• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Any info on old "Cosmos" amp'?

Jonathan B,
I did a restoration on one of these about 5 years back and sold it to one of my apprentices (at the time) who has been using happily ever since (for $100).

I'm not at home at the moment having been posted from Adelaide to Cairns (your kneck of the woods) for 4 weeks work on the Navy Laser Airborne Depth Sounder. Back in Adelaide 10th August.

If you haven't got any info by then pm me - I'm fairly sure I have a full circuit trace in my "Resurections" file at home. I can photocopy and send to you.

From memory I had trouble with leaky coupling caps (those Toshiba Oil Caps) and ended up replacing the lot. This had dragged output tube grids high (6BM8s as you rightly state) and had cooked the tubes. Also did the usual replacement of all electrolytics.

Cheers,
Ian
 
radiomuseum.org seems to think this was manufactured by Encel Stereo of Richmond, Melbourne, Australia, but this is certainly false. Encel's was a great hifi retailer, at least while Alex Encel was still around, but never a manufacturer, nor even a rebrander as far as I know going back over 50 years. The amplifier is clearly Japanese made, full of a remarkable number of Japanese electros; SS rectifer/voltage doubler PSU; germanium transistors in the phono section, which puts it not later than mid-1960s; a pre-Baxandall passive tone control section; and a rather prehistoric phase splitter.

The line voltage is 230V: any product made in Australia would have been 240V. Uses 1 x 12AX7 for the input stages, and the phase splitter triodes are the triode sections of the four ECL82s. The pentode output sections of these are strapped as triodes straight to the HT. Output transformers look rather puny, and the example in front of me has a major problem in the bass region: that is probably mostly the 55-year-old capacitors, but the OTX looks like it may limit extreme bass performance.
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
> The amplifier is clearly Japanese made

Then probably the same to-order maker known for ELK guitar amps; also the later UniVox amps, and the same parts and techniques in many-many small amplifiers. I once knew the name but I have no head for Japanese names.

I always thought they were built well for their price-point. Which does mean so-so output transformers. But all are so old that electrolytics are weak.

EDIT: Miyuki Ind. Co.
 
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The main problem in this one turned out to be that at least half of the rather mingily sized 0.02uF coupling capacitors were leaky. One of them was leaking 57V onto the following grid. Looking into the 470K grid resistors this gives an Ft around 16Hz, which is way too high. If customer wants to spend any money I will try upping these to at least 0.1uF.
 
Well I replaced all 8 coupling caps and the thing is now working. Still needs all electros replaced, but we are leaving that to a buyer-renovate step.

If I was keeping this one I would at least remove the cathode bypass cap from the preamp stage to linearize it, for which there is presently no provision at all, or perhaps add 100R below it. More adventurously, I might replace the tone control section with a Baxandall, which would linearize the preamp, lower the noise floor, and flatten out the response completely.
 
I have just traded some unwanted gear for one of these. I checked inside, all looked pretty good so I hooked up to my gear.
I was pleasantly surprised how sweet it sounded. I don't think it was tonally perfect but it did perform well against much more modern audiophile gear.
Bass was a little muddled when pushed but still was punchy and authoritive, I think the muddiness is due to the components getting old (it doesn't look like its been recapped at all), the highs were "nice" and a little brighter than flat, which I prefer as my ears are getting old. You have tone controls if you want to modify for your ears and room capabilities.