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

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Old 20th Aug 2017, 8:06 am   #1
GW4FRX
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Default Radford SPA50

In my giddy youth I had a Radford SPA50 amplifier and recently thought it might be fun to find and restore one. Looking around online it seems that there were two versions – the original and a ‘Series 2’ which seems to have had a different internal architecture. However, the information available online is very limited. In particular there’s no sign of the ‘Technical Instructions’ which Radford apparently issued for maintenance and repair purposes.

Does anyone have what the lawyers call further and better particulars? And what’s the general consensus in respect of the SPA50? My memory is of a fine-sounding and unfatiguing amplifier but it was a long time ago…
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Old 20th Aug 2017, 6:38 pm   #2
Trevor
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Default Re: Radford SPA50

I purchased an SPA50 only to find it was retro fitted with a pair of SPA60 modules, the unit sounds great but the build quality is not as good as I would expect.

I would say that the schematic is simple but very fine tuned, very tough to get one In good condition.

Trev
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Old 21st Aug 2017, 7:27 am   #3
Synchrodyne
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Default Re: Radford SPA50

I have a schematic for what I think is the original version of the SPA50 – please PM me if you would like a scan.

It is a fully complementary design with a single-ended power supply, and evidently optimized for 8 ohm loads, with reduced output into 4 ohms, as was not too unusual at the time it was released (1971). It looks as if it could have been a development of the earlier (1968) SCA30, which I think was based upon the 1968 Bailey design.


Cheers,
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Old 21st Aug 2017, 3:21 pm   #4
GW4FRX
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Default Re: Radford SPA50

>I have a schematic for what I think is the original version of the SPA50 – please PM me if you would like a scan.<

That would be very helpful -- many thanks indeed. I seem to recall the output stages being a 2N4906/4915 complementary pair and the power-supply arrangements being a little peculiar.

It would be very interesting to know more about the 'Series 2' version and its relationship to the SPA60, about which there's almost nothing online.
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Old 22nd Aug 2017, 3:26 am   #5
Synchrodyne
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Default Re: Radford SPA50

Quote:
Originally Posted by GW4FRX View Post
>I have a schematic for what I think is the original version of the SPA50 – please PM me if you would like a scan.<

That would be very helpful -- many thanks indeed.
OK, I’ll await your PM.

Quote:
Originally Posted by GW4FRX View Post
I seem to recall the output stages being a 2N4906/4915 complementary pair and the power-supply arrangements being a little peculiar.
Yes, 2N4906 and 2N4915, and a regulated power supply using a 2N3233 or 2N4348.

Quote:
Originally Posted by GW4FRX View Post
It would be very interesting to know more about the 'Series 2' version and its relationship to the SPA60, about which there's almost nothing online.
I have not seen anything on the Series 2, although as you are probably aware, the SPA60 schematic is available on-line at: http://www.vintageshifi.com/repertoi...-Schematic.pdf.


Cheers,
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Old 24th Aug 2017, 9:59 pm   #6
GW4FRX
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Default Re: Radford SPA50

Very many thanks to Synchrodyne of this parish for providing a wealth of technical information about the Radford SC24/SPA50 combination. There's enough material there to carry out a really good restoration if I can find a pair to restore.

This forum is truly a wonderful resource. In return, if anyone needs information or parts for Racal RA177x and RA179x receivers I'll be delighted to help.

John
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