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Rohde&Schwarz, EK07D Restauration
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01.10.17 08:33
Martin 

Administrator

Re: Rohde&Schwarz, EK07D Restauration

Wout:
I am surprised how accurate the frequency dial actually is! CW and SSB reception works as well with the built in BFO.

The tuning capacitor in the oscillator part is made from one massive block of a spezial metal alloy what have extremly low temperatur drifts. (may be this is a OEM part from the Tronser company)
There are 32 screws for adjust the liearity.
A mechanical peace of arts in that radio, typical for Rohde+Schwarz. A normal emplyoee was working up to 3 years to get the money for one of this radios that time. The oscillator self is hermetical closed and have inside a chemical dryer what ca be reactivated by put it for one hour in the kitchen oven at 70 degrees C

greetings
Martin

07.10.17 19:55
Wout 

Picoskop

Re: Rohde&Schwarz, EK07D Restauration

Last weekend I was looking at the schematics and sitting stand-by with my old Philips oscilloscope to find out why the receiver LO was not locking/synchronizing. I was suspecting something would not be OK in the 'Steuerteil'. Fault analysis in this receiver is particularly complicated because of the weight (65kg) - you don't easily turn this 'tank' around when you want to put a probe at a certain point. Also, all 'modules' are well shielded and encapsulated with heavy CuAg . Not to mention the main oscillator enclosure Martin talked about in his last post, what a piece of mechanical and electronics art!

Sometimes things are more easy than expected. I should have better looked at what the R&S Engineers and designers had already thought of. I am always impressed by R&S equipment and how it's designed (and built). Here, the 'Überwachungseinrichtung' helped me out - quickly. The switch in position 14 indicated a way too low current flow through Rö47. I noticed this earlier but somehow didn't pay too much attention to it - wrong!

I took the simple (perhaps quick and dirty) approach to just replace Rö47 to see what would happen. As I didn't have an ECC801S or even an ECC81 in my junkbox, I 'borrowed' the tube from the 'Eichoszillator'.

I switched on the filaments again... then the high voltage and... BINGO! The receiver LO worked (locked) immediately in all band positions and the meter reading in position 14 of the Überwachungs switch was right in the middle of the red mark on the scale. I will look out for a pair of these triodes to have the 'Eichoszillator' working again and to have one as a spare.

All other tubes measured (with the Überwachungs switch) as the manual indicated.

I couldn't resist to connect an 'antenna' (10m of wire outside of the house) immediately and started to listen on various bands. What a joy to listen to this receiver and to go over the long dial with that very smooth running tuning wheel! Although I didn't measure anything specific, the receiver looks quite sensitive to me. The conditions on the 14MHz radio amateur band were quite good as after a while I received 2 radio amateurs from the East Coast of the US with very high signal strength in single side band (the BFO only is not ideal for SSB but it works). Radio stations in AM are sounding really nice despite the somewhat limited band width. All features on the received seem to work fine.

Date codes in this receiver are indicating it's from 1960. All components and perhaps even the tubes are original. Just one double triode gave up and after replacing this one everything works perfect again! What a quality product.

07.10.17 19:58
Wout 

Picoskop

Re: Rohde&Schwarz, EK07D Restauration

See attached pictures. You will see the mechanical issue I was facing. In-between the frequency scales on the 'frequency band drum', there are white colored, brass strips. One of those apparently came partly lose and 'hooked' or snagged behind some metal parts of the received close to the drum. These strips are not al all easy to remove without taking out the complete drum (something I didn't dare to do, yet). Carefully bending the strip in shape again and very carefully tapping the strip into place (using a very light hammer (!!) with soft rubber head) I was able to get it back in place again (see pictures). The strip is not perfectly straight again but you can't see this repair from outside and the band switching is now smooth and without any issue.

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07.10.17 20:02
Wout 

Picoskop

Re: Rohde&Schwarz, EK07D Restauration

I cleaned the back panel with the C-connectors and switches, cleaned and lubricated the cooling fan (huge improvement, much more air flow now!) and put fresh grease on the rails of the cleaned enclosure so the receiver chassis would slide in smoothly anyway, I think I put quite some TLC in the receiver!

Thank you all so far for your attention, tips, hints and advice! Also to the blog reader who offered me the PSU, thank you very much again!

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