Restoring my Telefunken Opus 7 - some pointers welcome
 

Well, the time has finally come for me to get to work on restoring my aging Telefunk Opus 7. It was given to me by my parents, who got it from a friend who passed away about 10 years ago. Up until now, its mostly just been sitting in a box in the basement for a good 20 years. However, its in overall excellent condition with only a few minor nicks here and there on the wood finish.

The radio powers up and actually runs pretty well. I get excellent reception on FM/AM/SW. Volume knob works, tone controls work (somewhat), tuner eye works great. There is a faint hum in the background that stays at the same level no matter the volume. After about 5 minutes, the quality of the sound starts to sound rather poor and "farty", especially on FM where there is more bass. AM/SW either aren't affected or it isn't as noticeable.

I've gone ahead and opened up the back side. The service manual was unfortunately missing from the small yellow envelope. A fellow AK member was nice enough to send me a replacement copy (thank you!). I've taken some pictures of the innards.

http://members.bellatlantic.net/~doa/tele1.jpg

I've cleaned up the dust a bit. Seems like good condition to me. Its pretty obvious that the set has been repaired in the past. Two of the tubes aren't original (unless telefunken ships with other branded tubes). There is a half torn piece of paper on the back with the address of the repair place - somewhere on 3rd avenue in brooklyn ny. I've checked the maps and a repair store no longer exists at that address, so it must have been a long time ago.

From what i've read online, I basically need to replace all the capacitors, and that should be all I need to do. I'm not sure if I need to replace the resistors though. There are a LOT of capacitors and resistors in this set, especially on the underside. I would like to replace them all, but it seems like such a huge undertaking and one small mistake could ruin the entire thing. There also seems to be some bypassing done in previous repairs, which makes it even more confusing.

There are also a lot of strange looking caps on the underside - unusually long and encased in clear plastic. I have to get a closer look to see what these actually are.

Right now, I have a few basic questions -

1.) Do remove the chassis, do i just unscrew the bolts from the underside of the wooden case, and it should come right out?

2.) I would have to disconnect the speaker system to get the chassis out. However, the speaker connections aren't soldered, they are wound several times around a long pin, like this:

http://members.bellatlantic.net/~doa/tele2.jpg

It doesn't pull right off and I don't see how to unwind it. How do I get these off?

3.) In the first picture I took, there are 2 oval cans in the center next to the EF89's. Is there anything important under those that I need to replace? The can is bolt on from the underside. How about the circular can on the left next to the antenna? How about the two square looking cases where ECC85 and EABC80 reside in? I have no idea whats inside of those housings and if I should touch them.

I'd like to bring this radio back to "regular" usage. Hopefully I can do that without blowing anything up :)

Those connections in that last photo are called wire wraps. Supposed to be just as good as a solder joint. Just unwrap them to disconnect.

As they were applied at the factory with a special tool, you cannot simply rewind them by hand, and therefore must be soldered when reconnected.

Check the resistors with an ohm meter. Almost always, if a resistor fails it reads high. Check them in circuit, and as long as they show at or below their marked resistance, they're almost certainly fine. If one reads funny, pull one end and check again. If its more than 20% out of tolerance, replace it. I wouldn't bother bulk replacing all of them but you'll probably find a couple that are out of whack.

Also, there are some things in these that look like the old dogbone resistors. They're ceramic capacitors, and very seldom go bad. Don't worry about those.

The chassis probably has a few screws through the bottom, and it will slide out.

The oval cans are your IF transformers. Leave those alone, theres not likely to be anything of concern in there. Some American radios have capacitors built into the transformers that go bad, but I'm not aware of this being a problem on Euro radios.

I am no tech but if you do the work yourself do one thing at a time (ie capacitor) then test the radio before moving on. If you do a wholesale swap and mess one up you will have no idea where it occurred.

Alright, I took some time today to finally disconnect the speaker wires so I could remove the chassis. The underside certainly looks frightening, to say the least:

http://members.bellatlantic.net/~doa/tele4.jpg

There is just an insane number of resistors and caps under there. Probably the main reason these sets sound so good. Its probably not the best radio for me to work on as my first, but I think I can get it working great again.

I started making a long list, writing down each of the caps that I come across and their values - especially the paper caps. There are a few buried deep under a ton of wire that i'm not sure how i'm going to get at. The wires are old and brittle, and i've already had one just randomly snap on me as I tried to bend it out of the way to get a better look at a cap's rating.

I also came across a large black can. I assumed that it was the filter capacitor, but after undoing the hinges so I could turn it around and read the specs, it seems to be something else - a rectifier?

http://members.bellatlantic.net/~doa/tele5.jpg

Is there anything I need to do with this, or just leave it alone?

Once i'm done mapping, i'll drop over to a local shop and pick up the replacements that I need, and start replacing them one by one.

Make sure you take a lot of large file photos detailing the underside of the chassis. I am pretty sure you need to pay close attention to the position of the cap you are replacing.

The tech I know has a fantastic setup for working on these. Essentially looks like a captial H with the chassis the bridge between the two columns mounted constructed with plywood and rotatable. The chassis is mounted to the columns. Somewhere I came across somthing similar that you could purchase online but you could build something similar if you wanted.

Either way take it slow and be careful around those angel hair wires!

Edit-
Heres a chassis cradle sold by Steve Strong of the Oklahoma Vintage Radio Club. It says he offers two sizes; small $37.50 & large 55.00 plus shipping. Email [email protected]
No affiliation but thought it might be helpful if you don't want to construct your own.

http://i77.photobucket.com/albums/j6...ringCradle.jpg

Cool chassis thingy! Always wanted to build something like that. Very elegant design.

Re your audio distortion on the bass after warmup - what are the audio output tubes - ECL86's? They are prone to grid emission when they get a bit old. Monitor the voltage across the pentode cathode resistor - if it stays at about 6volts then all is OK but after about ten minutes or so it may start to rise and keep on rising - once it gets to 9 or 10volts turn it off! You're in danger of burning out the cathode resistor, the smoothing resistor and the tube - although the tube is a throwaway!

Output is EL84's. Does your post still apply to these?

Your brownish disk ceramic caps are probably OK, I would leave them alone, as you say reception is good and those are mostly in the RF sections, it would appear. I would stick to replacing the electrolytic and paper caps. Very good advice earlier in the post about changing one or two caps and then trying the radio before changing any more. What one guy does when changing caps is to put clip leads on the two terminals where a cap is connected for identification purposes before taking the cap out. Then he knows for sure where to install the new one. Also earlier in this thread was a comment about the output tubes drawing more current as they warmed up and giving distortion: beat me to it! True of any output tubes whatever the tube number. Definitely check. This ought to be a great radio when done. Yes, it's daunting for a first set, but do it one part at a time and triple check everything as you go and you'll be fine.

Reece

Hello!
Yes, you are right-this is a rectifier. I'm going to translate the words printed on the can:
Gleichrichter> rectifier
Blau> blue
Rot> red
In this radio it is also not usefull to replace all the caps. The smaller valued silver coloured caps are usually very reliable. Only replace the black caps.
The EL 84 is a very common and extremely reliable tube. It is used in my daily player and it works well since decades:thmbsp:
Greetings Josef

Wow its been a while since i've been in this thread. I thought I would just update all of you.

I finally got around to picking up the caps I needed for this project. I worked on it last night. I replaced 1-2 caps at a time and then plugged it in to make sure I didn't screw something up. So far so good. I replaced the filter caps on the top of the chassis as well as an electrolytic and some other paper caps next to the speaker output terminals. The sound so far is much improved! The constant hum is gone and the overall volume is much, MUCH louder. There is actually some decent bass response now. I can also now hear the tweeters working - something I couldn't hear before even with my ears right up to them.

The "farty" sound on FM when warmed up is still slightly there but I still have a good amount of caps to change still. I did have a couple of questions though.

1.) I was unable to find one electrolytic cap in the proper value, but I did find the proper value in non-electrolytic cap. Is it ok to substitute a non-electrolytic in its place?

2.) One of the EL84 tubes seems to be running very hot. Its the one closest to the rear of the unit by the AC line cord. The other one runs no where near as hot. If I switch them around, the heat remains coming out of the same socket, so its not related to that specific tube. Is this normal? The other tubes doesn't seem to generate anywhere close to that amount of heat.

3.) For the 2 50uf caps in the can, I assume that the negatives go to the ground (chassis) and the positives go to their respective leads?

I'm going to replace the electrolytics connected to the EL84 tubes tomorrow and see if that helps with the hot tubes. But i'd still like to know if hot output tubes is considered "normal" or if its something I should be concerned about.

EL84's do run pretty warm, but it's strange that the pair are different temperatures especially as the one out in the clearer air is the one getting hot. Is it a push-pull output stage or bi-amped with one amp for each bass speaker. Check the value of the cathode resistor, the cooler running one may have gone high which will cause your distortion maybe....and yes, EL84's can and do suffer from grid emission when they get old - measure the voltage across the cathode resistors - they should be about equal and a reasonable value, say 6 volts or so IMHO.

Its push pull as far as I know, especially since its mono only output.
Right now everything is out of the chassis, so there is plenty of airflow. I can feel the heat rising from the top of the EL84's, but one of them is certainly hotter. I cannot touch it with my fingers - its about as hot as a 40w light bulb i'd estimate. I'll check the resistors tomorrow.

As an update, I replaced about 10 more caps this evening. At this point pretty much all of the high voltage paper caps that were leaking/melted are replaced. I tested after each replacement, unfortunately I didn't hear too big a difference after replacing one.

The last one I did for the night was disconnecting the 50/50uf can at the top, and putting new ones on the underside. After turning it back on (and hoping they wouldn't explode :D ) I was greeted to a HUGE improvement in sound. Almost all the distortion is gone at this point, and the volume and clarity are much improved. The amount of bass this guy puts out is amazing! There is still a little bit of "looseness" to the sound, especially in the lower frequencies, but I hope that the remaining caps will fix that.

There is still one electrolytic left to replace - a 2uf unit. I ordered one online since I couldn't find it locally, however what came was a 2uf unit, but not an electrolytic. The voltages exceed the original, but i'm not sure if I can replace an electrolytic with a non-electrolytic. Would this be ok?

Nice to see you are making some progress with this incredible radio. I wish I could answer your question on substitution but can't. Maybe someone on the Tube audio subforum could?

Well, at this point I am more or less finished. I spent about 4 hours polishing up the gold trim around the front of the stereo. It looks gorgeous now! The Telefunken logo just gleams. For those curious as to what I used - I actually tried a few things. The trim was badly tarnished and looked a dull brown. Rubbing alone was getting me no where. I found an old "polish cloth" in the basement and tried using that. It worked well and soon the gold color started to shine through. But the work went VERY slow - I managed to polish a small 2 inch section in about an hour of rubbing. At that rate I would be polishing to the next day and still not be finished. Not to mention have some not-so-fun pain in my hands. So I tried something a bit more aggressive. I mixed some "bar keepers friend" scrubbing powder (google it) with a bit of water to make a nice paste. I applied a bit of that to some paper towel and rubbed. This managed to remove the tarnish and shine up the rest of the trim in about an hour, without scratching mind you. I then made another quick pass with the polish cloth to bring out the luster, and finally used a rag to buff it to a nice shine. I still have yet to polish the knobs (cough), but once thats done, it should look amazing.

I went ahead and installed the non-electrolytic. Tested it and it seems to work/sound just fine so I left it there.

Then I turned it over and installed one more cap by the crossover section - a 1000pf @ 1000v paper cap which I replaced with a mica unit. Mica was the only one I was able to find in that high a voltage. However, after testing, it seems changing that out made the sound somewhat worse. Before the bass was very punchy, but now it seems a little garbled and strained. Its difficult to put into words but i'm almost positive it doesn't sound as good as before. I'd almost put the old cap back but its paper and in terrible shape. Is this kind of cap not a good idea to use in crossover or am I doing something else wrong?

Wow, its been a long time since i've touched this thread. I actually finished my restore back in February, but I haven't gotten around to taking any pictures until now. Well, here she is...

http://members.bellatlantic.net/~doa/0896s.jpg


http://members.bellatlantic.net/~doa/0898s.jpg
Ignore the date on the camera... I never bothered to update it after putting new batteries in.

I'm very glad the way it turned out, although honestly, it was in almost perfect condition to begin with. All I had to do was give the chrome a good polish and the rest a nice cleaning.

The overall sound is very good. Not perfect, but good. I am sure that audio on FM is still slightly messed up. Even tuned in, I can still hear some garble/static on stations, so it might need to be retuned. I dare not try that though. AM and SW performance is perfect though. Overall i'm happy, and I listen to her almost daily.

I know we spoke a while ago about the radio.

It looks great.

Did you replace the caps in the enclosure holding the EABC80 tube.? If you didn't be very carefull if you try it!! The coils are very fragile and there are some hair thin wires in the enclosure.

Jon

When you say hot do you mean the plate is glowing red? If so the coupling caps NEED to be replaced. Do not operate it like this for any length of time as the tubes are quickly going to be ruined,. EL84s do run hot normally, and probably much hotter than the RF tubes in the set but should never run with red plates.

I had a Heathkit amplifier with push-pull EL84 outputs where one output tube ran hot after a few minutes of operation. The cathode bias voltage was going down. Removing the electrolytic across the cathode bias resistor eliminated the problem.

You SURE you really wanna keep that junky ol' Kraut thing ? I mean, I got a bran-spankin NEW Ichipusy KRP-1000X AM/FM/SW that is made from genuine Black Plastic that I'll GUARANTEE will pull in Uranus on a clear day...And sound good doin' it...I'll trade you even, FAIR 'n' SQUARE, for this refugee from the Cold War...The KRP-1000X, being those new "miracle" technology, transistors, NEVER gets hot...Unless you leave it out in the sun, in which case it transforms itself into Moderne Art. You'll NOT hafta worry about some dumb ol' tooob gettin' to hot, or the bass sounding like grandpa clearin' his throat...Whaddya say ? (grin) (Serious note- I LOVE yr set !! It is Gorgeous !!)

That will work fine, maybe better than an actual electrolytic. It won't dry out like a lytic can can.

No I didn't bother to go in there at all. I would have had to disconnect a ton of wires to get into the enclosure and honestly I didn't have it in me.

When I say hot, I don't mean the plates are glowing. I just mean the tube is physically very hot. Most of the tubes I can actually touch and hold for a few seconds without burning myself. But one of the EL84's is more like a 60w lightbulb after its been on for a while - you can't touch it without burning your fingers. Everything seems to be running well so I assume its ok. I'm sure there are some resistors that are out of spec but replacing them would be such a chore.

I'm gelaous on you, U.S.A. guys. The tube radios made in West Germany for U.S.A. market had all F.M. band (88-108 M.Hz.), whyle the one ones made for Europe had F.M. only on 88-100 M.Hz., and some, later on 88-104 M.Hz; and in Bucharest 2 of the stations that sometimes I listen much are on 106.7 and 107.3. I had an "Grunding" radio made for U.S.A. market ... but it wasn't sounding to good (bad caps I think), and it broke, and stupid me just salled it... now I regret that I did that, becuase it'll be very hard to find an full range F.M. radio with electronic tubes (valves)... probably I'll by one from U.S.A. when I'll have the money (one that will be stereo with 4 speakers - the front speakers to have the same size, and the 2 side one to have the same size between them to and to have the stereo decoder installed).