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Old 26th Sep 2020, 5:19 pm   #1
Fumblefingers
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Location: Saxmundham, Suffolk, UK.
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Default Linear Diatonic or RSC A11 valve amp. East Anglia

Hello!
I'm trying to restore an RSC A11 valve amp. which is a close relative of the Linear Diatonic.
Is there anybody out there in Forum-land who can finish off fixing it for me?

When I got it (from eBay.. sorry about that) it hummed and buzzed like a badly adjusted manure lorry and produced a horrible distorted sound.
I got the schematic and went through it bit-by-bit, fixing many of the errors made by the original builder (it was a kit amp).
I substituted a few components to make it more like the Linear Diatonic design and it started sounding very nice, but with a noticeable hum.
I've done everything recommended, and changed all the caps, and checked the HT smoothing caps, but to no avail.

IS THERE ANYBODY OUT THERE, PREFERABLY NOT TOO FAR FROM SUFFOLK OR NORFOLK, WHO CAN FINISH THE JOB FOR ME AND STOP THE DARN THING HUMMING?
I am willing to offer a miserable amount of money in exchange for your time, expertise, burnt fingers, and spare parts.
Cheers..
Fumblefingers.
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Old 28th Sep 2020, 5:31 am   #2
Diabolical Artificer
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Default Re: Linear Diatonic or RSC A11 valve amp. East Anglia

You're welcome either to pop over to mine and pop it on the bench, have a cuppa/natter and try & fix it while your here or you could pop it in the post. I live not far off the A15/A52 in Lincolnshire, about 2hrs from you.

Drop me a PM if of any use, Andy.
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Old 30th Sep 2020, 6:25 pm   #3
agardiner
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Default Re: Linear Diatonic or RSC A11 valve amp. East Anglia

I don't usually fix amps, but would take a look at it for you if you like?

I live near Thetford.
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Old 2nd Oct 2020, 5:12 pm   #4
Fumblefingers
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Default Re: Linear Diatonic or RSC A11 valve amp. East Anglia

Crikey!
The power of the internet!
A fine fellow on this forum has offered to have a look at the Linear Diatonic/RSC-A11!

I sent it to him via UPS couriers who have a splendid reliable service, in my experience, and a rather strange user-unfriendly website.
This time, it kept freezing and crashing and asking me who I was, over and over again, like a confused older auntie at a Christmas party.
In the end, on advice from this forum, I tried accessing UPS from "Interparcel" which was a million times easier.

I'll keep everybody posted on the little amp's progress.

Cheers and toodle pip!
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Old 16th Oct 2020, 6:05 pm   #5
Fumblefingers
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Default Re: Linear Diatonic or RSC A11 valve amp. East Anglia

Hello Chums!
Well... a fine fellow on this forum by the name of Diabolical Artificer took my amp under his wing, and has done a magnificent fixing job.
The RSC A11 wasn't exactly state of the art... more like state of the Ark, and the transformers were fairly weedy (and dated from the 1960's!).

I am also fairly weedy, and date from much earlier.

The main problem was the hum, and I'd tried to fix that by earthing everything in sight.. This cured some of it.. but probably also produced earth/hum loops.
I'd reached the limit of my technical know-how.. but riding to the rescue came The Diabolical Artificer.
He spotted, among my repairs, a couple of wrong value resistors (I was only out by a factor of ten!) but that wasn't the complete answer.
He replaced the HT capacitors and tidied up the HT wiring, and then did a major re-routing of just-about every other component, to avoid picking up hum from hither or thither.
He was battling against the work of the original builder (these were kit amps) and the ham-fisted repairer (me) so it was basically back to the bare chassis, although using my components (I'd replaced almost every darn component in the flippin' set!).

How he stayed sane, I do not know.

This pesky amp had me banging my head on the work bench for weeks, as every little adjustment cured one problem but then threw up another!
Anyway.. the Diabolical Artificer performed miraculous heart surgery, and the amp is now back at my place and sounding WONDERFUL.
I intend to use it at record fair/meets (where I go to sell and swop old records.. including 78s) to demonstrate dodgy old discs. It will replace the hissy old Linear Conchord I've been using up to now.
If ever Boris and The Virus allow record fair/meets to open up again, I'll be there with a turntable and the little RSC A11 (eleven watts of throbbing power) playing old Frankie Laine 78s much too often and much too loud.
Thanks again, Andy the Diabolical Artificer
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