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Recreating the GEC 8161 Mirror Lid TV

 
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Re: Recreating the GEC 8161 Mirror Lid TV

Post by crackle » Sun Aug 21, 2016 3:32 pm

Hello Brian
I dont often pop into the TV threads and even seldom make a post, but have just come across your thread and as you had not been active for a while decided to catch up on it.
I do sincerely wish you well, and I am really sorry that you could not continue with the fantastic work you were doing on that sparkling new chassis I saw in your workshop.
I am sure Mike can get it completed and working again.
Take it easy.
Mike

 
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Re: Recreating the GEC 8161 Mirror Lid TV

Post by Michael Watterson » Sun Aug 21, 2016 10:19 pm

I'm sorry to hear about your health, Brian, but I'm glad you have a "good egg" to pass the stuff to. I've been concerned of the last year that my stuff doesn't just get dumped one day, but I don't have a solution yet.

Best Wishes.

 
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Re: Recreating the GEC 8161 Mirror Lid TV

Post by Briancuff » Sat Aug 27, 2016 10:42 am

Than you Michael, for your thoughts.
It's a real problem with a hobby like ours when there seems to be no-one to "take over" a collection, a project or even research. Sarah, my wife, is very understanding and will do what she can but there is so much STUFF that there will be problems. I have arranged that an acquaintance of mine will have my Bridgeport vertical mill, Myford Super 7, large pillar drill and associated tooling and accessories. for a largish donation to the Duchess of Kent Hospice near us which I where I get my Hemoglobin boosting blood transfusions. My pre-war TVs will have to be auctioned but there a few later TVs which are not that commercial!
At least I won't see what happens (or will I :) ) but I do not envy Sarah.

 
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Re: Recreating the GEC 8161 Mirror Lid TV

Post by Cathovisor » Sat Aug 27, 2016 10:59 am

This has been discussed before here.

I have no dependants, so the task will fall to my immediate siblings to sort out - and if Brian thinks he has a lot of 'stuff'.... :ccf

After my wife died, I realised the most pressing thing I had to do after the funeral was to write a will; we never did one together, felt it was tempting fate a bit. In my will, there are specific bequests - the SABAs and Körtings are headed to one person, a particular RGD radiogram to another - but the dispersal of my collection is basically down to auction by the BVWS after my family have picked any mementos out (assuming they want anything) and the named people I've asked to handle this on their behalf have likewise, taken anything they want. (And that reminds me that I should add a codicil to take my pre-war TVs into account as I didn't have those when I made the will)

The other approach is really, to start slimming down an unwieldy or just large collection now so that too much of a burden is not left for our executors. For some of us, it's not so much a collection as a hoard. I probably fall into that category.

 
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Re: Recreating the GEC 8161 Mirror Lid TV

Post by Cathovisor » Sun Sep 04, 2016 4:36 pm

Some of you might be aware that recently, a GEC 4603 CRT became available on eBay; the 4603 is a remarkably short 12" electrostatic tube used in their 1939 models. It was suggested it was NOS. Well, I was the successful bidder on it and yesterday I collected it from the seller.

Today, I decided to try testing it, so a particularly messy rig was created which involved my Radar 202 CRT tester (to provide the heater volts - 4V @ 1A), a Farnell 0 - 30V PSU to provide a grid-cathode potential and a 47kΩ resistor to limit the current from the PSU. The idea is to draw a current between the grid and the cathode, to see if the cathode has emission.

The base of the 4603 CRT is as shown here:
GEC_4603.png
GEC 4603 base connections


So then the rig was connected, the heater current adjusted for 1A at which point there was 4V on the heater terminals. I had to open up the base connector (two screws) to solder some wire tails to in order for the various croc clips to get a purchase on; it also gave me a chance to freshen up the old solder. The DC power supplied was connected via a kindly-donated Fluke 25 DMM and the 47kΩ resistor.

The DC PSU was switched on, and the voltage slowly advanced. I didn't want to draw too much current from the cathode for fear of stripping it, so I settled on a current of 300µA. I wonder how many volts it would take to achieve this current?

Well, the results are below.
GEC_4603_test.jpg
I think that's a result...


As you can see, just 15V was needed to provide the desired cathode current. For the record, with the resistor missing I briefly drew over a milliamp from the cathode with but a few volts applied - so I think that unless my methodolgy is flawed, that's a win for the GEC! :cca

 
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Re: Recreating the GEC 8161 Mirror Lid TV

Post by marc » Sun Sep 04, 2016 5:08 pm

Excellent result Catho :aad
and no doubt a heck of a relief too :bba

Marc.

 
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Re: Recreating the GEC 8161 Mirror Lid TV

Post by Briancuff » Sun Sep 04, 2016 6:07 pm

That really is excellent news Cathy. The BT8161 will be so much better with a proper monochrome picture. It will be interesting to see whether the deflection sensitivity is greater for that tube although its reduced length suggests otherwise!

 
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Re: Recreating the GEC 8161 Mirror Lid TV

Post by Cathovisor » Sun Sep 04, 2016 7:09 pm

Brianc wrote:That really is excellent news Cathy. The BT8161 will be so much better with a proper monochrome picture. It will be interesting to see whether the deflection sensitivity is greater for that tube although its reduced length suggests otherwise!

You've no idea how much of a sigh of relief I made when I saw the meter rapidly increase its count, I can tell you!

I have a copy of the manual for the BT9121 which uses the 4603 CRT, and that seems to use a broadly similar scanning circuit to the BT8161.
GEC_BT9121_scan_generators.PNG

What I may do is buy one of those £20 (or so) oscilloscope modules from China from eBay and run it up with my x100 probe attached and a battery to power it, so I can happily float the thing up to EHT and look at the deflection plate waveforms directly. At £20, it can be treated as disposable should a flash-over annihilate it!

 
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Re: Recreating the GEC 8161 Mirror Lid TV

Post by crustytv » Sat Sep 10, 2016 2:14 pm

Even though this forum has now closed I have discussed this thread with Mike. He will be continuing the story of this GEC's return to working order over on the main sites E-CTV forum. I suppose it is quite fitting that the first stage under Brian watch is all contained here and the second stage under Mikes watch will be over one the main sites forum.

Mike is hoping to have the new CRT fitted next week, like many I'm looking forward to the continuation.

The continuing story: https://www.radios-tv.co.uk/community/b ... -part-two/

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