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Sugden A21 Series II rebuild.

Arkless Electronics

Arkless Electronics

Trade: Amp design and repairs.
Another one! A Series II and under Sugden's own name by now rather than Richard Allan. It had been repaired before in 1992 and had odd pairs of output transistors...

This one was looking a bit poorly... check out those capacitors!
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Caps on the power amp boards also looking rather suspect...
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I've found the TO39 outline transistors on this board to be not all they should be also and these will be replaced in the rebuild.

The awful carbon composition resistors had to go as well so this is in effect a new amp after completion of all work.

Here's a completed power amp board. The non electrolytic caps are of types which just don't go wrong.. ever... and so have been retained. The wirewounds don't age and were fine and the 4 10R resistors are in a place where it wouldn't matter if they were out by 20% so were retained. All electrolytics replaced with 105C temperature rated low ESR types and resistors are metal film. The TO39 drivers and pre driver have been replaced by modern improved varieties which I matched.

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Here's the pre amp board after the same treatment. Removing all the old components without damaging the PCB rather more tricky than fitting the new ones!
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It's getting there... rebuilt boards back in, new smoothing caps and output coupling caps are 3 times the capacitance of the originals at 6800uF and are 105C rated and rectifiers are replaced with fast soft recovery ones. Some of wiring loom replaced as new caps are so much shorter that the original wiring wouldn't reach!
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Original output transistors were replaced with better modern ones, new speaker sockets fitted, all controls and sockets treated with contact cleaner, internal adjustments for quiescent current and tone control flat settings made and jobs a gud 'n:)
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That's not a scratch but a hair that the flash made really stand out!
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A rebuilt and in effect "new" A21 which should be good for many years now and sounds most valve like:)
 
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Nice. I still have my late grandfather's immaculate looking A21 Amp & tuner. I haven't tried them at all, as I haven't got the cables.
 
Nice one Jez, if sounds anything like as good as my Richard Allan version then they're in for a treat, I really can't see me being able to afford whatever would be a significant upgrade from this.

PS I think that's an original Sugden, the Series 2 usually say 'Series 2' on the front.
 
matt j said:
Nice one Jez, if sounds anything like as good as my Richard Allan version then they're in for a treat, I really can't see me being able to afford whatever would be a significant upgrade from this.

PS I think that's an original Sugden, the Series 2 usually say 'Series 2' on the front.
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Thanks Matt:)

It's definitely a series II. The first ones were the same as your RA (identical amps of course but originally marketed under the RA name and with a white front panel) but these have a redesigned bias control system which obviates the need to match strings of diodes and then set quiescent current by selecting and soldering in specific fixed resistors.
Other differences are the position of the smoothing and output caps which have a space between them for the fuses on a series 1. The fuses are on the boards on series II. Then there is the provision of a headphone socket on series II.
The series III is completely different and uses A48 like power amps with higher output power and less of it in class A.
All use the same (near as damn it) pre amp board.
 
matt j said:
Oh, I was going by this from Jim's site



http://www.audiomisc.co.uk/JES/A21series2/A21series2.html

I thought it went: Richard Allan -> JES series 1 -> JES Series 2
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Definitely series II as it says so on the circuit diagrams that match the innards! They weren't averse to things like using up one batch of front panels before starting on the new ones.... or, disappointingly, even using slightly different boards for left and right power amps or even using different power transistors on the left and right channels... I can't prove the latter but on the series 1 the original devices were BD121 and these were later changed to BDY38 and I've seen BD121 on one channel and BDY38 on the other with date codes not far apart and looking original and untouched! It's possible that a fault occurred within months of brand new and it came in for repair just after they'd moved to using BDY38's and the repair was done so neatly that it's impossible to tell... but seems unlikely.

On the one in this thread one channel had 4 x 1R wirewound resistors connected to make a 1R resistor of 4X the power handling but just 1 x 1R resistor in the same place on the other channel! I made them both 1 x 1R as the power handling is adequate with just one and it makes them visually matching...

Another detail I didn't like was that on the series 2 the power for the pre amp is taken via a resistor directly from one channels smoothing capacitor (on series 1 the resistor is on the power amp boards which looks neater) and on this sample the resistor had not had its leads trimmed down at all or any insulation fitted! It was just "hanging in the air" with 2" leads at each end! I trimmed it down to size and fitted heat-shrink sleeving.

They're a twat to work on (series 1 worse) due to the mechanical design... you have to completely remove one part in order to get at the screws that hold the next part together and this can be a few "layers deep" so to get at the back panel where the speaker sockets are you have to remove the front panel, take the power supply apart and remove the mains transformer on a series 1!! Series 2 not that much easier...

To prevent induced currents from the magnetic field of the mains transformer from causing hum, one side of the front panel and one end of the central "bar/tray" that takes the big caps are insulated from chassis by.... insulating tape in strips and nylon screws with fibre washers! "Shed technology":) So you even have to check for no continuity of sections of the chassis when putting it all back together:rolleyes:
 
mhv said:
Nice. I still have my late grandfather's immaculate looking A21 Amp & tuner. I haven't tried them at all, as I haven't got the cables.
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You can easily have the cables made and you're missing out on a real treat not trying the amp.
 
I would love to revisit this amp i sold to upgrade to the a21a which was a little disappointing it never had the same charm to my ears anyway.
 
That old vintage wonder looks amazing - I read that you favour class A designs over all others. What about these new B&O ICE powered amps, I understand they are extremely good sounding too (with the bonus of being very energy efficient!).

I was thinking of buying a well designed ICE amp in the near future.
 
beammeup said:
That old vintage wonder looks amazing - I read that you favour class A designs over all others. What about these new B&O ICE powered amps, I understand they are extremely good sounding too (with the bonus of being very energy efficient!).

I was thinking of buying a well designed ICE amp in the near future.
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Other than that they are class D I couldn't comment on ICE amps other than I replaced one in a bass guitar amp a few years back...

It's technical fact that class A amps are superior to all other types, and for many reasons beyond just the absence of crossover distortion. Implementation and topology though are more important still... probably 90% of hi fi amps are class A/B and think how much difference there is between them!
 
I remember trying a Sugden A21 Class A amp some years ago with my Triangle Comete loudspeakers - the sound was rather bland. I had since found out (from Sugden themselves) that the Sugden A21 does not drive 4 Ohm speakers well (despite being 91dB efficient).
 
My dad is giving me his rather battered A21, the case work is in desperate need of some care, there is no volume dial and no idea about the internals. Just seeing if Patrick at Sugden has spares to begin bringing it back to life. It hasn't been used for probably 30 years.
 
beammeup said:
I remember trying a Sugden A21 Class A amp some years ago with my Triangle Comete loudspeakers - the sound was rather bland. I had since found out (from Sugden themselves) that the Sugden A21 does not drive 4 Ohm speakers well (despite being 91dB efficient).
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This type of class A amp can not move into class A/B so whilst the A21 SII gives 10WPC into 8R it will only give 5WPC into 4R. (ish. The A21 S1 was optimised into 6R to give a reasonable compromise into either)

Edit: Engaged keyboard before grey matter there... The above is true of a "plain" single ended class A amp with a fixed current source but the Sugden has a modulated current source and can do rather better into low impedance's than this... see later post with available power into various impedance's listed.
 
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