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Concertino 8

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Select picture or schematic to display from thumbnails on the right and click for download.
For model Concertino 8, Telefunken Deutschland (TFK), (Gesellschaft für drahtlose Telegraphie Telefunken mbH:
Radio de ma collection que j'ai restaurée il y a quelques jours...
 
Country:  Germany
Manufacturer / Brand:  Telefunken Deutschland (TFK), (Gesellschaft für drahtlose Telegraphie Telefunken mbH
Year: 1957/1958 Category: Broadcast Receiver - or past WW2 Tuner
Valves / Tubes 7: ECC85 ECH81 EF89 EF89 EM80 EABC80 EL84
Main principle Superheterodyne (common); ZF/IF 460 kHz
Tuned circuits 8 AM circuit(s)     12 FM circuit(s)
Wave bands Broadcast, Long Wave, Short Wave plus FM or UHF.
Details
Power type and voltage Alternating Current supply (AC) / 110, 125, 150, 220, 240 Volt
Loudspeaker 4 Loudspeakers
Power out
from Radiomuseum.org Model: Concertino 8 - Telefunken Deutschland TFK,
Material Wooden case
Shape Tablemodel with Push Buttons.
Dimensions (WHD) 630 x 380 x 285 mm / 24.8 x 15 x 11.2 inch
Notes Bandbreite schaltbar; Kurzwellenlupe; baugleich mit AEG 6077WD
Net weight (2.2 lb = 1 kg) 14 kg / 30 lb 13.4 oz (30.837 lb)
Price in first year of sale 429.00 DM
External source of data Erb
Source of data HdB d.Rdf-& Ferns-GrH 1957/58


All listed radios etc. from Telefunken Deutschland (TFK), (Gesellschaft für drahtlose Telegraphie Telefunken mbH
Here you find 3440 models, 3024 with images and 2020 with schematics for wireless sets etc. In French: TSF for Télégraphie sans fil.



 


Forum contributions about this model
Telefunken: Concertino 8
Threads: 6 | Posts: 37
Hits: 725     Replies: 11
telefunken: Help With Telefunken Concertino 8
Michael Boessen
13.Feb.20
  1

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
13.Feb.20
  2

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.

 

Michael Boessen
13.Feb.20
  3

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
14.Feb.20
  4

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
14.Feb.20
  5

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

Attachments

Mau VanDuren
20.Jul.20
  6

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
21.Jul.20
  7

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
24.Jul.20
  8

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
24.Jul.20
  9

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
24.Jul.20
  10

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

 

Mau VanDuren
25.Jul.20
  11

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
25.Jul.20
  12

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.

 
Hits: 1599     Replies: 2
telefunken: 8; Concertino
Stuart Matousek
10.Nov.10
  1

I was wondering if anyone can explain the purpose and function of the bandwidth switch. Presumably it is to increase or decrease the range of frequencies tuned in to at one time, but for practical purposes what should it do?  

James MacWilliams
11.Nov.10
  2

The bandwidth switch, which only functions for the AM bands -- Lang, Mittel, Kurz, narrows the bandwidth of the IF section.  If you have two closely spaced AM stations in frequency, one station may interfere with the other.  The selectivity of the radio may not be enough to eliminate one of the stations.  This is particularly true on the shortwave band.  Local MW stations are usually spaced in frequency far enough, to prevent this.  The bandwidth switch increases the selectivity of the radio allowing you to tune in one station while keeping the other from interfering.  It is not always desirable to do this, however, as it reduces the audio fidelity of the station you want to listen to (the high frequencies are attenuated), hence the switch and your ability to turn it on and off.  This doesn't explain everything, but I hope it helps.

Stuart Matousek
11.Nov.10
  3

Thanks that does answer my question clearly.

 
Hits: 2379     Replies: 7
telefunken: 8; Concertino, need Dial glass
James MacWilliams
13.Nov.09
  1

I recently purchased this radio.  When it arrived I found that the Dial glass was broken -- the radio had been poorly packed.  I found another Concertino 8 and purchased it.  When it arrived, guess what, its Dial glass was broken too.  So now I have two Concertino 8's both with broken Dial glass.  I would be happy if I could make one good radio out of the two.  Please, if anyone should happen to have a scrapped Telefunken Concertion 8 that I could purchase the Dial glass, let me know.  I would be happy to purchase it plus shipping costs.  Thanks

 

Marco Gilardetti
17.Nov.09
  2

Hello James, I am very sorry to read about your misfortuned case, I have as well purchased a Concertino 8 lately and it's very sad to figure your units with broken dial glass. The Concertinos are terrific radios.

Did you try to fix the glass with cianoacrylate glue while you wait for a replacement glass? If you work with a small amount of glue FROM THE BACK and remove the excess on the front with a blade, most of the times you get fairly good risults. If you then overimpose a new transparent glass, correctly shaped, over the repaired one, in some cases the crack lines may be hidden enough to consider the overall result as acceptable.

 

James MacWilliams
17.Nov.09
  3

Hi Marco,

I appreciate your sympathy.  Unfortunately, both dial glasses were broken in too many pieces to hope to be able to glue the pieces together.  In addition, both dial glasses broke on the same side, so I can't use two to make one (that is use the good right side with a good left side).  I have thought about having a new glass cut, but I don't know how to go about painting the stensil on the glass.

Jim

Marco Gilardetti
17.Nov.09
  4

Hello James. The topic of reproducing glass dials has been already discussed here. The following topic is especially interesting: US fellow Dennis Wesserling shows how to do it with inkjet printers and molding powder, while Mario Coelho and José Duarte Costa go even further with professional-style serigraphy. Results are often "as the original":

http://www.radiomuseum.org/forum/dial_scales_homemade_with_inkjet_printer.html

You may want to try it on your own or contact those gentlemen and ask if they may do the work for you.

There is even a simpler and faster shortcut: printing the dial with inkjet on a transparent foil, and then put it in a "sandwich" of two glasses. The usual drawback of this method is that white colour is impossible to be printed, but the Concertino's dial has only black and gold if I remember correctly so it doesn't matter. Ther result is obviously not perfect but decent, and it's a speedy way to have your Concertino rehauled rapidly while you work on / wait for something better.

James MacWilliams
17.Nov.09
  5

Thanks Marco, I'm going to try the wet decal approach.  I'll have to have glass cut but I know where I can get that done.  Scanning in the original dial will be tricky since it's bigger than A4 paper, but I'll do that in sections anyway, since transfer the wet decals to the glass would be difficult if the decal was that large.  It'll be fun to give it a try.

Jim

James MacWilliams
18.Nov.09
  6

I have tried to scan what remains of the original dial glass, but since the dial markings are on the back side of the glass and the glass is about 6mm thick, the scans are out of focus.  Any suggestions on how to scan the original and get a sharp focus?

Marco Gilardetti
19.Nov.09
  7

Not really rather than to change scanner type or try with a fine-detail photograph. However, your question risks to go unaddressed here as not many users own a Concertino 8. I then suggest you to open a new, specific topic on this matter and ask other users which scanners have a depth of field not as shallow as yours. Many others probably went through your same problem already and can suggest you a good model.

Michael Boessen
17.Feb.20
  8

Hi James:

This is a very old post and I don't even know if you are still watching the forum. I am restoring a concertino eight.  It is missing the grill on one of the side speakers. From your post here, I gather you might have an extra one of these. I am in the United States, so I know shipping will be a little high, but if you get this message and you have one would you please contact me:

mboessen@ktis.net

thanks!

Mike

 
Hits: 2604     Replies: 5
telefunken: 8; Concertino. Equalization keys etc.
Marco Gilardetti
30.Oct.09
  1

Good morning fellow radio enthusiasts!

I recently bougth a Telefunken Concertino 8 in Germany to replace another FM radio in my house that got broken and will take a very time-consuming repair.

First of all please let me express my admiration for the german radio industry of those times and the goals it achieved with outstanding products like the Concertino series. I am impressed by the overwhelming quality of this radio and by all the facilities with which it is equipped. The sound especially left me literally open-mouthed. The rotating ferrite antenna is another great feature.

Now to my question. It seems to me that the only "usable" setting for the equalization buttons is the "orchestra" setting. With "jazz" and "solo" my unit emphasises the high frequencies to such a point that the audio gets extremely fatiguating. Low frequencies are emphasised as well, but not as much as the high ones. In addition, the "treble" control, which is very effective when the radio is used in the "orchestra" setting, seems to have almost no effect when in "jazz" or "solo" mode. The bass control, instead, always effects the sound as it should.

I would like to read other owner's impressions on this topic. Is this expected? Perhaps those settings were designed to be used on AM broadcasts, where high frequencies are much less than in FM and thus need to be emphasised? Or does the equalizer of my unit definitely need to be checked?

Thank you.

Stuart Matousek
30.Oct.09
  2

Hello Marco, I have this radio and it does have magmificent sound. The bass and treble controlls on mine only function in the "orchestra " position, and from what I can work out that is the way it is intended.I  was wondering about that myself, perhaps someone else has some info on that? I usually keep it on the "bass" setting when playing at low levels,and use "jazz" which emphasises treble with less bass if I want a bit more volume, as the high bass drains too much power and distorts too much if playing louder. I use "orchestra " a bit if i want to manually controll the equalisation. The "solo" is quite flat and suitable for hearing a voice/news or something clearly. It is worth dismantling and cleaning all the contacts on these switches so you know they are working correctly. Let me know how you get on with restoration! 

Stuart  

Emilio Ciardiello
30.Oct.09
  3

Dear Marco,

yes, FM German radios were true high-quality sound systems. Every circuit was carefully designed with no compromise, and the same was true for the speaker system and for the cabinet. Their only imperfection was the FM band limited to 100MHz for the domestic models. I have no experience with this model, but I often use a Telefunken Opus 2430 UKW or a Hymnus Hi-Fi Stereo 5014WK, US version that tunes up to 108MHz, to enjoy classical music. I find that their sound is excellent, even when I listen to deep and loud pipe organ performances.

The audio circuit of good quality German radios usually has two major tone control systems. The first one uses two potentiometers to manually enhance or attenuate trebles and basses. The second one uses register keys to have more or less fixed response curves. Usually there is also one hidden response control depending upon the listening level, the physiological volume control. When you select a particular register, as the ‘Solo’ or ‘Jazz’ or whatever named, you are bypassing the tone manual controls. You are giving the amplifier a response best suited for, say, reproducing the sax sound, but cutting at all the deep bass notes. In general the combined effect of tone controls and of register keys results in an overall attenuation of some high or low notes. In some radios, as many Graetz models Melodia, Sinfonia or Fantasia, the backlights of both manual tone controls are switched off when any tone register key is depressed. I never examined in details their circuitry, but this means that the manual tone controls are ineffective when registers are switched on.

To have the best sound you should not use register keys at all, unless the ‘Orchestra’ position gives simply a flat response.
 

Enjoy your radio, Emilio

Marco Gilardetti
02.Nov.09
  4

Hello Stuart and Emilio and thank you for your kind replies. I took some time to check the schematics this weekend (it was placed in the back panel inside a cardboard pocket, what a nice touch from Telefunken!) and it seems you both are right. Although not easy to read out, both tone controls are bypassed with a switch when anything but "orchestra" mode is selected.

My impression that the bass control was always on was probably due to a bad contact, or a wrong acoustic impression. I redid some careful testing yesterday and it's definitely off as well.

I agree with Emilio that these pre-set curves are not very impressive. The emphasis is much exaggerated; it may have impressed casual customers of the time but it is seldom useful under normal listening conditions. But perhaps radio broadcasts of the time had a different frequency range.

I listened to the radio all through the weekend and I am delighted, I will never part from my Concertino! I agree that the extended UKW band could be a nice addition, however I can live with 100 MHz as RAI 1, 2 and 3 are all below that frequency, I only miss the Filodiffusione channel 4 which is over 100 in my area, but you can't have everything, right? In change, there is the LW band which is almost always omitted in italian radios and with which I can very easily tune in the interesting french broadcasts.

Emilio, do you perhaps know of italian radios of the time that reached this level of perfection? I must admit that I always undervalued radios of the fifties/sixties because of the pitiful quality of the italian radios with which I have to do almost daily. I first got the impression that there was a part of the world I was missing when a customer brought in his Blaupunkt Arizona for repair and I saw how well it was made. This Concertino (and some other radios you have linked to, like the Graetz with the horn driver: impressive!) again changed my point of view.

Emilio Ciardiello
02.Nov.09
  5

Dear Marco,

the purpose of register keys can be partially explained considering the state of art of broadcast transmissions in a given period. Early FM radios were just AM sets with an added FM tuner. Very soon the audio sections became evolving, to match the increased bandwidth available both from the music sources, tapes and microgroove records, and from the FM broadcast equipment. German radios first were equipped with one or more additional electrostatic speakers and then with some dynamic mid-ranges and tweeters, to increase mid and high-frequency response and offer space-surround or full stereo sound. But all the audio section was carefully designed to give high-quality sound extending to some 15KHz. The cabinet itself and the high-compliance speakers were all part of the audio system, in a sort of high-efficiency speaker enclosure. Here you can find a poor (space-limited), yet significative overview of the evolution of FM German tube radios through the years.

With audio sections designed for FM, register keys had some usefulness when listening to other sources: ‘Voice’ key could be useful in AM reception to attenuate high-frequency noise, hiss or heterodyne whistles; ‘Jazz’ probably was used in record reproduction to mask-off rumble from the turntable. Today broadcast stations on AM bands are closing out and shellac or vinyl records are no longer in use.  So, you can just listen to FM sources and register keys are useless.

In my opinion, Italian radios, when compared to the German sets, are just rubbish and often also harmful rubbish. When looking to the inside of them, the first sensation is to see a handful of components placed here and there inside the cabinet: no care for the acoustics, for service accessibility or for cooling-air flows. The cabinet itself, apart from its more or less attractive look, was of soft and often worm-eaten wood. Even simple solutions, popular in German radios, such as the tuning flywheels, the separate AM/FM tuning dials, the built-in ferrite antenna, the dual tone controls or the loudness (physiologic) volume control, are not available in Italian sets. Circuits are elementary, also in big sets with 8, 10 or more tubes. Try to give a look to the diagrams of top models from the major brands, Allocchio Bacchini, Ducati, Geloso, Imca or Marelli: no complex audio filters, no loudness, no feedback loops, no RFI filters, no safety devices, as simple fuses. Components were usually of poor quality and not safe, when used in critical applications. In my experience, almost all the electrolytic capacitors were fully dried, almost all the paper capacitors were leaky, and several mica capacitors were out of tolerance. Most of the ANIE approved sets did not use power transformers and the urea plastic knobs were often crumbled or broken, leaving hot metal parts exposed. In some sets I found asbestos sheets under the cabinet ceiling to prevent fire from too close power tubes.

I am sure that you will appreciate more and more the quality of your radio. May be that very soon you can find one of the latest German tube radios, those with stereo decoder inside and with FM ranging up to 104 or 108MHz. They have a sound quality not far from the best hi-fi equipment and fully compatible with the quality of the available FM sources.

After all, today the ‘Filodiffusione’ channel plays the finest classical stereo music!
 

Regards, Emilio

Marco Gilardetti
04.Nov.09
  6

Hello Emilio. Unfortunately I have to second your sentiments about italian sets made after WWII, from which descended my (now reviewed ) dislike of sets of the fifties. Let me just add to your list the vast use of zamak in some parts: an alloy that one would prey had never been invented. Dried-up crap would probably be more resistent.

I agree especially on your point about maintenance and repair. This has always been an awfully weak point of italian sets, and it got worse and worse during the 50s and the 60s.

Thanks for the link: it has been a very nice reading and a very amusing survey over many beautiful sets of that era. Too bad that when stereophonic broadcasts were introduced, the aesthetics of these radios became objectionable (at least for my taste, obviously). One can only imagine the wonders of a Concertino 8 with a stereo decoder!

With my best regards, Marco.

 
Hits: 1934     Replies: 5
telefunken: 8; Concertino
Stuart Matousek
24.Apr.08
  1

Hello I am beginning restoring a concertino 8 and have never worked on german radios before,only Australian ones. the sound is distorted and "blotchy" when connected to an external line in source suggesting problem is in audio amplifier.Does anyone know of a common cause for this before I go replacing all the capacitors in the audio amp section? From studying the circuit it appears that the triode bit of the EABC80 is part of the audio amp and the rest of that valve is for something completely different,is that correct? the voltages are about 20% low,is that enough to make a difference? They are high on switch on but drop with warm up and the rectifier gets warm suggesting there is some power dissipation in the rectifier,I thought of changing for new silicon rectifier diodes,is that a good idea?

If anyone can advise me it would be appreciated, I have some but limited knowledge of radio cicuits.

thanks

Stuart Matousek  

Emilio Ciardiello
24.Apr.08
  2 Dear Stuart,

The problem you describe seems related to a positive grid bias of the output tube, due to a leaky coupling capacitor between the plate of the triode section of the EABC80 and the control grid of the AF power tube. If you have a leaky capacitor, the grid goes positive and the output tube drains a heavy current, so causing a drop in the anode voltage as soon as the cathode temperature goes to its normal emission value.

Try to measure the control grid voltage of the output stage.

Emilio
Stuart Matousek
24.Apr.08
  3

Thanks very much emilio for the advice,as it turns out just as I got your reply I had just replaced that coupling capacitor anyway,and it has improved a lot,however still not quite right(im fussy about the sound quality) The control grid (thats pin 2 i think?) now has a positive potential of nearly 1 volt,should it be zero?

The rest of the voltages are now closer to what they should be but not quite.should I replace the main rectifier with new silicon diodes?and the em80 is very dim,would that be the tube itself?

Stuart

Emilio Ciardiello
24.Apr.08
  4 The voltage on the control grid, pin 2, must be zero. You can also check the cathode voltage. When all is working fine, the voltage should be around 7 to 8 Volts: any higher voltage could be due to an improper bias.

Another way to fix the problem is to open one of the two connections of the coupling capacitor itself. Even if in this case the amplifier cannot work, the DC bias conditions should return to their proper operating conditions. You should then find normal voltages on the cathode (about 7 to 8 volts), on the control and the screen grid and on the plate of the EL84. The control grid must go to zero volt.

If a positive voltage is still present on the control grid with the coupling capacitor disconnected, the EL84 may be gassy and should be replaced.

Emilio
Stuart Matousek
26.Apr.08
  5

Hi Emilio,I tried that,disconnected the coupling capacitor the voltage on pin 2 was still about 0.8v,so I replaced the el84 with another(old one from other radio) and a bit better but still 0.2v,though connecting the coupling capacitor does not effect this,so probably I should get a new el84.Any brand ok? the cathode voltage is about 6 so thats OK I think.was wondering out of curiosity why the csathode is not directly earthed therefor 0v but connected via 120ohm reststor and capacitor?

Thanks for your advice,its helping me learn more about the circuitry,if only Id known that years ago it would have helped with many other things Ive tried with some but limitted sucess to fix!

another question,originally the main chassis is not connected to mains earth,maybe because there was not mains earth in those days,should I connect it to mains earth?

thanks Stuart

Emilio Ciardiello
26.Apr.08
  6 Hi Stuart

First of all, the 120 ohm cathode resistor sets the proper grid bias working point. As soon as the emission starts, the current in the tube is limited by the sole cathode emission, since no negative bias is applied to the control grid. The cathode current, flowing in the 120 ohm resistor, causes a voltage drop on it. The cathode then becomes positive with respect to the chassis ground. The control grid, which is at the chassis zero potential, becomes negative with respect to the cathode. By design, in this case, the equilibrium is reached for a cathode voltage of about 6.2V (the voltage drop given by the sum of anode and screen grid current, about 51mA, flowing in the 120 ohm resistor).

The voltage you find on the cathode may then be considered normal, although close to the lower limit. The cathode electrolytic capacitor acts as a shunt to ground for AC signals: it does not affect the DC operating conditions of the tube, unless for heavy leaks or shorts.

The little positive voltage you still find on the control grid with the 22nF capacitor disconnected may indicate that the EL84 should be replaced again: I do not see on the diagram any other path from where this bias voltage can reach the grid.

About the latest question, a connection of the chassis to the mains earth can be advisable for safety reasons.

Regards, Emilio
 
Hits: 2242     Replies: 1
telefunken: 8; Concertino
Franz-Josef Haffner
29.Oct.03
  1

laut der AEG - Telefunken Vergleichsliste:

http://www.radiomuseum.org/dsp_forum_post.cfm?thread_id=4482

ist der Concertino 8 baugleich mit dem AEG 6077WD:

http://www.radiomuseum.org/dsp_modell.cfm?model_id=21101

Daniel Doll
30.Oct.03
  2

hallo,

passt!

vielen dank für die schnelle hilfe!

 
Telefunken: Concertino 8
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