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Samos


hcs
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  A few days ago I picked up this Samos FuMB 4, it was used in western part of Denmark.

I need to restore some of the changes that was made of one of the previous owners.

Unfortunately, he made some holes in the front, that I have to close and paint.

The fuseholders is missing, but I have two spares, that I'll use for it.

The banana sockets missing, will be rebuilt with some used ones, I'll modify for correct looks.

I need to find another main switch, that fits the original hole in the front.

Some of the capacitors has been replaced, but I'll have to replace them by correct values.

 

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Edited by hcs
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Powersuply has been repaired, I can't find the two 5uF capacitors in correct physical size and style, so I had to make a tradeoff and construct a plate of pertinax to mount the capasitors. I replaced the capasitors for axial types and the correct values.

Power before:

 

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After:

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Next step:

Replacing the capasitors in the LF amplifier, for the correct values and construct the missing part of the cabinet, for it.

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Some progress...

The fuseholders is now in place and the modified banana sockets has been mounted, I made a fitting for the existing power switch, since I don't have the correct one.

I cleaned the front with water and soap.

In the NF block, all non correct capasitors has now been replaced.

  

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Banana sockets, Left original.

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NF block.

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  • 4 weeks later...

Some progress...

The holes in the front is now closed using chemical metal, still need som fine filling and finish, before painting.

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The missing cabinet has been constructed in cobber plate, need painting...

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Testing of the tubes, showing that one of the RD12Ta tubes was defective, so I had to buy a new one.

(This is test of the new one).

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Finally I made the first power on without tubes, all measurements was okay, then tubes was installed and first test was performed, radio is working ok, frequency readout is spot on. AM is very fine, but FM is distorted, if modulation is to high. I need to check the limiter and FM demodulation stage...

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Edited by hcs
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Yesterday I painted the front, with a paint mixed in a paint shop, it is not perfect, but close, I guess 78 years of smoke and dirt added to the original color.

I really don't want to repaint the complete front, so this is how it looks like now: 

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I checked the sensitivity and both AM and FM, seems to fulfill the specification of 1 V output in 4000 ohm @ 0,3 V noise, with 12 uV input level at the antenna. I don't have any impedance correction for the antenna, my signal generator is 50 ohm and the Samos is 150 omh balanced, so some tolerance is to be accepted.

Regarding the distortion, with deviation higher than around 13 Khz, I checked the IF, limiter and demodulator circuits, all seems to be working okay and all components are within specifications, my conclusion is that the radio is working, as intended, since it was made for measuring and detecting, not for hifi broadcasting. 

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The homemade BNC adapter, that I got together with the Samos. The tip from unbalanced BNC is connected to one of the balanced inputs of the Samos, the ground/shield of BNC is connected to the other balanced input and ground of Samos.


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