Can you identify these early 1950's (?) TV bits ?

[GrimJosef]

I came by part of a TV chassis today, and the tube which I believe goes with it. I know nothing of the history I'm afraid, other than that it seems to have come from the workshop of an enthusiast or repairer. I was wondering what it once was, and whether any of it might be of value to anyone ? Here's the chassis.

Cheers,

GJ

[FERNSEH]

Bush TV22 or TV24.

DFWB.

[GrimJosef]

And here's the tube. There are one or two dirt specks on the front, although I think those should be removable. I can't see any marks on the phosphor. The paper label is all but gone, but it looks like it once said Mullard. The words Made In Holland are printed on the glass alongside the connector cap on the side.

Cheers,

GJ

[Tractorfan]

You beat me to it by a couple of seconds!
Cheers, Pete.

[GrimJosef]

Wow, that was quick David ! Some of the capacitors are labelled Oct 50 if that helps any.

Cheers,

GJ

[FERNSEH]

I reckon that CRT will be OK.

DFWB.

[beery]

Hi GJ,
I can't tell the size of the tube from the photos, but if it is a 9" screen then the tube is an MW22-16 and the chassis a TV22 (top deck only).
If the screen is 12" diameter then it will be an MW31-16 or MW31-74 and the chassis will be the top deck from a TV24 or a TUG24.

Your spare chassis has the line output transformer present as well as the tiny frame blocking oscillator transformer (on the side), so I'm sure it will be useful to someone.
9" and 12" tubes are in demand also.

Cheers
Andy

[GrimJosef]

The chassis's serial plate says 82/11026 and there's what looks like a stamped washer screwed to the top surface which says A7 11057.

A significant amount of the black coating on the LOPT has melted and dripped onto the chassis and a fair bit more has cracked away too.

The CRT is barely 12" in diameter at its widest point which, of course, is right round the curve at the edge. So I imagine that makes it a 9" tube ? I could check the filament continuity but I don't have an EHT supply. Is there any quick and easy way, with a few hundred volts, of learning anything useful about the emission ? If this were a power valve I might just power the heater and measure the voltage that the unaccelerated emission develops across a high resistance between grid and cathode. For a KT66 in a Quad II -0.5V to -1V Vgk indicates that the valve isn't stone dead. But I'm completely unfamiliar with the characteristics of CRTs.

Cheers,

GJ

[murphyv310]

Hi.
Power the heaters with 6.3v and connect a milliamp meter in series with the grid 1 to a 100k resistor then to 200v dc positive connect the negative to cathode. You should get 4 or 5 ma on a very good tube, 1 to 2 means its serviceable but could be dull or go negative with high brightness.
Pin connections below

[GrimJosef]

Sounds like exactly the info I need Trevor. I'll give it a go in the morning. It'd be a shame to risk carrying the tube over a wet patio in the dark now, and slip and drop it !

Cheers,

GJ

[slidertogrid]

The threaded studs on the front of the chassis is where the wooden support for the larger tube was mounted. The 9" TV 22 did not have them so my guess would be 12 " tube. TV24 .

[GrimJosef]

Originally Posted by slidertogrid

The threaded studs on the front of the chassis is where the wooden support for the larger tube was mounted. The 9" TV 22 did not have them so my guess would be 12 " tube. TV24 .

Is the dimension the display diagonal or is it the actual physical size of the tube ? The actual physical size of the tube is, near enough, 12" dia, in the sense that you could post the whole tube through a 12" dia hole. You couldn't display a 12" diagonal picture on it though. But a 9" diagonal picture might fit.

Cheers,

GJ

[Radio Wrangler]

It's got a 'bent gun' ion trap, so it'll need a magnet to get a beam to reach the screen. A test of emission to G1 won't be affected.

David

[AdrianH]

Originally Posted by murphyv310

Snipped You should get 4 or 5 ma on a very good tube, 1 to 2 means it's serviceable but could be dull or go negative with high brightness.
snip

I have to ask about this for a couple of reasons:-
1 ) My maths says it can never get more than 2 mA current as 200/100,000 = 0.002
2 ) I have been looking for a method to test my tube in a 991T and I found an article in Practical Television June 1964 with a CRT Tester and rejuvenator, which when watching out for a few errors in the articles suggested nearly 1 mA with 300 Volt HT and 330K resistor, it only used a boost current of 2 mA for when trying to rejuvenating the CRT.

So anyway to my real questions on this testing a CRT how do you calculate the correct values from data sheets or is there a feel for it? I appreciate you are basically turning the Cathode to grid into a diode be used to test if a tube. If it has a low voltage drop you will get close to V/R = current through it, and I guess you need to see at what point the cathode fails to emit enough electrons, so how do you work out the values before the grid heats up and shorts?

Sorry to jump in and ask what may be a daft question, on someone else's thread?.

Adrian

[murphyv310]

Hi.
Sorry I just noticed there is a typo. The last one I did I used 100v and 10k not 200v and 100k. This gives 10ma but with the CRT in circuit its 4 to 5 ma with a good CRT but much less with a low emission one. Glad you noticed the error and thank you.

[AdrianH]

Hi Trevor, I am just trying to figure the rational behind it all. Just found another CRT tester in PT December 1968 that goes over 30mA, so I am really trying to understand it all. I guess that the control grid is not really a grid as in valves, but a metal cup with a hole in it, so the issue would be stripping the cathode if going to far?

Adrian

[murphyv310]

Hi Adrian.
You are correct the grid in a tube is not the spiral wire we are familiar with in a valve. If you look at a CRT gun there are cup shaped electrodes with a hole for the beam, these are the grid and A1, focus etc.

The cathode current in a tube is normally very low and some believe it causes cathode poisoning. Sometimes passing a larger current between grid and cathode seems to waken it up and clean it for better emission, this is not always the case though. Tube testers measure the current between grid and cathode with a given set of parameters, some also bring in the A1 into the test for accuracy.

The method above is not foolproof though. A recent test this way and with a tester gave excellent results but in the set it was poor, only raising the heaters above 6.3v to 8v gave a good result. Very odd indeed.

[Nickthedentist]

Originally Posted by GrimJosef

Is the dimension the display diagonal or is it the actual physical size of the tube ? The actual physical size of the tube is, near enough, 12" dia, in the sense that you could post the whole tube through a 12" dia hole. You couldn't display a 12" diagonal picture on it though. But a 9" diagonal picture might fit.

Traditionally, quoted CRT sizes were the overall diameter of the glass envelope, measured in inches. So yours seems to be a 12" tube.

(But when metric units are used, the number tends to represent the length of the diagonal of the viewable area, AFAIK).

Nick.

[GrimJosef]

Thanks Nick, as far as I can tell the dimensions of the tube correspond to those on the MW31-16 datasheet here http://electronbin.com/sheets/030/m/MW31-16.pdf, which would make it a 12" one as you say.

It seems to pass Trevor's test. The heater current was 298mA (i.e. nominal). With a 10k series resistor and about 105V DC supply (the yellow meter reads a little low, and the 100V Zener was running rather warm) I got 4.43mA. This value took a couple of minutes to come up - it started at around 1mA - but maybe the cathode needed a bit of reviving ? At a second attempt it reached 4mA much more quickly. It was still climbing, albeit very slowly, when I took the picture. But given Adrian's comment about stripping the cathode and also the bad consequences if the Zener were to overheat and go o/c I took a quick snap and turned everything off.

Cheers,

GJ

[murphyv310]

Hi.
I agree with Nick. It's most likely a 12 inch from a TV24 or consol variant.
The CRT neck clamp is on the outer part of the focus assembly and certainly on any TV22 its nearer the scan coil side.