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Old 4th Jan 2020, 11:59 pm   #1
MrJohn_IOM
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Default Voltage reg tube

working on another old scope, a Philips pm3262.

voltages all seem ok, but there is arcing towards the base of this old voltage regulation tube. V103r2 - it makes up part of the focus unit - it glows briefly, arcs and glows again, eventually just peters out

I have a schematic (see attatched) that philips produced to replace this, with them not being produced anymore except maybe some NOS, somewhere on the planet. so im just going to do it.

i have zero experience with tubes, and was wondering the failure modes of these things, as even google is refusing to help me.

Pic of the tube on this site https://www.radiomuseum.org/tubes/tube_v103r2.html
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Old 5th Jan 2020, 12:18 am   #2
Argus25
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Default Re: Voltage reg tube

Quote:
Originally Posted by MrJohn_IOM View Post
working on another old scope, a Philips pm3262.

voltages all seem ok, but there is arcing towards the base of this old voltage regulation tube. V103r2 - it makes up part of the focus unit - it glows briefly, arcs and glows again, eventually just peters out
The fact it strikes in the first place may well mean that the voltage regulator tube is ok. Initially to ionize the gas in it, the voltage has to be high enough to strike it, but then it adopts a much lower resistance, so if the applied power source cannot support that, it could go off again after that, possibly even come on again later (like a relaxation oscillator). In any case, before suspecting the tube itself, double check the values of all of the resistors in the circuit surrounding it are in spec and check any capacitors for leakage.

If it turns out to be the tube, and you cannot get one, it may be possible to replace it with some zener diodes. The arcing is obviously not a good sign. But that mod sheet option looks like a good solution too.
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Old 5th Jan 2020, 7:24 am   #3
Diabolical Artificer
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Default Re: Voltage reg tube

Unfortunately a neon won't replace it as the voltage is 103v. As Argus check R's and voltages. from a bit of checking online this is a not an un-common fault on these scopes.

Andy.
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Last edited by Diabolical Artificer; 5th Jan 2020 at 7:29 am.
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Old 5th Jan 2020, 5:31 pm   #4
WME_bill
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Default Re: Voltage reg tube

Minature neon voltage regulator tubes.
These have quite disappeared. But take heart. These small stabiliser or indicator neons were used in many oscilloscopes in 1960s to 1970s as a protection device to limit the voltage between CRT grid and cathode. It sometimes also served to hold a steady voltage across the brilliance control to make the control easier to operate.
Used on many models of Philips and Solartron, Tektronix, Telequipment.
Sometimes a stabiliser version of these neons was used (Hivac/General Instrument, Signalite Z82 or 116 or wider tolerance V82 or 116, Mullard ZZ1000, US 8228, Philips/Valvo ZA1004, ZA1001) at 82v or 116V at 0.6ma. Other manufacturers used two or three neon indicator tubes in series (Hivac NT2 CV2213 or the similar US NE2, or CC3L CV2266.) All around 60v.
I have data upon all these types.

In your PM3262, you could replace them by a couple of indicator neons, or a high voltage zener diode. Really not critical in this application.

The original makers life expectancy of V116 is 20,000 hours. Signs of failure are blackening of the bulb, or random variation of the voltage across the tube. But some stabiliser tubes have a fully blackened bulb anyway.

Your neon flashing on and then off could indicate it is doing it's job properly of limiting the voltage while the tube warms up. But the erratic behaviour suggests it has failed. I suggest replace with a couple of indicator neons (usually about 50-60v) in series or a high voltage (80v to 100v)zener diode. As used in the Cossor CDU150/CT531 of 1969.
The zener will have a very poor variation with temperature factor, which is of no importance here.

The problem is when these neons are used for voltage stabilisation in the power supply, for as they begin to fail the voltage varies erratically. This is a big factor I believe in the poor reputation which HP scopes have for triggering. The early 1966 HP180A series used individual neon stabilisers (V116) on each power rail. As the neons aged, so each rail varies few tens of millivolts at random. This severely affects the tunnel diode triggering. The later HP180C /D avoids this by a different design and later scopes by most other makers used a single zener stabilised rail for the whole power suppply. Until the use was developed of a single oscillator stabilised by feedback from a zener diode reference to power all the power rails as in your PM3262.

Touches upon one of my grouses about Philips scopes of that era. Nice performance, lovely to use but each model had a different design of switching power supply. All which seemed to fail. Philips obviously had great difficuty settling upon a reliable design configuration until the 1980's PM3082, PM3380. Though Advance and Tek seemed to have difficulties also in coping with supply mains transients.

These small neons had ceased by 1982. I see you have found my posting of the Philips substitute circuit. I have used this several times as it fits easily on the PCB in place of the neon tube. On Solartron CD1740, HP180A and Philips scopes.

I fear Andy Diabolical Artificer and Argus25 are being unduly pessimistic for the use of this neon in this circuit.
wme_bill

Last edited by WME_bill; 5th Jan 2020 at 5:42 pm.
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Old 5th Jan 2020, 6:34 pm   #5
MrJohn_IOM
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Default Re: Voltage reg tube

Thanks a lot for that, like i said, I'm completely new to tubes (I'm 37), was never an A/V guy, so never had any contact with them. so when i saw it and google only pulled up one page that actually details that specific component, i was a little lost. until i saw the Mod sheet... and you folks.
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