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Identify Unusual Amplifier

Posted by strijw426 (A) on June 6, 2016 at 14:25:04

Years ago I worked on an audio amplifier that used a different design approach to a common push-pull output stage that used 6BQ5/EL84 tubes. The unusual aspect was that instead of having around 350-450VDC applied to the plate circuitry of the output tubes the center tap of the transformer was connected to ground. The screen grids were returned to chassis ground either through screen grid taps of the transformer (ultra-linear design)or through bypassed resistors connected to chassis ground. The cathodes of the output tubes had a high negative voltage applied to them (the 350-450VDC B Minus). At the same time a high negative voltage was applied to the tube heaters through a bleeder network to prevent cathode to heater breakdown. The cathodes were bypassed with electrolytics installed with their negative pole connected to the cathodes.

I remember that the tubes were on a PC board with circuit traces rather than point-to-point wiring.

Do any of you know the manufacturer of this type amp? It appeared on my work bench some time in the 1963-1966 time period.

Thanks in advance.

Joe

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