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Old 10th Aug 2017, 9:09 pm   #1
matspar
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Default And the next one! a GEC BT2147

Had a look inside my latest wreck tonight! doesn't it look nice!

All present and correct except the B36 audio output valve, which someone pinched many a year ago by the look of things.
The shadow mask is in a state and has 'sank' a bit over the years. Probably going to be a challenge to correct this! It was totally fused to the cabinet front and took about half an hour trying to (carefully!) separate the two with a knife blade before I could persuade the chassis out. I don't think this has ever been dismantled in its life and it's totally original in every respect.

What do you think my chances are with the tube and the lopt??!! Anything else I can usually overcome. I've read about the shortcomings of these 6505a crt's. I've wiped its neck clean and its not cloudy. The base is tight and the heater is intact. It will be interesting to eventually find out.

So this weekend I't'll be a very careful cleaning session and hopefully I'll find a valve and all the capacitors that will no doubt be needed!!

Matt
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Old 10th Aug 2017, 10:04 pm   #2
Lloyd 1985
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Default Re: And the next one! a GEC BT2147

Quote:
Originally Posted by matspar View Post
doesn't it look nice!

Matt
It does indeed! The mask is going to be fun to sort out, and a problem that can only get worse with age. More and more sets are turning up with gooey mask's now, even my TV62 is starting to go. The only thing I can think of is to make moulds of good masks while they are still about, and cast new ones out of some sort of silicone rubber.

Good luck with the set! It's another that I've had on my wish-list for many a year

Regards,
Lloyd
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Old 10th Aug 2017, 10:45 pm   #3
rambo1152
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Default Re: And the next one! a GEC BT2147

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Originally Posted by matspar View Post
The shadow mask is in a state
I suppose it is a mask, and it casts a shadow.

Graham.
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Old 11th Aug 2017, 6:03 am   #4
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Default Re: And the next one! a GEC BT2147

Great performers. The only let down is the GEC triode tube that tends to go O/C, low resistance heater and low emission. You probably have one of the good ones!
The B36 is the line and frame oscillator. It can be replaced by a 12SN7GT. I have a few spare B36's if you would like one.
The sound output valve is the little N37. John.
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Old 11th Aug 2017, 7:46 am   #5
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Default Re: And the next one! a GEC BT2147

You may find it is worth while turning the mask upside down, the weight of the glass will then be on the better top edge that hasn't been weight bearing all it life.
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Old 11th Aug 2017, 12:45 pm   #6
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Default Re: And the next one! a GEC BT2147

Hi Matt,
I'm not sure I like them as much as John (HCS). The circuit design is fine, but the components are not so good...
I never tried re-stuffing the brown GEC capacitors, but it should be worth a try.

Points to look out for:-

The CRTs are usually bad, I fitted an MW22-18 in my set, taking the A1 supply from the boost capacitor.

The B36 is a weak point, but I managed to find a good one. The 12SN7 that John suggests is much better.

The U31 is also a weak point. I've had such a bad run with these that I won't use one now. Every time they develop a heater-cathode short the boost capacitor fries. I used a PY33 in my set.

The line output transformers can give trouble. Definitely worth drying out the overwind by passing a small current through it.

The set has those nasty sliding preset pots, but the ones in my set are just about ok.

The metal rectifier often goes leaky.

However the RF unit does not give any trouble.
Once restored these are good sets.

Hi Freya,
I might try that on my own set. I did wonder if the recent sagging of the mask on my set was due to me using turps based cabinet cleaner in the same room.

Cheers
Andy
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Old 11th Aug 2017, 1:37 pm   #7
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Default Re: And the next one! a GEC BT2147

A shadow mask is what is inside a colour TV tube.
Your item is just a mask. Hence the joke in post 3.
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Old 11th Aug 2017, 4:57 pm   #8
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Default Re: And the next one! a GEC BT2147

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Originally Posted by beery View Post
I never tried re-stuffing the brown GEC capacitors, but it should be worth a try.
Have you ever tried restuffing a treacle toffee?

Good luck with this one. If you need any valves for it, don't be too timid to ask me. Regards, John.
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Old 11th Aug 2017, 7:54 pm   #9
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Default Re: And the next one! a GEC BT2147

A lovely looking set. I wish I had your luck at finding that. Good luck with the restoration.

Regards, Robin.
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Old 11th Aug 2017, 9:04 pm   #10
matspar
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Default Re: And the next one! a GEC BT2147

Thanks all! plenty of food for thought. Thanks for the offer of valves John. I'm pretty sure I've got a 12SN7 up in the loft but I will give you a shout if not. Andy has filled me with dread but I'll keep on the positive side! I would love to get this working.
I suppose it'll be 50/50 if that tube is any good. I might be in with a chance, but I think the first power up will be a way off yet! Will let you know how I get on

Matt
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Old 12th Aug 2017, 7:21 am   #11
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Default Re: And the next one! a GEC BT2147

Don't go mad recapping and scrubbing everything. Power supply first followed by the line timebase. You should then be able to visibly check the tube. J.
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Old 12th Aug 2017, 10:19 am   #12
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Default Re: And the next one! a GEC BT2147

Hi Matt,
I don't mean to put you off.
It is worth the effort as you will end up with a great looking and reliable set when it is finished.
As John says, take it one step at a time. A chassis like this which has the tube mounted on it makes easy to test as you go. You can lear a lot by changing one capacitor at a time.
Keep the old brown GEC caps for a rainy day when you might want to rebuild them. They are only found in GEC equipment sets.
The low nF value decoupling caps in the receiver unit are ceramic and usually give no trouble. I think I only changed the waxies in mine and there is only 2 or 3 of them.

John, I'm going to see if I can rebuild a treacle toffee capacitor!

Cheers
Andy
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Old 12th Aug 2017, 12:06 pm   #13
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Default Re: And the next one! a GEC BT2147

There's a bashed up example of the 12" version of the BT2147 upstairs.
Let's find out if it is any good?

DFWB.
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Old 12th Aug 2017, 12:13 pm   #14
D Cassidy
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Default Re: And the next one! a GEC BT2147

Hello DFWB.
I very much like looking at your wreck projects, your commitment is excellent and shows huge dedication.
I also was watching your thread 're the "green" cabinet, I'd like to have seen how you would have tackled that one.
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Old 12th Aug 2017, 2:15 pm   #15
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Default Re: And the next one! a GEC BT2147

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Originally Posted by FERNSEH View Post
There's a bashed up example of the 12" version of the BT2147 upstairs.DFWB.
Is that the BT5145 David?

I have a couple of BT2147s, one with a duff tube and the other, with a good tube awaiting restoration.

I also have a superhet version of the BT5145, the BT5146 in good working order. The circuit and design remained much the same with GEC models right up to the end of production with the BT336 series [1961] John.
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Old 12th Aug 2017, 2:29 pm   #16
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Default Re: And the next one! a GEC BT2147

"There's a bashed up example of the 12" version of the BT2147 upstairs." Hi John, It's a BT5144.
Hi D. Cassidy, A wreck project? Just check out that chassis metalwork.

The B36 is not a good valve and as suggested the American 12SN7GT is an excellent replacement. This valve is essentially two 6J5 low impedance triodes in the same bulb.
The characteristics of the 12AU7/ECC82 are very similar. Has 6.3volt 0.3amp heater Needs B9A valveholder. OK to use but a 21ohm resistor should be inserted in the heater chain.

DFWB.
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Old 12th Aug 2017, 3:37 pm   #17
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Default Re: And the next one! a GEC BT2147

Hello Matt,
A bit of encouragement here from David and myself.

I restored a BT5146 back in 2011.

http://www.vintage-radio.net/forum/s...ght=GEC+BT5146

It has a lot in common with the BT2147 and may be a guide to get you started.

I dug it out a few moments ago. You can see the similarity from the back view.

David's BT5144 is almost identical to yours other than the CRT and the cabinet.

The 2147 and 5144 are both TRF RF plates.

The tube troubles were sorted by 1951 as you can see from the picture. John.
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Old 12th Aug 2017, 8:21 pm   #18
matspar
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Default Re: And the next one! a GEC BT2147

These look great John and David, I am a bit of a GEC fan. I've got several bakelite radio's as well as a couple of their tellies now.
So, todays update.

I got the filthy BT2147 on the bench and before I knew it out came the WD40 and it was soon all in bits. Lopt cover off, all the valves and tube out and bits and pieces everywhere. It was just too dirty to start any testing or replacing anything. A lot of the wiring is brittle and a few broke off as I was cleaning.

I've got it in a cleaner state now so work can commence once I've gathered up all the bits I need. I managed to get the shadow mask off the face of the tube in one piece. Its pretty bad but I reckon just about saveable. I've put this to one side now. I will refit it upside down when the time comes as recommended!
I've put the tube back in place using an old leather belt and a few turns of red insulation tape as a cushion for the rim band. Has clamped it all up nicely.

Made a few discoveries also. 2 more valves (a pair of Z77's) were missing from the lower deck. I've fitted 2 new EF91s in their place. I've found a good used 12SN7 to replace the B36.
The EHT rectifier (a tiny U37) has turned white and looks full of air so this will have to be replaced as well.
One of the dropper sections is o/c
The width slider core was broken and jammed. I got all the bits out and repaired it using a steel core from a slider on a scrap Pye V4 chassis. The original was ferrite - will this be ok?
I can't see any aerial connection on the chassis. The Trader sheet that I'll work from says there is a coaxial socket on the lower chassis but there isn't! there is what looks like a dipole socket but there is nothing the other side. The last 2 pics show what I mean. Any thoughts on this?!

That's about it for today! Thanks all for your advice. John I'm about to have a good read of your thread on your BT5146
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Old 12th Aug 2017, 8:24 pm   #19
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Default Re: And the next one! a GEC BT2147

And a few more
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Old 12th Aug 2017, 9:03 pm   #20
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Default Re: And the next one! a GEC BT2147

Has the CRT in the BT2147 a flat faceplate? The GEC 12" CRT manufactured by GEC in the BT5144 has one.

DFWB.
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