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Mw.E.c in bits
Old 12-31-2017, 09:17 AM   #1
Funksammler
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Default Mw.E.c in bits

After finishing the 80 W.S.a's, I decided to tackle some Mw.E.c receivers. I had three that needed some work. The Mw.E.c is compactly build, to reach components needing work the receiver has to be partially or completely dismantled:



You can see the chassis with the HF part; in front of it from left to right: Beat oscillator unit, IF unit and audio stage. These pictures demonstrate the modular design. Another "exploded view":



to interconnect the various modules, there are many wires screwed to connection boards. This is the main connection board on the back of the audio stage:



One of the challenges of repairing a Mw.E.c is to remember which wire goes where and not forgetting any of the minor connection boards... This was actually the main reason for taking this particular picture, to remind myself during the reassembly how the wires are supposed to be connected (hoping that a previous owner has not messed things up)....

Another particular feature of the Mw.E.c is the "integrated circuit" HF design:



Each porcelain ("Kalid") unit holds the complete coil and trimmer sets (one for each band) for the HF and local oscillator stages. A beautiful design but an absolute nightmare to repair. On one of the receivers one of the trimmers was damaged, it was virtually impossible to gain access. You do not want to destroy a trimmer, as it would require you to source a complete replacement unit....

On one of the receivers I encountered another weird problem: I could not get the beat oscillator to run. I measured everything and everything seemed correct and yet the oscillator refused to produce a signal.

The beat oscillator unit is fixed to the IF unit with three screws. Two are easy to see; a particularity of these screws is that they are electrically insulated from the chassis by Pertinax bushings.

The third screw is a bit more difficult to find and turned out to be loose. This third screw is important though since it forms the only electrical connection between the chassis of the beat oscillator and the rest of the radio. Because the screw was loose there was no electrical contact and there was no path for the filament current of the oscillator valve to flow back to earth. After fastening the screw the oscillator ran without problems!

Simple enough to fix, but it took me quite a few hours to find!

regards,

Funksammler
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Old 12-31-2017, 05:16 PM   #2
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Funksammler, can you show your workbench more closely?
It's always interesting to look at the setup people using to repair those
quite often very heavy sets.
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Old 01-01-2018, 07:03 AM   #3
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Not a lot more to see on my workbench.... There are a lot of different screwdrivers, screwdrivers are key! With seized screws it is essential to use a correctly fitting screwdriver that allows you to apply great force.

I have managed to downsize my test equipment considerably. I had a lot of 70' and 80's test equipment taking up a huge amount of space and getting less and less reliable, so I bought a handheld digital oscilloscope/signal generator/multimeter, all in one. A cheap and versatile piece of kit which does more that my old equipment put together. Above all it is battery powered, so I can take my whole electronics lab to my equipment if I need to.

regards,

Funksammler

Last edited by Funksammler; 01-01-2018 at 07:22 AM.
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Old 01-01-2018, 09:53 AM   #4
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Quote:
Originally Posted by Funksammler View Post
Not a lot more to see on my workbench....
Funksammler, i'm more interested in your desk itself. German radios are quite heavy so the desk must be able to support them. And not only the radio itself, also the test equipment, tools, spare parts, schematics, light, proper power supply etc. And then you must have enough room to operate there too... Also lot of repairs are not 10 minute job so you must be able to leave all this sometimes for weeks - not a ad-hoc setup in the corner.

From the pictures i can't figure out your desk - is it just some old sturdy desk, something improvised or something special?
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Old 01-01-2018, 11:57 AM   #5
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Ah I see.... Well, I use my father's work desk, which was his father's before that and probably goes back a bit further (I had some guests over the new year so I tidied up a bit, some other random projects are already starting to fill the desk again):



It is a nice old fashioned pure wooden desk with lots of drawers to store tools and other bits and bobs! I also use the original wooden chair with it, much more comfortable than any modern desk seat I have had the displeasure to sit upon....

The desk top is covered in a layer linoleum, which is an ideal work surface as far as I am concerned. It is relatively soft, so it does not damage the equipment or paintwork but even heavy equipment can easily be slid and handled over the surface If it gets too worn over the decades you just replace the linoleum and you have a brand new work area (I remember my father changing it in the late 1970's, I recon it still has a decade on it....).

Apart from lots of screwdrivers you need lots of electric sockets, so I fitted plenty of earthed and non-earthed sockets so I can plug in all sorts of old equipment using their original plugs.

Last but no least you need a hard wearing floor covering. During the work there are always lots of bits of debris ending up on the floor, if you do (de-)soldering plenty of drops of solder end up everywhere, so don't use a nylon carpet (as was the original floor covering in my hobby room, so I have now covered it up with hard wearing rugs).

Those are my tips for setting up a Wehrmacht Radio restoration studio!

regards,

Funksammler
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