Deacyfunken

After butchering the poor old Telefunken reel-to-reel I wanted to build a Deacy-style using the salvaged transistors and transformers and give it a new life. For the most part, I used Mullard’s amp schematic from below and tweaked few component values to match with some of the Deacy schematics I found around. Few other changes were made to accommodate the parts I had available.

mullard_amp
Changes

Comparing the Mullard schematic to various Deacy schematics that are floating around, I made the following changes to the Mullard amp:

  • Used AC117P output transistors that came from the Telefunken. They seem to be a bit more powerful than AC128 and can output over 1W in push-pull configuration.
  • Used AC150 for input transistor and AC122 for driver transistor, also pulled from the Telefunken. AC150 is commonly used as the first gain stage in many Telefunken devices from that era,
    so I guess it’s good for that purpose.
  • Instead of a 39 ohm resistor that biases the output stage, I used a 56 ohm resistor in parallel with the 350 ohm thermistor that was originally mounted on the Telefunken transformer. It will provide temperature compensation and make the amp run more stable.
  • Instead of two 10uF coupling capacitors in the signal path I used 1uF cap at the input and 2.2uF poly film cap to couple the first and the second stage. There’s no need for such a large capacitors for guitars, we don’t want to go that deep.
  • Omitted the 390K input resistor and input volume pot.
  • Added a 2.2K resistor downstream from the first coupling capacitor. I saw this resistor on few Deacy schematics.
  • Omitted input volume pot.

I ended up with something like this.

Construction

I’ve had a cool looking, compact tag board for years and couldn’t find a good use for it, as it’s often too small for tube projects. But it turned out to be perfect size for this project. All components fit on the board (except for the output transistors that are mounted on the transformer) and it fits perfectly inside the aluminum project box I got from Radio Shack years ago. To make it possible to try other transistors, I used individual IC socket pins soldered on the board.

Fast forward to the completed board. I didn’t have a 220nF capacitor for the output transformer zobel network, so I replaced it with two Panasonic 100nF capacitors in parallel. I did not have any axial electrolytic capacitors, so I faked them using radial capacitors mounted horizontally.

Comments
One Response to “Deacyfunken”
  1. Carl says:

    Never worked with a thermistor before. my local guy only supplies NTE components? Will 02−P331−1 work?
    It is 330 ohm with a trip of 75 mA the pdf sheet is http://www.nteinc.com/thermistors/thermistors.pdf
    I have all other parts including transformers and raytheon ge substitutes. What is the amperage on power transformer? I rebuild ever-ready #266 nine volt batteries and would like to try one.

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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.