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Forum 141

B&W TV Ultra 6816 Thorn 1590 Chassis

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WayneD
(@wayned)
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Thought I'd try to get this early 70s Ultra 6816 working, it was very kindly donated by Chris @crustytv and this is the first chance I've had to look at it.

Screenshot 20231025 183405 Gallery

Very neatly laid out chassis: 

Screenshot 20231025 183334 Gallery

The tuner looks like it might be a bit beyond saving though. The circuit seems pretty straightforward though, I might just tap into the video signal as it's an isolated chassis.

 
Posted : 25/10/2023 5:49 pm
Lloyd reacted
crustytv
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Posted by: @wayned

The tuner looks like it might be a bit beyond saving though.

Absolutely not true! The Thorn tuner is totally serviceable.

It was working fine, but admittedly I'd not turned it on in at least 10-years. If it's not latching, this is a known problem with the plastic washers rotting (see below example). I've had this fault on every Thorn tuner, and I've repaired every single one of them.

If you'd have looked on the main website there are loads of hints and tips, here is how you fix the tuner

https://www.radios-tv.co.uk/vintage-electronics-blog-forum/repairing-a-brcthorn-tuner/

Posted by: @wayned

I might just tap into the video signal as it's an isolated chassis.

In light if of what I detail above, it's totally unnecessary.

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Posted : 25/10/2023 6:10 pm
WayneD
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@crustytv aha! I just looked at the tuner, saw lots of springs and kinda thought "Aaaggghhh!" but if it's repairable then that's fab.

I had done a search for "Thorn 1590" as well as a few other terms, but I didn't realise that the tuner was common across different models.

 
Posted : 25/10/2023 7:18 pm
WayneD
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Ok, I've managed to get BBC 2 to work on the tuner: 

20231026 151312

Kinda precarious though! It really needs dismantled and repaired but for now it'll do as long as I can tune the RF modulator in.

20231024 210434
Screenshot 20231026 210314 Gallery

Bit of tweaking with the colour bars and that's a fantastic picture! Although I've noticed that it really doesn't like the colour burst of a PAL signal for some reason. I couldn't get my PS3 to work via the RF modulator at all however I tried it through the JVC HR-7350EK switched to black and white and this works really well:

Screenshot 20231026 210435 Gallery

The picture seems to have less interference when playing a VHS tape too. I noticed something similar with the Rediffusion Guildford. 

Oh yeah, whilst trying to get one of the channels to latch I started picking up Russian shortwave radio! 

😱

 
Posted : 26/10/2023 8:27 pm
Lloyd and Cathovisor reacted
sideband
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Must be something around 6Mhz trying to get through the sound I.F.....

 
Posted : 26/10/2023 8:35 pm
WayneD
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@sideband there's a lot of increased Russian and Ukrainian activity on the shortwave band at the moment, for certain reasons. I don't think I've heard stations this strong since the end of the Cold War.

 
Posted : 26/10/2023 8:43 pm
Jayceebee
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Superb little sets which sold in huge numbers. The tuner was used in all  mechanical tuning sets from the late 1400 series to the 8500. The ones destined for CTV use had a varicap diode in the local oscillator for AFC from the IF stage. 

While you have the tuner apart, with a high wattage iron remove the thin metals strips which earth the tuning gang. Clean off the grease, retention the fingers and refit using a minimum of solder. One of the strips is backed with a thin piece of plastic tape, don't worry to much if it shrivels a little.

I can think of only one UK mono TV that had a 4.43MHz subcarrier notch filter in the video stage, that was the RBM A816 chassis.

John.

 
Posted : 26/10/2023 8:52 pm
WayneD reacted
WayneD
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Posted by: @jayceebee

don't worry to much if it shrivels a little.

To be fair it has been really cold recently and... oh you mean the piece of tape! 😳

 

 
Posted : 26/10/2023 9:02 pm
Michael Dranfield
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Got a few 1590s in various cabinets styles but what I would really like is the valve version, can't remember the chassis off the top of my head, was it 1580, it was in the same cabinet I think as the transistorised set. 

 
Posted : 04/11/2023 6:45 pm
WayneD reacted
Jayceebee
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1580 chassis is correct. Only available in two models, the Ferguson 3805 and Marconi 4805. Same cabinet as the 1590 except the Ferguson model had vertical speaker grille slots. 

John.

 
Posted : 04/11/2023 7:08 pm
WayneD
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@jayceebee was the 1580 chassis dual standard?

 
Posted : 04/11/2023 7:57 pm
Jayceebee
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@wayned No UHF 625 only, but interestingly the line timebase is a very close copy of the 405 VHF 980/981 chassis. The IF strip has a lot in common with the 1500 and 1590/1591 but I don't think it used the printed coils.

John.

 
Posted : 04/11/2023 8:08 pm
WayneD
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The most recent Show 'n Telly episode featuring this very set: 

For some reason this has been blocked in "some territories" due to copyright. It's the few seconds of A Flock of Seagulls yet it has no problem with AC/DC, L7 or Red Dwarf 🙄

 
Posted : 15/11/2023 4:10 pm
slidertogrid and Lloyd reacted
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