Thread: Pye V4
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Old 15th Apr 2019, 6:42 pm   #56
Vintage Engr
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Join Date: Jan 2008
Location: Shrewsbury, Shropshire, UK.
Posts: 824
Default Re: Pye V4

Quote:
Originally Posted by Davewantsone View Post
Quote:
Originally Posted by Vintage Engr View Post
I've just purchased a VT4 today, so everyone's hints & tips are most useful.The one I have looks as if it has had no previous repairs. The chassis has never been out, no rust, just a very thick 'carpet' of fluff.

I used to repair quite a few of these in the early '60's, but it's a long while ago now, so hearing from others in respect of possible problems is very useful.

I have recently had a couple of Philips 17TG100U LOPT's fail for similar reasons, i.e hygroscopic windings, so I shall be especially careful, as I need to get these two re-wound.

David.
I hope you will be successful.
The way I got mine going was to first of all replace every 3nF capacitors (most will be U/S) then the 0.001, 0.01 and 0.1uF capacitors.
Replace the v24 and v25 diodes with 1N414 diodes.
Check R126, R127 and R129 for correct values
Whilst doing this you may want to first remove the LOpT and connect to a DC power supplyand pump some power into the windings for at least 3 days.
If you could I would "ring" the transformer to see if it appears OK.
I would then reconnect the LOpT.
Remove fuse F3 and using a variac connect power to the set and slowly run it up to the mains potential and see if you get all the valves to light then maybe sound (with a suitable modulator on correct channel).
Now check pin 2 on PL81 and see if you get a negative voltage of around -27V.
Switch off then connect a ammeter across fuse F3. Turn variac up again and monitor current it should not exceed 150mA.
If you are lucky you may see EY51 light up and get some sort of picture!
Good luck.
Thanks for all the useful info, of course when I used to repair these in the early '60s they were not so old. However, one of the biggest problems with LOPT's & EHT circuitry, was the thick black sooty deposits from the smoke drawn in from coal fires. This was attracted by the High voltages & deposited just where one didn't want it.

It was the end of many Ekco LOPT's, both the cardboard & later plastic varieties.
I have actually seen a CRT that, due to this tarry deposit on the flare, arced over sufficiently to destroy the CRT! There was a groove melted into the flare, where the arc had progressed from the final anode connector, to the aquadag coating.

I shall take great care before applying any power. I nearly didn't get to purchase this TV, which came from a local junk-shop. The proprietor was most insistent that he wanted to plug it in & 'Test it" before selling it...

What did he think he would receive, even if it 'fired up'? (No pun intended).
Needless to say I put him right concerning both the safety & the possibility of destroying what could be a perfect working example, given the right expertise & TLC.

David.
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