When I was around 15 years old my father gave me a transistor amplifier in form of a kit, it was a small amplifier that gave only 2 W but I built it and had a lot of fun when i connected it to a home built speaker and a portable battery powered grammophon.
Soon I wanted to have more power and I knew that my father had a lot of tubes in his workshop at our home. After promising to be careful with the high voltages he gave me some parts for an amplifier, it was two 807 output tubes, a 6SN7GT driver tube, a high voltage transformer, a choke and his own hand built output transformer.
I built an amplifier using a simple schematic with 1/2 6SN7 as voltage amplifier, the other 1/2 as phase splitter connected to the two 807's, I used feedback from the output amplifier to the cathode of the first amplifier stage. The output power I got from this amplifier was ~50 W.
As this was a mono amplifier I soon thought about building a stereo version but as I didn't had two output transformers I decided to wind my own. I found articles in some old electronic magazines and I decided to use split anode and output windings in order to get good frequency response.
I used standard iron E cores around 90mm size and wounded ~800 turns of 0.25mm enamelled copper-wire for each of the four primary windings. I started with a primary then added a secondary aso. I used insulating paper between each layer of wires and all wires was carefully laid side by side. It took me about four weeks of evening work after school to finish the two transformers.
I then built a stereo amplifier using these transformers and 807's in class AB2 with the same circuit as before but using 12AX7 instead of 6SN7 as voltage amplifier and phase splitter. The power supply that used electronic voltage regulation for the screen grid supply was built in separate box. The output power with this amplifier was 100W before clipping and the -3dB frequency response was 30Hz to 200kHz, not bad for home made output transformers!
After two of the 807's broke down I changed the output tubes to 6146B's that I got for free. With the 6146B's the output power increased somewhat so now I had 120W with the same frequency response. I used this amplifier daily until 1996 when I moved to Japan.
After I built this amplifier I built a Dynaco PAS3 copy! for use as a pre-amp.
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Created on ... december 16, 2000