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From: Mike WB2MEP on 24 Jul 2010 03:52
On Jul 23, 12:59 pm, "Arfa Daily" <arfa.da...(a)ntlworld.com> wrote:
> > Another Zenith had one in the HV regulator circuit that went open and
> > lost regulation. The HV was running around 30 kV on a 19" set.  A
> > regular resistor did't work on that set and I had to get the correct
> > part.
>
> > It looks likewww.moyerelectronics.comhas a 63-5440 sub. in stock.
>
> > Mike WB2MEP
>
> Good grief ! Did you not have x-ray protection circuits on the sets your
> side of the pond ?
>
> Arfa

Not on tube sets, and early solid-state ones. X-ray protection came
into widespread use when they started running the horiz. sweep from a
regulated B+ supply and did away with regulation of the HV itself.

Mike
From: Arfa Daily on 24 Jul 2010 08:50


"Mike WB2MEP" <michael.w.appenzeller(a)lmco.com> wrote in message
news:d7e2b8d5-52eb-49ff-acba-60225081f059(a)5g2000yqz.googlegroups.com...
> On Jul 23, 12:59 pm, "Arfa Daily" <arfa.da...(a)ntlworld.com> wrote:
>> > Another Zenith had one in the HV regulator circuit that went open and
>> > lost regulation. The HV was running around 30 kV on a 19" set. A
>> > regular resistor did't work on that set and I had to get the correct
>> > part.
>>
>> > It looks likewww.moyerelectronics.comhas a 63-5440 sub. in stock.
>>
>> > Mike WB2MEP
>>
>> Good grief ! Did you not have x-ray protection circuits on the sets your
>> side of the pond ?
>>
>> Arfa
>
> Not on tube sets, and early solid-state ones. X-ray protection came
> into widespread use when they started running the horiz. sweep from a
> regulated B+ supply and did away with regulation of the HV itself.
>
> Mike

That surprises me. It's of course been a very long time ago, but I'm sure
that the early tube sets that I worked on, which employed a type PD500 shunt
stabilizer for the HV. had at least some crude form of x-ray protection, in
the form of sensing the beam current and using the result to back-bias the
H-out tube into cutoff. At 30kV on a 19" CRT, the average beam current must
have been well over the top, and fairly easily sensed as a fault condition ?
Perhaps they were just a bit more 'picky' about such things this side of the
pond ? :-)

Arfa

From: David Nebenzahl on 24 Jul 2010 14:44
On 7/24/2010 5:50 AM Arfa Daily spake thus:

> "Mike WB2MEP" <michael.w.appenzeller(a)lmco.com> wrote in message
> news:d7e2b8d5-52eb-49ff-acba-60225081f059(a)5g2000yqz.googlegroups.com...
>
>> On Jul 23, 12:59 pm, "Arfa Daily" <arfa.da...(a)ntlworld.com> wrote:
>>
>>>> Another Zenith had one in the HV regulator circuit that went open and
>>>> lost regulation. The HV was running around 30 kV on a 19" set. A
>>>> regular resistor did't work on that set and I had to get the correct
>>>> part.
>>>
>>> Good grief ! Did you not have x-ray protection circuits on the sets your
>>> side of the pond ?
>>
>> Not on tube sets, and early solid-state ones. X-ray protection came
>> into widespread use when they started running the horiz. sweep from a
>> regulated B+ supply and did away with regulation of the HV itself.
>
> That surprises me. It's of course been a very long time ago, but I'm sure
> that the early tube sets that I worked on, which employed a type PD500 shunt
> stabilizer for the HV. had at least some crude form of x-ray protection, in
> the form of sensing the beam current and using the result to back-bias the
> H-out tube into cutoff. At 30kV on a 19" CRT, the average beam current must
> have been well over the top, and fairly easily sensed as a fault condition ?
> Perhaps they were just a bit more 'picky' about such things this side of the
> pond ? :-)

So at what HV voltage do (did) TV sets start emitting X-rays?


--
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.

- Comment from an article on Antiwar.com (http://antiwar.com)
From: Chuck on 26 Jul 2010 10:01
On Sat, 24 Jul 2010 13:50:38 +0100, "Arfa Daily"
<arfa.daily(a)ntlworld.com> wrote:

>
>
>"Mike WB2MEP" <michael.w.appenzeller(a)lmco.com> wrote in message
>news:d7e2b8d5-52eb-49ff-acba-60225081f059(a)5g2000yqz.googlegroups.com...
>> On Jul 23, 12:59 pm, "Arfa Daily" <arfa.da...(a)ntlworld.com> wrote:
>>> > Another Zenith had one in the HV regulator circuit that went open and
>>> > lost regulation. The HV was running around 30 kV on a 19" set. A
>>> > regular resistor did't work on that set and I had to get the correct
>>> > part.
>>>
>>> > It looks likewww.moyerelectronics.comhas a 63-5440 sub. in stock.
>>>
>>> > Mike WB2MEP
>>>
>>> Good grief ! Did you not have x-ray protection circuits on the sets your
>>> side of the pond ?
>>>
>>> Arfa
>>
>> Not on tube sets, and early solid-state ones. X-ray protection came
>> into widespread use when they started running the horiz. sweep from a
>> regulated B+ supply and did away with regulation of the HV itself.
>>
>> Mike
>
>That surprises me. It's of course been a very long time ago, but I'm sure
>that the early tube sets that I worked on, which employed a type PD500 shunt
>stabilizer for the HV. had at least some crude form of x-ray protection, in
>the form of sensing the beam current and using the result to back-bias the
>H-out tube into cutoff. At 30kV on a 19" CRT, the average beam current must
>have been well over the top, and fairly easily sensed as a fault condition ?
>Perhaps they were just a bit more 'picky' about such things this side of the
>pond ? :-)
>
>Arfa

Early Zenith solid state sets had a horizontal tuning cap that would
open, then the high voltage would skyrocket until the neck would fall
off of the crt. RCA sets with SCR sweep had a failure mode where the
high voltage would go over 60 KV. The vertical deflection was
designed to collapse, when the hv rose, which was supposed to signal
the customer that they should shut off the set. However, many people
would leave the set on and just listen to the sound. I always
wondered why RCA didn't just kill the horizontal drive. Chuck
From: Jim Adney on 26 Jul 2010 11:19
On Jul 21, 11:22 pm, Jim Adney <jad...(a)vwtype3.org> wrote:

> Finally, I checked the DC bias on the HOT. The Zenith manual says it
> should be -80 V, so I was expecting it to be lower. It's actually -65
> V. So there must be something else wrong in that circuit.

In comparing my Sams & Zenith manuals, I find that Zenith says the HOT
control grid bias should be -80 V but Sams says -48 V. I now have -65
V. I'm going to guess that Sams is right and I need something closer
to -50 V, which should turn things up a bit more and get me to the 26
kV that I should have for the HV. I also checked the tube data sheets
for the 20LF6 and 26LF6 and found that typical control grid bias
values are -10 and -20 V. So I can afford to boost that voltage quite
a bit higher (more positive) than the -65 V where it's at now.

The set is put back together now, but I'll pull it apart again once
our houseguests (arriving tomorrow) are gone. In the meantime, it
looks like I should try to buy one of those odd 63-5440s. AFAIK that's
the one remaining part in there that might be the problem, but I'll
check around the circuit, too, to make sure I haven't missed
something.

As an aside: Was it common for the Sams to be more accurate than the
Zenith manual? Or, to put it differently: Did the Zenith manuals have
a poor reputation?

thanks,
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