Telefunken 302TS

Being a fan of German engineering, I really wanted to get my hands on one of German-made devices from the 60s, peek inside and convert it into a cool little guitar amp. I came across a broken Telefunken reel-to-reel on ads and bought it for 10 euros after confirming with schematics that it has amplifier topology that I’m after.

At first glance, it’s a well made, hefty thing, mostly metal (\m/) and weighs over 3kg. That makes it impractical to reuse the whole chassis, as I’d have to haul around tons of metal I don’t need. Also, tape heads look corroded, so it’s not practical (for me) to restore it. Inside we have two PCBs – one for driving the motor and the other with (mostly) the amplifier circuit.

I decided to take it apart, extract components that could be useful and rebuild the deacy-style amplifier from scratch. Here’s what I kept:

  • Hefty looking interstage and output transformers.
  • 3x AC188K that used to drive the motor, similar to AC128. Should be great for another power amplifier or (even better) in fuzz face, as they are high gain.
  • 2x AC117P IV used as power amplifiers, I intend to reuse them for the same purpose.
  • 7x AC122 used gain stages and to drive the interstage transformer. Versatile transistors. Can be used as amp gain stages, or in a treble booster or fuzz. Telefunken marked their transistors with colored dots to designate their gain ranges (red=40-60, yellow=55-95, green=85-140, violet=130-200, white=170-300). 3 of mine are violet, one is green (insterstage driver), one is yellow, one unmarked and one marked “dc”, whatever that means.
  • 1x AC150 used as the input gain stage.
  • A handful of film and polystyrene capacitors.
  • Few germanium diodes.
  • Cool looking “Telefunken” metal logo that I plan to attach to the finished amplifier.

Below is the photo of interstage and output transformer (note that interstage transformer is larger than output, it’s usually the other way round). It’s interesting to note how they mounted power transistors directly on the interstage transformer and used the transformer as a giant heat sink. Also, there’s a 530ohm thermistor mounted directly on the transfrormer, right between the two transistors.

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    The idea behind this site is to share my experience with Do It Yourself approach to guitars, amplifiers and pedals. Whether you want to save a couple of bucks by performing a mod or upgrade yourself instead of paying a tech, or want to build your own piece of gear from scratch, I'm sure you will find something interesting here. Also, this is the home of DIY Layout Creator, a free piece of software for drawing circuit layouts and schematics, written with DIY enthusiasts in mind.