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Old 10th May 2010, 1:15 am   #1
dominicbeesley
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Default Oh no - another V4!

Hello all,

Spent a couple of enjoyable hours at the NVCF this afternoon...and managed to pick up a V4. Its in a pretty shoddy state...full of spiders and rust. Doesn't look to have been touched for a while at least though has had some repairs in the past evidenced by some soldering iron burns on some wires!

Thanks to John (Heatercathodeshort) for the advice - no doubt I'll be needing some but have picked up a few hints from Chris's thread.

I'm hoping I'll be able to work most of this stuff out myself but will no doubt have lots of questions before I finish.

Now this TV has a plate on the back of the EHT cage that states it is a V4 but it has what appears to be a factory fitted Band I/III tuner so it is a VT4. Not sure what's going on there?!?

First up - I've got the trader sheets, which should be enough to get me started but would like to get a copy of the proper Pye manual - not sure where to start looking!

Here's a few pictures before I started....

Dom
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Old 10th May 2010, 1:44 am   #2
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Default Re: Oh no - another V4!

And this is what I've done so far - I hope to be able to get this running (badly) fairly quickly and then diagnose with a picture. Not sure how far I should go before tidying up the rusty chassis (or whether I'll bother - there's far too many components to strip it down for my liking!).

I decided to just snip / replace "those" capacitors - not sure if I've picked the right ones! I just went for those that looked like they'd damage a wound component if they caused a major leak - all the others I'd like to replace one at a time to see what difference they make!

Any advice as to whether I'm on the right track very much appreciated - only my third valve telly!

C49: LOP Valve coupler replaced old part measured <2M leakage "cold"
C80, C83: AF coupling caps - managed to break the tag strip doing this! Both measured bad "cold"
C84: Replaced - this was a 0.004 not 0.01 as stated on Trader sheet, uised a 0.0047
C92,C94,C96,C97: Frame coupling caps: Was thinking of replacing these but they all look to have been done already - replaced with big mustard caps, left them for now.
C104/C105: Mains conditioners - snipped for now

Noticed F3 was blown and only 500mA (Trader stated 850mA) - replaced with my last 500mA fuse

I was going to replace all the heater chain caps but decided I'd risk it and ran the set up on an isolating tranny and variac....
Wound up gradually (just under 2 minutes) to about 200V - all valves lit and faint whistle...500mA fuse popped!

This is when I spotted that F2 was a 850mA and F3 was a 500mA! Swapped the 850 int F3 position and put 350mA slow blow (all I've got to hand in F2). This seems to work and set can be run at full mains without tripping.

Set runs ok - no terrible smells though a nice brief wisp of smok from the area round the thermistor - not too worried as the 350mA fuse seems happy enough. All elctrolytics cool.

No sign of raster but a good loud line whistle and a healthy quiet-but-raspy 50ish hertz buzz from the frame stage. Also a faint hum from the speaker.

I'm fairly sure there's no EHT - there was no crackle and the fluff and dead spiders aren't standing to attention on the EHT lead!

Enough for tonight!

Questions:

Are my assumptions right about fuses? It looks to me like a medler has swapped them over for some reason!

I intend as my next step to open up the EHT can and see what's lit up in there - if the EHT rec is lit then I was going to try and draw sparks - is this ok?

Are there any "those" caps that I've missed?

Here's a couple more pictures: healthy glow from all valves and CRT - those heater chain caps can't have been dead short at least!

Cheers

Dom
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Old 10th May 2010, 9:41 am   #3
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Default Re: Oh no - another V4!

Hi , I saw you purchase this set & thought at the time you would have you work cut out with this one , You have made a great start , The set you have is a PYE VT4 with the wrong line can fitted , not sure what you can do about all that rust ! Good luck & keep us posted, Chris..
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Old 10th May 2010, 10:06 am   #4
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Default Re: Oh no - another V4!

Yes try and draw a spark with good insulated screwdriver from EY51 input ,not eht end.Amazed anything works after the disgusting conditions its been stored in going by the rust.

David
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Old 10th May 2010, 10:50 am   #5
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Default Re: Oh no - another V4!

What's the date on the bottom of the cabinet? My VT4 is May 1954.
If you've got a healthy spark at the EY51 turn up the brightness on the
front-Edge control is clockwise of course and rotates from right to left throught the cabinet for max.I had to adjust/fiddle with the ion trap magnet to get brightest picture.

The CRT on mine was initially very weak with an intermittent grid cathode leak
but a blast or two on the reactivator cleared it and now seems quite healthy.
It had a 40 year "rest" not being used between 1969 and 2009,,,

Almost certainly the line sync etc diodes will need changing.I treated the whole thing as a long term project.

Hugh
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Old 10th May 2010, 11:52 am   #6
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Default Re: Oh no - another V4!

Where exactly should I look for the date - I've not found one yet! Just had a good look round and can't find one...

Dom
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Old 10th May 2010, 11:54 am   #7
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Default Re: Oh no - another V4!

Mine was ink stamped on the base, quite faded though "July 1953"
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Old 10th May 2010, 12:30 pm   #8
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Default Re: Oh no - another V4!

Mmm will have another look later - I take it you mean the wooden cabinet rather than the fibre cover?

Dom
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Old 10th May 2010, 1:01 pm   #9
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Default Re: Oh no - another V4!

It will be a V4 with a retro fitted pye conversion kit.
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Old 10th May 2010, 1:31 pm   #10
dominicbeesley
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Default Re: Oh no - another V4!

Funny thing though is that the VT4 (factory fit) is internal whereas the usual retro fit hangs off the back cover.

It looks like its a factory fit from new as you can't remove the B****ing thing without removing the focus collar - which I'm very much loath to do....

Dom
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Old 10th May 2010, 2:10 pm   #11
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Default Re: Oh no - another V4!

Is the EY51 lit up? Is there EHT at the anode?

Let's get the picture up first and other things will follow.

Check the ion trap if there is EHT there, and try grounding the cathode of the tube.

Cheers,

Steve P.
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If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?
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Old 10th May 2010, 2:35 pm   #12
dominicbeesley
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Default Re: Oh no - another V4!

I'm going to knock off work for an hour in a bit and see whats going on inside that EHT cage...I couldn't get at it last night as everything was on its side while I glued and clamped the knackered plies of the cabinet up.

Anyway I hope I've done ok so far and not swapped too many caps before I started - and I hope my guess with the fuses was ok....

Thanks for the replies lads...I'll be back with any progress in a couple of hours!

Dom
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Old 10th May 2010, 5:04 pm   #13
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Default Re: Oh no - another V4!

Good luck with this one. I'm sure you will get it up and running. This is a VT4 as the front end is original with all the Pye wiring and no Band 1 adjuster wheel. The V4 was converted by an external box [Type 47] mounted onto the back. The R.F. and mixer valves were replaced by B9A plugs from the converter unit but everything else was left in place. More likely it had the incorrect blue plate from new or someone put the wrong line can on when in a busy workshop. It is an early one due to the pink Perspex filter.
J.
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Old 10th May 2010, 5:15 pm   #14
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Default Re: Oh no - another V4!

My VT4 has a pink perspex filter and it's May 1954.
Date is clearly visible on the bottom of the wooden cabinet.

I assume this is a fairly "early" VT4 so maybe the change of colour wasn't done exactly at the same time as the tuner change.

Hugh
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Old 10th May 2010, 8:26 pm   #15
dominicbeesley
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Default Re: Oh no - another V4!

Thanks lads,

I've still not managed to find any date but will try turning everything over for a proper look later.

It looks to have never had V1 fitted instead wires go through V1's hole to a tag strip and thence to the tuner unit. I'll get pictures if it seems like an oddball!

Had a quick play this afternoon with mixed results:

Checked for EHT bt drawing sparks from EHT reccy, anode=purple, filaments yellowish
EY51 lit, very dimly
Checked CRT base voltages - all come out around 120V?!?
swapped boost cap (c57) and what I think is A2 decoupler (C56)

On turning back on got no filaments and spent next hour tracking down the break - turned out to be a wire had popped off the tuner and wedged in focus assembly - how it didn't short out and blow the valves I don't know...

Line whistle now sounded a tiny bit livlier but no big change in CRT base volts

Tried fiddling with ION trap and got tube to light up - wouldn't call it a raster as it was so defocussed, there was an interaction between ion trap and focus collar - if set at certain angles got a flicker but no discernable lines - hopefully due to low A2 and EHT rather than gassy tube...

Turned brightness down to see if that brought up focus but now I just can't get any sort of picture back! Spent half an hour mucking around but no joy - a bit stuck now!

Also a worrying measurement - I checked the brightness pot in case that was playing up but it gives a nice smooth variation between 0 and 120ish volts. The grid is then fed via a 150k resistor (R66 100k on trader sheet). However gid voltage only varies between 100 and 130V - so I think its leaking to A1.

Decided to give it a rest and spend an hour in the pub - these things best left when I get stuck...

Not sure what to tackle next - low A2 voltage or high G1 voltage - I'd really like to get some light out of the CRT again just so I can tell whats going on.

Off to do a few cold resistance measurements now round the CRT base to see if there's anything obvious like a h-k, a2 short etc....

Dom
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Old 10th May 2010, 9:40 pm   #16
dominicbeesley
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Default Re: Oh no - another V4!

Grrr!

This is a tad confusing...

Measured (and re-checked with DVM and Valve voltmeter) CRT cold resistances:
H-H 3.1R
G-K >20M
H-all others >20M
A2-all others >20M

Sounds too good to be true

Swapped R71 - by accident! measured it wrong

Measured CRT base voltages hot with brightness at full
G1 114V
K 111V
A1 140V
Video drive (before 10K resistor) 110V
Boost 260

With brightness at min
G1 80
K 93
A1 140
Video 92
Boost 270

This just doesn't seem right to me why is K going down when brightness goes down!?!

Then I knocked the ion trap again and got a raster of sorts - this time with brightness at minimum! fiddling about with ion trap and focus I got blurry but distinct lines then it went again when fiddling with ion-trap.

Then I noticed the CRT base is loose!

My conclusion: broken K wire in CRT base which is occassionally making contact...but what to do? Is it as simple as solder sucking the pins and sliding off or will that knacker the job?

Any advice gratefully accepted if no better ideas while I have my dinner out comes that sucker!

Dom
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Old 10th May 2010, 10:22 pm   #17
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Default Re: Oh no - another V4!

CRT bases are often loose with these CRT's.Secure it to the neck with a bit of tape for the moment.

I would suggest firing the wee beasty up again and tapping the tube neck
whilst watching the screen to see if any on screen variation

A combined CRT checker and tube reactivator is a great help with this sort of situation.

Hugh
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Old 10th May 2010, 10:35 pm   #18
dominicbeesley
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Default Re: Oh no - another V4!

Thanks Hugh,

I've tried all manner of wiggling and tapping but no joy - I'm becoming convinced that there is a broken wire in the base but not sure whether I'll do more harm than good trying to mend or check it!

Dom
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Old 10th May 2010, 10:41 pm   #19
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Default Re: Oh no - another V4!

The bad contact may be inside the tube neck rather than the tube base....

Just try turning the set (and CRT) upside down(or rightside up if upsidedown now) and see if any on screen difference


Good Luck

Hugh
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Old 11th May 2010, 1:45 am   #20
dominicbeesley
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Default Re: Oh no - another V4!

Doh, sorry I see what you mean now!

Anyway I spent some time fiddling with the CRT neck and ended up resoldering it and taping it up...but no difference will try turning over tomorrow.

Anyway I thought I'd double check the EHT and now I'm not getting much of a spark. A smallish purple spark from the AC end (about half inch max) and nothing much from the DC end a bit of a sizzle if I'm lucky. So not at all sure what's going on. Trouble is its night on impossible to get at the EHT cap as the tuner is in the way.

Would it be worth unsoldering the EHT lead and trying again?

The EY51 is glowing dimly but its never looked too bright - testing on another on a bench supply I get a similar glow for about 3.5V on the filament.

Dom
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