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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
 
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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
 
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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
 
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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
 
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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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Mau VanDuren
Mau VanDuren
 
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20.Jul.20 23:07

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This thread was very useful for me. A couple of months ago I was so lucky to be given a Concertino 8. It had been sitting in a basement for many many years and was very dirty and grimy inside. I did a lot of cleaning, replaced all tubes with NOS, and followed the advice of the knowledgeable people on this forum.

As a result the amplifier works really well. It reminds me of the monoreal sounds I grew up with back in the Netherlands in the 1950s. AM or medium wave is good, too. However, UKW and KW are very weak. KW probably needs a long wire antenna, so that is perhaps no surprise.

But UKW should have good reception with the dedicated roof antenna I hooked up using the 300 Ohm twin wire. I do get a couple of very distorted signals when the volume is turned to the max.

One would suspect the UKW tuner, but which component?

By the way, the "eye" barely blinks on any of the bands.

Any thoughts are most welcome!

Thanks!

Michael Boessen
Michael Boessen
 
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21.Jul.20 16:11

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Hi, Mau!  

This is a fairly complicated radio and will be very difficult to troubleshoot using an online forum.  I had a lot of trouble with the band switches  on mine.  It is not easy to gain access to them. I spent a lot of time with pipe cleaners dipped  first in contact cleaner, and then DeOxit.  I would soak the pipe cleaner in contact cleaner, slide it in a long the side of the contacts and operate the switch several times.  Then do the same with the DeOxit
It sounds like the FM at least needs alignment.  This was a very big problem for me because I could not find alignment instructions in English.  The alignment is very complicated and requires some fairly sophisticated test equipment.  It took me three days to get it right.
I don't think my expertise with this radio is sufficient to be able to help you much further than that.  Hopefully some of the guys there in Europe will be able to help you better.
Good luck!
Mike

 

 

Mau VanDuren
Mau VanDuren
 
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24.Jul.20 14:22

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Hi Mike,

Thanks much for your kind response. Complicated indeed. I did replace most capacitors, bad or not, just to get ahead of the eventual failure. That improved AM/Medium wave reception significantly. I did leave the tuner capacitors alone since it would throw it out of alignment. I will try your cleaning suggestions.

I still know enough German to be able to read the manuals, but I do not have any equipment beyond a multimeter. So, I'll leave that alone. Maybe I can find someone in the Washington, DC, area who has the knowhow and equipment. It would be nice to have it working properly.

But hooking up my iphone to the "toneband" input gives a very nice sound reminding me of my youth. Monoreal audio has something going for it.

And then, the beautiful shell fits right in with all the family antiques I shipped from Europe after I moved here 38 years ago. At least I don't have negative nostalgia to deal with ;)

All the best!

Mau

Michael Boessen
Michael Boessen
 
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24.Jul.20 18:11

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Hi, Mau:
I do not believe that changing the paper capacitors in the tuning circuits will affect the alignment very much if at all, and might cure your problem.  Paper capacitors are not used as frequency determining components.  They are too unstable temperature and moisture wise. The frequency determining components should consist of  the tuning capacitor and any tuneable coils and trimmer capacitors.  Telefunken must have been confident in the stability of those tuning coils as they poured hot wax in them after doing the factory alignment, and it is extremely difficult to get it out and get the coils where you can tune them.  I would go ahead and replace any paper capacitors in those tuning circuits if you have that skill.
Good luck
Mike

Bernhard Nagel
Bernhard Nagel
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24.Jul.20 19:38

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Hello Mau,

before attempting any change/replacement of capacitors from L/C circuits or starting an alignment procedure, please check the FM reception for sensitivity. If tuned to no station, the typical static should be noticed. If tuned to a local FM station, the tuning indicator eye EM80 should close.

At the point of max. closing, normally the sound should be clear and undistorted. If this is not the case, a possible reason is often a defective electrolytic capacitor, the so-called Ratio Capacitor. This part is unfortunately "hidden" in the last IF can where also the EABC80 tube sits.

First the situation in the schematic, can be enlarged by clicking.

Here we see the last IF stage, followed by the detector and audio preamp tube EABC80. All parts inside of the dotted square are located in the alumnium can.

At test point 3, you can measure the capacitance of this electrolytic cap C209. It should read about 2µF or more. After more than 60 years, it could be dried up and lost it's capacitance.

For a fast test, you can solder in parallel to point 3 the negative of a 2.2µF 63V electrolytic, the positive pole to the chassis/ground.

Maybe the FM reception improves now clearly...!

In the schematic, you will find a "pin-out" of this IF can to locate the point 3. This is the view from the bottom (solder side).

Good luck!

Regards
Bernhard

 

This article was edited 24.Jul.20 22:47 by Bernhard Nagel .

Mau VanDuren
Mau VanDuren
 
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25.Jul.20 15:59

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Hello Bernard,

Wow, what a useful idea. Indeed, the symptoms you describe are correct. I will try this and report back when done. That may be a while since I'm away from home.

You suggest that the positive goes to ground? I thought ground was negative?

Thanks much!

Mau

Michael Watterson
 
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25.Jul.20 16:46

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The FM dectector is one of the few things (apart from negative PSUs and thus Germanium radios) where the + is almost always is to the 0V/ chassis. The Eye also uses a 0V for no signal (maximum gain on AM AGC) and increasing negative to chassis.

In general the FM dectector capacitor is usually 2uF or 4uF. A 2.2uF will do for 2uF and a 4.7uF for 4uF. The voltage gets higher than the AM detector, so the voltage rating can be any rating up to 150V as long as it exceeds the minimum required, I forget what, but certainly a 35V part will be fine. Likely a 3.3uF or 4.7uF will work fine if it's supposed to be 2uF and you don't have a 2.2uF.

  
rmXorg