This Theta power amp has been fully serviced, tested, and the output tubes biased. A new mains cord, fuse holder, and power switch were installed and wired to modern electrical safety standards (live wire to fuse, then switch; neutral wire to power transformer; earth wire to chassis). The eight 600uF 350v B+ filter capacitors were replaced with 560uF 400v caps, and the three 100uF 150v bias voltage filter capacitors were replaced with 100uF 160v capacitors. Rectifier diodes were replaced with 1000v 1A devices.All resistor values were measured and found to be within tolerances. All coupling capacitors were tested for DC leakage, with none detected. A new matched pair of Tung Sol brand 6550 power tubes were installed and each biased at 28 watts of plate dissipation (70%) at idle approx. 53mA per tube with a plate voltage of approx.
520v into an 8 ohm speaker load. Phase inverter tube is an old stock Sylvania 6AN8A pentode/triode. NOTES: this is a rare amplifier and little information exists on this model. An 8 ohm secondary load was chosen for the purposes of measurement and biasing on the reasonable assumption that the three secondary OT taps are the standard 4, 8, and 16 ohm. Also note that biasing was accomplished via direct measurements of plate current, and that the built-in bias meter should NOT be used to set plate current; in the case of the currently-installed tubes, biasing with this meter would cause the tubes to idle at an excessively high current and negatively affect tube life.The item "RARE Theta SCN OPT Tube Stereo Mono Block HIFI Power Amp" is in sale since Wednesday, March 24, 2021. This item is in the category "Consumer Electronics\TV, Video & Home Audio\Home Audio\Receivers & Amplifiers\Amplifiers & Preamps". The seller is "thesurfer" and is located in West Palm Beach, Florida. This item can be shipped to United States.