sell: SR1S variant?

Dear Members,

This Sell & Stemmler tube tester is an unknown model for my. Probably it correspond to a SR1 S variant 

The Service Manual was professionally translated to English language by the respected members Mr. Robert Sarbel and Herr Fred Zeeb but the manual is very discreet in the operation instructions.  The Service examiner inside paper is dated 1956. Unfortunately there is not an model identidficación plate inside or outside  of the wood box.
Finally is not the SR1 or SR2 model and with the the SR1-S model has important differeces.  My model does not have the top grid cap elektrode and the 7 elektrode. 

I will be very grateful if some member has some information or Herr Klaus Ortwein who upload the SR1-S model can do some comment. 

Respectfully, Bruno.

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