The last mention of the above on this forum seems to be around ten years ago. I've had this one for about a year and wasn't sure how it had been stored so kept it in a warm domestic environment for a couple of months. There was a fair bit of woodworm damage, but the basic veneer was ok save for some water marks on the top from a vase or similar. Probably manufactured around late 1949 early 1950, speaker is date marked October 1949.
Into my damp unheated workshop (ie garage), chassis pulled out, and the usual LOPT gentle DC warm up procedure commenced, luckily all appeared ok, but I kept the heat from my bench lamp playing on the LOPT whilst working on it. Changed all the waxies and most electrolyics. It needed an EY51 as one of the cathode legs had broken, the top cap of the PL38 had come adrift breaking the wire connection to the anode, and the rear contrast control was smashed beyond repair, but most of the rest looked in quite good order.
I found a weird bodge where a thermistor had been connected from the rectifier to the 100uf smoothing cap which then went nowhere! All the smoothing was being done by the choke and the 200uf (other half) of the smoothing block. This work was all covered in the same amount of crud and dust as the rest of the set, so I assume it had been done many years ago. I stuffed the smoothing block and reverted back to the correct layout. I'm still trying to work out the rationale behind this....
Time for the first power up. The variac was slowly turned up over about an hour or so. Nothing - Mind you I wasn't expecting much! I let it run for a while, it appeared dead but I was surprised to draw a slight spark from the PL38 (I cursed my hearing, to think I used to complain about the 625 line whistle, now I can't even hear 405). Flicking the workshop lights off I noticed a faint glow on the CRT, So I was getting somewhere! Measured the EHT, it was around 4.5Kv. Thought I might as well change the Visconol cap for a 10Kv rated disc, this seemed to improve things (thanks to Sideband's advice (on UKVRR)).
After some fiddling with the contrast pot (temporary wrong value), brightness, focus and picture shift etc I had a noisy raster with a bit of blooming. Throughout all this I had no sound, no hiss or pops, nothing at all, so time to take a look. Hardly anything on the anode of the EL42 audio output, yes the SOPT primary was o/c!
On connecting the Hedghog and more fiddling I got a picture with what looks like a decent tube, although slightly dim in the centre, so quite straightforward so far. What's impressed me most with this set is the rock steady image, much better than my TV22 with it's somewhat poor interlacing.
Main things to address now are finding/rewinding a SOPT, freeing up the brass focussing sleeve on the CRT neck to give a better focus and smoother operation, replacing a few broken ceramics, and sorting out the cabinet woodworm. However the main problem is curing some line foldover on the left hand side - the sort of niggling fault that can take time to pin down, so any suggestions very welcome!
However the main problem is curing some line foldover on the left hand side - the sort of niggling fault that can take time to pin down, so any suggestions very welcome!
For that fold over I'd look in the line scan cct, perhaps it might be the hoz hold not quite right or a fault in the sync circuit? Worth a look.
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Thanks Chris, Yes the horizontal hold locks perfectly, and adjustment either way makes no difference to the foldover. The screen shows the Hedghog raster on 5:4 aspect ratio, on 4:3 it is much reduced, so I'm assuming it's a scan problem.
Pete
Components in the tail of V16, and check: C47, R68, C51, R62 & C52
My 50 cents'
Thanks, I've changed C51 & 52, need to check the others and get the scope on it.
Pete
If memory serves, you need to be looking at why the line flyback is slower than it should be.
Check R29 as known issue, see trader sheet 937 for more info, here is the jist.
"The value of R29 affects the extreme left hand of the line scan, a reduction of its value cramping up the line, even to the extent of folding it over in extreme cases. Conversley an increase in the value will open out the line at that point. R29 was ommitted in early chassis."
Thanks I'll check it out.
Looks like a good tube! I wouldn't think the Sound output transformer is special just about anything that will fit should do . Something from a 50's radio etc, anything that uses a ECL82/6 EL84/42. If you struggle to find one let me know and I'll have a look to see what I have.
Rich.
Thanks Rich, I may well get back to you! Plenty of room so no problem with size or mounting really.
Pete
I've got some output transformers in a box somewhere. What is the output valve?** I've taken the transformers from scrap sets and marked the output valve they were used with.
**Edit....sorry missed that in your first post, it's an EL42. I'll see what I have. The Ra of the EL42 is 9000 ohms. Doing the math that works out to a transformer ratio of around 55:1 (assuming a standard 3 ohm speaker). Nothing unusual about that and almost any pentode output transformer will be close enough.
I would love to see the finished set. The family had one of these and it's the first TV I remember. I would have been watching 'Watch With Mother' in the afternoons circa 1954/55. When ITV started in 1956 (although I didn't have any idea then of course), my older brother who was a TV engineer brought home a mystery box called a converter we could watch the new channel. We were very close to the BBC mast at Beulah Hill....we could see the mast from the back garden in winter when there were no leaves on the trees and the interference on ITV from direct pick-up of BBC was quite bad....we could even see BBC floating in the background of ITV sometimes but this didn't seem to bother anyone. Eventually my brother did something that eliminated the direct breakthrough (probably a trap or an attenuator) and we had interference-free reception of ITV. I was very pleased to be able to invite friends round to watch 'Popeye' on ITV.
Sadly, I know I bought a 941T cheaply and gave it to a mate for the tube surround and mask, keeping the tube for myself. I expect he has binned the chassis.
Yes it's an EL42 and a 3 ohm speaker. The closest I've got is transformer from a UL41 (Ra 3K ohms) output stage. I'd be grateful if you could find something closer!
My sister and I loved 'Watch with Mother', and a real treat was to go to our posh neighbours two doors down to watch 'Laramie', 'Four Feather Falls' and 'Twizzle'!
Pete
If you plan to run the set before you find a replacement output transformer, disconnect the HT to the screen grid of the EL42 otherwise that will pass all the current that would normally be drawn by the anode, resulting in a red-hot screen grid and probably a dud valve....
A good match impedance-wise is a transformer from a valve portable using a DL92; however, the question of anode current and core size then comes to mind.
Thanks, when I realised the op tx was oc I already had the transformer and speaker hanging out of the set, so I just stuck a handy 6.8K across the oc winding, which although not ideal will hopefully be ok till I've sorted it out.
All we've got to do now is to find you a transformer!
Yes please!
@petedox Out of curiosity, what are the fixing centres of the transformer? One might even turn up when I empty the Ford 'shed' on my drive prior to it going for scrap, you never know!
I also noticed the 'Trader' sheet mentions line foldover at the LHS being down to low emission in the recovery diode - the PY31.
Thanks Cathovisor, I'm away from home at the moment, but I'll measure tomorrow evening and get back to you
Edit: BTW I'm away to pick up a lovely 20" 1500!
Pete
