Multibroadcast 7776 TV - what chassis?

[1100 man]

I'm trying to identify what chassis is used in the above set. I suspect it might be a Thorn 9600. I was hoping it was going to be a 9000 as I've been after one for ages! I can't find any information on the 'net or Thorn chassis guides for this model. It uses the same two button remote as the 9000.

How similar is the 9600 to the 9000? Is it still a PIL tube?

Many thanks for any information,

All the best
Nick

[jayceebee]

Hi Nick, yes it is fitted with the 9600 series chassis using a 110 degree PIL tube most likely an A56-611X. It does use SYCLOPS terminology but bears no resemblance to the technique used in the 9000, the PSU and line output stages are separate but the line drive is obtained from the chopper transformer.

A very good and somewhat over engineered chassis, reliable and capable of good results but often let down somewhat by the poor longevity of the RCA CRT.

John.

[Red to black]

I think it is a 9K6 (9600) the main difference between the 9K and the 9K6 is the former uses a 90 degree tube while the latter uses a 110 degree.

They both had Pil tubes and both used Syclops but there the similarities more or less end, the front end and signal/colour circuitry was very similar if not the same but the line timebase and PSU sections were very different, they do have a family likeness though.
The above is greatly simplified of course there will be a number of similarities and differences throughout.

Edit: cross posted with JC

[1100 man]

Hi John & RTB,
Many thanks for the swift response!

Is it possible that it could be a 9900 chassis? From the very few pictures I can find, the rear view of the set with the back on, looks the same for the 9600 or the 9900.
Would it be safe to say that if it was a 9600 it would be a 22" and if a 9900 it would be a 20"?
As far as I can find out, the 9900 used a 90 degree tube but different to the 9000.

Can you think of any other way of telling which chassis might be fitted from purely external photo's of the front and rear?

Cheers
Nick

[Red to black]

There was a 9800 chassis but this was mainly an update of the 8800 chassis with a diode split lopt and different psu with nearly all the sets voltages being lopt derived, it really had nothing in common with any other 9K series at all (no Syclops) except maybe the colour decoder part and some of the front end again.
The model number given earlier strongly suggests a 9K6 though.

Edit: The 9900 might have been the export version of the 9800, JC will no doubt clarify in due course he is an ex-Thorn man and I forget these days.

[jayceebee]

Hi Nick, if you are correct about set being a 7776 then it is most definitely a 9600. Externally I can describe the set as having a control panel with four horizontal sliders, the on/off button below and six silver touch buttons on the top of the cabinet. Internally a look at the bottom timebase board you will see a very substantial heatsink which runs along the full length of the rear.

See here for some pics of a 9600 https://www.radios-tv.co.uk/1977-ferguson-3734/

The 9900 was very similar to the 9000 but had changes to drive the Mullard AX51 CRT. One of the 9900 series chassis sets, a 9905 version here https://www.radios-tv.co.uk/1979-der-5511/

[1100 man]

Hi John,
You are obviously the man for Thorn identification! As you have probably guessed, it is a potential purchase. I've been after a 9000 for ages, but none have ever come my way. This one is not exactly local, so I was trying to work out what it was from the pictures. The seller was not confident enough to take the back off, but did confirm the model number.

It looks exactly as you describe with the horizontal sliders & power button below them. I can't see the top but assume the touch buttons are there. The tuning controls on the rear look to be the same as either the 9000 or 9600.

So I guess there is no doubt that it's a 9600 which is a shame! As I definitely never saw or sold any of these as ex rentals, my self imposed rules dictate I'm not allowed to buy it!

I bought a whole van load of those 9900's with grey fronts as 'untested' ex rentals years ago. They looked really smart and much newer that the standard DER 9000. I didn't realise then that 'untested' was a euphemism for totally f! Most needed tubes & triplers!
I stuck to 9000's after that and got good deals on workers which I was allowed to test myself to at least assess whether the tube was viable.

Many thanks for your help,

All the best
Nick

[jayceebee]

That is a shame. Is it anywhere near my part of the world? I'd love to have a 9600, although I don't have a lot of space they are quite a compact set for a 22".

Yes, the Mullard AX51 series CRT in it's A51-570X guise was not one of their finest products.

John.

[McMurdo]

I've got a multibroadcast-badged 9600, can't remember the model but it has the one-touch auto sweep tuning and the anodised touch tune button at the top with little holes where you put your finger to change channel, also full-feature ultrasonic remote.

When I first got it and tried it, the crt flashed over and took out all the sweep tuning and remote ICs, took me ages to get it working again. Quie a beast!

The CRT is rather tired though.

[jayceebee]

Hi Kevin, full ultrasonic remote and sweep tuning, I don't remember those. I'm intrigued, could you find the model number for me if possible? The only sweep tune sets I recall were all infra red using a Philips SAA5000 in the RCU and SAA5010 in the set, these were 9640 and 9650 versions if my memory is correct. The full ultrasonic models including the first teletext set featuring the TiFAX decoder I recall used the ITT SAA1024 and 1025 chips but all had manual tuning pots.

Sweep or ramp tuning for anyone who wants to know is what Thorn used before frequency synthesized tuning arrived. An ascending voltage between 0 and 30V was generated when the tuning button was pressed. The tuning processor then looked for valid video and sync pulses which then slowed the increase of the ramp voltage, it would then look for the characteristic S curve of the AFC voltage and then wind back to the centre point. The ramp voltage was then stored in memory but unfortunately it was volatile memory and required a 1.2V NiCad to keep it stored, this as with all sets of the time was a weak point with the battery either going flat or leaking and depositing electrolyte all over the PCB.

John.

[neil29]

I've got a 9650 chassis set that I've removed the battery from which was starting to leak. if anyone is interested send me a PM.




Cheers
Neil.

[Welsh Anorak]

I was never that keen on the 9600, probably because the few I saw had nasty faults. The chopper transformer (if you can call it that) was the case of one unpleasant problem - it didn't look guilty! They certainly did work well and owed much to the 9000 (and, oddly, the 4000) in design.
The 9800 was cheap and plasticky by contrast and looked like it was made to use up the 8000 series panels before the TX series arrived.

[McMurdo]

I'll have to dig my tv out from an old railway wagon at Dad's.

The tv had the rear tuning pot flap but there was nothing inside. The touch tune was under a flap at the front and when you pressed the button, a yellow LED flashed as it was sweeping.
I think I got the sweep tune ICs from Grandata. I borrowed the service manual from a local TV shop, came in a ring binder with a giant colour circuit diagram made out of some glossy paper. I had to fix an old photocopier so I could copy it as the shop wanted the manual back before the weekend.

[jayceebee]

Originally Posted by McMurdo

The tv had the rear tuning pot flap but there was nothing inside.

Other than four holes, you inserted a screwdriver to set the normal level of the Vol, Bri etc. This sounds very much like a 7242 but that was infra red not ultrasonic.

John.

[Welsh Anorak]

Wasn't that a TX10 in a fairly ugly cabinet? Easy to tune, though!