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telefunken: Help With Telefunken Concertino 8

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Forum » Radios and other type of sets (Physics) etc. » MODELS DISPLAYED » telefunken: Help With Telefunken Concertino 8
           
Michael Boessen
Michael Boessen
 
USA  Articles: 49
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13.Feb.20 20:30
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Hello everyone:

I am hoping some of you German guys can help a poor American with a very nice German radio. I have many questions.  I am sorry if this is a little long.

My nephew has given me a Telefunken Concertino 8 radio that needs a lot of work.  I do not know how this magnificent radio came to be in the United States.  I have never seen a table size radio with 2 huge bass speakers and 2 tweeters.  I am very excited to see if it sounds as good as I think it will.

I have cleaned and repaired all of the pushbutton switches.  They all test good now. I have replaced all of the dial cord.  The radio still has all of the original Telefunken tubes.  One of them is a little weak, and the rest of them all test about half way between good and bad.

1: a question about the pushbutton switches.  They are labeled, from left to right AUS, TONBD-TA, LANG, BANDBREITE, MITTEL, KURZ, AND UKW.   Can someone translate the names for me and tell me what each button is for?  I think I understand "aus"="off" and "UKW"="FM"

The second row of buttons are labeled BASS, ORCHEST, JAZZ and SOLO.  I think these are preset tone controls.  My question about them is this:  One of them must always be down.  Therefore, how does this affect the "TIEFEN" ( "BASS" ?)  and "HOHEN" ("TREBLE" ?) controls?

2:  There are three wires on the EL84 output tube that have been cut off.  A blue wire on pin 4.  A yellow and green wire on pin five.  Since they are across the filament, I suspect they are for pilot lamps, but I do not have any pilot lamps that have no wires to them.  I am wondering if the "bass" and "treble" controls are supposed to have a light behind them.

I have printed a schematic I downloaded from radio Museum. The writing is very tiny and hard to read. I will do my best to guess what the numbers are for this next question.

3:  I have the radio plugged into a variable transformer.  As I bring up the voltage, the bridge rectifier labeled (I think) GR1 on the schematic (a large black object that looks like an electrolytic capacitor) gets a little warm.  There is a 1K ohm 2W resistor that I believe is labeled "W40" on the screen grid of the EL84 output tube that gets very hot.  I have only the large speakers connected.   Can anyone give me some advice about this?

I hope you guys can read my English. I would very much appreciate any help.

Best regards

Mike

 

Michael Watterson
 
Editor
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13.Feb.20 21:05
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Off, Tape/Gram, Long Wave (no use in USA, still works in Europe), Medium Wave (USA= Broadcast), Shortwave. UKW = Ultra Kurtz Wave = VHF, i.e. FM.

It will need some leaky paper dielectric capacitors replaced.

Any Selenium bridge needs replaced, 4 x 1N4007 are fine, but add maybe 150 Ohm 5W in series from + out.

It will be good.

Edit:

BANDBREITE = Bandwidth. I'm not sure what it does on this model, it's probably for better selectivity on Shortwave. See other notes on this model.

 

This article was edited 13.Feb.20 21:07 by Michael Watterson .

Michael Boessen
Michael Boessen
 
USA  Articles: 49
Schem.: 1
Pict.: 42
13.Feb.20 22:46
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Thank you Michael:

I did not know the black object that looks like an electrolytic capacitor was a selenium rectifier! I have done electronics all my life and I have never seen one of these. The wires going to it are very small, which made me think it was some kind of IF coil. I will replace it with a solid-state bridge rectifier.

After that I will get to work on the capacitors. They did not look like paper capacitors to me, and since it is from 1956 I did not think they would be a problem.

Thank you for the translation4 of the words for the buttons.

 

Best regards

Bernhard Nagel
Bernhard Nagel
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14.Feb.20 01:37
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Hi Michael,

Michael Watterson did a good job in translation of the dial and push button lettering.

But I like to give some hints for the electronics in this radio from 1957/58.
Since foil capacitors were used in German tube radio sets from about 1962/63 and onwards, the Telefunken Concertino still has leaky paper capacitors. In most places, they are uncritical - as long they have no short. Leave them where they are. No planless "recapping"...

But at least one capacitor is mandatory to have it replaced! See part of the circuitry.

This is the coupling capacitor C55, 22nF, coming from the audio preamp plate (triode of the EABC80) to the grid of the EL84. Replace it with a good polypropylene one rated to 400 VDC. Since the output tube EL84 is the biggest load in these radios, a proper biasing only by the cathode resistor W36, 120Ω, is very important.

A leaky paper cap can deliver some positive voltage to the grid, so the plate (and screen grid..) current will exceed safe ranges. The EL84 and the power supply can become overloaded.

W40 is a filtering resistor for the screen grid current and other rf and if stages of the radio. So it's normal that it becomes a bit warm. Don't worry here. It is rated with 2 watts capacity.

After replacing the coupling-C, please measure the voltage across the cathode resistor 120Ω, you should read ca. 7.5 volts (if the plate voltage has about 250 volts). After this, you can measure in addition the D.C. voltage behind the C55. Simply put the DVM across W31, 820kΩ. It should read near zero here. Then the EL84 is ok.

And at last the tubular selenium rectifier. It's also normal that these will become warm (not hot!) during operation. As long as the DC voltages are in it's normal range after replacing C55, there is no need to replace the rectifier. If eg. the plate voltage of the EL84 comes below 240 V, you can change it with a silicon bridge. Don't forget the series resistor as mentioned above ... good luck!

Michael Boessen
Michael Boessen
 
USA  Articles: 49
Schem.: 1
Pict.: 42
14.Feb.20 02:16
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Hi, Bernhard!

Thank  you very much for all of the good information.  I found a 50UF 4 volt capacitor in the audio output that was shorted, causing the problems.  I have  tested about 10 capacitors in the radio and they all test good.  I did not want to have to replace all of them so I am glad to hear you say I do not have to replace all the capacitors.

I will certainly replace the one you mentioned.  

I think the bridge rectifier was probably just fine, but based on Michael's input I have already pulled the insides out of it and stuffed a silicone bridge rectifier on a heatsink in the black can.  The insides of that are a very interesting and ingenious design.  I have never seen anything like it in the U.S.  I have attached photos.

Just now, the FM works great and the sound is incredible!!  The AM is not working very well.  The closest 5W resistor I had was 270 ohms, so possibly that is the problem.

My wife has called me that she has dinner ready, so I will have to leave it until tomorrow.

Again, thank you very much for your  kind assistance.

Best regards

Mike

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