Hello all! New to tube radios (been a collector/repairer of mechanical clocks and watches for some years) as of this afternoon. I picked up a Telefunken Allegro which seems to be in very near brand new condition, it even has the original wiring schematic inside. A couple cracks in the varnish (poly?) around the brass trim on the face, and a bit of gold leaf missing on the volume dial, but absolutely pristine otherwise. The set tunes fm and am very well, although the fm indicator seems to be off a couple MHz. The side speaker (there is one large speaker and one small speaker in the face of the set, and one on the left side, as viewed from the front) doesn't seem to work either.

Are there any beginner maintenance/repair tasks I could/should be doing? I'm fairly handy with a multimeter and electrical theory, but radios are a new world to me. Any books I should pick up?

The Set:

Very attractive radio. I have thought that European radios are far more attractive than USA.

Thanks! I have a special place in heart for mid 40's Zenith tombstone/console sets (with the big circular black dial) but this set was quite attractive and the price was not something I could pass up. I'm thinking audio quality is better too.

I've come up with a few more questions:

I've done a little more research, and It appears the first thing to do is replace the paper and electrolytic capacitors, as they can degrade over time, potentially affecting other components. To my untrained eye it looks like there are about 18 or so paper caps, and the only thing that looks like an electrolytic is attached to the power supply. Does that sound right?

Where would I get (make?) a conversion plug for the five pin phonograph/reel-to-reel inputs that would let me use a 3.5mm headphone input from an mp3player/etc. ? What is the difference between the two inputs?

EDIT: Discovered these are 5-pin DIN connectors, and converters are available online.

Is SW worth messing with? I can't seem to pick anything up on either band, but I've read that a fairly large antenna is needed for SW to work at all, and that there are not many stations left these days.

Probably my favorite German table set, nice nice score.

You are absolutely correct about changing out the caps. The tape input on the back will match up with an ipod. You will need what's known as a DIN connector. They used to be common, not so much now. Phono input will probably work fine also if it's wiring for a non-magnetic phono cartridge, which it probably is.

Not much left on shortwave and it seems to be getting less and less everyday but there still are stations out there. Try the lower end at night and the upper end during the day.

These sets have a nice sound and sound great on FM.

Thanks for the response greg! Shame about the SW, but I'll have to try to see what I can find once I get the Radio restored properly.

Took the chassis out of the case and went on a cap hunt to see what I could find. I see a lot of "ERO 100" branded caps with paper labels, I wrote down values for all, but have a few questions still.

1. Some of the "ERO" caps appear to be made of some kind of translucent material and have a third lead attached, what's the deal with these? (center and left in image, also has a third larger one of this type elsewhere on the PCB)


2. There is a paper capacitor attached to the "Bass" "Solo" selector switch which looks different than all the rest. It's labeled as 4700 pF, 500v DC, no ac voltage labeled. Should this be replaced with any special type or not at all?


3. What should I replace on the power supply section? There are two pink paper caps labeled 1000 pF 1000v dc, 500v ac, 250 ac (b); none of the other capacitors have this third voltage listed. Also what are the larger can capacitors facing downward (multi Electrolytic?) and should I swap those also?


4. What are these silver translucent caps with radial leads? Two of them on the mainboard, each labeled 4700pF 500v dc, and with a 15% mark also.


5. This is one of the Electrolytic caps, correct? If so what does the "GD" immediately before the 4uF label mean? Also, are the temperature markings important?


6-8. What is this red plastic coated thing that looks like a small Electrolytic cap (lower center of pic)? It's marked "frako +" and "50/12 -". Also, are the little tiny clear guys mica caps? The one just above the left side of the red fellow is labeled 650 pf. Finally, there's a translucent greenish cap with an orange label above the clear one, not sure what type this is or if I should replace. Labeled 0,022uF 250v dc, no ac rating.



Sorry for all the questions, this has got me scratching my head a little.

Man, that's a cool radio. Good luck with the resto!

Mike

1. The third leg is usually for a ground to shields the capacitor and keep noise down. Measure it first. I usually use just a poly film cap.
2. Just use the same poly film cap there as well.
3. The pink caps on the power supply should be noise caps. Now a days we use x-y safety caps. The silver can is a multicap usually 350 volts 50uf + 50uf. The black can is a selinium rectifier.
4. The translucient caps are usually good.
5. Don't know what the GD is for. If it's a low voltage (20-50 volts)it is used for FM. Electrolytic temperatures are usually 85 deg C or 105 deg C.
6. Looks like a cathode bypass cap for the EL84.
7. Looks like film, might be mica, I'd leave them.
8. Might be a replacement, but you can use another poly film.

These are great sounding radios with good Am sensitivity. I have owned one of these for about 20 yrs. Mine was in really nice condition like yours. I think the large black cylinder is the rectifier bridge. I need to get mine back on the bench and give those push button switches a good spraying with contact cleaner. i have replaced a lot of those shielded caps in German sets with regular ones and didn't notice any problems.

Thanks for the help, Tin! That clears up a lot of things for me, but still have a couple questions.

Should I be replacing the selenium rectifier? What would I replace it with?

Should I replace the cathode bypass cap? If so what should I interpret the markings as? Not sure what the "50/12" is indicating, and I can find no uF or pF value on it. There appears to be another one of these red guys in the top right of the same picture which reads "2.5/30", should I replace that also?

There's a smaller electrolytic (2f) that reads 70v (for the fm tuner)?, the larger one pictured is 350/385v, the can cap is indeed 50uF + 50uF, and all are rated -20 +70 degrees. I can replace these four with any old electrolytic so long as it exceeds those values, correct (other than uF obviously)?

Finally, there's an enclosed assembly on the left side (viewed from the rear) which has a single tube and a tuning wheel protruding from it. Looks like the FM tuner assy. to my untrained eye. Do I need to bother removing/disassembling this? Will there be more caps inside?

P.S. yes, the third lead on the resin looking caps is grounded to the chassis, so I'll order caps for those.

Nice set. Ive repaired many of these sets that were intermittent or non operative from cracking in the circuit board around where the tubes plug in. Seems the boards get brittle over the years and the force from plugging or unplugging the tubes can and will crack the board. So be gentle unless you enjoy soldering delicate circuit traces.

You should replace it with a silicon bridge and add a dropping resistor between the + lead and the original wire coming from the selenium bridge. 100 ohms at 5 watts usually works good.


I'd replace all electrolytics while you're in there. 50/12 means 50uf at 12 volts.

I try to keep voltage ratings close. I.e., I don't substitute a 20uf at 450v for a 20uf at 25v. Stick with the correct capacitance values


LEAVE THAT ALONE. Did I say LEAVE THAT ALONE? If not, then LEAVE THAT ALONE.



BTW, looking at your third photo, I see 2 very charred resistors on top of the power supply board. Not sure what those are for, but you should replace them.

Note about those 3-leaded capacitors: They didn't do this just for fun, those capacitors do need an outer shield.

The last radio like this that I refurbished, it hummed like crazy until I replaced a capacitor near the volume control with a shielded one. They often used very high impedance volume and tone control circuits that are very prone to hum pickup.

You can wrap copper foil around the outside of a standard cap and solder a ground wire to it. Even aluminum foil will work as long as you get a contact with the chassis. Sometimes carefully re-orienting the cap works too.

Thanks for the extra tips guys! I didn't really want to mess with the tuner anyhow . The resistors you mentioned are a little cooked looking, but they are still in spec. Is there an easy way to tell what wattage resistor I need to replace this with? Neither the resistors or the diagram mentions this, only the resistance value.

I've read it's possible to put silicon diodes inside the old selenium can, which seems like a decent idea here given there's not much space to mount a square bridge. Any special diodes required to do this? Can't seem to find an amperage rating on the thing either; the diagram labels it as "B250 C125 N 2 bt".

Ancient Hacker: Where did you get shielded capacitors? Can't seem to find a supplier. Seems simple enough to make shields myself if necessary though.

Where are those in the circuit? I doubt they are more than 1 watt, but you can go with a 2 watt just to be safe. Newer resistors are often smaller than older ones for a given wattage.

As for the rectifier, it's only rated at 125ma and 250volt ac input. 4-1N4007 diodes in a bridge, or a small button style bridge rectifier, e.g. 1 amp, 600PIV.
Don't forget the series resistor. Important so you don't get too much of a current surge at turn on.

Not very adept at reading this diagram, but the only two 1.8k resistors I see tied to a common point (as these are) seem to be in the circuit with the left channel speaker and external speaker output. I've highlighted the resistors in a red box on my scan of the diagram:

http://img254.imageshack.us/img254/5631/telefunkenwiringdiagram.jpg

(Hyperlink because it's a VERY large image, even at half resolution)

Looks like I can pick up the diodes and resistors at radio shack easily, and the caps here: http://www.justradios.com/captips.html He claims that there should be a 20% tolerance built into the engineering design and so caps that are within 20% can be substituted. Is this likely to be true of this radio? One or two exact matches for my caps aren't listed in his shop unless I go drastically north on the voltage rating.

I don't think those are the resistors in question. Have a look at the 2-1.8k resistors (w701 and w1701) coming off the primary of each output transformer.
I think these are the ones. It would make sense that these are fried because of excessive current being drawn through the transformer due to leaky grid coupling caps. I'd use a 2 watt 1.8K flameproof resistor for these if available.

Regarding the caps, which I didn't answer in the previous post, yes 20% tolerance for these caps is usually fine. There are exceptions to this, but usually not where paper caps or electrolytics are used. Electrolytic caps normally have a pretty wide tolerance anyway, so don't worry too much about that. Paper caps are used most of the time for bypass purposes or plate to grid coupling. These are fine within 20%. Your best bet is to just stay close to the values listed. You can always parallel capacitors (or even put them in series) to get the correct values. The place where caps become more critical is in the RF/IF/Oscillator sections of the radio. Hence my warning to stay out of the FM front end if it's working. But usually, critical value caps won't be these film types anyway. If you learn a little more about how a radio functions, it becomes easier to determine which caps are in critical positions. Otherwise, just play it safe and use the same values whenever possible. Most newer caps are normally better in terms of tolerance than the old ones they replace.

...I think that actually IS marked 50+50µF 350/385V...use two 47µF 450V electrolytics...



...the 'tiny clear guy' is a polystyrene (aka 'Styroflex') cap (that one looks from here to be C303, 680pF, according to your schematic). They appeared a lot more in European and Japanese radios than in American radios, mostly in RF and IF applications (those critical applications mentioned above), and are generally pretty stable and not particularly failure-prone (just be careful of those thin leads). As Tin stated, you usually don't have to worry about them...

Well after a couple weeks of work (had to wait for some extra parts; I broke two resistors when removing the capacitors, and I missed two caps on the volume/balance pot assembly) I just put the chassis back in the case late last night and the radio plays better than ever! I ordered a 5 pin DIN to 3.5mm cable and successfully played some tunes from my phone through it, and even tuned in a few spanish short wave stations!

FM reception seems a little fiddly, but I think that's the internal antenna (clarity improves while near/tuning the set but when I walk away it starts to distort a little bit). The left tweeter still doesn't work, but I think I'll enjoy the set a bit before I start mucking around with that. There's three leads connected to the top of the power supply, a yellow and red which are common to all three speakers, and a green which connects to the left tweeter only. Right tweeter has a big electrolytic cap attached.

Can't seem to wipe this silly grin off my face, though! Many thanks for all your help guys, definitely couldn't have done it without you!