Ferguson 352u

The repair
When I first spotted this radio for sale I was transfixed by the simple, but effective layout of this 1955 Bakelite design. The seller said that some wires were lose but otherwise it was complete but when I checked the photos that he put on-line using the radios layout manual I could see that the audio output transformer T1 was missing.

So while I waited for the radio to be delivered after purchasing it, I ordered a second hand transformer that was quite similar in size to the missing one. The manual (can be found on-line in Pdf) quoted 500 ohms primary impedance and the one I found was 300 ohms, but close enough I think, if anything I might give a louder output than the original. Funny enough I received the parts in the post before the radio, lol, anyway when it arrived I drilled an extra hole for the transformer fixing, it was about 10% larger than the original, but fit quite well. The wires were a little more tricky as they were short without terminals to solder too. So I glued a neon 2 pin fixing (without neon inside) to the chassis for solder points, this also allowed me somewhere to fix the tone correction capacitor (C26)  that I found lying inside the cabinet. It was obvious that at sometime in the past a repair-man gave up on this one and left it on the stock room self forever.

Showing replacement audio transformer and wiring, new rectifier not fitted yet.

Anyway soldered all the wires in place and powered the set up, nothing? no HT even.  So I turned my attention the the mains rectifier diode a huge Westalite contact cooled type, and it read open circuit. This diode is a later development of the Selenium type that had cooling fins looking like a radiator, this type needed to be bolted to the chassis for its heat transfer. Little information can be found on-line about these and from previous repairs I remember that if you replace them with a BY127 or similar modern diode then the HT will rise due to the lack of forward resistance of modern diodes, so I fit  about 100 ohms in series, should be enough. When fitting a new diode beware of the polarity of the terminals as in the 1950's they labeled them different, use the circuit as reference, not the component's '+' and '-' tags.

Original rectifier was open circuit (positor X1 wired to left tag)

Next I checked the mains dropper resistances and 3 out of the 4 winding were open circuit, the top 3 are for the mains adjustments 200, 220 and 240 volts. A 1.1 K and 2 x 200 ohms, so as the lower voltages were not needed I bridged them all with a 1.5k wire wound 7 watt resistor. The remaining winding was in the HT supply and I fitted a 220 ohm, 7 watt  to cover the increased output from the BY127 that I had fitted. All wires near the dropper need to have fibre heat resistive sleeving fitting. Would you believe it when I switch on the set was still dead, it tuned out the be the '-VE' contacts of the mains on/off switch that I next found open circuit. It's hard to believe all these faults happened at once, I think the last repair-man was having a bad day, we've all had one of those!  Now when turned on, great! sound came through the speaker the first time in god knows how many years. In-series with the HT supply (X1 & X2) and across the light bulbs are resistors known as a Positors, these vary in resistance with heat/current drawn.

The dial insert was lost, so I made a new one from gold cardboard & glued in place

They were commonly used in colour televisions of old in the de-gauzing circuit, giving maximum current when first switched on and going open circuit when hot, this demagnetized the shadow mask of the colour tube every time you switch the set on. In the case of the radio it works in reverse and halts any sudden high voltage to the heaters and light bulbs. They are quite bright in this set, having a total of 15 volts AC across them as they are wired in series, giving 7.5 volts to each bulb, they are rated a 8 v, 100 mA, so quite rare today and I expect 6.3 ones have been fitted in the past. Switch cleaner was applied to the band switch and volume control to remove internal dust and this cleans the contacts to give less crackles. I was surprised that none of the wax capacitors were playing-up, no need even for high value resistors to be replaced and even the 50uF x 2 smoothers were fine, I suppose it was on a shelf for many years, so not too worn out.

Cabinet repair
I was lucky with this buy, the cabinet was near mint, just needed a quick polish and tooth brush around the speaker grille. I cleaned of the tuning dial and bulbs and we were away. I find after cleaning Bakelite it goes a little dull, this is because modern cleaners remove the top layer of oil from the molding, this can easily be returned with a cloth soaked in '3-in-1' oil. The gold disc was missing from the tuning dial, so I cut a new one with some shiny gold card I keep for fascia repairs.

Underside view of chassis, showing all the 'good' wax capacitors?