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Old 27th Oct 2021, 3:41 pm   #1
matspar
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Default Sobell T90 (1949) 9" table set

Good afternoon all,

Currently rebuilding this rusted wreck of a T90. 3 weeks in and I have stripped, de-rusted and fitted a replacement Ferranti CRT to replace the original and very low CRM92.

Now stuck on a bizzare front end fault. Good clear sound on CH4 but no vision. Weak, cogged, rolling and noisy off tune testcard on CH3.
I can't see this being a CH3 set but can't decide how it's wired or if the alignment has been messed with.

I have the very basic Newnes circuit which doesn't go into much detail. Ideally I'm looking for a copy of the factory manual for the T90/T91.

As far as I know a Trader sheet was never published unless anyone knows different!

If anyone can help with a copy of the manual it would be appreciated.
Kind regards
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Old 27th Oct 2021, 3:48 pm   #2
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Default Re: Sobell T90 (1949) 9" table set

A few more
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Old 27th Oct 2021, 4:23 pm   #3
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Default Re: Sobell T90 (1949) 9" table set

What an unusual set! Nice looking but a strange layout inside. Well it is to me.. You are making a great job of the restoration! I am sorry I cannot help with service info but I am sure you will get there!
Rich.
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Old 27th Oct 2021, 4:24 pm   #4
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Default Re: Sobell T90 (1949) 9" table set

Hello Matt,
This is a superhet that can be changed from channel 1 to channel 4 with minor component changes. It appears to be the oscillator well out of adjustment. I had this fault on a Ultra V470 and it turned out to be a very old solder splash on the oscillator coil.
original service info is very hard to find for the T90.
It may have been modified to work on an odd channel but I doubt it. Regards, John.
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Old 27th Oct 2021, 7:03 pm   #5
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Default Re: Sobell T90 (1949) 9" table set

Hello Matt

Lovely little sets. Mine has a very nice cabinet/back but came with the usual CRM 92 problems. I have replaced it with CRM93 a bit of "Faff" but well worth it.

I can't hope to reach your standards but I do my best with help from some of the "Old Lags" (term of endearment) on here - You know who you are. I copied all your mods and tips with my 1807HMV.

I have a photocopy of the T91 (almost identical to the T90) Sobell factory manual. If you would like a copy PM me with your address.

Regards Steve.
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Old 27th Oct 2021, 7:39 pm   #6
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Default Re: Sobell T90 (1949) 9" table set

Hello John,
Thanks for the hint. I will delve into the oscillator on my next attempt and see what's what. I'll give you a call as suggested if need be! thanks as always!

Rich, making good progress although there will be a lot of tidying up to do plus a cabinet refurbishment. It was a very derelict chassis on arrival!

Steve, PM sent! thanks for the very generous offer. This should certainly make light of things in due course!
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Old 27th Oct 2021, 9:02 pm   #7
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Default Re: Sobell T90 (1949) 9" table set

I once owned a Sobell T90, in 1961! Got talked into getting rid it.
"Why bother fiddling about with a nine inch TV set?" I was told.
Wish I hadn't took any notice of such suggestions.
The circuit diagram can be found in one of the Malloy and Poole TV servicing books.

DFWB.
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Old 28th Oct 2021, 9:19 am   #8
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Default Re: Sobell T90 (1949) 9" table set

The Newnes book gives the procedure to reset the front end for AP or SC. For AP make sure C102 is in circuit, C60 is short circuited. Note the anode end of L8 is disconnected for AP. Retune T6 oscillator for best sound vision balance.
C60 20pf. C102 5pf.

Hope this helps. John.
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Old 28th Oct 2021, 1:17 pm   #9
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Default Re: Sobell T90 (1949) 9" table set

Circuit diagrams show that the Sobell T90 was a well designed set.
Note the damper diode V19 heater has a separate winding on the mains transformer.
Last Sobell TV set to employ Mazda valves.

DFWB.
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Old 28th Oct 2021, 6:36 pm   #10
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Default Re: Sobell T90 (1949) 9" table set

Hi Matt,

You have a P.M.

Sorry I'm a little late to this thread!



Regards,


Adrian.
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Old 3rd Nov 2021, 1:06 pm   #11
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Default Re: Sobell T90 (1949) 9" table set

Marvellous news. I now have a very happy and up and running Sobell T90!

Big thanks to Adrian and Steve for copies of the factory manual which proved to be an enormous help, and huge thanks to John for assisting me with some of the missing valves at the very beginning of the project.

The T90 was found to be a CH3 receiver in the end (my only one) and after slightly adjusting the oscillator coil (T6) a very non-linear and cogged test card came into view. Replacing the sync coupling cap C42 smoothed things out but the Sobell was then found to be suffering from very poor frame hold. R55, 57, & 58 had shot up in value but didn't provide a cure. I tried another T41 thyratron (V14 frame osc) as the old one looked extremely tired and happily this locked the scan and also opened up the height excessively.

Frame linearity could be better. Dreadfully cramped at the bottom and no adjustment provided on the T90 however I have found the best compromise was to increase R59 (390k) to 1.5M and omit C46 (0.015uf)

This leaves a test card with a very slightly stretched centre but very stable and watchable. Would the frame lin have been perfect from new?

Plenty of tidying up to do now and the cabinet is going to need work, but I'm very pleased to have saved this rare little telly.
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Old 3rd Nov 2021, 1:52 pm   #12
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Default Re: Sobell T90 (1949) 9" table set

Great job Matt, picture no 3 is good, capturing those glowing valves, I'm sure the tele guys on here will love that, personally would scare me! But another piece of history kept alive.
Regards, Alan.
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Old 3rd Nov 2021, 3:13 pm   #13
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Default Re: Sobell T90 (1949) 9" table set

Nice one. A very rare and well built receiver. Channel 3 for a receiver of this age is unusual. Regards, John.
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Old 3rd Nov 2021, 7:55 pm   #14
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Default Re: Sobell T90 (1949) 9" table set

Well Done young Matt. I should mention that Adrian was kind enough to send me a copy of the the manual sometime ago. The best looking of all the Sobell sets IMHO (but to be honest it does not have much competition in that department)
Regards Steve.
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Old 4th Nov 2021, 1:20 pm   #15
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Default Re: Sobell T90 (1949) 9" table set

Brilliant job!
Rich.
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Old 4th Nov 2021, 5:53 pm   #16
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Default Re: Sobell T90 (1949) 9" table set

A great job, Matt!

Regards,

Adrian.
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Old 4th Nov 2021, 6:13 pm   #17
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Default Re: Sobell T90 (1949) 9" table set

A sweet little telly - I hope you do the cabinet proud. Well done - to-date!
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Old 7th Nov 2021, 1:48 pm   #18
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Default Re: Sobell T90 (1949) 9" table set

Your patience has paid off. What's that rectangular speaker?
Never seen anything like it. The closest I can think of are the infamous 8" x 2.5" elliptical "slot" speakers of the late 1950s....
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Old 15th Nov 2021, 2:06 pm   #19
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Default Re: Sobell T90 (1949) 9" table set

Quote:
Originally Posted by Edward Huggins View Post
Your patience has paid off. What's that rectangular speaker?
Edward a test speaker I quickly lashed up. A 50's Ferguson item if I remember rightly!
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Old 15th Nov 2021, 2:13 pm   #20
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Default Re: Sobell T90 (1949) 9" table set

After a week's work the cabinet has been restored to her former glory. The original finish was sadly too far gone so I ended up stripping it bare. Lots of historic woodworm flight holes to fill and a few days of waxing and French polishing carried out. All that's needed now is the reassembly!
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