TELEFUNKEN E52 KÖLN Restoration
Here I describe
the restoration of another legendary receiver from the second
world war (WWII), the Telefunken E52 Köln, which was mainly used by the
German Luftwaffe for ground stations and vehicles.
The receiver was far ahead of competing designs of that time both in construction and performance. The chassis was molded in an aluminum alloy which gave good stability and heat dissipation, and the receiver was built in modules, interconnected with a back plane, the valves were interchangeable from the outside. Sensitivity, selectivity, resolution and stability were outstanding with 2 RF and 3 IF stages, with continuously variable bandwidth crystal filters, with a projected photo scale and carefully temperature compensated circuits.
This E52 was a Ebay Special, that had been recovered from a Barn cellar in Russia, it was with a whole load of WWII German artifacts, that looked like they had been there some 70 years.
All seemed to be going well it looked like it was original and unmolested with the original trimmers covers and optional motor tune.. That was until it came time to ship the radio. Despite paying for DHL, my Russian buddy, found that there was additional paperwork needed to ship this type of equipment and it was costly. Thinking he was doing the right thing it went EMS express post. Well two of the five boxes initially turned up. After waiting another 4 weeks I could see that the shipment was stuck in the tracking system. E-mails to the EMS Russia office initially received a response, but as soon as they realized that they had lost the other three boxes, everything went quite.
After repeated e-mails and eight months of chasing the seller they finally retuned to boxes to him. What he didn’t tell me was that the radio had been damaged while with EMS.
It appeared that Russian customs had taken the chassis apart by ripping the band change rod through the switches and the chassis had been dropped breaking one corner. The small switch finger separators had also been damaged, and when I opened the new boxes, a found a BAG of smashed parts.
Note the tuning capacitor and other parts on the bench..! The porcelain shaft was smashed and many parts were broken. At this point I seriously started to think about conversion to spares, but as this is a rare radio in this part of the world and it was an original set.
I decided to move forward with repair. It was going to be a huge effort having to cast new switch cams and contact separators so I started with the most difficult parts.
The first part I started with was the switch CAM This second photo shows its final home and also the home of one of the switch separators I made.
The separators new and the original to the right, these were made after coating the original in a nonstick wax, and pushing it into a clay mold, then pouring resin into the mold, the cams were made in a silicon mold made the same way.
Above shows test fitting of the new Cams with a PEN holding them in place. Painting the rear of the chassis after sand blasting, the paint was matched to the rear of the front panel.
The Chassis after the repaint, I kept the original serial number and manufacturers stamp
Chassis ready for its parts, Test of the Micro dial, I was worried that it was worn but on this E52 its white with black writing
My Other E52 is Black with White writing, See photo of it at the beginning of this page.
The RF module after repair of the cams, The auto tune after repair and cleaning, Rectifier after repair to the Bakelite
The dial after cleaning The front before stripping for paint.
Rebuilding the tuning capacitor. I replace the original shaft with a 9mm Nylon one Capacitor and coils back in the chassis
Switch Shaft goes in and all of the spacers for the new cams The RF and Oscillator decks clean and in, with all original trimmer caps and coils.
Installing all of the top electronics Shot from the bottom of the set Front modules in and ready.
Power Supply Rebuild:
The Original power supply in this set had a faulty main transformer in the HV winding, caused by a shorted choke.
I managed to get a few basket cases from the internet and a mate and set out to rebuild two working power supplies.
Above the Bench with candidates Above is one of the Donor supplies, I used this to transfer all of the Battery Inverter circuitry
Close up shots of the Donor supply showing the Filter section for the Inverter supply and the switch section, both were transplanted into a good chassis.
More closups of the donor chassis.
Rebuilding Chassis -1 Rebuilding Chassis -2
Above Chassis -1 you can see that there is no Inverter supply as yet, I transferred this from one of the donor chassis. Also the Power Transformer has been changed, as too the HV choke.
Note: I found that there are two types of transformer in these supplies, one has an extra Tap and the wiring is different. Also note that there is an extra board in the inverter section.
Close Up of the Receiver assembled and running.
I went through a lot of trouble to do the full alignment and get everything right. The Receiver performs very well and has good sensitivity. Area’s I can improve on are the switch Cams I recast.
I noticed that the switching was not as good 180 Degrees around from the home position and when I rotated it 180 Degrees again it was great, This is due to uneven cams and I am working on
A CNC program to cut 4 new cams from Nylon stock. This should make everything perfect on Receiver Number One, My Second E52B is already restored fine-tuned and runs great although not
as pretty as this one.
Above are two shots of my Second E52, that was unmolested and in original paint. I rebuild and re-aligned this set and it operates very nicley. Note that this set has the optional BFO control.
It also differs from the top set by not having the mechicnisim for Auto Tuning and does not have the split RF gain / Volume Control.
These small changes were most likely due to material shortages during production in the war.
Copywright Tube Radio Australia Ray Poularas www.tuberadio.com