CHAMP ELECTRONICS -" THE VALVE AMP HOSPITAL"

NOTTINGHAM, ENGLAND

 

REPAIR OF TWO ELPICO AC-85 GENERAL PURPOSE AMPLIFIERS

 

Elpico Amp No 1

 

 

Elpico Amp No 2

 

 

A PAIR OF ELPICO AC85 AMPS:

Coming from a very nice gentleman, Jerry down in Essex, UK, this pair of Elpico AC85’s needed some serious attention and renovating. Though a pair, they are not actually exactly the same. One was an early version which had a tube line-up of 1 x EF86, 2 x ECC83, 2 x EL84 and 1 x EZ81. (Elpico Amp No 1 above.) The slightly later model was pretty much the same but with some sensible factory modifications/changes. (Elpico Amp No 2 above.)

One of these changes was the omission of the EF86 (what a good move!!) and a juggle about of the layout. Another change made was that the later model used a pentode output mode as opposed to ultra-linear on the earlier version.

Amp No 1 was in a more sorry state so I started on Amp No 2 (later version) first; this one being more likely to be the easier of the two. Jerry had been told initially by a previous local technician that both of these had duff output transformers. Now, whilst this was certainly a possibility, I did find it a bit too ambiguous. I did indeed find the output transformer on the early model kaput, but the later one was fine!!

This later model basically needed a lot of the small coupling capacitors changing, as is the case with many amps of this age, although the electrolytic caps were all fine. The EZ80 rectifier was the incorrect type, so this got changed for the correct EZ81. Neither of the amps had any output tubes, so they were both kitted-out with my fave-rave JJ’s.

I did of course do all the obvious servicing like spray/cleaning all the tube bases and pots. These are normal requirements.

Springing into life, Amp No 2 one now looked good on the test gear, and sounded something more like it should too.

On Amp No 1, the earlier amp, things weren’t quite so good or easy. I had to rewind the output transformer of course, and this time I did away with the screen grid ultra-linear tapings, putting this one into pentode connection as on the later model. There is no point in using ultra-linear on an amp like this. They were basically a sort of PA amp-stroke-record player amp, hence the RIAA standards equalization for the use of the “normal", "LP" and "78’s” tonal correction control.

With a guitar shoved into the microphone input though, by-golly they don’t half sing well through a suitable speaker cab!

Like Amp No 2, most of the coupling caps needed changing on Amp No 1 also, together with a few resistors. On completion, there were some instability problems due to the layout. This would suggest the reason why the layout had been changed for later production models. Nevertheless, I sorted this out, and this included the necessary screening of all the smaller pre-amp tubes. There were no white chicken-head knobs on the amp, so I supplied/fitted these. After a little while following the first power-up, the main smoothing cap was getting warm! However, after some time it seemed to “re-vitalize itself” so, as they say, “if it ain’t broke, don’t fix it”. This I didn’t do, and the cap seemed to end up being fine. Once finished, this one “kicked ass” too.

Both amps provide about 15 watts now. The later model (Amp No 2) would have been about this, but the early version (Amp No 1) in ultra-linear would possibly have struggled to make 12 watts.

As I had to rewind the output transformer on Amp No 1, I liased with Jerry on the choice of output impedances required. Whilst I was winding it anyway it was no big deal to change the choices. He chose 8 and 16 ohms whereas the other, untouched output transformer has 4 and 16 ohm outputs.

I have since heard from Jerry and he informs me he is more than pleased with both amps! Like many other of my customers, if and when Jerry sends me any kind of testimonial I will present it on the web-site.

Cheers to you all for any interest in my work and site.

John

 

ELPICO AMP No 1:

 

Completed amp, with re-wound output transformer.

 

 

 

As completed under-chassis view - many components changed.

 

Re-wound output transformer awaiting installation.

 


 

ELPICO AMP No 2:

 

Amp shown after work completed.

 

 

 

 

 

 


 

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