RCA P46720LV Bad Green CRT

[Kirk S.]

Found this set at a garage sale, owner indicated that he had service people
come out and they told him the green "bulb" was bad. I'm taking this to
mean the CRT is bad. Given that this set is probably ten years old and a
replacement CRT is about $250, I didn't grab it for the $60 he wanted.

What do these sets go for in working condition? I do like tinkering however
that is a rather expensive tinker in my book. I don't have access to used
parts either.

Just wanting a few opinions... Would you buy it?

Thanks,

Kirk S.

 

[[email protected]]

Found this set at a garage sale, owner indicated that he had service people
come out and they told him the green "bulb" was bad. I'm taking this to
mean the CRT is bad. Given that this set is probably ten years old and a
replacement CRT is about $250, I didn't grab it for the $60 he wanted.

Fix the existing crt. Every repair tech I know says its impossible but
its not difficult.


NT

 

[James Sweet]

Fix the existing crt. Every repair tech I know says its impossible but
its not difficult.


NT

There's not much you can "fix" on a CRT without completely rebuilding it,
which I suppose is within the realm of a very persistent amature who happens
to have a diffusion pump and glassworking equipment but I've not heard of
anyone doing that sort of thing at home yet.

If the set is HD capable I'd haul it away for free, might even pay 10 bucks
or so for it, but if it's only a SD projector forget it, he should be paying
you to dispose of it. There's some cool optics in a CRT projection set
though if you're into experimenting with that sort of thing.

 

[Kirk S.]

There's not much you can "fix" on a CRT without completely rebuilding it,
which I suppose is within the realm of a very persistent amature who happens
to have a diffusion pump and glassworking equipment but I've not heard of
anyone doing that sort of thing at home yet.

If the set is HD capable I'd haul it away for free, might even pay 10 bucks
or so for it, but if it's only a SD projector forget it, he should be paying
you to dispose of it. There's some cool optics in a CRT projection set
though if you're into experimenting with that sort of thing.

James, thanks for the opinion... That's what I needed. He indicated the
repair shop offered him $50 for it.

 

[[email protected]]

Found this set at a garage sale, owner indicated that he had service people
come out and they told him the green "bulb" was bad. I'm taking this to
mean the CRT is bad. Given that this set is probably ten years old and a
replacement CRT is about $250, I didn't grab it for the $60 he wanted.

What do these sets go for in working condition? I do like tinkering however
that is a rather expensive tinker in my book. I don't have access to used
parts either.

Just wanting a few opinions... Would you buy it?

Thanks,

Kirk S.

The "bulb" he was referring to would be the "green gun" All color
CRT's have 3 guns, red, green, and blue. If the"bulb" is shorted, i.e.
the cathode shorted to the heating element or possibly to the screen
grid, it's possible to remove the short.You would have to have access
to what is referred to as a CRT Tester/Rejuvenator. Sencore and B&K
are still around. If the cathode or grids are open there's no hope.
Either rebuild the tube or replace it. They are available for a lot
less than $250. You'll never recover you costs for this, but if you
like tinkering, enjoy.
Have a good day!
Mike

 

[Meat Plow]

The "bulb" he was referring to would be the "green gun" All color
CRT's have 3 guns, red, green, and blue. If the"bulb" is shorted, i.e.
the cathode shorted to the heating element or possibly to the screen
grid, it's possible to remove the short.You would have to have access
to what is referred to as a CRT Tester/Rejuvenator. Sencore and B&K
are still around. If the cathode or grids are open there's no hope.
Either rebuild the tube or replace it. They are available for a lot
less than $250. You'll never recover you costs for this, but if you
like tinkering, enjoy.
Have a good day!
Mike

Do those work on projectors like the P46720LV ?

 

[Kirk S.]

Thanks for the information. Where would I obtain a replacement green CRT.
This is a projection set that uses three separate CRTs...

Kirk S.

 

[[email protected]]

Please, elaborate on this if you would...

Sure. I've done this many a time, so wont take much notice of the
naysayers that always come along.

The trick is very simple, boost heater voltage. Not by a measly 10%,
thats semi-pointless, 33% V boost for mild cases, 66% for the worse
ones. The simplest way to boost is to add an extra turn round the
LOPTR core, just thread some pvc wire through it and hook up in series
with the heater feed. If V drops, connect the turn the other way round
to get boost.

I once did an experiment, took a set with nothing visible on screen at
all, solely due to dire emission, and hit it with IIRC +70& Vboost and
+10% EHT boost. All guns came up, brightness was fine, but tracking of
the 3 channels was a mess.

Dont boost EHT unless you understand the issues involved, dont do it
at home and dont do it on repair sets.

Ah, there is one gotcha with this boost method: the tube must never
have been touched by those dreaded cathode zapping rejuvenators. If
you see a tube that smears, boosting it is a waste of time IME.


NT

 

[[email protected]]

Thanks for the information. Where would I obtain a replacement green CRT.
This is a projection set that uses three separate CRTs...

Kirk S.

Not recommended. Gamma changes significantly over time, and a new tube
working with old tubes makes for bad colour tracking. If you do
replace a tube, putting an old one in from a scrapper would give a
better picture.


NT

 

[Kirk S.]

Not recommended. Gamma changes significantly over time, and a new tube
working with old tubes makes for bad colour tracking. If you do
replace a tube, putting an old one in from a scrapper would give a
better picture.

Hence my dilemna... No spare parts...

Thanks...

Kirk S.