Peter's Nostalgia Site
Sheets for the HMV 901
The Timebase with the System Selector Switch (S1) is shown below.
The additional triode in the line
timbase was apparently to compensate for the lack of line synch pulses
during the frame synch.
EHT Transformer Design
Apart from the usual leaky capacitors and high resistors the most challenging repair for me
was the re-wind of the burnt out mains derived EHT transformer. Initially I tried to simply copy
the original structure but ran into insulation problems so I redesigned it a little
by separating the primary and high voltage windings with the 4 volt tube heater winding.
For both the tube heater and the EHT rectifier heater windings I used PTFE insulated wire
and this (touch wood) has now survived for nearly 30 years.