HISTORY OF THIS EQUIPMENT & COSMOS THE COMPANY
Wow!
Now I am digging out some of the OLD audio equipment which has been sitting in my storage units since I closed down my audio post business a few years back.
We had this amplifier RUNNING and then one day back in the late 1990's, a puff of smoke/bad smells and it was put aside to be looked at "one day" but "that day" never came so now I am offering this audio amplifier to a techie for restoration and possible improvement over the original design by selected higher grade components.
This is 50+ year old audio equipment of "average quality" and anyone who thinks their old Japanese gear is going to make it without needing work through those years is "dreaming" Cosmetically the amplifier is in really good condition, but it DOES NEED SERVICE! Please read ALL about this in my COSMETIC CONDITION and TESTING sections below...
I am providing a LOT of information because I am trying to be helpful to someone who may be considering this "project amplifier", my career background is electronics and surely anyone who may consider this audio equipment would want to know as much as possible!
To restore this tube amplifier to it's former glory (or even improve it further) you need to have medium level electronic skills and understand vacuum circuit design plus average soldering, identification of components skills.
If you do not possess these abilities, either find someone who can help you out and do the work for you OR DO NOT ATTEMPT TO UNDERTAKE THE RESTORATION!
This is valve equipment (mainly) and it runs a B+ supply of around 300 ~ 325V DC at a pretty decent current, just a simple slip of the hand (when powered on) and you will suffer a serious electric shock which could result in terrible health outcomes! If you don't know what you are doing inside a piece of valve equipment WALK AWAY!
I am well and truly past my servicing days and no longer have the patience or good eyesight any more to safely undertake service or restoration of this equipment. But my brain is still functioning! (so far) and I have provided a very detailed account of the amplifier cosmetic and electronic condition below.
This COSMOS Stereo Amplifier is provided on an "AS-IS" basis
HISTORY:
COSMOS were a Japanese designer and manufacturer of tube (valve) based audio equipment way back in the 1970's for both the domestic and international market.
This amplifier was imported into Australia by a company called Encel Stereo, located down in Richmond Victoria. The AC input transformer is 230~240V "ready" and it looks as though the local Australian supplier fitted a local power lead and Australian 3 pin plug for a standard GPO
The equipment has been imported ready for 230~240V AC operation but a local lead/plug has been fitted before sale.
Now keep in mind that the 1970's was a time when Japanese gear was often considered "pretty crap" to be honest and it was not uncommon to hear tech's refer to Japanese equipment as "Jap crap". It wasn't the designs that were the problem (often using stock standard design philosophy) but local Japanese electronic component manufacture was often lacking in quality or consistency, particularly those designated as "domestic grade"
The overall build quality is very very good, solid metal and hand assembled but the colour scheme is a bit "unexciting" A sort of military green for the top cover? Not much imagination here...perhaps the mindset was still stuck in the WWII era some 25 years earlier?
Polished aluminium front panel with those lovely solid aluminium knobs do really scream out "Hey look at me! I'm from the '70's" Very nice and then, when it was running, you look down inside and there is that nice comforting glow from the valve heaters!
COSMOS STEREO AMPLIFIER
Made in Japan
Circa early 1970's
Actually, in truth this is a hybrid amplifier. The phono input stage (ONLY) is based on Ge semiconductors but the remaining audio amplifier is all valve based
1x 12AX7
4x 6BM8 (pairs working in push pull)
NOTE: this appears to be one of the "early" releases, the serial number is missing and the front panel decal layout is different to other COSMOS amplifiers I have come across over the years. The COSMOS text is printed on the front panel up in the top left hand corner, not the centre area as with most others.
Bookshelf size (nice compact size)
DIMENSIONS: 335mm x 125mm height x 230mm
WEIGHT: 6Kg
10W RMS per channel audio power output
Input sensitivities are not known although it would be reasonable to expect Tape, Tuner and Aux to be around 1V line level, phono somewhat more sensitive, probably around 50mV or so
Phono (turntable) input is semiconductor based (sub-board)
Australian market model (AC power transformer)
Fitted with a local power lead (jute is used inside the lead - that is SO '70's!) with an Australian standard 3 pin GPO plug
Unlike much Japanese equipment of the time, this audio amplifier does have power earth connected.
So what are the controls, sockets etc?
FRONT PANEL:
Power ON-OFF toggle switch
Bass control
Treble control
Mode control (Mono, Left channel only, Right channel only, Stereo, Reverse Stereo)
Input select: Crystal phono (yes, crystal!), Magnetic phono, Tuner, Tape, Auxiliary
Concentric Volume control (each channel volume can be independantly adjusted)
REAR PANEL:
Source input sockets (all RCA type)
DIN 5 pin socket for tape connections input and output
Fuse holder
Auxiliary AC power out (240V but 2 PARALLEL PINS ONLY - not earthed)
Speaker outputs are screw terminal type and each channel has terminals for 4,8 or 16 Ohm impedance systems
COSMETIC CONDITION:
The case is steel based, very strong.
ALL four knurled side bolts are present as are the six screws underneath securing the base plate - no missing pieces!
The front panel is polished aluminium sitting on top of a steel frame.
Quite frankly, I was amazed! While it has never been exposed to the elements, I expected some dust but the unit is incredibly clean (inside and out)!
Front panel is substantially undamaged, little tiny dots here and there (don't seem to be oxidisation marks though)
Labelling front and back is clear, unworn and easy to read
ALL knobs (SOLID Aluminium with slot grub screws) are unscratched/marked. I love the use of "real" metals, not the later Japanese gear with fake metal coatings over plastic. The concentric volume control shaft is brass too!
NO scratching to the front panel
Only very light marking to the top of the casing.
The case/chassis is straight and has not been "bent" due to drops!
Inside I can see some slight discolouration to the chassis but NOT rust!
Inside the top of the case I can see just the slightest hints of rust towards the rear - I have seen far worse than this in my days!
Bottom removeable panel is also very clean and free of any oxidisation signs.
There are 4x ORIGINAL rubber feet, one looks a bit sad (worn at a slight angle so the amplifier probably will not sit level on a surface properly) - replacement feet (easy to find) would be a good idea.
Off comes the base plate and I take a look around ...
INSIDE:
Light signs of oxidisation on the top of the AC transformer and 2x Output transformers but nothing serious
ALL VALVES ARE FITTED (condition now unknown though)
TOSHIBA 12AX7 for the preamplifier
2x pairs of TOSHIBA 6BM8 power output tubes, running in push pull
The 6BM8's also have marked on the glass envelope HI FI
The small sub-board that looks after the phono input looks clean and I believe this has 2x 2SB439 & 2x 2SB54 transistors (GERMANIUM)
On the underside, it looks as though this is the first time anyone has looked at this in 50+ years! There is no evidence of past repairs, modifications or any other work undertaken.
All electrolytic capacitors are original Riken Japan, not one capacitor has been changed! For that matter, it looks as though no component has ever been changed!
This is good in that you can be assured no-one else has been messing around inside, but that has a flip side, you can be sure that some components have failed or gone out of spec and my brief measurements (detailed below) confirm this.
MEASUREMENTS & OBSERVATIONS:
Let me make on thing very clear, I am NOT going to service this equipment and in fact my diagnosis of the condition has been severly limited ...
There is no way in the world I will power up this amplifier, to do so could cause damage and serve no real purpose because I can see what has happened and based on the quick measurements I made of components, the circuit will be totally "out of whack!" Not even with my variac and slowly increasing the AC input is not a sensible idea, it just serves no purpose to fire up this amplifier at this stage and could result in catastrophic component failure.
Inside, there is extensive work to be done replacing components - please read further down in this description for the details
Immediately I noticed the rubber grommet where the AC lead enters the chassis is all but gone. Old rubber does this, it sort of melts and it will need to be replaced for safety reasons. The AC lead is not damaged (no sheath cuts etc)
I then made DC resistance tests of the AC power transformer and the two audio output transformers, these are all measure fine.
I have NOT tested the valves (although they SHOULD be fine) as I have already sold my AVO valve testing equipment - drat!
Next I looked over the whole "rats nest" for component stress, it is very easy to see that one of the 20uF (350V) can capacitors has had a catastrophic failure . Viewing from the topside, nothing looks amiss with the capacitor but underneath (where the solder terminals are) it is black and some signs of heat (melted insulation on a nearby component) This is where the equipment failed for sure but fortunately it appears that no physical damage has occured to nearby components (no "fire in the hold" type of problem)
I then checked the main AC fuse (holder on the rear) and it is intact, so the current flowing when this component failed was not enough to "blow the fuse"
Next I measured a number of the resistors and oh my! the resistors I measured are way out of tolerance! For example, a 474K is now measuring 800K+ and as I went around the circuit I found more of the same thing, the resistors have all gone substantially high in value - way way out of specifications. That's old "cracked carbon" for you!
There are a few wirewound resistors and fortunately these still measure up fine.
I did not bother measuring the capacitors but it would be a pretty sure thing that they have gone leaky at the very least.
I even checked the 6.3V edison screw incandescent front panel lamp, that too is open circuit.
The power ON-OFF front panel toggle switch didn't feel "right" and yes, that has also failed - now permanently open circuit.
The slide switch for switching audio from the loudspeakers to headphones is working though! Small mercies!
I would suggest that the new owner needs to change ALL resistors and capacitors - if they haven't failed yet, they soon will!
While digging up some information about this amplifier online, I found a person who has actually undertaken a full restoration of a COSMOS stereo amplifier (and he seems to be mighty happy with the resulting amplifier too!)
Take a look at his "story" HERE
SUMMARY:
This amplifier was a personal favourite of mine in the 1980's ~ 1990's, they provide that nostalgic nice warm analog "valve sound" We used to run this often in my audio post business office area, providing background music via a tuner - it always bought comments from clients visiting.
The COSMOS is old and many components are now very tired - it is time to replace them ALL (electrolytic caps and carbon resistors) with modern replacements.
Replace the panel lamp and the miniature switch too.
NONE of these components are difficult to source BUT the electrolytic capacitor seems to be more special because it looks to be a dual 20uF 350V in the one can - that may pose challenges to replace.
Some innovation might be required when replacing this electrolytic capacitor.
