Zener noise / oscillations

"Fred Abse" <excretatauris@invalid.invalid> wrote in message 
news:pan.2012.07.28.08.29.28.86129@invalid.invalid...
> On Fri, 27 Jul 2012 19:38:01 -0400, Michael A. Terrell wrote:
>
>>    You can also trim the drive to the Horizontal Output tube.
>
> How? It's effectively a switch. Flyback pulse amplitude, hence HV, is
> largely determined by the inductance and parallel capacitance of the
> deflection coils. During flyback, the system is resonant for a half-cycle
> at 1/(2*t(flyback)). The tube will be off.

Transistors make poor ideal switches, and tubes even less so.  Examples: 
weaker grid drive will increase "saturation" voltage and shorten the 
conduction angle, resulting in less energy, less width and less HV.  Screen 
supply has a similar effect, and series resistance to the screen controls 
saturation voltage and peak plate current.

> Capacitance from the HO tube plate to ground *will* affect the HV. Some
> unscrupulous "repairers" used to hang C off the plate to get the HV down,
> and increase width, rather than fix the underlying problem.
>
> A controlled reactance from plate to ground would control HV.

Typical pulse regulators used another sweep tube, or a different beam 
triode, to carry a little current out of the peak.  Basically the same 
thing, as the beam triodes used in this application were ordinary sweep 
tubes with a finer control grid and no screen grid.  The other electrodes 
(cathode, beam forming plates, anode) are identical to the respective 
sweeps, and the mica supports have unused holes for a screen grid.  Result: 
high gain (gm 30~60mmho, mu > 100) and very low perveance (maybe 100mA at 
zero bias, 1kV plate).

Tim

-- 
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms 

On Sat, 28 Jul 2012 12:54:05 -0500, Tim Williams wrote:

> Transistors make poor ideal switches, and tubes even less so.  Examples:
> weaker grid drive will increase "saturation" voltage and shorten the
> conduction angle, resulting in less energy, less width and less HV. 
> Screen supply has a similar effect, and series resistance to the screen
> controls saturation voltage and peak plate current.

Unfortunately, the idea is to maintain HV, hence deflection sensitivity,
hence size, with fluctuations in beam current. That scheme modulates scan
current, as well as HV. Perhaps usable for setting, but no good for
dynamic modulation, apart from, maybe East-West pincushion correction.

> 
> Typical pulse regulators used another sweep tube, or a different beam
> triode, to carry a little current out of the peak.  Basically the same
> thing, as the beam triodes used in this application were ordinary sweep
> tubes with a finer control grid and no screen grid.  The other
> electrodes (cathode, beam forming plates, anode) are identical to the
> respective sweeps, and the mica supports have unused holes for a screen
> grid. Result: high gain (gm 30~60mmho, mu > 100) and very low perveance
> (maybe 100mA at zero bias, 1kV plate).

That's a much more viable scheme.


-- 
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

Fred Abse wrote:
> 
> On Sat, 28 Jul 2012 12:54:05 -0500, Tim Williams wrote:
> 
> > Transistors make poor ideal switches, and tubes even less so.  Examples:
> > weaker grid drive will increase "saturation" voltage and shorten the
> > conduction angle, resulting in less energy, less width and less HV.
> > Screen supply has a similar effect, and series resistance to the screen
> > controls saturation voltage and peak plate current.
> 
> Unfortunately, the idea is to maintain HV, hence deflection sensitivity,
> hence size, with fluctuations in beam current. That scheme modulates scan
> current, as well as HV. Perhaps usable for setting, but no good for
> dynamic modulation, apart from, maybe East-West pincushion correction.


   The newer flybacks could supply enough current that the change in
beam current didn't affect the HV regulation.  If you did see a change
the HV rectifire was failing.  That was rare, with triplers.  They
either worked or didn't.  The usual failure mode was a cracked case, and
arcing.

   The H drive was more than just a pulse.  It had to be properly shaped
to maintain good H linearity.  That wasn't done in early TVs, Monochrome
or Color.

Jan Panteltje wrote:
> 
> On a sunny day (Sat, 28 Jul 2012 09:09:43 -0400) it happened "Michael A.
> Terrell" <mike.terrell@earthlink.net> wrote in
> <4qSdnUDuqewBeY7NnZ2dnUVZ_jKdnZ2d@earthlink.com>:
> 
> >
> >Jan Panteltje wrote:
> >>
> >> On a sunny day (Fri, 27 Jul 2012 15:06:23 -0400) it happened "Michael A.
> >> Terrell" <mike.terrell@earthlink.net> wrote in
> >> <P6KdnXvQBpove4_NnZ2dnUVZ_smdnZ2d@earthlink.com>:
> >>
> >> >> Yes, but then he has to put them in a closed metal cage agaisnt roentgen radiation.
> >> >
> >> >
> >> >  No, you don't.  There are some types with enough lead to stop the
> >> >radiation.  At least in the US.
> >>
> >> Type number?
> >> I KNOW US is heavy, but....
> >
> >
> >
> >   But what?
> 
> But lead tubes?


   yes, the jacket was about 1/4" thick green or grayish and made with
lead dust & a synthetic rubber.  You could sometimes peel it off of an
old tube, while the glass would break on others if you tried.

On Wednesday, July 25, 2012 8:06:05 PM UTC-7, Robert Baer wrote:

> >>    Range needed: 10uA-500uA.
>
>    I need a 2-terminal device so tat i can put hundreds of them in 
> 
> series for 25KV.

Instead of a 25 kV breakdown device, how about a 25kV resistor and
a series of current limit diodes...if you feed 27 kV in, at 100V per
diode, it only takes twenty-one CL diodes and a single resistor.

If the CL diodes are set at 500 uA, the resistor will dissipate
12.5 watts, and the CL diodes another watt or so.

josephkk wrote:
> On Thu, 26 Jul 2012 22:20:37 -0700, Robert Baer<robertbaer@localnet.com>
> wrote:
>
>> Tim Williams wrote:
>>> "Robert Baer"<robertbaer@localnet.com>  wrote in message
>>> news:IpqdnflGK8W9KY3NnZ2dnUVZ_uWdnZ2d@posted.localnet...
>>>> I need a 2-terminal device so tat i can put hundreds of them in series
>>>> for 25KV.
>>>> So far, only one person divined that and his comment was trounced, and
>>>> not politely.
>>>
>>> Like I said before (though possibly not in this thread), cascode some HV
>>> MOSFETs. Only way you'll get the stability and noise you demand, without
>>> stacking a bajillion 431's.
>>>
>>> Tim
>>>
>>    Stacking 431s does work, but that cannot be used for this app as the
>> standby or keep-alive current is too high.
>>    And the other reference voltage parts cost too much (say 2.5V times
>> 10,000 times price each).
>
> Perhaps you need to be more creative in how you use the 431.
>
> ?-)
   Well, ASS-u-ME-ing an additional supply, one could use a 431, a FET 
and a few resistors (variant on our original Codatron(TM) design) to 
produce a decent 500V reference, and then stack a bunch of FETs and 
resistors to multiply by 50..too expensive.

Jan Panteltje wrote:
> On a sunny day (Fri, 27 Jul 2012 15:06:23 -0400) it happened "Michael A.
> Terrell"<mike.terrell@earthlink.net>  wrote in
> <P6KdnXvQBpove4_NnZ2dnUVZ_smdnZ2d@earthlink.com>:
>
>>> Yes, but then he has to put them in a clsed metal cage agaisnt roentgen radiation.
>>
>>
>>   No, you don't.  There are some types with enough lead to stop the
>> radiation.  At least in the US.
>
> Type number?
> I KNOW US is heavy, but....
   The original Corotron(TM) 25KV regulator IS made with a metal shell.

Fred Bartoli wrote:
> Robert Baer a �crit :
>> Jan Panteltje wrote:
>>> On a sunny day (Wed, 25 Jul 2012 20:06:05 -0700) it happened Robert Baer
>>> <robertbaer@localnet.com> wrote in
>>> <IpqdnflGK8W9KY3NnZ2dnUVZ_uWdnZ2d@posted.localnet>:
>>>
>>>> Jan Panteltje wrote:
>>>>> On a sunny day (Tue, 24 Jul 2012 23:39:15 -0700) it happened Robert
>>>>> Baer
>>>>> <robertbaer@localnet.com> wrote in
>>>>> <WeudnYHn_bcLCZLNnZ2dnUVZ_jOdnZ2d@posted.localnet>:
>>>>>
>>>>>> Tim Williams wrote:
>>>>>>> "Robert Baer"<robertbaer@localnet.com> wrote in message
>>>>>>> news:y4CdnbWbSZcVtpPNnZ2dnUVZ_rGdnZ2d@posted.localnet...
>>>>>>>> Yes, a TL431 is cheap but the minimal standing current is way above
>>>>>>>> what is needed.
>>>>>>>
>>>>>>> 1mA? TLV431 is 100uA and 1.240V, much improved.
>>>>>>>
>>>>>>> Tim
>>>>>>>
>>>>>> Range needed: 10uA-500uA.
>>>>>
>>>>> It is interesting to note that the PIC 18F14K22 is specified with
>>>>> FVR only running at:
>>>>> 1.8V 28 uA
>>>>> 3V 65 uA
>>>>> 5V 101 uA
>>>>> For a reference output of 1.024V
>>>>>
>>>>> I would think that if you put it into sleep mode, that would make
>>>>> your specs...
>>>>> Datasheet page 337
>>>>> It is possible to send the Vref output to a pin in that mode AFAIK.
>>>> I need a 2-terminal device so tat i can put hundreds of them in
>>>> series for 25KV.
>>>> So far, only one person divined that and his comment was trounced,
>>>> and not politely.
>>>
>>> OK, so I did not see you mention 25kV @ say<100uA.
>>> That will not be easy with zeners.
>> * Tell me about it; seems almost all have a negative R region right
>> where i need to operate.
>>
>>>
>>> You also need to mention stabilisation factor in percent for example,
>>> for anybody to even think about it.
>> * What exactly do you mean by stabilization?
>> See below.
>>
>>>
>>> I could easily generate 25kV locally with a transistor circuit and
>>> even some feedback turns, without a bleeder on the whole HV.
>>> Any decent last century CRT solid state color TV does it that way.
>>> Zeners do not make that much sense here to me.
>> * This is a TV restoration project; ideally the looks are preserved.
>> ***
>> Have done some suggested testing of the 75V part and compared the
>> result to the same testing of the 68V part.
>> What i find interesting is that for negative resistance parts, the
>> (what i call) the "N" type where voltage goes down as current
>> increases (eg: Esaki or tunnel diode), it is very easy to get to
>> oscillate; for the (what i call) the "S" type where current goes down
>> as voltage increases (eg: Zeners with "switchback"), it is hard to
>> make it oscillate.
>> The 75V part looks good, now i will chain some together..
>>
>
> Maybe try a few avalanche rated mosefts? You'd have to test them...
>
   Put 9 in series; noise seen from 20uA to 100uA then gets quiet above 
that; noise increases with current.

whit3rd wrote:
> On Wednesday, July 25, 2012 8:06:05 PM UTC-7, Robert Baer wrote:
>
>>>>     Range needed: 10uA-500uA.
>>
>>     I need a 2-terminal device so tat i can put hundreds of them in
>>
>> series for 25KV.
>
> Instead of a 25 kV breakdown device, how about a 25kV resistor and
> a series of current limit diodes...if you feed 27 kV in, at 100V per
> diode, it only takes twenty-one CL diodes and a single resistor.
>
> If the CL diodes are set at 500 uA, the resistor will dissipate
> 12.5 watts, and the CL diodes another watt or so.
   The TV shunt regulator is to keep the voltage constant, and so must 
pas varying current..

On a sunny day (Sun, 29 Jul 2012 00:29:49 -0700) it happened Robert Baer
<robertbaer@localnet.com> wrote in
<XeGdnYL1n4Xye4nNnZ2dnUVZ_jSdnZ2d@posted.localnet>:

>Jan Panteltje wrote:
>> On a sunny day (Fri, 27 Jul 2012 15:06:23 -0400) it happened "Michael A.
>> Terrell"<mike.terrell@earthlink.net>  wrote in
>> <P6KdnXvQBpove4_NnZ2dnUVZ_smdnZ2d@earthlink.com>:
>>
>>>> Yes, but then he has to put them in a clsed metal cage agaisnt roentgen radiation.
>>>
>>>
>>>   No, you don't.  There are some types with enough lead to stop the
>>> radiation.  At least in the US.
>>
>> Type number?
>> I KNOW US is heavy, but....
>   The original Corotron(TM) 25KV regulator IS made with a metal shell.

I did some google searching.
seems hard to find the TV version,
is this it?
 http://www.ebay.com/itm/HV-173-Victoreen-Corotron-High-Voltage-Regulator-NOS-/200726098581?pt=Vintage_Electronics_R2&hash=item2ebc353295