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  • A visit to Karel Mars - a man who was clearly a vacuum tube baby.

I drove down to the wild western cape recently and made a point to pay a visit to The Man. I took my Gibson GA-79 and 1940's cinema amp to Karel for their doctor's appointment. The GA-79 was acting wonky and the cinema amp was screaming loud noises as soon as you put it on. Sitting in 35'C heat (in the shade) in the Paarl, under a corrugated steel roof (you can imagine what that is like), I watched him go to work.

What a guy to meet - I have never met a more genuine, humble person in this industry. In amoungst all the 'new' guys on the block claiming to know everything about tube amps just because they downloaded some schematics - yes you know who they are - is a man with genuine experience, who will not only have a cup of coffee with you as though you have known him for ten years, but also teach you much more than you could understand about what it is that he is doing to the amps. Most people I have met are rather secretive about the details, but Karel took pride in explaining to my dumb ears how everything works. He is also incredibly knowledgeable. Our conversation went from tube amps, to transformer manufacturers, to radio transmitters, to HAM radio, to the Masons and conspiracy theories, to Roman and Viking mythology (perhaps it was the heat!)

He started with the cinema amp. It turns out that some of the big caps have failed, no doubt due to age. After poking around, measuring, replacing some caps and consulting some books on tube pinouts for these old tubes - the amp sounds ten times better than before. I really mean it. It sounds fantastic. You cannot believe the warm sound that comes out of this amp, with bass and low mids that just fill the room, but not at all in a boomy way - a jazz dream tone. Interestingly, by looking at the components such as the wax filled paper caps and the magnavox speaker, Karel reckons that the amp is definitely pre 1945 and possibly even from the late 1930's. Even more interesting, is that the amp is american, yet was repaired at some stage using english parts from the 1950's - Karel tells me that in those years the South African technicians could only get english made caps to do their repair work. This indicates that this amp has been in SA for a long long time. Typically these amps were sold in kit form, with only the chassis and electronics. It was up to the owner to decide what enclosure to use and what speaker. It is entirely possible then, that this amp has been in SA its whole life, around 70 years! Even though the amp has been heavily modified and is no longer true to the original circuit diagram, it sounds amazing and it is my favourite amp.

This is what the amp looks like:








First, replacing some of the caps:


Poor little amp ☹


When Karel consults an impedance meter, the schematic and a tube pinout manual all at the same time, you know things are getting serious.


Due to the heavy modifications and the odd use of transformers, it was quite a task to trace all the wires and follow the old schematic. He needed to repair some dry joints as well.


When you look at the bird's nest in there you can understand how difficult it can be:


After all that, it was done. Some serious amounts of sweat left our foreheads that day. And Karel drinks lots of piping hot coffee - he takes it black mind you - to cool down on a hot day ??? I tell you, he is like the stig.

After that came the GA-79 - all that was needed was to repair some solder joints here and there and now it is doing great. There is work that remains to be done - the one speaker has a buzz, the pots arent perfect and the cab has to be recovered in its original cover, but that is for another day.





Only took one photo here, the sun was too bright, hence the hand to shield the camera.



You will not be disappointed if you send your amp to him. He also ships amps to anywhere in SA so you do not have to be in the area to use him.
    a Good story and some great pics of the amps Aja...! Oooh and Karel is also fairly photogenic.... despite the heat ?
      A lovely account. Thanks.
        Great post. Would love to meet Karel. I'm sure he's forgotten things that most of us have yet to even learn.
          shaunf wrote: Great post. Would love to meet Karel. I'm sure he's forgotten things that most of us have yet to even learn.
          Yeah he really understands the old tech stuff. It goes beyond simple schematics and such. He knows all about how the amplifier designs have changed over the years - and I am talking about stuff from the 30's and 40's here. The amp technicians I have met up here in JHB pretty much follow the schematics and that is about it. I am sure many of them would not be able to work on anything older than the late 50's designs. How many amp tech's in gauteng would know how to work on designs that use a field effect coil speaker where the speaker coil is typically also used as a choke? Not many, I am sure. To give you an idea, he looked at that cinema amp and then showed me parts of the circuit that match up to radio amplifier designs of the 40's in this old book he has. Not the whole circuit, just parts of it.

          I am a mechanical engineer and I love asking questions - lots of questions. I have asked some amp techs questions before and the difference between them and Karel is like night and day. You can tell by the way that people answer you. You can see when someone is hopping around trying desperately to avoid admitting defeat. I like the fact that Karel often answered me by saying: "I am not sure, but let's look it up..."
            aja wrote:
            shaunf wrote: Great post. Would love to meet Karel. I'm sure he's forgotten things that most of us have yet to even learn.
            Yeah he really understands the old tech stuff. It goes beyond simple schematics and such. He knows all about how the amplifier designs have changed over the years - and I am talking about stuff from the 30's and 40's here. The amp technicians I have met up here in JHB pretty much follow the schematics and that is about it. I am sure many of them would not be able to work on anything older than the late 50's designs. How many amp tech's in gauteng would know how to work on designs that use a field effect coil speaker where the speaker coil is typically also used as a choke? Not many, I am sure. To give you an idea, he looked at that cinema amp and then showed me parts of the circuit that match up to radio amplifier designs of the 40's in this old book he has. Not the whole circuit, just parts of it.

            I am a mechanical engineer and I love asking questions - lots of questions. I have asked some amp techs questions before and the difference between them and Karel is like night and day. You can tell by the way that people answer you. You can see when someone is hopping around trying desperately to avoid admitting defeat. I like the fact that Karel often answered me by saying: "I am not sure, but let's look it up..."
            All i can say or add to what has been said here.... is that we are lucky to have a guy like Karel on our doorstep 8). I mean he even fixed my old solid state WEM copycat ! ? PLUS he's not a bad sound guy too....
              +1, where's a "we're not worthy" smiley when you need one?
                Gearhead wrote: +1, where's a "we're not worthy" smiley when you need one?
                GH, not only that...but I would welcome the following icons...

                run into brickwall, floggin' a dead horse , cork sniffter.... and I really mean it to be humorous..

                ?
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