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Pye B18T Holiday Excuse !

 
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Re: Pye B18T Holiday Excuse !

Post by marc » Sat Feb 27, 2016 2:06 pm

Hi all,

Sorry for the delay in getting back to this set but it's the first chance I've had to get back in the workshop for a couple of days.

Anyway here goes......
PL38 top cap is now fixed back in place so on with testing.
Firstly I tried to draw a spark from it, nothing :cch so onto voltages...not good, control grid is +17 (should be -27) and screen grid is 216 (should be 232)

Marc.

 
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Re: Pye B18T Holiday Excuse !

Post by freya » Sat Feb 27, 2016 2:29 pm

Assuming your using the trader sheets, then first suggestion is swapping V15 over with V11. Has C52 0.01 been changed. Screen grid variation is probably R129 330 ohm being slightly high.
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Re: Pye B18T Holiday Excuse !

Post by Terrykc » Sat Feb 27, 2016 2:42 pm

occiput wrote:Stranded equipment wire inside e.h.t. sleeving makes a very good replacement. 
Find an old bit of coax - not low loss - with a stranded inner. Remove the sheath and screen and you are left with an EHT cable that looks - and performs - like the cable used for many EHT rectifier heater windings.

We used to have a lot of trouble with Bush TV105/115/125 EHT valveholders - all of the pins turned green and disintegrated! (This was generally believed to be caused by the excess moisture in the air caused by paraffin room heaters but I found many cases in homes which  didn't use them.)

A normal Cinch B9A valveholder with its mounting saddle removed was an identical replacement and, in most cases, it was possible to re-use the existing heater winding. However, there was no slack so, if the verdigris extended back along the wire, a replacement was needed and the coax inner always did the trick.

 
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Re: Pye B18T Holiday Excuse !

Post by marc » Sat Feb 27, 2016 2:52 pm

freya wrote:Assuming your using the trader sheets, then first suggestion is swapping V15 over with V11. Has C52 0.01 been changed. Screen grid variation is probably R129 330 ohm being slightly high.

Hi Stephen,

C52 has been changed already, I was just in the process of testing V15 and it shows "earthy electrodes" on the Mullard HSVT, checking V11 also shows an anode fault.
I don't have a spare EF50 so will look to see if any of my other set have a donor I can borrow.

Marc.

 
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Re: Pye B18T Holiday Excuse !

Post by freya » Sat Feb 27, 2016 3:01 pm

Swap them over for some in the rf section v1,v2 etc. mark them before so they go back in the right places.

 
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Re: Pye B18T Holiday Excuse !

Post by marc » Sat Feb 27, 2016 3:23 pm

Hi Stephen,

OK as you said I used V1 which checks out as good on the tester and placed it in V15 but still have a +17 on the grid of PL38

Marc.

 
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Re: Pye B18T Holiday Excuse !

Post by freya » Sat Feb 27, 2016 4:25 pm

What are the voltage conditions on V15

 
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Re: Pye B18T Holiday Excuse !

Post by marc » Sat Feb 27, 2016 4:44 pm

Hi Stephen,
Valve 15.....
Grid -1v
Anode 1v (should be 17)
Screen grid 234v (should be 238)

Marc.

 
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Re: Pye B18T Holiday Excuse !

Post by freya » Sat Feb 27, 2016 4:53 pm

So what voltage is on the other side of R64 820k

 
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Re: Pye B18T Holiday Excuse !

Post by marc » Sat Feb 27, 2016 5:22 pm

Hi Stephen,

Ok, so V15 side of R64 is 0v and other side is 220v.....R64 (820K) is O/C
Off to find a replacement.

Marc.

 
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Re: Pye B18T Holiday Excuse !

Post by marc » Sat Feb 27, 2016 5:31 pm

Hi Stephen and all,

Looks like you were bang on the money again Stephen, R64 was the culprit, EHT has come up along with narrow band of raster ! :aad
Off to do some tweaking and see if it's possible to get a picture.

Marc.

 
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Re: Pye B18T Holiday Excuse !

Post by sideband » Sat Feb 27, 2016 9:29 pm

marc wrote: R64 was the culprit, EHT has come up along with narrow band of raster ! :aad
Off to do some tweaking and see if it's possible to get a picture.

Marc.


It never ceases to amaze me how little work some of these old sets require to make them function again. Getting them to work properly is another story.....

 
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Re: Pye B18T Holiday Excuse !

Post by marc » Sun Feb 28, 2016 3:32 pm

Hi all,

There is the resemblances of test card but the picture is very dim and focus is very poor.
EHT is only around 4.1kV instead of the 6.5kV it should be, I have a sneaky feeling that the LOPT may have to be removed again and given a stint in a low oven. :aaq

Another issue is that the frame amplitude slider pot had fallen apart (as they do) so I tacked in and old 10K rotary pot, it works but seems to get very warm, any idea of the minimum wattage required for a pot in this position would be very welcome.

I also need to track down a couple of EF50 valves to replace two poor ones.

Marc.
DSCF3572 forum.jpg

 
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Re: Pye B18T Holiday Excuse !

Post by crustytv » Sun Feb 28, 2016 4:12 pm

marc wrote:Another issue is that the frame amplitude slider pot had fallen apart (as they do) so I tacked in and old 10K rotary pot, it works but seems to get very warm, any idea of the minimum wattage required for a pot in this position would be very welcome.

here's my thoughts, I would go on the anticipated maximum not minimum. Looking at the manual R7B is 10K with the minimum voltage expected to be 75V and the maximum voltage being 209V. Based on those figures and taking the min voltage of 75V, max voltage of 209V, applying ohms law, I get 0.5W@75V and 4.3W@209V.

Based on that I would put in a 10K 5W.

 
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Re: Pye B18T Holiday Excuse !

Post by marc » Sun Feb 28, 2016 4:18 pm

Hi Chris,

Thanks for that :aad
I'll see what I can find in my stash or try and find an original from somewhere. :aaq

Marc.

 
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Re: Pye B18T Holiday Excuse !

Post by freya » Sun Feb 28, 2016 4:56 pm

My lopt spent 40 mins in the oven at about 200 degrees, the pitch had started to melt at this point. Its still great today though pushing almost 7Kv
How does the tube test Marc ? it could be a bit low.
Is the focus magnet shunt gap almost closed, the magnet may have lost some of its effect.

 
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Re: Pye B18T Holiday Excuse !

Post by marc » Sun Feb 28, 2016 5:52 pm

freya wrote:How does the tube test Marc ? it could be a bit low..

Hi Stephen,

The CRT is as flat as they come, I've left it simmering on the B&K but I don't hold out much hope for it.
Still at least the rest of the set is now usable and it can be sat on a shelf until a CRT becomes available for it so no harm done.

Marc.

 
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Re: Pye B18T Holiday Excuse !

Post by freya » Sun Feb 28, 2016 6:11 pm

One of my lv20 tubes was so flat it didnt measure on the B&K. I used the rejuvinate and it came up and stayed at 90%.to this day. Might be worth it as its so bad.

 
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Re: Pye B18T Holiday Excuse !

Post by marc » Sun Feb 28, 2016 6:24 pm

freya wrote:One of my lv20 tubes was so flat it didnt measure on the B&K. I used the rejuvinate and it came up and stayed at 90%.to this day. Might be worth it as its so bad.

You were lucky there Stephen, This tube has been simmering for a while now but it's still showing nothing, I can't even set the cut off. I'll give it a few hours and see what happens with the clean and balance before I try booting it with rejuvinate.
The anoying thing is that I could have sworn that I tested the tube when I first got the set and it showed to be 'fair' I'm now wondering if I got it mixed up with another telly. :aaq

Marc.

 
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Re: Pye B18T Holiday Excuse !

Post by freya » Sun Feb 28, 2016 6:49 pm

I only keep the rejuvinate pressed for 4 second burst. Then monitor on test to see result. Don't carried away though. If its that dead then anthing above red when on test then stop, change to clean and balance if need be.

 
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Re: Pye B18T Holiday Excuse !

Post by marc » Sun Feb 28, 2016 10:02 pm

Hi all,

Damn and blast it, the CRT is dead !
It's had several hours of simmering without any improvement so a clean and balance was tried but still the same, another hour of simmering and still nothing so rejuvenate was attempted....Nothing ! The needle just sits at the bottom of the red.
So guess who needs a MW 22/14 CRT :cch

Marc.

 
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Re: Pye B18T Holiday Excuse !

Post by freya » Sun Feb 28, 2016 10:20 pm

That is a real pity. Hopefully somthing will turn up. Its odd you got as much as you did with zero emission though.

 
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Re: Pye B18T Holiday Excuse !

Post by crustytv » Sun Feb 28, 2016 10:33 pm

Its possible the tube had been bopped before, perhaps more than once. The little emmissive layer that was left supplying the raster Marc had earlier, was finally blown away when Marc did the rejuvenate.

There was a tube on e-bay this week but I'm blowed if I can find it now, they do turn up often not as rare as Early CTV tubes. Also try contacting Luke as I'm sure he had a whole load of B&W tubes, he may still have them, though I cannot remember what he had.

 
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Re: Pye B18T Holiday Excuse !

Post by marc » Sun Feb 28, 2016 10:39 pm

freya wrote:That is a real pity. Hopefully somthing will turn up. Its odd you got as much as you did with zero emission though.

Trust me what you saw on the photo was better than to the naked eye, even turning on the angle lamp on the bench would make the picture disappear it's really is that dim.

Marc.

 
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Re: Pye B18T Holiday Excuse !

Post by marc » Sun Feb 28, 2016 10:44 pm

CrustyTV wrote:Its possible the tube had been bopped before, perhaps more than once.

try contacting Luke as I'm sure he had a whole load of B&W tubes, he may still have them, though I cannot remember what he had.

Hi Chris,

I think you're probably in the right ball park there, I reckon it's been bopped before too. :bbd

Luke as in 'mendipviews' ? It would be nice if he has a CRT available. :aaq

Marc.

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