EB5AGV's Workbench: Rohde & Schwarz NV 1/156 VHF MULTI-COUPLER repair
A classic tubed multi-coupler
This page is devoted to the repair of my Rohde & Schwarz NV 1/156 VHF MULTI-COUPLER.
Tube lineup is: EC80, E180F, 5x EF802, 85A2. It covers from 100 to 156MHz.
What is a MULTI-COUPLER?. Well, basically it is a distributing amplifier (one input, several outputs) with (generally) unity gain. So I can use just one antenna for several receivers. My intended use is to monitor VHF frequencies.
Unit as received
Sadly, I got the unit with some transport damage.
A broken meter glass:
A bent handle:
A damaged something (don't know yet what it is!):
This is the label of the mystery part:
UPDATE: I have got several e-mails (thanks!) regarding this part. It is a double selenium rectifier: 2x 400 V / 100 mA
Internally, it was dirty but complete:
Here you have detailed views of the tubes in the amplifier section:
And the ones in the distributing section:
Repair works
First thing I needed to do was to try to repair the meter. I got it out of the unit and found it had also its casing broken:
First, I made a replacement glass out of a 1mm thick Lexan plastic, as it can be cut with scissors and it is very convenient. Here you have the piece still with the protecting plastic layers:
I glued the broken part, put the new glass and reassembled the unit. Here you have the results (note the 12.66 datecode):
The meter is back to life:
I removed all tubes to (carefully) clean them:
I glued also the mysterious thing and added some rubber band below it to prevent further breakings:
UPDATE: I have got several e-mails (thanks!) regarding this part. It is a double selenium rectifier: 2x 400 V / 100 mA
This is the aspect of the refurbished meter on its place:
And this is a general view of the top side, once tubes were back:
The bottom of the unit was very clean and shows some plated areas, plenty of high quality components:
I gave the unit a try, after measuring resistance in critical areas (power capacitors and such). Here you can see some glowing tubes:
First checks suggest unit works, with very close level in all outputs, but it is a bit deaf.
Here you have a view of the unit working with my R&S CMD-84 as signal generator and my Yaesu FT-212RH as the test receiver:
Using the front panel meter, which has 8 measuring positions, I have found that tubes 2 to 7 are OK but tube 1, first amplifier (an EC80) is soft. Of course, I have none in my stock. So I need one... any taker ;-)?
To be continued...