15 watts ECL86 Push Pull guitar amp

I have now for some time slaughtered old tube radios and bought tubes from abandoned stores.

Now it should be tested if I could make an instrument amplifier out of the waste pieces in the boxes on the shelves.

I circled a little about Marshall 18 watt model, witch I have tried with success.

There was a "lite" version where the tremolo part was cut away. It had to be tested.

I had some tube type ECL86, it's basically an EL84 and 1/2 ECC83, which could then cut a Tube, I found a schematic from "Bogen" which has used this output stage.

I was given a sheet of fibre-plate from Bjarne Hansen, and with this layout as an example, I started to make component placement.

I had between the electrolytic capacitors found a suitable containing 3 capacitors in the same sheath. That removed the capacitor in front off the input tubes from the component table.

The finished result seen below.

I was not happy with the finished result, which was evident 50 Hz hum in the speaker immediately when there was lit for filament voltage, and was turned up Force began the amplifier to distort violently at ¼ strength and impact on the guitar came some Ugly percussion in speaker.

I tried different things, I could measure the voltage at ECC81-83 input tubes fell from no load at 245 volts 70 to 110 volts when the tube was in the socket. The Cathode resistor was 820 ohms I change it to 1.8 kOhms, this elevated the power on the tube to 145 volts.

The lattice resistance at the output tubes was 470 kOhms 8.2 kOhms, I change it to 330 kOhms + 270 kOhms to lower the signal level,

The output transformer was moved ca.10 cm away from power transformer. After tense all screws should I just measure the power through and with my measuring probe I pushed a few wires in place, so I got a big bang in the speaker.

IT WAS a bad soldering!!!

Capelin items were warmed through and the amplifier is well, hum distortion and percussion are gone it plays as a Marshall now.

Marshall did in 1972-73 a 1930 model that was marketed as a 10 watt.