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Old 21st Jul 2017, 2:16 pm   #1
Argus25
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Default Marconi Mark IV PWM video & waveform monitor

Does anybody have the circuit data on this monitor ? I am trying to find out the type number of the picture tube (not the waveform monitor tube) used in it and if there was more than one type number of CRT used.
Thank you for any help.
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Old 21st Jul 2017, 3:54 pm   #2
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Default Re: Marconi Mark IV PWM video & waveform monitor

Not certain what model mine is but please post a picture.
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Old 21st Jul 2017, 6:28 pm   #3
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Default Re: Marconi Mark IV PWM video & waveform monitor

Yes mine is MK 1V to and model I think BD283. Yes I think some where in the archives I have the manual.Could not see the crt type on mine as yet.

It has always worked very well despite years sometimes between firing it up.Looks great on test card C .
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Old 21st Jul 2017, 6:46 pm   #4
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Default Re: Marconi Mark IV PWM video & waveform monitor

Marconi's give the number for the picture CRT as " PMT58/1" which is their internal number scheme for the BD873 PWM. Only a little help.

The tube looks to be a standard 14" type widely used in broadcast kit of period (1958-62).


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Old 21st Jul 2017, 11:41 pm   #5
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Default Re: Marconi Mark IV PWM video & waveform monitor

Quote:
The tube looks to be a standard 14" type widely used in broadcast kit of period (1958-62).
Brian,

I have seen the photos of the monitors on your site. I once owned one of these Marconi MkIV monitors, but unfortunately I had to sell it back in the early '70's to help buy my first car and lament its loss. I remember the CRT in it very well, with the very rectangular face, like you say typical of broadcast kit at the time. I also found an American crt at a broadcast house that was the same physical size and worked as a substitute, but alas I didn't record the numbers of either type at the time.

I now have another type of monitor that coincidentally requires exactly the same type of CRT, so I'm trying to find out the number to locate one. I looked at the MW36-24 and 36-44 and 36-67, but all these appear to have magnetic focus, and I'm pretty sure that the Marconi MKIV has electrostatic focus which is the type I'm looking for.

Last edited by Argus25; 22nd Jul 2017 at 12:01 am.
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Old 22nd Jul 2017, 12:07 am   #6
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Default Re: Marconi Mark IV PWM video & waveform monitor

Quote:
Originally Posted by HamishBoxer View Post
Not certain what model mine is but please post a picture.
The model is shown in the attached photo.
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Old 22nd Jul 2017, 10:24 am   #7
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Default Re: Marconi Mark IV PWM video & waveform monitor

I had a look at my PWM, the tube is an electrostatic focus one, no magnets. Alas the tube type label is not visible without major disassembly.

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Old 22nd Jul 2017, 1:34 pm   #8
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Default Re: Marconi Mark IV PWM video & waveform monitor

Thank you for taking the time to have a look anyway.

Hugo.
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Old 23rd Jul 2017, 5:38 pm   #9
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Default Re: Marconi Mark IV PWM video & waveform monitor

Hello.

I have six of the Marconi MkIV units (that's one of mine in your posted picture) and they're all electrostatic focus as per the manual. Two are fully operational to a good standard, two to a rough but functional level and the other two are 'pending' but do work (sort of). As Hamish says, they are capable of extremely good pictures and the waveform part is quite versatile for something designed almost 60 years ago. BTW, Hamish, you're quite close to me! Never twigged your address before.

I do have all the manuals and also the official Marconi Company mod notes. There may be some clues in the latter volume about replacement types, I'll have a look.

For its time, a great unit (as was the MkIV camera chain) but I wish that it wasn't so heavy!

I have some 14" RCA monitors of the same period which have electrostatic RCA tubes and the same general shape/size but they have a bonded safety glass (the Marconi has a Perspex panel, of course). Is the monitor you're trying to repair an RCA by any chance? All of mine of that model have very bad cataracts and so far I've only 'processed' one (it takes so long to do).

Best regards,

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Old 23rd Jul 2017, 5:47 pm   #10
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Default Re: Marconi Mark IV PWM video & waveform monitor

There you go Paul, all but around the corner .PM me if you ever want to call in.
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Old 24th Jul 2017, 10:54 am   #11
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Default Re: Marconi Mark IV PWM video & waveform monitor

Quote:
Originally Posted by Argus25 View Post
I now have another type of monitor that coincidentally requires exactly the same type of CRT, so I'm trying to find out the number to locate one. I looked at the MW36-24 and 36-44 and 36-67, but all these appear to have magnetic focus, and I'm pretty sure that the Marconi MKIV has electrostatic focus which is the type I'm looking for.
It wasn't until later that the M was for monitor tubes. In those days the M stood for magnetic focus while electrostatically focused tubes were designated AW in the pro-electron scheme.
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Old 30th Jul 2017, 11:06 am   #12
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Default Re: Marconi Mark IV PWM video & waveform monitor

Paul M
The monitor I have is American made but it's not an RCA. And there is no data available on it. If you do ever find out the type number of the CRT's in your Marconi monitors I would be interested to know. The one I had was a good monitor and I was particularly impressed with the edge lit acrylic panels with the engraved white writing and the black background.
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Old 31st Jul 2017, 1:43 pm   #13
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Default Re: Marconi Mark IV PWM video & waveform monitor

I've had a look in the mod book for these PWMs and there's no clues about the CRT type. Marconi hide that completely in the in-house name/number. It could be that several manufacturers supplied suitable tubes.

I've also had a look through some of my units (and the similar picture only models) and the only clue I've found is a 'Brimar' sticker on one. That would make a lot of sense.

Have a look here and find the data for M36-141 (it's a long way down):

https://ia601707.us.archive.org/4/it...978Volume2.pdf

I reckon that the M36-141 looks like the tube in question. It would need a slightly more detailed comparison with the schematics and mechanics to be sure, but it looks superficially right.

I'll keep an eye open on this - it can take a while to find this kind of thing!

Best regards,

Paul M
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Old 1st Aug 2017, 9:20 am   #14
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Default Re: Marconi Mark IV PWM video & waveform monitor

Hi Argus25,

The issue seems to be with the narrow neck diameter. Most 14" tubes of the time had 38mm necks. How about the AW36-48? It has P4 phosphor. You can get one of these from a scrap Polyskop II.
http://www.datasheetspdf.com/PDF/AW36-48/1055792/2

Cheers
Andy
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Old 2nd Aug 2017, 12:35 am   #15
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Default Re: Marconi Mark IV PWM video & waveform monitor

Hi again Argus25,
Ignore what I said about neck diameters being 38mm as these 14" tubes all seem to be about 36.5mm anyway.
The AW36-48 is quite long in the neck. The Mullard AW36-20 or AW36-21 might be a better fit. I might have something, but I'm really not sure about shipping such a tube overseas.

Cheers
Andy
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Old 2nd Aug 2017, 3:42 am   #16
Argus25
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Default Re: Marconi Mark IV PWM video & waveform monitor

Hi Andy, Thanks for that info, I think the AW36-20 is most likely the tube. I'll have a go at getting it or something similar locally or from the USA, and if I'm stuck it probably would work to send one here via the postal service, I have had quite a few CRT's shipped this way without too much trouble, but I think it looks like I have a solution.

What is a "polyskop II" ?
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Old 2nd Aug 2017, 8:20 am   #17
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Default Re: Marconi Mark IV PWM video & waveform monitor

A Polyskop II is an early 60s Rohde and Schwarz scalar network analyser without log amplifiers. See: http://www.radiomuseum.org/r/rohde_p...p_ii_swob.html

I bought mine in the late 1970s from Marconi reclaim stores and with no maintenance whatsoever it still sort of works. I can't say that the tube has ever particularly impressed me but then it's only in xy mode and not raster. Tubes removed from a Polyskop may well have raster burns as the display is xy with a baseline. Long necks with electrostatic focus tubes usually equate with better focus and that would be a superior choice for a quality monitor.

The Mullard tube is almost certainly interchangeable with the Brimar M36-141 but Marconi probably went for the Brimar as original fit simply because it wasn't a Philips/Mullard! Probably explains why they were cagey about it and hid behind an in-house number.

Best regards,

Paul M

Last edited by PaulM; 2nd Aug 2017 at 8:25 am.
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