Export to USA for Delmonico model Novum
This radio's name is Delmonico model Novum. It was made by Korting in Germany. Chassis number 24433 model 1047. Six tubes single ended output and an EM84 tuning indicator. This chassis incorporates single sided Printed Circuit (PC) boards. In my 44 years of repair experience I have found these PC boards are prone to cold solder joints where the tube sockets are soldered to the copper traces. I believe this is due to the thermal cycling of the solder joint and not a factory failing. This same problem can also be seen in modern electronic equipment (computer monitors, printer power supplies, etc) where a component heats up with normal use. Another noted problem of PC boards of this vintage unit (not this particular chassis) can be carbon trails from cathode to anode across the grid in the audio output tube. This causes the grid to go positive and make the output distorted. More can be read about this carbon trail at: http://people.cs.uu.nl/gerard/RadioCorner/Sets/Ko23621.htm
My biggest challenge with this chassis was finding an alignment procedure that I could read. Most of the procedures for this radio are printed in German. I compared a few similar chassis against the circuitry of this chassis, identified similarities and used an English procedure to properly align the chassis. www.Radiomuseum.org is a great resource for such information.
The restoration is quite straight forward. One note is this manufacturer used uncoated carbon composition resistor unlike other manufacturer use a resistor that has a plastic coating keeping the moisture away from the core. I found two or three out of tolerance resistor so I "Shot-Gunned" replaced all of them as in an American made chassis. The electrolytic and paper capacitors were also replaced. The original ceramic and polystyrene capacitors were left in. I have found Polystyrene caps to be stable and good as is the same for Mica and ceramic capacitors.
Three Electrostatic tweeters are in this chassis. The suffer from deteriorated foam rubber pressure pads and corrosion. See also the "Electrostatic" page for additional How To restoration tips.
Korting 1047 #2
Here we have just about the best example of a finely finished cabinet that I have ever seen on a European Radio. No sun bleaching. The front plastic is all intact and a great dial scale. This radio will receive the usual restoration like the Korting featured above. The Gentlemen at http://www.radiomuseum.org/r/korting_novum_1047.html assisted me by translating the German alignment procedure to English.
See: http://www.radiomuseum.org/r/korting_novum_1047.html for more information.
I had a failure after a restoration. The above radio experienced intermittent FM reception a few days after it was received by its owner. The owner unsuccessfully, kindly performed a few simple steps (reseating the tubes, checking for a disconnected antenna, etc). I had the unit sent back to me. It had dead FM on arrival.
After proceeding with another FM alignment L104 had no effect on the IF signal strength and did not peak on 10.7 MHz IF frequency. Further poking around found no B+ making it to pin 6 plate of the ECC85 tube. Using an ohm meter verified no connection from B+ to pin 6. I was hoping coil L104 was not open circuit. Especially since these coils are not made any more (i.e., containing "Unobtainium"). Close inspection reveled a loose wire held by flux and no longer attached to the solder post with solder.
Most likely when the 22K ohm resistor R105 (circled in red below picture) was replace, the heat from the soldering gun allowed the fine wire from the coil to become move from the solder post. It is the wire protected by a greenish insulation sleeve in the picture below. Once re-soldered the static returned and stations could be received. I completed the FM alignment and burned-in (operated) the unit for a few more hours.
I will continue to burn-in the unit longer before shipping it back to the owner.
Click to enlarge.
"Every man makes mistakes. It takes a good man to fix his mistakes." Once told to me by Nick, my best friend for over 35 years.
Unobtainium - A substance, part or product that is no longer being made or manufactured.
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