UK Vintage Radio Repair and Restoration Discussion Forum

I bought this (IMHO) rather attractive battery/mains valve portable radio at the recent Royal Wootton Bassett auction. I particularly like the three concentric controls for tuning, wavechange and on-off/volume. Having the option of battery or mains operation is also a bonus and the mains lead, with its special connector (never seen this type before), was stowed in the base of the radio (where the absent LT and HT batteries are located). The chassis mounted half of the mains input connector also incorporates the battery /mains changeover switch contacts.

As this radio will operate on ac or dc mains, the mains voltage adjustment is a 1.5 kOhm wire wound pot that forms part of the HT smoothing resistance connected between the reservoir and smoothing capacitances. The slotted top of the pot’s knob protrudes through the “millboard” battery/mains lead stowage area and voltages are marked on that in 10V steps between 200 and 250. The user rotates the pot to the appropriate local supply voltage.

After uncasing the radio, I gave the chassis a dusting out and a visual inspection for any obvious issues. I saw that someone had in the past disconnected the small “Westinghouse Brake & Signal Company” metal rectifier unit and fitted a “BY100 lookalike” Silicon rectifier instead (leaving the original part in situ and using one of its tags to connect the cathode of the BY100 and the wire that goes to the HT reservoir capacitor). Probably at the same time, the surge limiting resistor, R22 (500 Ohms, 3W), was replaced by a 560 Ohm part, to compensate for the lower forward voltage drop of the Silicon rectifier.

I then connected the set up to my Variac’s output. I measured the HT line as I slowly increased the ac supply voltage. Although there was increasing HT, not a squeak from the loudspeaker, so I then measured the heater supply and found it to be absent, due to an open circuit R19 (3000 Ohms 3W wire wound) which drops dc from the HT line on mains operation. R19 and R20 are a small “mains dropper” type of power resistor assembly. I bridged the o/c section with a nice period “Radiospares” 3kOhm 5Watt wire wound type, which is grey and has radial lead out wires.

I then got some crackling from the speaker and intermittent signals, which was due to a faulty “Willow Vale” branded DK96 mixer/oscillator valve. I fitted a Mullard “pull” in its place.

I then disconnected the supply and replaced the six brown “Hunts” Moldseal capacitors fitted in this set, which all had severe leakage (down to 70k in one case).

To avoid incorrect running of the valve heaters, I also replaced two valve heater current bypass resistors across the DL96 audio output valve’s centre tapped heater, which had gone high (“Erie” ceramic bodied carbon composition types; R16 5% 240 up to 256 Ohms and R17 10% 330 Ohms up to 383 Ohms).
I also replaced the DL96’s cathode bias resistor, R14 560 Ohm 10%, which had gone up to 648 Ohms.

In this set “that capacitor” (output valve control grid coupling) is a 500pF “Suflex” Polystyrene type, which was OK.

The final electrical work was to spray some contact cleaner/lubricant into the on-off switch (ganged with the volume control), as the contact resistance varied wildly as the contacts were operated. The treatment restored very low resistance across both sets of contacts. The set was now performing well and was surprisingly sensitive on both Long and Medium wavebands.

The cabinet (with loudspeaker removed) was also dusted out and cleaned with foam cleanser; it scrubbed up rather well.

The chassis was refitted and the set tested again – still working!

I’m very pleased with both the appearance and performance of the set. The only query I have is whether there should be some sort of grill to cover the large rectangular opening in the case, below the handle. A finger can easily be put through it and make contact with what is a “live chassis” on mains operation (and the mains connector is not polarised).