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Sets, Parts and Service Information Wanted (private buyers only, no swaps) If you need help obtaining components, sets or equipment, post a message here. Private buyers only - no traders. No swaps.

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Old 15th Feb 2018, 7:44 pm   #1
NANETTE
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Default Sinclair Z12 wanted!

For some strange reason, I am looking for a Sinclair Z12 amplifier.
Fortunately, I do not mind if it is not working. In fact a cheap duff one would be preferable to an expensivce working (rare?) one! David
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Old 15th Feb 2018, 8:06 pm   #2
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Default Re: Sinclair z12 wanted!

A schoolfriend of mine had a pair of those in his homebrew stereo. AFAIR, they were quite passable, but sadly they went the way of all things. A couple of years later we built a mobile disco amp with a pair of Z50's and a PZ8 PSU. Talk about asking for trouble....
Oops, drifting off topic again.
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Old 16th Feb 2018, 12:15 am   #3
nicam49
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Default Re: Sinclair Z12 wanted!

They were very popular with ice cream vans for their chimes as they operated from 12volts. Quite a successful product from Sir Clive.
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Old 16th Feb 2018, 5:19 am   #4
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Default Re: Sinclair Z12 wanted!

Did a mobile PA for the election in 1966 with one, and a carbon mike!
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Old 16th Feb 2018, 7:31 am   #5
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Default Re: Sinclair Z12 wanted!

Quote:
Originally Posted by NANETTE View Post
For some strange reason, I am looking for a Sinclair Z12 amplifier.
I don't think it is strange at all. I can see why you are interested in these. I think it was pretty clever the way Sinclair organised the output stage with two pnp transistors, but no driver transformer (split or otherwise) and no output transformer. Plus they seem charming to me and capture an era where amplifier modules were coming into their own. I hope you can find one. If not, it would be a good project to build a replica as all the parts are still available. Perhaps somebody has a photo of the original pcb detail.
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Old 16th Feb 2018, 3:50 pm   #6
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Default Re: Sinclair Z12 wanted!

Useful info here -
https://www.vintage-radio.net/forum/...ad.php?t=67468
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Old 16th Feb 2018, 7:32 pm   #7
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Default Re: Sinclair Z12 wanted!

There is some useful information about the Z12 on this thread - www.vintage-radio.net/forum/showthread.67468
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Old 17th Feb 2018, 11:51 am   #8
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Default Re: Sinclair Z12 wanted!

Quote:
Originally Posted by Argus25 View Post

I don't think it is strange at all. I can see why you are interested in these. I think it was pretty clever the way Sinclair organised the output stage with two pnp transistors, but no driver transformer (split or otherwise) and no output transformer.
The output stage looks like a conventional quasi-complementary one of the period to me.

Dinsdale pops up from the depths of the forgettory?
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Old 17th Feb 2018, 12:06 pm   #9
barrymagrec
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Default Re: Sinclair Z12 wanted!

The design is very similar to a circuit my Dad got from Mullards Mitcham when he was working there in 1960. I think it is basically H.C. Lin from 1956.

The Tobey - Dinsdale amplifier was one of the first decent transistor designs, Wireless World November 1961.

Last edited by barrymagrec; 17th Feb 2018 at 12:08 pm. Reason: Corrected date
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Old 17th Feb 2018, 12:58 pm   #10
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Default Re: Sinclair Z12 wanted!

There was a Z12 lookalike amplifier in the October 66 PW but rated at 5W rather than the Sinclair 12W. I've also added the Z12 advert from the same issue.

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File Type: pdf PW 5W amp.PDF (484.3 KB, 49 views)
File Type: pdf Z12 ad.PDF (307.5 KB, 38 views)
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Old 17th Feb 2018, 2:40 pm   #11
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Default Re: Sinclair Z12 wanted!

Quote:
Originally Posted by barrymagrec View Post
The output stage looks like a conventional quasi-complementary one of the period to me.
Yes and it is a good example of how creative early transistor circuit designers had to be, when they were stuck with PNP power transistors and wanted to avoid transformers. Designing with one polarity part remains a major limitation with valves. At least NPN germanium signal transistors were about fairly early.

Germanium NPN audio output transistors turned up in the end, like the AD161 for a true complimentary, but they were pretty limited and were not nearly as good as the silicon devices which followed.

Probably the most revolutionary transistor of all time, to turn up in the early '60's was the 2N3055. But they became so common and out spec'd by modern devices that few people are impressed with them any more, but given the history, I still really like them.

Does anyone know what the original NPN transistor T6 was in the Z12 ?

Last edited by Argus25; 17th Feb 2018 at 2:47 pm. Reason: question
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Old 17th Feb 2018, 6:01 pm   #12
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Default Re: Sinclair Z12 wanted!

I wouldn't put any effort into trying to find type numbers for the transistors in Sinclair amplifiers, they were almost certainly all out-of-spec dropouts. So they weren't really any particular type. The best that can be done is to look at what they're doing and to pick something adequate.

David
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Old 17th Feb 2018, 6:37 pm   #13
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Default Re: Sinclair Z12 wanted!

All fascinating and interesting info BUT, you may remember the original post was that I wanted to BUY one - working or not. David
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Old 17th Feb 2018, 7:32 pm   #14
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Default Re: Sinclair Z12 wanted!

Quote:
Originally Posted by Radio Wrangler View Post
I wouldn't put any effort into trying to find type numbers for the transistors in Sinclair amplifiers, they were almost certainly all out-of-spec dropouts. So they weren't really any particular type. The best that can be done is to look at what they're doing and to pick something adequate.
I've heard a lot of earlier Sinclair products used rejected components fudged so they would work.

I wonder how well something made from the schematics & decent quality parts would work for the Sinclair kits.
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Old 17th Feb 2018, 9:29 pm   #15
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Default Re: Sinclair Z12 wanted!

Assuming that the rumours are true, probably not a lot differently. All the devices used would have been OK for that particular position or application, just not for other aspects of their full spec.
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Old 17th Feb 2018, 10:59 pm   #16
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Default Re: Sinclair Z12 wanted!

Quote:
Originally Posted by Radio Wrangler View Post
they were almost certainly all out-of-spec dropouts.
David
I had no idea that Sinclair was all about passing off poor quality parts. I also read on the other thread that their IC output amp version used reject Texas Ic's. That is all very disappointing, I always thought that they were supposed to be high quality, the marketing/advertising looks like that. I guess I'm too trusting. I never got to evaluate any of these amplifiers when they came out, as they were too expensive at the time for me to afford and likely I was too young and inexperienced to be able to evaluate them properly anyway.
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Old 17th Feb 2018, 11:35 pm   #17
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Default Re: Sinclair Z12 wanted!

Shall we just say 'strongly reputed'. I was asked to fix quite a number of Sinclair amplifier modules in the sixties and early 70's, but I politely declined. I'd been warned off the things by several people, and the adverts seemed a bit more 'optimistic' than was usual back then.

If David (Nanette) finds one, I suspect he'll have to fix it and the schematics posted earlier could be a big help, unless it's just for a static display?

David
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Old 18th Feb 2018, 1:54 am   #18
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Default Re: Sinclair Z12 wanted!

What's the strange reason David? I have one [somewhere] I think. It was the left channel of my Hi Fi system in the early seventies, the right was via a tape recorder with a PA function. The speakers were from a blown PA stack courtesy of my brother's group-home made four channel sound [two car speakers] never had better! I still have the correspondence with Sinclair Cambridge who helped me to stabilise the Z12 with additional de-coupling capacity viz the psu. Is it a coincidence that you are in Cambridge? Clive Sinclair had a good "grasp" of SIRAlan Sugar all those years ago

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Old 18th Feb 2018, 8:21 am   #19
NANETTE
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Default Re: Sinclair Z12 wanted!

DAVE - You have seen through me. Yes I worked at the River Mill in St Ives and was fond of Sinclair products and the real Cambridge Audio which came later. I do vividly remember, when I returned my faulty Executive calculator seeing a JCB shoveling the returns into a skip.
Yes I do want one for display, so if you can find yours I would be appropriately grateful. David
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