indirectly, by rectifying it with
a signal diode
and a small cap (no load) and compensate the reading for the diode drop and
Peak
Value vs RMS value.
But apart from measuring, just looking at the schematics, I conclude that
it's 6.3V,
Up to serial number B129999 the heater voltage was DC, shunt regulated by
CR1514, C1514 and VR1514 (a 6.2V Zener) and mine doesn't have them (it's
B132839).
Since there are no other parts change coincident to that S.N129999
it means that units just prior to S.N. 129999 shared the same
transformer,CRT,
and everything else that matters like mine but still, they had the 6.2V DC
regulator
to the heater and mine doesn't, which means that my CRT must also be 6.3V.

That is a great idea. Make sure you include the connection between
the battery and the cathode supply at R1504 which is shown in the
schematic. The difference between the cathode and heater needs to be
small.
Absolutely, I know of the danger of arcing between the cathode and heater
that could cause the heater to blow, being why the heater is "elevated" to
the cathode's potential.

Maybe you can open W1514 and connect the battery there. The battery
circuit will be at a potential of -1470 volts so insulate it and watch
yourself.
That's a perfect spot to connect it. I will insulate the whole thing and
connect
it using some H.V. wiring (TV Flyback wiring...).

Watch myself... here's a good one!
Once when I was 15 years old, I did my first mains voltage doubler using 2
old aluminum can capacitors
scrapped from an old tube amplifier, 2 diodes and 1 mains wire.
It was meant to be the power supply to my first Xenon strobe light (to
boost my Disco parties).
It was all "air-mounted" in the best "Jim William's" style... and the two
capacitors were in series.
So, the the cans had about 170V between them...
At some point I needed to make some room in the table and had the
"brilliant" idea to move
the whole thing aside...one hand in each can :-) :-) ... My hands closed
immediately around
the cans i was stuck to the thing (it was still connected to the mains!!!).
I only got free because I got desperate and ran away... the mains wire
snapped-off and
finally the capacitors discharged (on me) and I was free....
I was home alone that day and I could have got myself killed! I never told
my parents!
Lesson learned... I was never so stupid again!
Still, throughout the years I had many electrical shocks (who doesn't?) but
never anymore
between my two hands, never on the inside of the hands... Always one hand
in the back pocket!

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