Viewmaster 12" Console set

[Sean Williams]

Well, just before Christmas Scott posted asking for info on this set, and shortly after, decided to sell it.

A nice early morning trip to Weston Super Mare yesterday, and I have the beast back here with me.

Seeing as SWMBO has gone out for the evening, I thought I would pop it on the bench and see what I had purchased.

Firstly, this is very much a set of two halves - the CRT and Timebase deck is built as per the drawings, and has been done to a fairly high standard.

The "RF" deck, however, is somewhat of a strange beast - and is much later than the rest of the set.

Fortunately, I did also purchase all the extra bits as the original post, so I can put the set back to being a proper Viewmaster

Please see the pictures I have added, which will give you some idea of the current state of play.

Good news, it has a Mullard tube, but it looks to have had quite a lot of use - I am hopeful it will be able to produce some form of picture however.

I have popped some power on the set, and for a very brief period there is line whistle, but once everything fully warms up, this goes, so I think the timebases will need some work as a first step.

Dates stamped on the smoothing block suggest construction around June 1950 ish, the date on the Clydon Tuner is late 1957.

So, the first and most important question - Am I right to put the set back to being a proper Viewmaster, or should I continue with this uncharted RF deck?

[Heatercathodeshort]

That looks like a modified EMI RF strip from the 1805 series. It's probably been aligned as an IF strip to accept the Cyldon tuner.
I would be tempted to get it working as it is then if you want to return it to Viewmaster spec it will be a lot easier. John.

[Sean Williams]

Thanks John

I sort of expected that answer, sat here looking at it, I almost heard you saying it

Will change a couple of caps around the 6P28 and see if I can get something on the screen.

[Heatercathodeshort]

A few moments ago I took these two rather poor pictures of the HMV 1805 RF deck but they will show the similarity.
[It's heavy and cold out there...]

It is probably the best RF unit ever constructed. Very high gain producing grain on the raster and a hiss on the sound with the aerial removed.The picture it produces in it's original form is truly astonishing. The Video output valve is a Z66 but you may have the original EF50 on the main deck.

You will have some fun with that. As I mentioned before, get it working as it is. It must have worked well back then after modification for the ITA. Your lucky to have the choice having all the original bits. Good luck with it. John.
PS The 1805 dates from 1948

[Sean Williams]

Huzzah, First Light is mine

Three capacitors on the line output valve - Grid drive, Cathode decoupler and Screen Grid decoupler all changed - result, a rather LOUD line whistle, and first light.

Picture taken in my workshop, with all the lights on and the bench anglepoise on too - safe to say the tube is fairly bright!

Surprisingly the Visconol cap for EHT smoothing seems not to be dragging the supply down, and the huge Rectifier stick seems to be happy as well. I can only think this will be a short term thing, so replacements for these two components will be a must do I think.

Frankly amazed just how easy getting the screen to light was - Perhaps I will now stick a decent mains lead on the set, instead of the perished rotting twisted rubber flex

[Sean Williams]

Originally Posted by Heatercathodeshort

That looks like a modified EMI RF strip from the 1805 series. It's probably been aligned as an IF strip to accept the Cyldon tuner.

Thanks for the pictures John, I can see the similarities in the components, but the chassis is much larger than the example you have shown - does give me a lead though.

As you say, it must have worked at some point in the past, for the sake of a few components, I will see if I can persuade it to go again.

[matspar]

Hi Sean I noticed the Viewmaster on ebay a little while ago and fully intended to bid, although the distraction of xmas caused me to forget when the auction ended!! either way I'm glad to see its in safe hands! Looks wonderful and I'm sure you'll have a picture very soon. Will be following with great interest

Matt

[Sean Williams]

After a little prodding around with a sig gen, it seems that the IF for sound is around 10Mhz, and the vision somewhere near 11.5 Mhz.

Ive managed to get sound through right from the antenna socket, but the Video stages are somewhere out to lunch.

Fair bit of work to do to get a test card up it seems.

Forgot how much fun old TVs are to play with.

Matt, I was surprised to be honest that I didn't have a fight to win this set - I bid very early, and thought I would have been beaten, fortunately not. The cabinet is quite good, will need refinishing, but importantly no worm, and the only serious damage is right at the base, so a bit of filling and some dark paint will hide that well.

Im battering through the set quite quickly, to make sure all the important bits are working well, before I do a really good job of going through everything.

[mark pirate]

Glad that it has gone to a forum member, I also quite fancied the set, but not the long drive to collect it!

Great to see you have a good LOPT & CRT, no doubt that replacing the usual caps should have it up & running in no time.

I agree that it makes more sense to keep it as it is rather than revert to the original RF deck, you could always have a go with it once the set is working well in it's current configuration.

Getting the original parts was well worthwhile, if for nothing more than keeping with the set as part of it's history.

Good luck with the set, I am looking forward to seeing it bought back to life after decades of storage, I would bet it was in working order before being retired.

Mark

[Heatercathodeshort]

Good news. It looks to be a Mullard MW31-18 straight gun CRT, hence the ion burn but it is only a small one and will probably vanish when you get the EHT up a bit. It's a long life tube.

The 1805 RF strip is quite large but appears small in the pics. I'll see if those chassis numbers come up with anything. J.

[Sean Williams]

A bit more progress.

Obviously there are focus problems - the HT is down on the set by about 80V and the A1 volts are low at 240V - I guess this will not help with the focus.

The picture goes heavily negative with either the contrast, or brightness advanced, but again, I hope this is just EHT related.

The RF chassis is almost completely recapped - lots of nasty Hunts and other ageing components all conspiring to stop the receiver from working.

Still some faults there to resolve - the RF deck acts more like a TRF when the fine tuning on the tuner is adjusted, and takes off into hoots of audio oscillation

But some progress for a couple of afternoon's work

Addendum..... Disconnected the Visconol EHT smoother.... Result - More focus!

[Sean Williams]

Just tried running the set from the bench HT supply - with the HT set to around 300V, the boost voltage increases to around 330v, and the EHT is now quite powerful (no means of measuring sadly, but around a 5/16" spark.

I think the Metal Rectifier is toast - Time for some sneaky silicon I think

Lots of fiddling to do on the RF chassis now - very poor definition.

[peter_scott]

Excellent progress! Looking forward to more.

Peter

[Sean Williams]

Had enough for today.

Clagged in a 1N5408 (on Death Leads) for now - this brings the HT up to as designed specs of 300V on load - the A1 Volts sit happily at 320V, sad to say the focus really isn't that good.

I found a nice 200pf "Doorknob" cap good for 20KV which is subbed in place of the visconol, somewhat lower than the 1000pf it wants, but a good stand in for now. I think the next line of reasoning will be to replace the selenium EHT rectifier with something else - Jury is out as to either an EY51, or a sand based alternative - in any case, this will require parts to be purchased.

I think the Phantom twiddler has been at work on the RF deck - aligning this will be a challenge!

There's some great sound on vision, ans also a nice background frame oscillator coming from the speaker - I cant live with that, so will have to resolve that problem somehow.

Otherwise it seems to be responding well to a bucket load of capacitors, and a few resistors.

[llama]

I remember Dad eagerly waiting for the "auto-transformer" to arrive - I think I've still got the original and the autotransformer. I imagine the standard version just used rectified mains for the HT but more was produced with the autotransformer. Either that or it was for low-mains areas.
Anyone else?
Graham

[Argus25]

Originally Posted by Sean Williams

The picture goes heavily negative with either the contrast, or brightness advanced, but again, I hope this is just EHT related.

One thing to watch out for when powering a set and working through the faults (rather than say re-capping the whole set initially) is that there could be a fault condition which allows the CRT's grid to go more positive than its cathode (not good for the CRT) for some positions of the contrast and brightness controls.

One precaution is to tack a silicon diode like a UF4007 across the CRT's grid-cathode connection (anode of diode to grid) and check the voltage range across the diode with control manipulation, the diode should always be reverse biased.

It is just a way of protecting the CRT's gun, to one extent, while the faults get resolved. Also faults can take the CRT cathode voltage too high with respect to the heater (depending on the set design) which poses another risk.

This is one reason why I never power a vintage TV chassis (with the CRT in it) initially at least until it is entirely re-capped first, these days at least. I admit though, that in earlier times, I would get very excited and turn on the set to see what happened, but I concluded later after some bad experiences, it was better not to.

[FERNSEH]

If the CRT has the aquadag coating then the Visconol can be dispensed with, that's I have done with my ViewMaster.

No need to worry about cathode to heater shorts in the CRT because the tube heater is supplied from an isolated winding on the mains transformer.
Under no signal conditions the cathode volts = heater volts.
Extract from the topic "Viewmaster Big Picture 1950s TV. Post No 18:
"The circuit design permitted the fitment of CRTs from various manufactures, Mazda, Ferranti and GEC triode gun tubes and also Mullard tetrode gun CRTs.
The mains transformer has a separate winding for the CRT heater which can supply 2, 4 and 6.3volts. The reason for the isolated heater winding was to permit a direct connection between the anode of the EF50 video amplifier and the cathode of the CRT. The video DC component is maintained from the vision detector to the CRT. One of the reasons why the ViewMaster TV displayed an excellent picture, another being the careful design of the vision RF circuits."

The modification to the RF circuits has been done in a very competent manner, although the choice of those low IFs seems to be a bit strange. EMI service retuned the channel 1 TRF units to 38Mc/s sound and 34Mc/s.
However, because the redesign of the front end of the set has been done by someone who knew about HF circuits I wouldn't attempt to return the set to it's original state.

DFWB.

[Sean Williams]

Hi David,

Thanks for the thoughts regarding the conversion.

For me the hardest part of this will be the lack of drawings for the IF and Video stage - I could draw the circuit out I guess, but have no way really of knowing if there are obvious howlers.

I could use the aquadag - Guess I just need to make up some sort of spring connection to earth the coating.

I had a dig through the spares I got with the set - there are two LOPT in the box, and one had an EY51 fitted - I have since subbed this into the set, but this has offered no improvement in the focus, so I guess the stick rectifier is working as well as it can.

So, I now need to figure out why I cannot get a decent focused image - any pointers here would be appreciated.

So far only the 1MC bars are clearly defined, but I think the video stages are working a lot better then the CRT is displaying.

[Heatercathodeshort]

The EHT voltage looks about right. If low the picture would be oversize. If high it would be difficult to obtain enough height and width providing of course that the HT is up to spec.

The tube looks original. If the original had been a Mazda triode I would say the focusing field is too high for the Mullard tetrode. Just a thought.

Have you tried moving the magnet assembly along the neck of the tube? Just for a quick experiment, try placing a couple of shunts across the magnet assembly, reducing it's strength. Mild steel is fine say 1/2" wide and just the width of the magnet front to back. I had to do this when fitting a tetrode tube in place of a triode in an Ekco T164.

I did post the restoration so maybe still in the archive. Great progress! John.

PS Just found it.
https://www.vintage-radio.net/forum/...d.php?t=136746

I used a number of shunts on this one but a couple will prove the point.

[FERNSEH]

Hi Sean,
The maximum EHT voltage in the ViewMaster TV is no more than 7KV which was OK for all the CRTs available at the time the kit set marketed in the early fifties.
The boost diode MR2 is a selenium device, perhaps it has gone high forward resistance? It could be substituted with a UF5408 diode for test purposes.
The boost diode is connected in series with the HT supply to the 6P28 line output valve. Reclaimed energy from the scanning coils is rectified by the diode and smoothed by C42 and the resultant 50 volts added to the HT supply as the first anode voltage for tetrode CRTs. Also extra HT for the 6P28 line OP valve. According to the voltage tables in the construction notes the smoothed high tension should be 285V and the boost HT 330volts.
The HT supply rectifier is connected direct to the mains supply. The 250 tap on the mains transformer could be used when the set was used on lower mains supply voltages.
The construction notes inform us that two types of focus magnet assemblies were supplied, one for the triode CRTs and the other for Mullard tetrode tubes.

DFWB.