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Richard Allan Class A (Sugden A21) rebuild

Lovely. It amazes me that unlike other brands from the 60s Sugden have managed to survived. I’ve no idea how they have managed that when so many others have disappeared.

They had the sense to remain comparatively small and family owned, plus they have a very clear brand identity as long as they keep making nice class A integrated amps. No idea what it is like now, but I had a tour around the factory a decade or more ago when a friend was collecting his ‘60s A21 from a service and it was totally old-school in a really cool way. No real clues it wasn’t still the 1950-60s, everything done properly by hand, tons of interesting stuff from the company’s history stacked up in cupboards, on shelves etc. If I was in the market for a new amp a Sugden would be top of the list I suspect (my only annoyance is they seem to have dropped balance controls fairly recently). I had to sit on my hands recently when a tidy fairly recentA21SE appeared in the classifieds here at a very good price - I really wanted it, but just didn’t have a context for it! I’ve a lot of time for Sugden anyway.
 
They had the sense to remain comparatively small and family owned, plus they have a very clear brand identity as long as they keep making nice class A integrated amps. No idea what it is like now, but I had a tour around the factory a decade or more ago when a friend was collecting his ‘60s A21 from a service and it was totally old-school in a really cool way. No real clues it wasn’t still the 1950-60s, everything done properly by hand, tons of interesting stuff from the company’s history stacked up in cupboards, on shelves etc. If I was in the market for a new amp a Sugden would be top of the list I suspect (my only annoyance is they seem to have dropped balance controls fairly recently). I had to sit on my hands recently when a tidy fairly recentA21SE appeared in the classifieds here at a very good price - I really wanted it, but just didn’t have a context for it! I’ve a lot of time for Sugden anyway.

Strangely enough I nearly PM'ed you a couple of days ago to suggest that from what I've heard from this amp and what I've read of your taste in amp sounds it could be your perfect amplifier!
 
Strangely enough I nearly PM'ed you a couple of days ago to suggest that from what I've heard from this amp and what I've read of your taste in amp sounds it could be your perfect amplifier!

I know it well as a friend has one and the similar period A51 power amp (the odd blue/green thing that looks like it belongs to an arc-welder or similar). The latter in particular is superb. The problem is the 303 is such a classic studio-pairing with the giant Lockwoods and the Stereo 20 sounds so damn good with the 149s I don’t want to disturb either system! It is the sort of thing I’d unquestionably buy if one cropped up at the local auction though...
 
So what does it sound like? REALLY good actually! Vastly better than an all original unsorted MkII version I sold a few years ago... So pretty much like a A21se but only 10WPC.... It would, IMHO, trounce a Quad 33 and 303 for example...
How was this decision taken.
 
Very nice work there, how do you think this would compare to say a JLH class-A?

Thanks:)
I reckon they would be very similar but 'friad I ain't spending hours reassembling my old JLH to do the comparison.... It would be interesting to try it as a power amp though as there is a pre-power plug internally... it's an odd plug and socket so I won't be trying it..

I'll have more to say about the A21 in an hour or so after some more tests I hope... ;)
 
OK well normal service is resumed with the Sugden.... Ah the problems of ancient electronic components... It was left on for 24 hours as a soak test and was fine but I've given it a lot of use over the past few days and... well I'm glad the new faults occurred whilst it was here!

A rectifier went for a start. The originals are only 1A and only just up to the task and so I wasn't that surprised when one went intermittently open circuit... al 4l now replaced with modern 6A rectifiers.

The biggy though, which took most of today to fix whilst I had other stuff to do, was an intermittent "frying bacon" noise noticeable only when music wasn't playing. This is the worst possible kind of fault and I wish I had a fiver for every time I've heard "it can't be much 'cos it all works great other than this little noise that comes and goes" argghhh!!! Smoke coming out and then it packs up altogether good. This kind of thing very bad!!

I suspected it would be one of the awful 60's carbon composition resistors and indeed it was but OMG did it take some finding! One 2k2 resistor (and it's pal in the other channel for good luck) replaced with a nice modern metal film and it's as quiet as a mouse and making lovely music once more:)

A few more hours under its belt tonight and it can go home to its owner tomorrow all being well:)
 
...A rectifier went for a start. The originals are only 1A and only just up to the task and so I wasn't that surprised when one went intermittently open circuit... al 4l now replaced with modern 6A rectifiers....
The modern reservoir capacitors will be much lower ESR than the originals, which will stress the rectifiers that little bit more. Intermittent open circuit means the internal wire bond has come adrift.
 
The modern reservoir capacitors will be much lower ESR than the originals, which will stress the rectifiers that little bit more. Intermittent open circuit means the internal wire bond has come adrift.

Indeed that was my thinking as well.... In fact I considered replacing the rectifiers during the rebuild but thoughts of "if it ain't broke...." won out...
Anyway there are 6 Amp 200V ones fitted now:) It uses bi-phase rectification with centre tapped TX BTW and has a separate winding for each channel.
 
Quick question for those familiar with JE Sugden amps - what are the differences between the original A21 and A48?

Thanks, Richard
 
The A21 is a little class A amp, 12 Watts IIRC, the A48 a conventional 40 Watt class AB amp.

Thanks Tony - I read somewhere the a48 had the first 8-10W was in class A - has anyone heard them side by side? Should I hold out for an a21?

Richard
 
Thanks Tony - I read somewhere the a48 had the first 8-10W was in class A - has anyone heard them side by side? Should I hold out for an a21?

Richard

More like 1-2W or so. I've had both and known other A48's friends have had. Early ones with a single pair of output devices sounded better to me but the A48 can get a bit rough if you play them loud. If you can manage with the 8-10W of an A21 it is probably the better amp. There are a few differences between A21 variants as well with the very first one (as in the rebuild in this thread. First Sugden branded ones were identical) probably the best as it takes feedback from after the output cap. Beware that there was a series 3 A21 which isn't class A and made about 20WPC.
 
Some of the kit I've rebuilt in the last few years includes Quad II's, Quad 303, Leak Stereo 20, Leak Varislope, Radford STA25, Pioneer SA-9500, Meridian 105's, Meridian M2's, Pye Mozart pre, power and tuner, various Musical Fidelity amps, just to name a few...

What did you do with the Pioneer - was it a refresh, or upgrades?
 
What did you do with the Pioneer - was it a refresh, or upgrades?

Long answer to a short question coming up... hopefully answering most of the more likely "matters arising" on the subject:)

Firstly it is important that folks realise that the processes used etc are the same for all amplifiers, give or take the odd idiosyncrasy... one of the most annoying questions I hear is "have you worked on one of these before?".... It makes no difference to a good engineer whether they have or haven't other than it can be quicker if one is really familiar with a particular piece of kit;)

The Pioneer was not modified but came in for a re-cap and general service so we could call that a refresh yes. The electrolytic caps were all replaced, but with better than original ones, so I guess that could be called an upgrade of sorts, and all things like bias current, regulated PSU voltages etc etc were checked and adjusted as necessary, all boards inspected for dry joints etc, switches, pots, connectors and fuses etc cleaned with contact cleaner and anything that seemed like it could do with some attention was sorted out. Same as with the Sugden featured here really.

I can carry out all sorts of upgrades to virtually any amp as well of course, the older and cruder it is the more upgrades are applicable/possible and the bigger the improvement generally. I.E. a modern, expensive and well designed and built amp may have many of the things I could do as upgrades on an older/cheaper/less well engineered amp fitted as standard anyway. I can do things like add regulated supplies, build better regulated supplies where already present, fit bigger and/or better caps, fit better signal caps, better op-amps, switched attenuator instead of vol pot if there's room etc etc.
I've gone as far as fitting extra output mosfet's to MF amps and fitting regulated front end supplies to Exposure amps in the past but much depends on the topology of the amp and whether there is the room to fit the prospective upgrades...

What is not possible is to say beforehand what exactly will be the nature of the subjective improvements and how much of an improvement each potential upgrade will give! Generally though we are talking greater openness, transparency, neutrality, improved separation between instruments (especially when there's lots going on) and less muddiness and confusion, tighter bass, more detail and better sound staging.

What you won't generally get is more "warmth and lushness" as these are often due to the amp being basically not very good and having lots of even order distortion and/or a rolled off top end... it's acting as a "tone control" or "nice colouration machine"! Some folk like this sort of thing and may find that by making it into a "better" amp it loses some of the "rose tinted specs" colouration that they like. I've not had a dissatisfied customer yet but could imagine that if someone's bought an amp that most of us would consider coloured and/or "wrong" sounding, and specifically because these aspects appealed to them, then they could consider the improvements a downgrade!
 
I've not had a dissatisfied customer yet but could imagine that if someone's bought an amp that most of us would consider coloured and/or "wrong" sounding, and specifically because these aspects appealed to them, then they could consider the improvements a downgrade!

Then they should have bought themselves a SET in the first place, no?
 
Another of these completed and this time taken to the extremes of ALL semiconductors replaced with better modern versions (transistors all matched, rectifiers now ultra fast soft recovery type) and all resistors replaced. This is as well as all the same work carried out on the last one... big job!! Nice though:)
 


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