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Old 23rd Oct 2015, 12:10 pm   #1
dragonser
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Default Decca varitune Colour portable

Hi,
I just took some photos of a Decca portable colour set from I would guess the mid 1970's ?
Anyone know more about it ?
I haven't dared to power it up yet, and if I do I will be very,very careful using a variac as it hasn't been used for a long while...
Looking inside I "think" it may be a prototype ? as the pcb layout doesn't seem to have the etch resist I would expect.
thanks for any suggestions.
regards Peter B
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Old 23rd Oct 2015, 12:17 pm   #2
bobbyball
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Default Re: Decca varitune Colour portable

"70" series if I remember correctly
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Old 23rd Oct 2015, 3:27 pm   #3
merlinmaxwell
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Default Re: Decca varitune Colour portable

Proper little telly, I like the tube base sepperation. Any chance of a picture of the other side of the PCB?
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Old 23rd Oct 2015, 3:58 pm   #4
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Default Re: Decca varitune Colour portable

Introduced late 1979. Excellent set. The switched mode power supply was a bit complex though.
Still got a few parts for them.

DFWB.
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Old 23rd Oct 2015, 6:12 pm   #5
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Default Re: Decca varitune Colour portable

Hi,
thanks to everyone who has replied. I've not seen a Decca Portable before.
a couple more photos included.
. the label does indicate it is a prototype set....
I will take some more photos as requested.
regards Peter B
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Old 23rd Oct 2015, 7:05 pm   #6
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Default Re: Decca varitune Colour portable

Very interesting. I recognise the cabinet styling with it's distinctive base and I'm sure the versions I remember had a simple rotary tune dial.

On your set it seems you have the lower three buttons as presets (hence home-made labels) whilst pressing the top button presumably activates the rotary tuner above it (with it's knob missing), hence ''Varitune" I guess. A rather over-elaborate system I would have thought, with no particular advantage!

Nice set though, well worth preserving (as are most 80s crt colour portables now I should think)

Steve
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Old 25th Oct 2015, 12:12 am   #7
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Default Re: Decca varitune Colour portable

Hi,
here are some more photos of the insides, as requested.
The main red smoothing cap I'm guessing may need replacing ?
regards iPeter B
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Old 25th Oct 2015, 11:49 am   #8
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Default Re: Decca varitune Colour portable

Hi there
That's an interesting set. It ust have been pretty close to production. As far as I remember the final version had a big tuning wheel for the 'top' channel. It was a good idea, as if the set was used in, say, a mobile home then the band could be swept to find the local channels without wearing the small preset buttons out which is easy to do, especially as the small tuning tool would be lost and the customer would apparently try to use a spade!
The 70 series was pretty good. The PSU was a little complex with an odd little driver transistor in the base circuit that needed to be replaced with the correct part - I think Decca supplied a more robust replacement.
A word of warning - take care you don't snap any of the tiny control shafts - we've all done it! Well, I have...
Now down to your set. I suspect it hasn't been used too much, and I'd think the main smoother is OK - it's a good relaible part. Snip the mains filter capacitor out (it's across the mains input very close to the switch, probably grey, around 0.1 uF and around 400v) - the set will work without it. The more cautious on the forum will suggest using a lamp limiter in series with the mains to reform the capacitors and save any alarming foreworks. Others, of which I am one, cheerfully switch the thing on, but we are reckless and should be kept at a safe distance.
Before powering up it might be an idea to check the fuses are OK and then check the chopper transistor and line output transistor for shorts, then disconnect the input to the tripler. Looking at the condition of the TV I don't think you'll have any unpleasant surprises, and the CRT should be like new.
Good luck!
Glyn
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Old 25th Oct 2015, 12:56 pm   #9
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Default Re: Decca varitune Colour portable

Definitely a "long distance portable" then! Makes sense if you were going to take it on your travels through the coverage zones of different transmitters, I suppose, giving you the best of both worlds: presets at home, searchability on the road.

Thinking back to caravans as per my other thread, my Grandad eventually sold his little one and bought a static caravan sited near Barmouth, on the pretty Snowdonia coast. That had a Philips mono telly with 6 channel presets that pushed down rather than in. Sometimes he and my Nan would take their colour set over to Wales. It did not need to be re-tuned from Sutton Coldfield to the local transmitter, though BBC1 and ITV would swap places!
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Old 26th Oct 2015, 8:32 am   #10
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Default Re: Decca varitune Colour portable

Quote:
Originally Posted by dragonser View Post
The main red smoothing cap I'm guessing may need replacing ?Peter B
I doubt it, it all looks like new. I don't think that this set has had much use. Its only in the G11 that you have to take the red ones out.
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Old 26th Oct 2015, 12:51 pm   #11
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Default Re: Decca varitune Colour portable

I think that I may know someone who designed at least part of this set. He was a former work colleague who worked at Decca in the mid to late '70s, and while there he designed an IF strip for a colour portable that was the first to use surface acoustic wave filters. His background was in radar where SAW filters had been in use for several years by the late '70s.
When we last discussed this, he couldn't remember the model name of the particular TV.

John
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Old 26th Oct 2015, 12:58 pm   #12
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Default Re: Decca varitune Colour portable

Yes, AFAIK, the 70-series was one of the first to use a SAWF, as mentioned in Television at the time.

Another variant of the 70-series chassis discussed here: https://www.vintage-radio.net/forum/...d.php?p=741109
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