Köln (Koeln) E52 XXX restoration project
Why do we need to restore Köln receivers?
We can distinguish between two major circumstances:
1. Aging defects and/or general re-adjustment
2. Often more serious, are “amateur-like modifications” or carelessness, which has to be reversed, as to bring the Köln E 52* receiver back to its original fashion. Sometimes, however, destruction of essential parts occurred, like burning-out of the power transformer, owing to the usage of a solid metal piece instead of a 1000 mA fuse! This actually occurred in a Köln owned by a Dutch collector, which he obtained from Russia some years ago! *The inconsistency of using E52 and E 52 might make it easier for web-search-machines to trace subjects on our website
For this occasion we consider our Köln E52a2 receiver, serial-number 2871.
The serial-number is not a straight succession (production) number, but was provided in so-called “lots”. These numbers are generally painted on the microfilm glass-disc and/or rubber stamped on the left-hand side of the projection housing (regard photo 0). See for Köln details also our E 52 main page and my paper on: Aspects of German electronic engineering in the 1930s (Synopsis), Luftboden-Programm
Our Köln E 52a2 might have been produced in late 1944 or early 1945. One never will find, in contrast to common German practice, a hint on a date of production in it. Only the date stamped on the valves might give a clue(hint), when most valve-base would carry similar date (only valid, when valves had not been changed since). German valves were stamped like: 45/43, which indicate that the valve was accepted (Abgenommen) week 45 of 1943.
It was obtained in Holland (1993), though, the previous owner told me, that he got it when he was to be sent home late 1945, after his engagement with the US Occupying Forces in Germany. Where he had worked as a translator (interpreter). He was asked, what he would like to bring home? He was then accompanied to a very large store, packed fully with German electronic gear. Cable rolls with fine (Vacha) coaxial cables (far too heavy!). He choose two receivers, one being a Köln E52a2 and an Ulm E53b VHF receiver (how he managed to transport (convey) 80 kg is an open question). Anyway, in those days priceless devices, which represented the best that was made in Germany (maybe elsewhere too). The E52 may have been the best military shortwave receiver of its time.
Until late 1940s it was “not done” in Holland, to mention a fine (high quality) German receiver, what was then stated was, for instance, “a 10 valve shortwave receiver” without further explanation (as did late PA 0 UM during an Electron interview, whereas the actual receiver was visible in the background). One reason might also have been, that the actual owner was not allowed(supposed) to possess such a device! After say early 1950s, no one dared these facts (circumstances) any longer.
I have been engaged for more than 40 years with Köln receivers.
In the early years between 1945 until say late 1960s, “Köln” (receiver) meant a magic word, and only very fortunate(lucky) people could afford one. I still remember vividly an intriguing advertisement of about 1961/62, in which a German company offered a Köln receiver for 1500 DM! Which kept it for most people an un-affordable dream (surely for me, as I was then a poor student, AOB). It was, however, not even in a genuine shape, as it had been “adapted” by Rohde & Schwarz in the late 1940s (for checking time-keeping signals).
But we then weren’t aware of “originality”, as collecting electronics was not yet “en vogue”. Collecting historical electronics started, world-wide, say in the second half of the 1980s. Since then, many devices have even become less affordable, owing to big money spenders (inflation?) and, since recently, due to the e-Bay’s aberrations (madness or is it lunacy?).
However, as long as real collectors dominated the scene (say until early 1980s), many collector items were regularly employed (utilized) too, as nothing else comparable was affordable.
Our Köln serial number 2871, was inflicted by aging defects and by amateur-like modification, as it had been re-painted outside. More serious is, that the original text at the aluminium* front-cover(plate) had been made invisible (it is not yet clear whether it was filled-up or that it had been rubbed-off). *Hereafter sometimes abbreviated Al.
Generally, however, one of the most serious problems is, that the ganged tuning capacitor (six fold) is of very unconventional, though sophisticated, design. Each capacitor section is fully separated (independent) from each other and its position (actual capacitance vs rotation-angle) to one another was adjusted(kept) by means of spring loaded ceramic shafts. These shafts-adjustment-screws are conveniently accessible. It relied, however, on spring loading. What does occurs in time is, that the ceramic shaft is, due to metal oxide, being hampered in its free movement. When, for whatever reason, the shaft is being forced a bit towards its spring tension, then its spring-force might be not sufficient enough to restore its starting position (insufficient shaft pressure). The down-side is now, that the tuning capacitor section can rotate(move) a few degrees around a free position, which is intolerable.
Getting access to the spring section (hole) is only possible by means of complete dismantling of the Köln receiver!
Never believe anyone, who claims to have overhauled his entire Köln receiver, without having dismantled it totally! As, 99 out of 100 Kölns suffer from this tricky down-side in some respect..
After having done this many times, dismantling can be accomplished within say 45 to 60 minutes (vice verse). We will closely show all steps necessary. Although not essential, also taking a closer look on various plug-in modules.
Part I pages 1 - 16 (1.5 MB)
Part II pages 17 - 22
Part III pages 23 - 31
Part IV pages 32 - 38
Instuctions how to align (adjusting) the the tuning capacitor gear wheels to the central wheel of the tuning-module. (pdf) (new) State of affairs 21 August 2008
Resently Luca Fusari asked me: how his Köln (Koeln) glass scale can be removed from the tuning unit. I have send him the following short information: Removal of the E52 glass disc. State of affairs 31 October 2010. (new) pdf
On 7 May 2008, though, I received an e-mail from Ron Brown GW6WRP with his enhanced instructions how to dismantle some parts of the Köln E52 receiver:
GW6WRP's instructions (pdf)
Back to: Köln E 52 main page