21FJP22 question

Keith Park

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Nov 17, 2009, 8:59:42 PM11/17/09

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Just put the new tube in the CTC 20,
this one has a glossy cover plate rather than a matte finish, its I rebuild
I belive, did they get new
glossy cover plates when they were rebuilt?

Got it in the set, cant turn the brightness down but thats probably because
everything
was turned up full with the old tired tube.. was it good practice to check
the HV when installing a new tube??

Thanks

Keith

Brenda Ann

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Nov 17, 2009, 10:10:17 PM11/17/09

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"Keith Park" <topn...@nycapnospam.rr.com> wrote in message
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Always a good idea. IIRC, 20-22KV for most of the roundies.

Keith Park

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Nov 18, 2009, 7:42:22 PM11/18/09

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Well I have ZERO HV regulation, need to look into it, the shunt regulator is
almost new, maybe I didnt get something seated right when I had the chassis
out but boy I hate to work with the HV part of these sets.

Keith

"Brenda Ann" <newsg...@fullspectrumradio.org> wrote in message
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paul @removeppinyot.removecom Paul_P

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Nov 18, 2009, 10:29:10 PM11/18/09

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> Always a good idea. IIRC, 20-22KV for most of the roundies.
>
>

At what voltage does the tube produce X-rays? I remember a red line on the
volt meter built into the CRT test jig at one TV shop I worked at.

Paul P.

jughead

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Nov 18, 2009, 11:17:53 PM11/18/09

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Can anybody post a schematic of the HV region of the CTC-20? It's been
decades since I worked on one, but if memory serves, there is a 1K
half-watt resistor in the cathode leg of the 6BK4 that goes open,
disabling the regulator. Can't swear to it, though. Been a lotta
years. Also, the HV is supposed to run 25KV, but can't swear to that
either.
Bill(oc)

John Stone

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Nov 19, 2009, 8:12:27 AM11/19/09

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On 11/18/09 9:29 PM, in article he2e28$ip4$1...@news.eternal-september.org,

My understanding was that it wasn't the CRT that produced Xrays, it was the
HV regulator. The HV to the CRT had to be regulated to keep it from arcing
with overvoltage and blooming with undervoltage.

frenchy

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Nov 19, 2009, 5:26:14 PM11/19/09

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On Nov 19, 5:12 am, John Stone <jmse...@comcast.net> wrote:
> My understanding was that it wasn't the CRT that produced Xrays, it was the
> HV regulator. The HV to the CRT had to be regulated to keep it from arcing
> with overvoltage and blooming with undervoltage.>>

The blooming might still happen of course on a really old color
roundie though, even though they were all regulated, some can still
easily bloom the picture partially or completely if brightness and
contrast are cranked beyond a certain point. Like my CTC-5 for
example.

Kenneth Scharf

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Nov 20, 2009, 1:03:07 PM11/20/09

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The CRT CAN produce xrays but they are of the soft kind and are mostly
directed backwards into the set. Even if you stood right in front of
the screen you'd not detect much.

mark

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Nov 21, 2009, 1:50:55 AM11/21/09

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You might check your HV rectifier if it blooms out with brightness.

doogie812

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Jan 3, 2010, 7:08:36 PM1/3/10

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Come on people this is not rocket science. First replace the 3A3 HV
rectifier. I have seen more fly back failures because of leaky HV
rectifiers. No the tube tester can’t test them. By definition the
6BK4 is a SHUNT regulator. Meaning excessive voltage is shunted to
ground. With any other tube the grid is negatively biased relative to
the cathode. 1. Check the cathode voltage It should be around 380 V.
2. With most tube circuits the grid is negatively biased with respect
to the cathode. (Around 365 V.)

I’m sure you have checked the static value of the resistors. If not
do so. Your dynamic problems could be the K to G cap, the cap to
ground on the horizontal output tube G2 circuit. And that is it.
Other wise you would be complaining about vertical deflection
problems.

Remember people, tubes are about timing. You don’t want the HV
section to start working before the horizontal oscillator does. You
want the HV regulator to start before the CRT worms up.

Doogie

P.S. CRT HV 21 KV Bright 23 Black.

Keith Park

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Jan 4, 2010, 8:49:33 PM1/4/10

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Thanks for the advice,
as it turned out the HV was not too bad, but the B+ boost was about 100
volts or so low, therefore I got focus problems with the brightness cranked
all the way up. Once everything was set up properly it worked fine with a
normal picture but I did suspect that the HV diode that gives that boost was
going bad with age,
is there a replacement for that that I can get??

Thanks

KEith

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