In a previous blog entry I discussed the early 50s vogue for transformerless techniques in television design, the manufacturers said it reduced set footprint, I said it was a cost saving measure, whatever, it caused the brainiacs at Mullard’s development lab to think long and hard about the next ‘World series’ valve to be brought out.

Transformerless is a good way to go but it means that realistically HT voltages much over 170V cannot be achieved, however, it would be better if more juice could be squeezed, after all, the anode of the line output valve as well as the first anode of the tube could do with a much higher belt.

This was provided by a handy little dodge in which the energy in the line output transformer which would be dissipated during flyback is used to boost the HT power supply after it had first been rectified – probably by another Mullard valve, the EY51.

The little gem doing the boosting is of course that redoubtable Booster Diode, the PY80.