[ARC5] WWII German Torn. E.B. Receiver Revived.

[David Stinson]

This lonesome WWII German radio,
a 1943 Telefunken Torn. E.b. regen set looked so forlorn
sitting on the auction table between a
Zenith Tombstone and the silver guts of a Scott
chassis. A hole cut in the case, an abortive attempt
to install modern tubes, savaged coil tuning slugs
fragmented and stuck, controls frozen- this poor thing
didn't just get "The Golden Screwdriver;"
someone beat the helpless radio with
the whole "Golden Toolbox," plus what
appeared to be manufacturing errors.

Introduced in 1937, it is a battery-
powered set with two stages of TRF amplification,
a regenerative detector and an audio output
stage.  Audio Output Z is about 4000 Ohms.
A matching transformer to an external speaker
provides plenty of audio.
The set was built in large quantities
throughout the war.

With the exceptional help of many of
our exceptional members,it is singing again,
needing only finish work and cosmetics.
https://photos.app.goo.gl/DGZSWmQ8zjPJ8K1PA
Nice introduction video by LA6NCA:

https://www.youtube.com/watch?v=9t8VTuLCjds

LA6NCA has an amazing collection of WWII German
sets, including many Kriegsmarine models.
His Torn E.b. page, detailing the recovery of
one of the late sets, which used a zinc-cast
front panel which crumbled:

https://www.la6nca.net/tysk2/torneb/index.htm
https://www.kriegsfunker.com/radios/torn_eb/torn_eb_1942.php

If you watched the videos, you saw that the radio
operates on eight bands, selected by a rotating drum.
Each coil module is shaped like a slice from a
tall birthday cake.  Each module contains three
tuned circuits.  The third coil includes a
tap for the regenerative feedback.
Here is a schematic:

https://photos.app.goo.gl/Vosnt9tNVjyJPBMg6
NOTE:
"+H" and "-H" are HEATER, 2VDC.
"+A" and "-A" are ANODE, 90V

As received, coil sets 1 through 6 had open
  coil windings.  I found and ordered replacement
  coils from a European gentleman.
Replacement Coils 1, 2 and 3 also had opens
(sold untested so that's OK; I got 4,5 and 6 back).
I disassembled one of the bad coil sets and found
that these lower-frequency coils were wound with
very thin and fragile Litz wire, which has oxidized
and opened right where it enters the winding.

Aged, oxidized and fragile thin Litz wire
  is becoming a problem with some of our old radios.
I have several SCR-183 transmit coil sets and an
intermittent winding in a National NC-44 IF.
I've found a couple of NOS IF transformers with
this problem.  The only band I'm missing which
I wish to have working is Band 3, because
that covers 630 Meters.  My plan is to eventually
replace the three coils with toroid cores which
will fit securely and still be tuneable by the
variable caps in the circuit.

If you decide to work on coils- the coil cores
are fixed with a glue which will dissolve in
Acetone. but sets again when that evaporates.
If you want to tune the cores, you'll likely
have to "re-wet" them with the acetone
to allow them to move freely.  The coil case
screws are locked with some kind of gray stuff
that seems like epoxy.  It will have to be chipped
off the screw heads and out of the screw head slot
to get the screws off.  Be warned by my earlier
post about using the proper screwdrivers on these
sets or one can destroy the screws in short order.

Here's an album of photos and videos.
  https://photos.app.goo.gl/HN3fhN4RqqqZjFfA9

TNX ES GL OM DE Dave AB5S






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