• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Troubleshooting a JAS Array 2.1 805 SET amp

Just received my non-working JAS Array 2.1, without 805s. I have this 100lb beast on the work bench and there is nothing obviously wrong that I can see or measure, so far, no black, exploded parts etc. I have 1 805 but am waiting for more to arrive. I have the 300Bs and all input tubes. I would like to power it up to check for PS voltages but not having worked with SET amps before, wondering if it would cause an issue with that 805 missing? I imagine not as it would be no different than if the filament opened.

It's a dual mono amp, and just stopped putting out sound one day, tubes still glowing, no blown fuses, just no audio. The only thing I can find common is the input 12AX7 and the line cord, all supplies and parts are separate for each channel. I think it's a pretty common 300B DC to an 805. I've attached the schematics. I suppose I could also just lift a primary winding on one channels' supply xfmr to keep the missing tube channel dead. The inductor in the cathode cct of the 300B measures about 800 ohm.

Thanks all.



  • JAS2.1schematic.JPG
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  • JAS2.1 power supply schematic.JPG
    JAS2.1 power supply schematic.JPG
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