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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 4th Jul 2023, 2:33 pm   #1
Julesomega
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Default Unidentified Fidelity '70s compact audio system

I have mentioned the chassis from this unit in the 'wants' forum a couple of times but it proved unsuitable. Recently the audio power devices proved unsuitable, by inspection of the number of pins, but to find out the device type number I'd have to pull it from the board, because I can find absolutely nothing on the 'web to identify the model, and without the cabinet I have no model number; the only clue is the legend "Integrated Circuit" on the front. The odd cut-out on the PCB looks as though it might have given clearance for the turntable deck. The speakers are external to the main unit.

Dating it is no problem, there are several components clearly date-coded: Stereo decoder SN76110N is dated 7415, the mains tfmr shows 00-7323, an electrolytic shows 23 75, so it was made some time after June 1975.

I fitted a few random knobs to make it more recognisable while I search through reams of Google Images, but the powerful Google Lens could only show a few images with a vague likeness. If it really is this rare I wouldn't want to part it out, just in case it might be of use to somebody.

Does anyone recognise this?
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Old 4th Jul 2023, 2:43 pm   #2
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Default Re: Unidentified Fidelity '70s compact audio system

Those amplifier modules, well the "hedgehog" heatsinks, look like the Sinclair IC12 ICs. Well I never did.
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Old 4th Jul 2023, 2:44 pm   #3
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Default Re: Unidentified Fidelity '70s compact audio system

It predates the BBC frequency rejigging in 1978.
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Old 4th Jul 2023, 2:50 pm   #4
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Default Re: Unidentified Fidelity '70s compact audio system

The audio amp ICs with the integral finned heatsinks, in a Fidelity of this era, are likely to be SN76013s. I did read somewhere on this forum that someone had made a connection between these and the Sinclair amp ICs before.

Unfortunately they were horribly unreliable in Fidelity units - again on this forum, I have seen it suggested that this was because the supply voltage they were run at in the Fidelity units was too high for comfort.
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Old 4th Jul 2023, 3:01 pm   #5
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Default Re: Unidentified Fidelity '70s compact audio system

The front panel bears quite a resemblance in terms of layout to the Fidelity 'UA3' record player / radio unit, which was a very common repair for me in the late 70s / early 80s and which definitely used those finned SN76013 audio amp ICs.

https://www.radiomuseum.org/r/fideli...aster_ua3.html

Unfortunately it's been so long since then that I can't recall the appearance of the chassis of the UA3, but I am sure the circuit diagram etc for the UA3 will be available from this website (top right of this page) or in the relevant issue of Radio and TV servicing, if you have those.

The most obvious difference is that there is no headphone socket on your front panel, so perhaps yours came from a unit with a more conventional radiogram form factor where it would be undesirable to have a headphone lead snaking in underneath the lid. That difference aside, it seems likely that your chassis is the same as or very similar to that of the UA3.

Edit: if you go to the website page linked above, where the initial image is of the front panel of the UA3, click on the left / right arrows next to the edges of the image to look through all of the available images of the UA3 unit. One of them shows a top down / component side view of the PCB which looks more or less identical to yours.

Last edited by SiriusHardware; 4th Jul 2023 at 3:09 pm.
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Old 4th Jul 2023, 3:30 pm   #6
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Default Re: Unidentified Fidelity '70s compact audio system

Les Lawry-Johns used to say that they ran within their specified supply voltage limits when both channels were working. But if one IC failed, perhaps because of an amateurish attempt at extending the speaker leads, the unregulated supply voltage would rise above the safe threshold, taking out the other IC too.

Love the UA3 pic on Radiomuseum of the unit's serial number label, showing the obvious pride that went into making these!

Back to yours... what a weird contraption. A radiogram with ICs!
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Old 4th Jul 2023, 3:31 pm   #7
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Default Re: Unidentified Fidelity '70s compact audio system

What does the lettering on the heatsinks say?
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Old 4th Jul 2023, 5:13 pm   #8
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Default Re: Unidentified Fidelity '70s compact audio system

Actually that does ring a bell (no pun intended, Steve). The heatsinks were non-removable so the IC part number was stamped on the edge of one fin of the heatsink. We can actually see that in the OP's photo but we can't read it due to the way the forum engine has scrunched the image down to its preferred maximum size.
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Old 4th Jul 2023, 5:32 pm   #9
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Default Re: Unidentified Fidelity '70s compact audio system

The pcb matches the Fidelity UA3 although the tuning scale looks different to the picture on the B/74 service card. According to the schematic the SN76013 is the audio output chip. The SN76013 is classed as 16 pins, the heatsink tabs are named as pins 4 & 5 plus 12 & 13. The chip type number is normally silk screened on top of the chip but under the heatsink. Later replacement versions had a squarer heatsink with vertical fins. If one of the 2 chips has failed then you must replace both at the same time, otherwise it will be a frequent visitor (bouncer) to your workshop, usually once a week, with alternate chip failure!

Also make sure that the correct impedance loudspeakers are used with this unit, unfortunately the service card has not got their impedance printed but from memory they may well be 16 ohm or possibly 8 ohm. Well worth checking the data sheet for the chip to confirm.

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Old 4th Jul 2023, 5:37 pm   #10
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Default Re: Unidentified Fidelity '70s compact audio system

Given the difference in colour scheme and lack of a headphone socket on the OP's chassis his would not appear to be from a UA3 but it clearly is the same chassis from the point of view of the circuit diagram / component layout.

It's not clear what the OP actually wants to do with this since he doesn't seem to have the unit this chassis came from.
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Old 4th Jul 2023, 6:19 pm   #11
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Default Re: Unidentified Fidelity '70s compact audio system

Those Texas Instruments audio output ICs [SN760xx] were truly horribly fragile and unreliable: they were used in a number of 1970s TVs - and would happily melt down if you cranked the volume up to max while watching Top Of The Pops.

The SGS TBA810AS - with a proper heatsink bolted to its tabs - was *much* better. Pye used this chip in a bunch of 1970s mobile-radios [Olympic series] and they never seemed to fail.
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Old 4th Jul 2023, 7:59 pm   #12
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Default Re: Unidentified Fidelity '70s compact audio system

These IC's were used in the Pye hybrid colour tv's and I don't recall changing many. That Fidelity chassis was a different matter. Always kept them in stock.
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Old 4th Jul 2023, 11:14 pm   #13
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Default Re: Unidentified Fidelity '70s compact audio system

Yes, as a young engineer I used to change them regularly. The UA3 used to oscillate at switch-off. I think now I'd be looking at the way they applied NFB on the chip itself. Chances are there's a data sheet out there for the IC. Fidelity always built to a price point.

Anyone recall the AVS 2000 etc? Used the same TDA4600 PSU IC as Sony did in their Tv's. The chip failed endlessly in the AVS' but not once did it fail in the Sony sets.

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Old 5th Jul 2023, 12:15 pm   #14
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Default Re: Unidentified Fidelity '70s compact audio system

The alternative after market device was an AC76013. This chip has a glued on heatsink and the taps/pins (4,5,12,13) are not used. Also the 'AC' version was supplied with straight pins, so you had to bend them into the Quil pattern.

Dave

ps yes Sam I remember the AVS2000, as I was one of the few in the Doncaster area that would actually attempt to repair them.
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Old 5th Jul 2023, 12:52 pm   #15
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Default Re: Unidentified Fidelity '70s compact audio system

Quote:
Originally Posted by samjmann View Post
Anyone recall the AVS 2000 etc?
Yes, I've got one, also the 'etc.' AVS1600!

The AVS2000 has packed up this last year with the famous EHT breakdown trouble. I killed the power before it was able to do any other damage, but as there's a lot of stuff both on top of it and on both sides in the room where it lives I haven't got round to pulling it out from the wall to have a look at it yet. The 1600 is still working perfectly. The original intention was that if anything ever went wrong with the 2000, then the 1600 would be used for spares to fix it.

Dave - seeing as you liked fixing them and you're in Lincolnshire, I'm bringing the 2000 over to you to fix to save me a job. .....Nah, only joking!

Fixing it will be a job for another day and another thread.
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Old 5th Jul 2023, 1:02 pm   #16
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Default Re: Unidentified Fidelity '70s compact audio system

Those UA3 type units with or without radio used to come my way for repair quite a lot back in the day and it was always the finned output chips. I think I've actually still got an example lurking somewhere in the loft, but I think it's just the record player version.
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Old 5th Jul 2023, 1:51 pm   #17
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Default Re: Unidentified Fidelity '70s compact audio system

The fins are stamped 516 X13, I presume that translates to the SN76013 as Dave posted. My intention in posting was find the Fidelity model, and to offer it to anyone restoring one, but I won't be testing the devices so maybe I'll just part it out for a few pots and IFTs
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Old 5th Jul 2023, 3:36 pm   #18
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Default Re: Unidentified Fidelity '70s compact audio system

Well, although it's not the right colour it would make a good complete replacement chassis for the common UA3, and no doubt the silver / black front panel and headphone socket of the UA3 could be transferred onto this chassis.

I spent quite a while looking and didn't find a single photo of whatever model used the 'black' fronted version of this chassis.
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Old 5th Jul 2023, 4:05 pm   #19
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Default Re: Unidentified Fidelity '70s compact audio system

I couldn't resist having a quick look in the loft and fairly easily found the one shown below. It's not what I was expecting to find and was one that although must have been acquired more recently, I'd completely forgotten about. The lid is missing and someone's cut the mains lead off, so had to get creative with the usual quick connection. When I saw the letters, numbers and post code that had been unbelievably scratched onto the left front side of deck plate I remembered that it came from a CB radio operator that had helped clear a deceased persons house and thought of me when he saved this player from the skip. There were no speakers with it, so I connected a couple of basic Ferguson types and other than slightly noisy pots it worked perfectly on both channels and I played a couple of record sides on it - good old BSR...although it's just possible that I gave the deck a little bit of a service when I was first given it, but I can't remember. BTW, it's fitted with a double LP ST17 stylus - just in case anyone thinks I'm playing a 45 with a 78 tip!

The IC heatsinks are different to what we normally see, so may be a later version. I still think I've got a version with the finned type somewhere, but it's too hot and too dusty to delve any further in the loft just at the moment. The one I'm thinking of could even have a radio, but it'll be 20 years or more since I've last seen it, so can't really be sure.

Another example of Fidelity showing the pride they had in their product, as mentioned in a previous post. It must be the same person that was responsible for sticking on all the stickers that showed real pride in their work and what they were doing...not!
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