Pye B18T/F (1948) Restoration

[Freya]

Put it back, that coil makes a big difference to the contrast ratio when its peaked up.
Is that a waxy on the heater decoupler still ?

[ukcol]

Another nice job Mark and an interesting write up.

Originally Posted by mark pirate

However, I am not happy with the picture ...

The only thing about the picture (on test card) that I would criticise is the focus, not quite pin sharp. There won't be many CRTs of that age with perfect focus of course.

[SteveCG]

Re: post no. 20,

From what I've read in Wireless World adverts of the late 40's, having a 75 Ohm twin feeder aerial connection was not uncommon. It is a good match to a plain dipole.

[mark pirate]

I am really scratching my head over the picture problems on this set, I did try reinstating the twin feeder and transformer, it actually made it worse!

Is that a waxy on the heater decoupler still ?

Yes, but now all the caps have been replaced

After competing all the cap replacements, the set refused to work at all
After much head scratching, this turned out to be caused by the PY31 heater going O/C!

A replacement got the set running again. But even with the last of the old caps replaced, there was no improvement.

It is hard to describe, but the symptoms are as follows: with the picture set up to give a decent image on test card C, switching to normal programmes makes dark scenes very dark indeed, when it changes to a bright image it is way too bright and I get a buzz on the sound.
when on an average studio programme such as a newsreader, the picture is pretty good, but any change of scene causes the above problems.

Mark

[Freya]

Sounds more like alignment, perhaps it was realigned when the feeder was changed.

[ukcol]

The test card picture looks too good to me to point to alignment, although misalignment can be detected by tuning the set through the correct point.

My first thought was AGC, but there is no AGC in this set of course. Since you get a cross mod buzz on bright pictures I would check the DC conditions on V1,V2 and V3. I would also check that the contrast control is acting on both V2 and V3 and that the gain pot is correctly adjusted.

[mark pirate]

I am sure it is down to alignment, replacing the capacitors has actually had a negative effect, even though they were replaced by the correct value and great care was taken to locate them in the same position as the originals

There are quite a few differences when comparing the RF sections of this set with my scrap (channel 1) chassis.

I will take voltage readings as per the Pye manual, dig out the Advance E2 then have a stab at alignment....

Mark

[mark pirate]

After digging out my trusty plastic trimming tool, I managed to tweak the alignment without resorting to instruments! The picture is much improved and the annoying buzzing on bright scenes has now been sorted, in fact the sound is excellent now.

I think the new capacitors (and there were a fair few) affected the alignment, some of the adjustments took a few turns to get good results.
Stripping and cleaning the contrast control also helped.

With the chassis now looking good, I set about refurbishing the cabinet.
A good polish with T-cut got rid of most of the surface scratches and gave it a nice shine, a generous application of Topps scratch cover was applied and allowed to soak in to the scratches while I cleaned and polished the plastic safety screen.

I fitted the speaker and output transformer to the cabinet, I needed to reglue the cloth on the opposite side as it was coming away from the cabinet.
The aluminium heat shield was then cleaned and refitted.

The cabinet was polished up and the safety screen refitted, finally the chassis was refitted.

I think the cabinet has come up a treat from what I started with, the Pye logo on top has really come up well.
I was undecided what to do about the screw holes in the front where a magnifier was once fitted, I was going to fill them and touch in with a furniture pen, but I will leave them for now as they don't notice too much and are a part of the set's history.

I have had a few sets that have been fitted with magnifiers, but I have yet to get one with it still in situ.

Mark

[Lloyd 1985]

Hi Mark,

that's looking lovely! I just flicked back to the original photo's you took of the cabinet, what a transformation! I hate to say, I would have probably been getting ready to strip the cabinet and re-finish it, but this just goes to show you can make it look great without having to resort to that. I really must get some Topps scratch cover and have a go with it, I have quite a few wooden sets with minor scratches.

Picture looks good too, I must get one of these little Pye's one day!

Regards,
Lloyd.

[Freya]

Excellent job as usual Mark, the cabinet has come up a treat.

[ukcol]

Well done Mark. Your instincts were better than mine.

[MonochromeMarc]

Again, well done Mark, the set looks excellent....can't beat a drop of "Topps" can you !

Marc.

[McMurdo]

my TV12 came with fitted magnifier and matchng drilled holes in the bakelite; it was held on by special brass knurled pins. I took it off while I did the chassis and when I went into the spare room to retreive it, it had leaked its oil all over the new carpet. I slung it in the bin in disgust, though I regret doing that a bit now.

[mark pirate]

Thanks for the compliments chaps, I have enjoyed restoring this set, despite the fiddly cap replacement on the RF deck.

The cabinet restoration only took about three hours, and I am pleased to have revived the original finish.
I swear by Topps, but I find it is best to ignore the instructions and leave it for at least an hour before polishing it off. For deep scratches I use a furniture pen, but my darker coloured one has dried up

I am certainly happy with the CRT on this set, despite what my B&K made of it!
It has definitely improved with use and has very little ion burn.
The EHT is rock solid as are the timebases.

I am rather fond of these little Pye sets, I have two of the console version and three LV20's. All use the same basic chassis. The odd thing is that the B18 cabinet is actually smaller than the later LV20.

they were certainly a popular set in their day, and are very reliable once restored.

Apart from replacing the PY31, all the valves are the originals. Not bad for a set that has been asleep for 55years!

I now have to get my TV22 back on the bench to fit the rewound LOPT.
before starting on the next set.

Mark

[AC/HL]

Originally Posted by McMurdo

I took it off while I did the chassis and when I went into the spare room to retreive it, it had leaked its oil all over the new carpet.

Liquid paraffin I believe, the medical stuff not the fuel.

[Boater Sam]

Yep, liquid medical paraffin, fairly innocuous stuff.
If you can't lose the magnifier holes, make a feature of them. Brass capped screws? Brown screw covers?

Interesting to see the odd EF50 with pushed in crowns, often wondered how some are like this. Service man with strong thumbs maybe.

[mark pirate]

I have seen a few magnifiers that seemed to have lost some of their liquid, I am guessing they were sealed when manufactured?

Were they all filled with liquid medical paraffin, or were some filled with other liquids?

I have been on the lookout for one for a while now, I would not be surprised if the one that had been on my Pye was still in the loft it was found in.
It appears that there were holes for a previous one that had been neatly filled in.

There were various types of magnifiers, some were on a freestanding wooden frame, one of my D18T console sets still bears the scars of one fixed to the set with straps. It has damaged the finish on the front edge of the cabinet

They certainly did not look pretty, but I am keen to see what difference they make to the picture, I suspect some distortion will be evident...

Mark