National TV-7M "Videometer" question
 

I won one of these at the ETF auction for a good price. They are rare.
I finally found a basic TV-7 schematic with the power transformer, which
mine has, at Sams and bought its.

But its lacking the meter circuit. Does anybody have that?

I has been semi-restored a goodly time ago. I removed the CRT, put
it on a dim-bulb and Variac and turned it on. At only 60Vac on the meter the
HF oscillator started up, which is good. I tested the CRT on my Sencore
(which does these electrostatic TVs CRTs the same as typical old
scope tubes) and it tests very good on both cutoff and emission.

The CRT however has some dark smudges on the screen. No solvent
I tried (water, alcohol, toluene, paint remover) had any effect.
A timid attack with Novus plastic polish removed the very mildest spot.
One spot looked shiny. A check with an ohmmeter says the smudges are
metal. Naval Jelly also had no effect. I'll have to try strong acids like HCl
or HNO3.

I've never heard of this before.

An attack with Novus #2 and the greem 3M dish scrubber got rid of it. This didn't
scratch the clear area, but left scratches below the metal ... something bad had
happened to this CRT, but left it electrically great.

After running a while there was a huge POP! and so I looked at the fuse ... OK.
But the Variac 10A fuse had blown! The tine bridge rectifier in the meter circuit,
which alwaus runs while its turned on, had dead shorted. I had to build a whole
new circuit with 1N4007s and terminal strips.

This set has been HIGHLY molested, especially in two H and V circuits. The vertical
coupling caps are a series kludge of a mix of paper and ceramic plus lots of slop-on
insulating glop. Sickening!

I have used cerium oxide powder to buff out blemishes in car windshields with good success in the past. Amazon has both cerium oxide powder and buffing wheels. Bought some just recently.

The only concern I would have is the heat generated by the buffing. A car windshield is thicker than the glass envelope of 7JP4.

Novus #2 sure looks like cerium oxide to me. There was no serious heat generated
by my buffing, done by hand.

Its going to take time to rid the set of the kludgy poor workmanship restore.