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Old 10th May 2015, 8:33 pm   #1
Sean Williams
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Default Pye D18T

Nice morning at the NVCF today - A D18T followed me home....

Instead of spending the afternoon doing boring work related stuff, I thought first light might be fun to see.

The chassis is in quite good condition, some evidence of previous repair work, with one mid 50s TCC electrolytic tacked in, and possibly a replacement cap that as far as I can tell is part of the boost circuit?

Anyway, after replacing the mains fuses (both o/c) and snipping out the mains filter cap I applied some mains.

After what appeared to be a lifetime there were signs of life - the smell that says "I haven't seen power for years" and a feeble squeak from the line timebases.

EHT at this point was sadly lurking around zero.

I then replaced what I think is the boost cap - 0.25uf - it tested leaky - powered back up again, and a much happier line timebase appeared - a quick check with a trusty screwdriver said that EHT was present.

Now, it seems that the sliders on the back of the chassis are a little sick - the brightness control is open circuit - tacking an external pot across this gave me a fairly bright raster.

So, what to do now - search for a replacement set of sliders, or build a replacement panel that has half a dozen small wirewound pots? Any reason why I shouldn't do this? - I understand that these slider pots are not so clever nearly 70 years on.

Be nice to have something to use the Aurora with again.
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Old 10th May 2015, 9:52 pm   #2
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Default Re: Pye D18T

That sounds a good buy.No those pots are not good in the sets I have rstored.
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Old 10th May 2015, 10:04 pm   #3
Sean Williams
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Default Re: Pye D18T

Twas a Danny set - fair to sat he had a good sized stall today - I am quite pleased with my purchase.

Had I more spare time (and a considerable pile of cash) I would have purchased more

It needs a fair bit of work on the cabinet - some cracking ex magnifier holes, and general wear and tear - cabinet refinishing is certainly not my strong point, but I will try to make a fairly tidy, if not 100% original job of it.

Will try to get some piccys up as soon as there is something worthwhile to show - probably won't be this week, Work and loft clearance getting in the way.
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Old 10th May 2015, 10:56 pm   #4
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Default Re: Pye D18T

Great little sets, I have two of them
One I already restored here: https://www.vintage-radio.net/forum/...ad.php?t=92661
And another I bought back in january this year, all this one needed was a couple of new smoothers tacked in and I got a pretty decent picture!

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Old 11th May 2015, 9:38 am   #5
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Default Re: Pye D18T

Hi Sean. A new pot panel is a fairly safe way of getting reliable controls - I did one for my D16T. The panel uses the original holes in the chassis and the controls even line up with the legends on the back. The pots are 5W wire wounds from Digidata.
I've included the drawing in case you want to use it!
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Old 11th May 2015, 7:18 pm   #6
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Default Re: Pye D18T

Thanks Brian - exactly the sort of thing I was thinking of.

Do I really need 5 watt pots? - I think I have a number of the smaller colvern wirewound pots here somewhere
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Old 12th May 2015, 9:33 am   #7
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Default Re: Pye D18T

I never did bother to work out the power dissipation in the pots, Sean, as I had a selection of the small 5W versions when I bought a job lot for stock during a sale period. They have since doubled in price.
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Old 26th May 2015, 7:18 pm   #8
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Default Re: Pye D18T

Some more progress over the past couple of weeks.

A bucket of capacitors across the timebase section (one at a time to prevent mistakes)

I also had luck and found a spare 10K slider in the junk pile, so the brightness control is now much happier.

Net results - I can't hear 10kcs any more - I had 4 test card C on the screen, but quickly reduced this to two by resetting the line frequency.

I guess the frame is running at half frequency, the frame hold control is on the endstop, but I still get two test cards, one above the other.

At present the tube seems quite poor - advancing the brightness just sends the picture white - I will reserve judgement until I have gone through the numerous remaining faults - the RF alignment has been twiddled with extensively, so I have completed a "quick and dirty" alignment by squirting a LOT of RF in progressively reducing the signal until some form of gain and image appeared - it is still as deaf as a post, there are a handful of waxies lurking in the sound section of the RF department - I don't think these will affect the vision circuit, but may well swap them out as they're bound to be leaky.

So, a question, while I am happy prodding around and swapping out parts, where should I be looking for the frame fault?
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Old 26th May 2015, 7:47 pm   #9
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Default Re: Pye D18T

It possibly is just caps and reses out of spec in the frame osc and I guess also the output stage having sorted the osc first.
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Old 26th May 2015, 10:08 pm   #10
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Default Re: Pye D18T

I think I have got most of the waxies out of the frame circuit - perhaps the usually reliable Sprague caps are not at their best.
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Old 26th May 2015, 11:36 pm   #11
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Default Re: Pye D18T

Nice to know the set has finally seen mains I bought this set a few Harpendens ago but never even removed the back until the NVCF I still have far to many TV's 100s of them . Danny
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Old 27th May 2015, 1:58 pm   #12
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Default Re: Pye D18T

Quote:
perhaps the usually reliable Sprague caps are not at their best.
These are miles better than any wax cap, but can still be leaky. I would replace them as a matter of course, they are over 65 years old now!

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Old 27th May 2015, 5:51 pm   #13
Sean Williams
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Default Re: Pye D18T

Righto, more caps to swap out - another 4 I think - at least it is putting up a fight!
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Old 27th May 2015, 7:08 pm   #14
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Default Re: Pye D18T

Just a point and I know you have replaced some pots (or all) I was going to say as a long shot just check the values to see if they are correct if any original ones left in the frame stage.

It is a bit like a resistor going low it does happen from time to time.
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Old 27th May 2015, 7:45 pm   #15
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Default Re: Pye D18T

Will do that as well
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