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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 3rd Oct 2006, 9:30 am   #21
ppppenguin
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Default Re: Pye V4 Restoration

I hadn't realised this could happen with a CRT but I suppose it's obvious if you think about it.

I remember polishing the perspex lid of a turntable and finding the pickup flying off the record! How that happened to a metal pickup arm, albeit tracking at not much over 1 gram, I really don't know.
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Old 3rd Oct 2006, 2:59 pm   #22
David_Robinson
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Default Re: Pye V4 Restoration

Quote:
Originally Posted by murphyv310 View Post
the funny folding effect I see on your photos is actually static on the screen.
Thanks very much for that - I have this effect on my Pye C17 and I couldn't work out what was causing it.
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Look that up in your Funk and Wagnall's
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Old 20th Nov 2006, 6:28 pm   #23
Ghostuser
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Default Re: Pye V4 Restoration

Hi to all Pye V4 Lovers,
I have suspected an EHT Problem with my set for some time but been unable to test the voltage. Today, I bought the last two 47M and 22M High Voltage resistors from my local Maplins and wired them in series to give 138M. With this in series with my AVO 8 on the 250 microamp range, I now have a voltmeter reading 13.8KV at 100 microamps on the scale. On powering up, I have an initial reading of about 80. This would be around 11KV, compared to the 14 KV which the LOPT should deliver. This probably explains the dim, out of focus picture I have been getting. Disconnecting my 'voltmeter' produced no change in the picture, suggesting that the odd extra 80 microamps was not overloading the system. After running the set for about 20 minutes, the reading had fallen to about 70microamps, or 9.7 KV and the picture width had decreased a little. Disconnecting the meter caused an increase in brightness and focus, though, interestingly, no change in width.

Are these classic symptoms of a failing or failed LOPT? The set's HT rail is at the specified 185 volts and does not change with time. Both the line o/p and booster diode valves are new and all capacitors have been changed. Cathode and screen grid resistors are new.

Cheers
Nigel
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Old 29th Jan 2007, 6:54 pm   #24
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Default Re: Pye V4 Restoration

I now have a complete V4 and VT4 and a scrap VT4! Some CRT swapping proved that both the VT4 and the scrap VT4 had much better CRTs than the original V4 and I have hopes of ending up with both a good V4 and a good VT4.
I have changed lots more waxies and moldseals and have the VT4 working quite well. Width was about an inch low, but I found that the line linearity adjustment did nothing. I swapped the linearity coil for one from the scrap chassis and got the width up to size, but only with the width control at max. Width still reduces as the set warms up.
The linearity coil lives near the booster diode and all three of mine look fried. I am having one re-wound, but wonder if anybody can comment on the durability of these coils?
Also, on the V4, I notice that there is a crack in the ferrite core of the LOPT. Is this a serious issue or is a small air gap acceptable?

BTW, The Aurora puts out a beefy RF signal. With a good set of EF80s in the RF section, the V4 worked fine. I then swapped some valves and lost contrast. To cut a long story short, I found that somebody had chopped out the cathode resistor of the RF stage. (They had also chopped off the components on the CRT base connector and a resistor from the HT supply, but I had found those) The Aurora clearly had given enough signal to couple to the second RF stage by stray capacitance until I put in some poorer EF80s!!

Ain't trouble shooting fun?

Cheers
Nigel
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