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Front View [24K]

  • Released September 1949
  • Band I T.R.F.
  • 9" MW22-14 C.R.T. with 6.5KV E.H.T.
  • 19 Valves (no less than eleven EF50's!)
  • AC/DC mains
  • Original Cost £39 18s
NOTES This is basically the same chassis as the Pye B18 / D18 released the previous year and whose chassis was probably the first British set to utilise the concept of a booster diode in the line output stage. This circuit recovered energy from the scan coils during the line flyback, damping any ringing. This rectified pulse would then be smoothed and used as an additional power supply for the line output stage itself, effectively boosting the available HT voltage available to the line output stage as well as providing the power for the first part of the line scan.

The concept of a boost diode is what also enabled this to be the first AC/DC chassis. With a transformer in a chassis it is easy to generate a higher HT voltage for for the line drive stage. However without a mains transformer you are limited to the voltage that the mains delivers. The booster diode, in providing an additional voltage, could thus go someway towards restoring the higher HT supply.

I guess this chassis must have been quite popular in its time as there seem to be a lot of surviving examples about, although perhaps the survival rate has been helped by the set's small dimensions.
SERVICE DATA A copy of the Trader service sheet #946 is available on the TV Service Data CD.
CURRENT STATE Basically sound and complete. But have you ever thought something wasn't quite right but you couldn't quite put your finger on it ?

The EF50 sockets are also a bit wobbly loose ; I gather this is a typical irritation of this type of set.

There are two versions of this set, the LV20 for the London area and the BV20 for the Birmingham area ; This set has "BIRMINGHAM" stamped on the front underside of the chassis, although the marking can appear in various places such as the back of the aerial panel.
WHERE FOUND September 2003 National Vintage Communications Fair for £80.

Chassis View [33K]
Pretty clean chassis ... with suspicously clean EL33 (left of center).

Page copyright
J.Evans 2003
Last updated
29th September 2003