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General observations:
(1) Misc: a few wrong screws fitted.
Feet detached, 4x cabinet stiffeners detached, Dial setting off.
On/off switch loose. Knobs loose. Volume scale poor. Mains lead
poor and dangerous. Case needs treating.
(2) Valve line-up: 6K8 frequency changer, 6K7 IF amplifier, 6Q7
detector, AGC and audio amplifier, 6V6 audio output, GZ32 HT
rectifier. The valves have reasonable emissions.
(3) Clock red/black disconnected. Clock field winding proved
to be open circuit. The winding uses 47 SWG wire. Open near to
inside rather than outside of winding.
(4) Critical components: I measured the critical components and
found a leaky audio coupling capacitor. This item is very important
as if even the tiniest bit leaky will forward-bias the output
valve, increasing its standing current to a much higher value
than it was designed to run at. As the valve it is operated in
Class A, and at only 30 to 40% efficiency this will rapidly reduce
the emission and drastically shorten the life of the valve. It
may also burn out the output transformer.
(5) Resistors:- (measured figures in brackets)
R100 47K (53.5K); R101 56K (55K); R6 220 (262); R103 15 (10);
R5 2.2M (2.7M); R2 500 (442); R103 10 (7.4); R104 470 (437);
R105 330 (314); R3 25 (26)
All these are tolerably OK. None are particularly critical.
(6) Capacitors: These are in average condition but some, in places
where it is advisable, will be changed for modern components.
(7) Voltages: HT1 measured 300V and HT2 216V. LT OK
(8) Lamps: The two dial lamps are blackened and inefficient.
Work carried out:
(1) Fitted replacement mains lead with
modern conductor colouring, with original 13A plug.
(2) Added a 22uF capacitor across existing 10uF cathode decoupling
component in audio output stage
(3) Fitted new audio coupling capacitor.
(4) Fitted new AGC decoupling capacitor; this must not be the
slightest bit leaky due to the extremely high impedances in the
circuit.
(5) Fitted two new dial lamps.
(6) Realigned the IF stages to 465 KHz. These were way off-tune.
(7) Realigned long, medium and short waves. All were badly off-tune
from ageing of components.
(8) Cleaned dial and lubricated mechanism; tightened loose parts.
(9) Removed and cleaned knobs and removed and cleaned fascia
and re-taped it to the chassis.
(10) Tested 3 wavebands. Treated with switch cleaner. Performance
is very good.
(11) Removed clock and dismantled ready for re-winding coil. |
