CHAMP ELECTRONICS -" THE VINTAGE VALVE AMP HOSPITAL"

NOTTINGHAM, ENGLAND

GENERAL SERVICING WORK CARRIED OUT ON SOUND CITY AMPLIFIERS - PART 1

 

Three Sound City Amps..........

Not belonging to the same customer though. Because there are no special stories to tell about any of them as they basically all needed the obvious kind of servicing that valve (tube) amps require after about 30 - 40 years, I decided to combine these three Dallas-Arbiter, Sound City’s onto one page.

The "50 Plus" belongs to a gentleman, Dave, from Scunthorpe England. The "Concord" belongs to Cliff in Preston England, and the "50PA Plus" to my dear friend Mervin, in Australia.

 

CLICK ON THE THUMBNAIL PICTURE FOR DETAILED PHOTOS OF THE WORK UNDERTAKEN ON EACH AMP:

 

 

SOUND CITY 50 PLUS

What I will say about Sound City amps is that they all used good Partridge transformers, usually Mullard tubes, and  were fairly neatly built with good quality components. Hence they tend to be very reliable. However after time, Sound City’s seem to suffer with the main smoothing caps…….usually Sprague!! Other than this, they just seem to “keep going”!

The "50 Plus" needed all the obvious things doing, along with a couple of broken potentiometers and missing knobs. 

 

 

SOUND CITY 50PA PLUS

The "50PA Plus" just needed a good service. However, note the added, non-original reverb unit and associated transistor components/reverb control! 

 

 

SOUND CITY CONCORD COMBO

The worst of the three was the Concord, this one was pretty tired. It had been worked on before and modified/bogged! The speakers were not original and wired as two 8ohm units in parallel equaling 4 ohms. However this one had at some point had an output transformer replacement (not Partridge) and had been set to 8ohms……..wrong for the two replacement drivers @ 4ohms! Whoever had changed this transformer had chopped the 4 and 16ohm outputs close to the core! What a stupid thing to do! As it happens, I managed to solder to the chopped 16ohm tap and then rewired the speakers in series to the correct 16ohms.

Another modification that had been done was to wire the reverb to one channel only. I put this back to original, i.e. working on both channels.

Though I quite like the Sound City products, the only one I don't care for is the Concord. Though it may have been “trendy” at the time, I'm not a big fan of the slide controls. One of these was not only broken but was completely OC (open circuit) too, making this channel unusable. As these sliders (75mm, 80mm hole centers, 500k Lin…….if anybody has stock of these please contact me, thank you) seem to not be available anymore, I simply soldered two 220k resistors across the back of the pot. This simulates the control, being about “half way”, and at least the channel is useable like this. As Cliff (the amps owner) so rightly said, he doesn't need to use this channel one, as number two is exactly the same.

 

Other than the few issues mentioned above everything else was straight-forward on all three units. A few components here and there, along with a few tube changes (where necessary) and that’s about it. Do enjoy all the photos.

 

Cheers everybody, John.

 

A COMMENT RECEIVED FROM TERRY WHICH PROVIDES FURTHER INFORMATION ON THE TYPES OF TRANSFORMERS USED IN SOUND CITY AMPS:

 

"I just read the service of the Sound City amplifiers, and your comment regarding the transformers not being Partridge. As you said Sound City used Partridge for many years.
 
The un-marked transformers were made by Electro-Voice (nothing to do with the US speaker company) and were based in Rickmansworth. The reason I remember this is because Roost used Partridge in the early days and changed to Electro-Voice about the time Sound City did (1975/6..??) - well Sound City were only across the town from Roost and there was a "flow" of parts to and fro between the two factories - ah what great days they were back then. I've also seen Electro-Voice transformers used in the Sterns Mullard 5-10 and 3-3 amplifier kits.
 
Before I go, the Electro-Voice logo was a mechanical or robotic mans head with lightning coming from is mouth - hence Electro-Voice.
 
Regards, Terry."

 

 

 


 

 

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© John Chambers 2007
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