After testing the RF24
I tried this RF26.
The results were not quite right.
I can see the oscillator but the tuning passband is absent indicating
a probable fault with the unit.
I checked three dial settings,
zero, a mid range and 100 corresponding to the oscillator frequencies
seen below, 50.175MHz, 53.55MHz and 66.525MHz. The EC52 oscillator
was OK but no sign of the receivers
pass-band (approx 8MHz below the oscillator) as can be seen in
the RF24 and RF25. This may
be connected with the cut wire at the centre valve (which I soldered
back in place). Maybe indicative of an old fault-finding exercise
by a previous owner? Maybe cracked glass around a pin of one
of the two EF50s?