Another Solartron SR153

[ppppenguin]

I once pondered stabilising my 153. As Mark says, the series pass devices are already there so a high voltage transistor or FET plus a simple feedback loop should do the job. Guaranteeing stability (in the nyquist sense, not voltage) shouldn't be too hard. You could get a bit more out of the supply if you replace the series pass valves with FETs. Mainly because they have an inherently lower voltage drop than the valves. As a minor effect by not having to supply the heaters the transformer has a little bit more in hand. Exactly how much depends on whether the main secondary winding is up near its thermal limit. For similar reasons replacing the valve rectifier with silicon will give a slight boost too.

I expect any gain in this area to be mainly at higher output voltages. The available current drops towards zero at 500V output. With all solid state there would be a significant amount available at 500V. Hard to say how much without doing some measurements.

One very useful mod I did to my 153 is a switch in the HT output. Allows me to switch the HT on and off safely and quickly. Also to preset the HT before applying it to the load. Much safer than plugging the HT leads.