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I got this amp about a year ago, and it was the best little amp I have ever owned. It sounded amazing with very little distortion even at high volume levels, and it would go pretty loud! I started to notice that my left or right channel would fade slightly randomly, and then all of a sudden one day it just stopped working. I blame the leaky oil capacitors.. So it's time I finally rebuild this thing.
It has quite a few options on it, like 4 selectable inputs, 4 different output types (normal, reverse, left, and right) bass and treble controls, and a motional feedback system. It used three 12AX7 tubes, one for a phono preamp, and two for the tone controls, two 6AN8 tubes for the preamplifiers, and four EL84 tubes for the two output stages, which were two tubes in a push pull configuration.
I'm still working on the amplifier design, so not much work has been doe so far. I have cleaned out the entire chassis, and cleaned everything I could keep. Here are pics of the cleaned chassis, transformers, switches, and potentiometers.
You can see I wired all the filaments up using the various taps on the transformer, each section of the amp has it's own filament power supply. Each of the EL84 pairs, and the corresponding 6AN8 are on 2.5A taps, and the three 12AX7 tubes are on a 1A tap so I'm kinda pusihing it, but it works with no problems. The rectifier tube also has its own tap.
I threw in some old tubes to check my wiring, and to measure the final voltages on the transformers, and here are the tubes glowing nicely. All filament voltages are within about 5-8% above nominal rating, so everything checks out good!
Here a few random pictures from when I was cleaning everything.
The power, and output selector switch:
The input selector switch:
The power transformer, and then the output transformer:
The original speakers which I will be restoring:
I am still working on the amplifier design, so I will post updates as I progress. I also will be going to the surplus store later today, so hopefully I will find some of the stuff I need for it!
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Vacuum Tube Amplifier Build
