Zellweger DF44 Telephone Amplifier

[don200002]

Hi All,

My friend from Switzerland bought this over for me in April thinking it was a Radio. It is of course an Amplifier with a Telephone connector plug. Everything was seized solid but I have managed to free up the pots and get it working although it still needs fully re-capping.
The volume, tone and various switches now work fine but the selector switch in the center appears to be locked in position but not seized.
Does anyone have any experience with these sets? I think the selector is possibly motor driven but I can't get it to shift. There is a circuit on the radiomuseum site but I am not a member and the valve line up is different to mine which is EF22 EBL21 and AZ21.
Some of the caps are rated at 3000 volts which seems somewhat excessive,
Any help would be welcome.
Thanks,

Don.

[cmjones01]

I don't think it's a telephone amplifier. I think it's a wired radio which allows the listener to select some pre-set stations. The names on the dial are of Swiss broadcasting locations: Beromünster for the German speakers, Sottens for the French speakers, and Monte Ceneri for the Italian speakers. I suspect it might have some remote control arrangement, and maybe that selector switch is solenoid-operated. The dial arrangement looks like the selector switch is allowed to rotate continuously, with the multiple pointers coming in to view to line up with the marked stations. I'd investigate the wiring to those three a, b, c terminals on the back which leads to the three-pin plug. It may be as simple as shorting together some of its pins to change stations.

A quick Google for wired broadcasting in Switzerland turned up the term 'Telefonrundspruch', broadcasting over phone lines because of the difficulty of conventional broadcasting in mountainous terrain. There's an article on it here:

http://de.wikipedia.org/wiki/Telefonrundspruch

which implies that it did indeed use radio frequencies in the long-wave band so your set is actually a radio, albeit a special one. I can't see the tuned circuits in your set but maybe they're hidden inside the selector switch unit, which seems to be quite big.

I hope this helps
Chris

[cmjones01]

I've just looked a bit further and there was another technique for selecting stations, which didn't use radio frequencies. It used the normal telephone line with a selector switch which earthed one side of the line to select the next station at the exchange, which may be what your unit does. There was an arrangment to cut off the radio service when a phone call was going on.

Diagrams and explanation here in German:

http://www.biennophone.ch/telefonrundspruch.htm

The first circuit diagram on that page is helpful. Quick translations of the key words:

Automat: telephone exchange/switch
Ortszentrale: local exchange building
Programmwähler: program selector
Teilnehmerleitung: subscriber line
Teilnehmer: subscriber
Wähltaste: selector button
TR-Empfänger: Telefonrundspruch receiver

Chris

[cmjones01]

More clues: the word 'Uster' appears at the top of the dial on your set. I think it's an Uster 5 made by Zellweger AG:

http://www.radiomuseum.org/r/zellweger_uster_5.html

The rectifier is different in yours, but other things look the same. I was wrong about the a, b, c terminals being for remote control. I'm pretty sure they're actually for the phone line plus an earth.

I don't know about the selector switch being stuck, though. That may be a mechanical fault. In any case, all it'll do is ground one side of the phone line for a moment to select the next station. Or it may be an arrangement like a phone dial to send a series of pulses.

Chris

[don200002]

Hi Chris,

Thanks for your help, it is all making sense now, I will finish the re-capping and investigate further. The vol/on off switch has an extra pull switch which operates the G1 G2 inputs enabling the set to be used as a phono amplifier and works very well. I am thinking that it would make an excellent workshop amplifier.
There are two 0.1uf 3000volt caps which seems a bit excessive perhaps someone can explain why?

Many thanks for all your help,

Don.

[cmjones01]

Yes, it would make a very cool workshop amplifier! The high voltage capacitors are probably to comply with some requirement of being connected to the phone line. Since this machine is never likely to be connected to a phone line again, I wouldn't worry about them too much.

Chris

[Walterh]

Hello

That's what we call a "low frequence telephone roundspeech receiver" (Niederfrequenz Telefonrundspruch-Empfänger).

These "radios" had to be connected to the telephone line and a special agreement/contract was necessary so the PTT connected the end users telephone line to the service.

These radios have a switch or dial like a telephone to select the desired program (in the telephone switchboard).

The later version (high frequency) was also transmitted using the telefone wire, but was in the range of the long wave band and therefore every normal radio could be used to hear Telefonrundspruch.

The specialised receivers for the high frequency Telefonrundspruch offered mostly program stations and a larger bandwidth than a normal radio. So it was possible to have good reception with no fading, noise etc. in nearly FM sound quality.

Find attached the schematic for the DF44.

Kind regards from Switzerland, Walter

[don200002]

Hi Walter,

Thanks for the info and the Schematic. Although the back cover on mine says Zellweger DF44 I believe it is a Zellweger Uster 5 suggested by Chris as the Valve line up matches this model, EF22 EBL21 and AZ21. I don't suppose you would have a schematic for this model?

Thanks for your help,

Don.

[Walterh]

Hi Don

of course i have the schematic for the model 5 (a) . You find it attached. The 5 (b) differs in the output tube being a 6F6, not an ELL1

But - your radio uses an EBL21 as final, not an ELL1 as in the schematic.

So, your radio must be a not yet in the RM.org documented version.

I already did an extensive search for a matching schematic for your radio, but wasn't (yet) successful.

Walter

[don200002]

Hi Walter,

Thanks for your help, I will finish the re-Capping and as the "Radio" is basicly working there shouldn't be any problems. But it would be nice to get a schematic just to check some voltages and see what's inside that selector switch without dismantling.

Thanks again,

Don.

[Walterh]

Hello Don

The selector switch is, as indicated in the schematic, a Zenith selector. These are well known of their use in old telephones. Do you know the old rotating 1 to 0 dials?

See also: http://en.wikipedia.org/wiki/Rotary_dial

The old NF-TR-radios with these selectors offered the direct selection of any of the 6 programs. And you see the push button on the back of your radio? This button serves to "reset", if the dial and the program did not match.

Walter

[Nickthedentist]

Hello Walter,

Most of us are familiar with rotary dials as described in your Wikipedia article - they were used on our phones here until the late 1980s at least.

But could you tell us more about the "Zenith selector" please?

Nick.

[Walterh]

Hello Nick

Sometimes, a pictures says more than a thousand words.....

Every impulse from the rotary dial switched to the next program. So, if one would like to hear program 6 he had to turn the rotary dial until the program 6 showed up in the window/dial.

Excuse me, if i have some difficulties to describe all that - english isn't my native language - but feel free to ask

Kind regards, Walter

[Nickthedentist]

Hello Walter.

Your English is perfect.

Your second picture reveals everything - it really is just like a telephone dial in every respect except that it has station names instead of numbers printed on it.

But Don's radio is different, surely?

Thanks again,

Nick.

[Walterh]

Hello Nick

No, Don's radio uses the same Zenith selector (but a different kind of dial). Please look at the pics 3 - 5. In pic 3 (bottom center) you can see the base plate of the selector that has an additional cover.

The contacts are inside the chassis and in a different arrangement (more contacts) that what is showed in my pics.

Kind regards, Walter

[Nickthedentist]

Hello again Walter,

Thank you for enlightening me. I understand now.

The glass scale with multiple pointers and a cord to drive it seems odd though. Presumably, the subscriber would turn the dial until the required station was indicated by a pointer and then let go, allowing the mechanism to wind back to its rest position and send its pulses to the exchange?

If Don's dial does not rotate, do you think the telephone dial mechanism is to blame rather than the pointer arrangement? Certainly in the case of our British telephones, one occasionally encounters instruments where the dial has seized, usually because its central spindle is lacking in lubrication. A full strip-down is the only cure (but not too arduous for someone like me who enjoys playing with clocks too).

Regards,

N.

[Walterh]

Hello also again Nick

Yes, i have also the same understanding of the mechanism of that radio.

And also yes - if Don's dial does not rotate the cause will be found in the Zenith selector - as you guess in a lack of lubrification or, more likely, hardened grease.

Kind regards, Walter

[Nickthedentist]

Thank-you, Walter.

[don200002]

Very interesting,

As the tone and volume pots were also seized it would seem the same for the selector switch. I will investigate further.
Thanks everyone for your help and interest,

Don.