The Myth of the Quad II/22/tuner power supply balancing

Submitted by dada on Tue, 02/09/2021 - 15:10

It has been claimed, and indeed I have uncritically repeated it myself in the past, that the Quad 22 and tuners draw heater and HT current from different Quad II power amplifiers, so that the heater and HT loads are distributed.

However reference to the Quad 22 and FM Multiplex schematics shows that this is simply not the case. Instead the distribution is simply such that the heater and HT that comes from the Yellow amplifier goes to power the 22 and also out the Yellow and Black rear sockets, and the heater and HT from the Blue amplifier goes out the Blue socket.

This means (1) that the 22, FM tuner, and AM tuner are all completeley powered by the Yellow amplifier, and (2) that the only thing that is powered by the Blue amplifier is the HT in the MPX adapter (which doesn't have valve heaters, being a transistor unit).

If you have a mono FM tuner (i.e. no MPX) and attempt to power it from Blue, to overcome this, it will simply not work unless you have Stereo selected on the 22 front panel.