bought at auction. It uses an AC/DC 5 valve
(inc. rectifier) chassis with medium and long
1948. AC/DC (live chassis). The cabinet is a bakelite moulding
in the typical 'Walnut' effect, but with an inset grille of cream self-coloured
plastic. The glossy quality of this leads me to think that it is an Acrylic
The cabinet has some rather odd design points. As the pictures show, it is an
unusual shape. This makes for an interesting chassis design, where a shallow
bottom section of metalwork supports the power supply components, with a
vertical chassis section carrying the rest. This means that the amplifying
valves are in a horizontal position, something that can lead to electrode 'sag'
with certain valves, although this is unlikely with the range of valves used
here, as it tended to affect the later frame-grid TV types which had extremely
closely spaced electrodes.
The chassis was, happily, not too corroded and the layers of
dirt cleaned away readily with the application of foam cleanser, using a
combination of toothbrush and paste brush. (I have a separate brush for my
teeth, by the way). An alternative method would have been to have damped
the brush with WD40.
There is no dial lamp as such, the single bulb being used to illuminate a
small circular beacon mounted centrally below the dial, on the front of the
cabinet. The controls are unusually placed, being diametrically opposite each other in
recesses in the sides of the cabinet. The 'knobs' are two large Bakelite discs which have a
finger indentation for adjustment.
I feel that nothing looks more unprofessional that messily
re-soldered tags on components, so the volume control was removed for
cleaning and rewiring. Parts of the main ballast resistor wiring was
changed at the same time, as was the wiring to the indicator lamp - and
the lamp itself, expired due to a failure of its shunt resistor
First things first...
The mains lead was in urgent need of replacement -
it had been cut off. I
bored out the hole in the chassis through which the lead passed and fitted a
grommet, to protect the new lead. The old lead clamp was brought into use to
tether the lead with a little slack behind the outlet.
Powered up using a test
lamp, it was obvious that the indicator bulb was o/c. Replacing this gave a
quite brilliant light and it was obvious that, off the test lamp, the bulb
would have a short if spectacular lifespan, measured in milliseconds. A glance
at the circuit showed a possible culprit - R21, a 33 ohm pilot lamp parallel
shunt. Cold checks with meter showed this to be very high resistance,
overloading the lamp. I fitted a 47 ohm 2 watt resistor and this worked well
with a 6V torch bulb. 33 ohms would have been fine, but the bulb seemed to be
rather dim with that value. Possibly the original bulb was rated at a different
current to the one I fitted - the data wasn't clear about that point and the old
bulb was completely corroded and unreadable.
Next problem was odd. The bulb would come on, then go off again, cycling
through this on-off state with a remarkable degree of regularity and never staying on
long enough for the valves to warm to operating temperature. It was clear that
there was an intermittent supply fault of some kind, but what? Again, the
circuit diagram was consulted. The dropper resistor taps were monitored 'hot'
but these only rose to full AC potential whenever the lamp went out. It wasn't
the dropper, then, or the voltage would have disappeared. This left only the
valves and as I'd had much trouble in the past with UL41s, I changed the output
valve and solved the problem. Intermittent heater.
Next, A quick cold check on the resistance of the smoothing and reservoir
combination capacitor, which in the event read comfortably high and swung the
ohmmeter needle in a way that suggested a fair amount of capacitance remained.
First full power test
Under full power, the set gave a good account of itself, working on it's
frame aerial. Various points were noticed - some rather excessive sound
distortion, crackling from the wave-change switch, crumbling insulation on HT
and aerial wiring. Time to get to work. After a general chassis clean, as shown
above, the dial drive components were disassembled, cleaned, reassembled and
re-strung. I Removed the heavy cardboard baffle that carried the loudspeaker to
gain access to the components. I replaced the following capacitors: C18 (AGC
decoupling), C21 (V2 cathode by-pass), C31 (tone correction), C25 (AF coupling),
C2 (earth isolator, C7 (HT decoupling) C10 (V1 cathode by-pass)
I also replaced the surge limiter R22. This large carbon stick component
looked very much the worse for wear, though it read fairly accurately. Changed
for sake of completeness - besides, I don't like the look of burnt components.
After partial rewiring to power circuits and frame aerial connections - the
latter butchered by someone at an earlier time), switch, valve-holders and
volume control cleaning, the set was reassembled and tested. Though still only
on the internal frame aerial, impressively good
results on medium and long waves were obtained. Short waves less so, but after dark, found to
work very well. A short aerial wire improved SW response, which was to be
Of course, all cabinet parts were fully restored but as
this section is about the chassis, the cabinet is another story...