Telefunken Opus Stereo HiFi 7084 W - Videokarma.org TV - Video

thenewguy · #1 02-01-2006, 07:51 PM

Just picked this up a week ago and thought I'd post a couple of pictures. It's a very cool radio

Even got the two external speakers with it

Spent a couple of days bringing it up on the variac and it does work,
but has a hum. It will receive on all bands using the internal antenna except for AM, can't pick up anything. There's a part missing that's attached with a string to a knob in front that I am guessing was some sort of ferrite wound antenna for the AM. Don't know where to start as far as eliminating the hum. I understand it must have something to do with the caps, but how do you figure out which one, short of replacing them all them? Varnish is crackled sort of, but overall I'm pretty happy to have it. Not bad for a dump find

Nolan Woodbury · #2 02-03-2006, 10:03 PM

You're probably going to have to hook up with some of the German radio experts NewGuy, and source the schematic. Is there a Sams for the Telefunken? I don't think so. As for the caps...yeah, that is the usual cause of hum (volume up or down) and when I've done it, I just replaced all of them. Then again, I'm not a pro/radio tech who may test and replace as necessary. I only want to go in there once and be done with it.

I'm looking for a suitable German table radio...Saba, Telefunken or whatever. That big, glossy cabinet and multi-speaker construction makes for a neat kit, but I HATE those broken/missing pushbuttons. I'd like to find one without that crap on it. Love those accessory speakers on yours though! That's a rare find, I'd think.

Chad Hauris · #3 02-03-2006, 11:02 PM

We replace all caps except ones we know are Mylar or ceramic on tube type radios, like Nolan says we want to fix it once and be done with it and have it work consistently good. We have done several of this type, Grundig, Telefunken, Blaupunkt. Also some new rectifier diodes may be a good idea too. New electrolytics ought to take care of that hum (please do observe proper safety precautions as there is more than 300 volts at the caps). You may need to mount terminal strips to hook up modern caps to replace the old ones.

thenewguy · #4 02-03-2006, 11:54 PM

Thanks for the info. Guess I'll start the hunt for the schematic. Haven't been able to find out much on this particular model. 1959/60. It's an 8 tube chassis. I've never done a re-cap job before, so I might as well start on this thing. There's a lot more room to move around in this radio than in my Zenith Transoceanic, which probably needs the same thing done to it. Let's just say that they're both humming the same tune

Nolan Woodbury · #5 02-04-2006, 09:30 AM

Although my family have been active audiophiles my whole life, I didn't get serious about this hobby until a year ago NewGuy. And what I mean by serious is doing more than just plugging a radio in and hoping for the best.

A.K. cornerstones like Chad and others have been very helpful, but I didn't want to post every time I had a small question (how can I tell a electrolytic capacitor / condenser from a resistor?) but a couple of things happened that helped greatly. I bought a non-working Zenith C730 that came with a batch of goodies (a slew of caps, tubes, filters and a test electrolytic with alligator clips) then I added a selection of new caps in various values from Radio Shack and new tubes for The Tube Source. I also purchased an ohmmeter, cutters, solder and a soldering iron. A book I found on the internet; "Antique Radio Restoration Guide" by David Johnson (ISBN # 0-87069-638-6) has been a great help. I've read and re-read it several times.

When I get an old set in now, I dust the chassis with a soft brush and careful shots of compressed air, then clean/re-seat the tube pins with a dab of dielectric grease. Although I now know just enough to get myself into trouble, I did manage to transform that old C730 into a reliable, daily listener.

The thing that really impresses and encourages me is the quality of these old radios. 95% of the time, the problem (if there is one) stems from either a bad tube or a leaky electrolytic. You sound fairly knowledgeable, I'm sure you'll do fine. Anyway, if I can do it, ANYONE can!

Chad Hauris · #6 02-04-2006, 12:24 PM

Also I seem to remember that the schematic is printed somehere inside the case on many of these German sets, look inside the back cover or on the inside bottom or side of the cabinet.

thenewguy · #7 02-05-2006, 11:13 AM

Thanks for the encouragement Nolan! Gathering the parts might take me a while, though. Chad, you are right. The schematic is "supposed" to be attached to the inside of the back cover. All I have are a few shreds of the envelope that held the plan. Oh well, I'll keep looking

Chad Hauris · #8 02-06-2006, 09:53 PM

http://www.justradios.com/

is a good source for capacitors, electrolytics and mylars.

You can get terminal strips for mounting the new caps at Radio Shack.

http://www.allelectronics.com/
is a good source too, you can get the 1n4007 diode 6 for $1.00.
This is a 1000 peak inverse voltage 1 amp diode which will replace most of the diodes in tube amp/radio power supplies.
Replacing the old selenium rectifiers with new diodes will give a performance boost too.

thenewguy · #9 02-07-2006, 08:15 PM

Thanks Chad! Justradios.com sure looks like the place to go. I'm on my way!!!

crooner · #10 02-08-2006, 02:29 AM

Beautiful receiver!
the Opus was Tele's TOTL receiver.
I am noticing from the pics that you are missing the ferrite AM antenna. This is quite common since it's simply glued to the rotating device.

It also appears to have been modded to accept standard RCA plugs, probably for the tape/pick-up input.

Does this unit have FM (UKW)? I don't see the shielded front end with the ECC85 on it.

thenewguy · #11 02-08-2006, 04:18 PM

Hey crooner, you're right about the rca jacks being a mod. I hadn't noticed that before. Doesn't appear to have FM. This is a 8 tube chassis, I think the 10 tube ones had FM. Quite difficult to find information on this particular model. I just joined radiomuseum.org in the hopes of finding the proper schematic before I start the recap on it. Great website, by the way, with an accessable tube substitution service. Lot of restrictions on non-members, but still great. Wonder what my chances are on finding that AM antenna?

crooner · #12 02-09-2006, 12:10 AM

Your unit is probably an international version intended for South America and other regions of the world where FM was not yet popular (1950's and 60s).

I had a big Telefunken back in Venezuela that was just like this. It had incredible tone quality on the regular AM band.

The ferrite antenna can be a tough one. I am guessing a discarded "for parts" Telefunken of the era will have a suitable antenna. It doesn't have to be the "Opus". Concertino, Gavotte and other models probably use the same antenna.

Best of luck!

crooner

crooner · #13 02-09-2006, 12:33 AM

Here's a shot of an old Telefunken I had (this one with FM):

thenewguy · #14 03-25-2006, 07:18 PM

Managed to find a schematic from a fellow in Germany, very helpful. Ordered the new caps from justradios and got them all installed. In the process I discovered three paper caps that I somehow missed the first time around, so I'll have to order some more. Couple of questions: I understand that the ceramic caps seldom need replacing, but what about the styroflex caps? There are 17 of them in this radio. Also, now don't laugh, I managed to get three of the electrolytics in backwards despite my careful one-cap-at-a-time method. I powered the radio up after finishing and am wondering if I ruined the caps that were installed backwards or can I still use them if I put them in right way round? They were 100uf@25V. Originals were rated at 6V and 4V. After powering up I still had the hum so I re-checked my work and discovered the backwardness, plus I took photographs beforehand and could see my mistakes. Another question on testing the tubes; all are Telefunken tubes, European numbers, can they be tested as their equivalents/substitutes in American numbers? Do I test a ECC83 as a 12AX7, or 12DT7 as listed substitutes, on my tester? So, I'm a little frustrated but not discouraged. Just ordered caps for my next project, a Zenith TransOceanic L600

crooner · #15 03-25-2006, 07:24 PM

Those are relatively low voltage caps so it is possible they are still good. In case of the filter caps at 300 ~ 400V, reversing polarity can cause a nasty explosion!

Check them with an analog ohmmeter in the x1 range. They should give you a kick in the needle following a bigger one with the probes reversed. Of course, if you see a short when testing, do not re-use them.

As for the tube substitutions, yes, you can use the american equivalents to setup your tester.

Remember to always power the unit up slowly using a light bulb wired in series with the AC mains, or if you are fancy, a dedicated VARIAC. This should prevent major damage to your equipment in case of a wiring error or sudden shorting of a power supply cap.

Good luck!