Recreating the GEC 8161 Mirror Lid TV

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Recreating the GEC 8161 Mirror Lid TV

Postby Brianc » Sun Sep 30, 2012 7:06 pm

Hi all.
As many of you know, I purchased the empty GEC 8161 TV on ebay. There are no known examples of this set and so this cabinet is very important. I am going to attempt to re-create the innards as closely as possible to the originals but unfortunately, there seems to be a dearth of info on this set or on its smaller cousin, the 9122. I have been trawling through my RX data for a likely candidate for the radio chassis. GEC seemed to have gone mainly for rotary pointers and dials and the (poor) pictures of the 8161 we have indicate a linear dial. Looking at the knob positions and scale size, I think that the radio could be a modified "GEC Fidelity SW5". Does anyone have one of these and even better, does anyone have one of these which they are willing to part with as a possible donor? As soon as I get the cabinet, I will clean it up a little and post some pictures. The vendor lives in Sudbury but I find that there are two Sudburys! One near Ipswitch :( and the other near London :D . I am waiting to hear which - I bet it's the Suffolk one!!!
This is going to be a loooooonnnnng drawn out thread I imagine and any advice is welcome.
Cheers
Brian
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby oldticktock » Sun Sep 30, 2012 7:14 pm

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Re: Recreating the GEC 8161 Mirror Lid TV

Postby KeithW » Sun Sep 30, 2012 7:26 pm

Very exciting Brian, good luck!

The brochure is a good start. I wonder if Ericsson might hold the GEC archives as I think they are the current successor of the company. Failing that, Marconi before them. I bet there's a wadge of design documents sat waiting on a shelf for you somewhere :) .

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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Till Eulenspiegel » Sun Sep 30, 2012 7:33 pm

Hi Brian,
Thank goodness it's you who has won the cabinet. I should be in the shop this week so I will take some pictures of the chassis of the BT9121.

Till Eulenspiegel.
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Brianc » Sun Sep 30, 2012 7:39 pm

Thanks guys. When I get the cabinet, I'll see if I can make some sense of the fittings that are left. Hopefully, the chassis mounts will be either threaded bushes or some sort of counter-bored holes which took rubber washers rather like the HMV 800 chassis mounts. I will also look for witness marks where the brackets were. This cabinet was rescued from an Attic. The builders rescued the cabinet because they recognizable it as a piece of furniture. I wonder if they skipped the chassis because they were not recognizable as anything.
Cheers
Brian
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby IJK2008 » Sun Sep 30, 2012 7:57 pm

Hi Brian

Glad to hear the cabinet is in good hands.

It make take a while but I bet you get there.

Ian
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Murphyv310 » Sun Sep 30, 2012 8:09 pm

Excellent news Brian.
I can get a good nights sleep with the knowledge that its in safe hands :grin:
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Katie Bush » Sun Sep 30, 2012 8:19 pm

Thank you Lord for prayers answered...!

I'm glad it came to someone with the skill and desire to recreate the original innards.. I was having nightmares about that cabinet ending up as a wine cabinet or a "retro" (you know, the more I hear that word, the more I hate it) housing for some hideous LCD TV, or worse still, some nasty amplifier with an MP3 player stuck on the end of it :mrgreen:

Somewhere, I have a GEC table top radio, and a GEC radiogram, of approximately WW2 period, but I haven't seen either in years, and I doubt if they'd be what you're looking for.. It's a pity you don't have any pictures or sketches of the radio chassis.

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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Michael Watterson » Sun Sep 30, 2012 8:31 pm

:thumbl: A vote of Moral support across the Irish sea. Nothing else I'm likely to be able to do.
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Till Eulenspiegel » Sun Sep 30, 2012 8:56 pm

Two pictures of the still not restored chassis of my BT9121.
Note the compact timebase unit.

Till Eulenspiegel.
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91211.jpg
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Brianc » Sun Sep 30, 2012 9:55 pm

Hi Till
Do you have the schematic for the 9121? The 8161 had 22 valves including the radio chassis. I counted 19 on your chassis which leaves only 3 for the radio chassis. That could be FC, IF and 1st audio but would mean strange switching for the power supply for radio only! These combined radio/TVs normally have 2 mains transformers to simplify this but the 9121 wouldn't show this which probably means that the chassis are not too similar. The layout of controls on your TB chassis also look too complicated for the 8161 with 7 controls whereas from the brochure pictures, it looks as though the 8161 has only three but there seems to be a little sub-panel which could hold the "minor" controls. This is going to be real detective work!
Cheers
Brian
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Till Eulenspiegel » Sun Sep 30, 2012 10:05 pm

Hi Brian,
I have a good deal of BT9121 info. I'll send you copies.
Another complete BT8161 does exist and I know the guy who owns it. I'll look back to my old emails in 2003/4 and try to contact him. He was very helpful when I was doing the cabinet reconstruction of the BT9121.

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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Brianc » Sun Sep 30, 2012 10:30 pm

Wow! That's good news, Till. Let's hope that he can help us.
Presumably you have pictures of the innards of the 6122 which you did the cabinet for - I would like to see those as well if you have them.
Cheers
Brian
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Till Eulenspiegel » Sun Sep 30, 2012 10:42 pm

Hi Brian,
I've just sent an email off to the 8161 owner. Let's hope I receive a reply. He could be using a different email adress now.

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Re: Recreating the GEC 8161 Mirror Lid TV

Postby KeithW » Mon Oct 01, 2012 7:24 am

Till Eulenspiegel wrote:Another complete BT8161 does exist and I know the guy who owns it.


Let's hope and pray that it's not the same set.

Keith
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Till Eulenspiegel » Mon Oct 01, 2012 10:18 am

Hi Keith,
I think that the other set is the 10 X 8 picture model BT8121, uses the 12 " CRT.
The CRT in the BT8161 must have a 15 inch diameter, even larger than the tube used in the Cossor 137T.

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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Brianc » Mon Oct 01, 2012 10:56 am

Yes Till, the 8161 uses a 15" tube giving a picture of 13.5" x 12". The 9122 uses a 12" tube with a picture size of 10" x 8". The height of the 8161 is 6.25" greater than the 9122 which shows how much longer the 15" tube is.
I got confused between the 9121 which you are restoring and the 9122 which is the mirror lid set so the pictures I asked for won't be that useful - sorry about that!
Cheers
Brian
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby KeithW » Mon Oct 01, 2012 11:26 am

I've just been checking through my magazines, brochures etc. Some pictures of the upright 1936 GEC models but nothing else that would help you Brian, I'm afraid.

Keith
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Brianc » Mon Oct 01, 2012 11:33 am

Thanks for looking Keith.
Cheers
Brian
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Till Eulenspiegel » Mon Oct 01, 2012 11:10 pm

Circuit diagrams of the GEC BT8161 and the GEC BT912. Although the two chassis are similar there a few noteworthy differences. Both are superhets operating with low IFs. In the TV only receiver 9121 the RF amplifiers and frequency changer are on the vision chassis section. In the more higher specced up 8161 it would appear that the television early stages are actually on the "A" chassis, the radio receiver section. We'll have to do more research to confirm that.
The vision demodulator in the 8161 is of the full wave type, which is desirable because of the very low intermediate frequency and the large 15" CRT. The much cheaper BT9121 has a simple half wave vision demodulator.
So it would seem that the main differences are in the signal circuits. The timebases and vision power supply arrangements are similar between the two chassis.

Till Eulenspiegel.
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Duke Nukem » Tue Oct 02, 2012 7:09 am

What's the record for the highest number of windings on a single mains transformer ? The GEC sure looks like a good candidate !

BTW, shouldn't the 8161 have a 16" tube not 15" ?

TTFN,
Jon
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Michael Watterson » Tue Oct 02, 2012 7:42 am

An AVO valve tester must be a contender
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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Till Eulenspiegel » Wed Oct 03, 2012 9:55 pm

More thoughts about the GEC BT8161 TV and radio receiver. The vision IF in the TV only BT9121 is 6Mc/s, the sound is 2.5Mc/s.
However I am becoming of the opinion the the vision IF in the BT8161 is even lower, as low as 4Mc/s. That's very low indeed but is worth bearing in mind that early Murphy TVs used a very low vision IF, in the V58A it was 4.25Mc/s. The sound was 0.75Mc/s.
I have no information for the front end of the radio, but it is most likely that the IF is about 500Kc/s, a bit higher than than the standard frequency of 465Kc/s.
Operating 405 television on a low carrier frequency was used by Rediffusion on the TDUK2 two channel wired system. One channel was 4.95Mc/s and the other 8.45Mc/s. The system frequency receiver used a full wave vision detector to reduce the posibillity of carrier dot pattern being apparant when the lower frequency was selected.
The GEC BT8161 has a full wave vision detector.

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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Till Eulenspiegel » Wed Oct 03, 2012 10:12 pm

News Flash: Found the circuit diagram of the radio part. The so called A chassis.

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Re: Recreating the GEC 8161 Mirror Lid TV

Postby Refugee » Wed Oct 03, 2012 10:37 pm

Would this be a possible temporary chassis while the bits are being collected for a full reproduction.
http://www.vintage-radio.net/forum/show ... hp?t=88718
It would appear to be an AC/DC set that has been converted with an isolating transformer for use with a radio and gram.
They are doing the same as you on a slightly more modern set.
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