Pye VT2 EHT problems

[matspar]

I'm getting a spark at the DC end, not fantastic but there is some activity there!
I have made a bit of progress however - got the day off today so have been playing musical Lopts again, this time with the Ferguson 991T coffin one.

Hung it in there loosely and I'm finally getting some screen illumination! I can get a very small dim defocused raster which can only be seen in the near darkness. All the controls seem to work and it does respond to width, height, brightness etc.

I also replaced the HT rectifier (a PY82) as the HT seemed to drop after a while, down to around 140v which wasn't helping matters. Its now up to 178v and stays there!

I've only guessed at the connections on the Ferguson Lopt. Its a bit confusing as there's 7 pins underneath. Looks like one winding on the circuit with a few tappings. I can now get the slightest suggestion of a spark on the PL and PY top caps, and the same quarter on an inch spark on the EY51 anode.

That damned EHT is still too low however!! can you think of anything I can try with this donor lopt?

Here's some pics of my work in progress - I've managed to get the scan centred a bit better to fill more of the screen but its barely visible. I've adjusted the ion trap for maximum brightness. The hanging blue wire on pic 2 is a deck connection for the lopt, but it doesn't make any difference if I ground it or not!

Matt

[PJL]

An amateur reading through this thread and I have a couple of question for the experts:
1) I assume the original post of a lit EY51 was a reflection or something?
2) Why is the HT OK with the original transformer even when the rectifier was tired? I would have thought damp or a shorted turn should result in higher HT current?

[matspar]

Hi,
The HT and EHT are two seperate supplies (High Tension, and Extra High Tension respectively)
The HT supplies the timebase/line output stage, along with many other areas of the set (should be 174v on my set) an this voltage was dropping after about 15 mins due to a tired HT rectifier valve, a PY82.

The EHT is the voltage generated by an overwind on top of a primary winding (which supplies the scan coils) and the high voltage which supplies the CRT to make the screen light up.
When these overwinds develop a shorted turn it tends to damp down the line stage ar mute it entirely. There's not normally enough current available to load up the HT stage to give a higher reading.

On the Pye I'm restoring, the EY51 would light up very slightly as it was probably still getting a couple of volts from the heater winding. The overwind did have one or more shorted turns but it didn't kill the line stage completely. I still had a good line whistle and could still drag a small spark off the EY51, but I would guess the output was down to around 50%

[matspar]

Good news!!

I have just decided to cut the overwind off the original lopt and try the Tripler Trick, and guess what? I have been rewarded with a nice bright raster (see pics!)

Took a while to set the scans up as someone had fiddled with the picture shift, the raster fills the mask very nicely now.

It was quite a moment when that tube lit up, as you could probably tell I was feeling quite defeated by this set.

Now all I've got to do is remove the crt, take the cabinet to bits, clean and polish everything, make up a small bracket to mount the tripler on (it will be concealed quite nicely under the metal lopt cover) and then sort out some signals!

This is going to be a cracking little set!

Thanks again to everyone who has advised me on my plight, John W in particular. Very much appreciated.

All the very best
Matt

[Freya]

Well done, I have been following this post with interest.
I look forward to seeing some signals fed in.

Stephen.

[IJK2008]

That's great Matt you must be delighted after the hassle you have had. I'm looking forward to seeing this continue on to completion!

Ian

[Boom]

Nice one indeed.

[murphyv310]

Hi.
Well done indeed. My last venture using a multiplier was in a Bush TV128 and a 3x multiplier resulted in over 25KV ! I then went to a doubler and had to feed it from the PY88 cathode to get 16KV on the CRT anode.
The VT2 is a really neat set and rare enough now to be a good restore. I can't wait to see the result that includes a full picture.

[jay_oldstuff]

Well done that man, I too have been following this thread with interest as i have a set with a lopt with an iffy overwind so may well have a play myself when time allows.

Jay

[Heatercathodeshort]

That raster looks really great Matt. Appears to be about correct in size too. I'm surprised as I would have thought the EHT would have been too high with a tripler. No problem if it is. A bit of 3rd harmonic tuning should put that right. Interesting to see a signal on it. The size of the picture will reveal how close the EHT actually is.
If you have any bubbles or folds in the glass of the MW31-74 CRT. don't panic! Quite normal with this particular tube. It was one of the first assembled by moulded sections rather than blown and the minor defects have no effect on the strength of the glass.
Regards, John.

[matspar]

Thankyou everyone for your kind words, I am chuffed to bits with the result so far.
I've never tried using a tripler before (been overly lucky in the past with lopts!) but from what I've discovered I'd definately recommend having a go with one.

I would just suggest a bit of care when cutting off the overwind, so as not to knacker the primary or the PL top cap connection. I used a scalpel to scrape the pitch off the edge, and then just cut away the turns a bit at a time, keeping pressure to a minimum.
I don't have an EHT probe so can't be certain how many volts the tube is getting now. Would be interesting to find out. I think its fairly near to what it should be (7.5Kv) as the set is behaving exactly like I'd expect it to with the original setup.

I had it running for about an hour yesterday and it was whistling away quite happily and gave me no cause for concern. Width, brightness, and focus are all spot on. The height wants to creep down a bit after a while but I'm sure this will be easy enough to put right. An iffy ECL80 or maybe R59/60 changing value!

I've got an idea that the reciever end will want work as I'm not getting any 'noise' when operating the tuner. No real output from the speaker either, just a gentle hum. Either way plenty to keep me busy!

Like I say my next task will be stripping and rebuilding the cabinet, its particuarly filthy but should clean and polish up beautifully. Once I've done this it'll be allowed indoors and I can then and try and persuade it to give me a picture!

I shall take plenty of photos and keep everyone updated, may well have to pick your brains again if I experience any weird faults and get stuck

Cheers!
Matt

[matspar]

Had a spare hour today so did some cabinet dismantling and removed the tube. Started fairly easily by undoing a pair of rusty nuts, one each side of the crt which clamps it to 4 opposed aluminium brackets which in turn secures it to the cabinet sides.

Once undone, the bomb disposal impressions began and the tube was lifted clear complete with its rubber mask and implosion screen.
I then had to seperate the two with was a bit of a delicate operation as I didn't want to risk damage to either.
The rubber didn't want to let go at first but I managed to ease it off the face of the tube with a bit of pressure. I was terrified the mask might break up as it looked like it had deformed a bit at the front immediately below the red 'Pye' badge (had this problem once on a TV22)

It had actually just dropped out of a locator on the cabinet front and when I finally got the bit of plate glass off the front it turned out to be in quite good condition and still fairly flexible. I've had to take this apart as all the individual pieces are filthy.

Took out the speaker and tuner mounting panel next, lots of rust on the screws to deal with. Two speaker screws sheared in the process but managed to remove what was left with mole grips.

As the cabinet is four seperate pieces I'll dismantle the whole thing so it can be cleaned and polished to perfection. I've slackened off most of the screws which hold it all together but some won't budge. I'm not going to risk brute force as if I crack that bakelite it will ruin my life!! The stuck ones have had a good old dose of WD40 and I'll try them again in a couple of days, normally works a treat.

Next all the bits will need a good scrub. No work on weds so will be making a day of it!

[Andy - G8MNM]

Hi Matt,

In addition to the WD40 you could hold a soldering iron on the rusty screws (until the WD40 starts to smoke a bit) and then try undoing the screw.
This method is used on vehicles where bolts get very rusty and stuck.
Good luck

Andy

[matspar]

Thanks Andy, got them all undone except one which sheared off. I drilled it out and retapped the brass insert without any drama! I'm no stranger to struggling underneath classic cars fighting with rusty bolts, currently got a 1976 Vauxhall Firenza which tries my patience from time to time. A subject for another forum no doubt!

Well today I've refurbed the VT2's cabinet all all its associated bits and bobs, got it all apart in the end, and spent 2 hours with the detergent, T-cut, and beeswax and now have a marvellous looking cabinet which you can see your face in. One hell of a transformation!

The shadow mask had discoloured and didn't really respond to any cleaning. I didn't like the appearance of it (way too dark) and its not helped by the implosion screen which it turns out has a darkened tint to it.
The area underneath the red Pye badge hadn't discoloured, so I sprayed the mask in the same slight off white colour which now looks 'correct'

Came out well so I'll give it a couple of days to cook in the airing cupboard, then I'll refit the glass and tube and see how it all looks! Coming together nicely

[Heatercathodeshort]

These Pye receivers were part of the Pye 'Black Screen' range and usually had quite dark masks and grey anti reflection implosion screens. The VT2 was the first to have the lighter mask. Really nice job. Should look good with a picture. Regards, John

[matspar]

Cheers John,

I've got quite a nice VT4 which also has the darkened implosion screen, no mask as such on this set. It has a weird sync fault at the moment however, and has beaten me for the time being. I may well pull it apart later this year and have another go.
Interesting to hear about the tube also - I did have a look for the bubbles and folds in the glass but couldn't see any. I've been watching one of the BVWS dvds lately 'Made for life' showing Mullard tubes in production. I imagine you have a copy!

Anyway, today saw the tube and mask being reassembled and being installed in the newly refurbed cabinet!
It was a swine getting the tube into the mask without any stray hairs/dust/fingerprints/graphite particles getting between it and the implosion screen. Had to have a few attempts!

The tint on the glass has given the mask the correct grey appearance, very pleased with how it looks!

The height problem is now sorted. There was a nasty wax cap in the frame stage that I'd missed (C38 0.01) none of the resistors were far off in the end.
The height is now spot on and doesn't wander. Had a go with some signals as well and as I suspected the front end is totally dead. There is a slight bit of disturbance if I probe around the V1 area. Think I'll have a close look at the turret tuner on my next session (ran out of time today!)
The tuner still has the factory seal on it so at least I know its not been fiddled with. Any ideas on this are more than welcome!

Here's some pics, enjoy!!

Matt

[Heatercathodeshort]

Unusual to have complete lack of signals. A simple signal generator would be useful. If you waggle V1 the common sound and vision amplifier you should get some flashes on the screen and crackles on the sound. Check the tuner valves PCC84 and PCF80. Also check they are in the correct positions. The PCF80 should be closer to the tuner spindle [knob end] If they were transposed you may find a resistor O/C. My guess is that the PCF80 is duff, maybe even gassed. The tuner is super reliable. Let us know if you have a signal generator and take it from there. Any generator will do even one with poor accuracy, it's only needed to test to see if the first stage is operating. The tuner is an incremental type and it is possible a tuning coil has dropped off. The later post 1958 models suffered from this and it used to take ages to see where it had been soldered but with this early version, very unlikely. John.

[HamishBoxer]

This is looking V.Good.

David

[Sideband]

In a word...impressed! That looks absolutely superb. Waiting to see some pictures.


Rich.

[mark pirate]

You have done a superb job on the cabinet, it really is amazing how well bakelite responds to a good T-cutting.

I had similar issues with lack of signal on my LV51, make sure the valveholders are clean & making good contact with the pins.

Mark