I’m normally more at home with “IT” than “IF”, and valves are a long way before my time, so here’s my first attempt at restoring a valve radio…
I bought the set off eBay from a trader I’ve used before, so I felt I’d be getting something genuine. I was attracted by the VHF coverage, but I also liked the look of it. Described as “working, but we cannot get any sound out of it” seemed an interesting assessment for a radio!
The set itself was complete, and had dots of white emulsion all over from where someone had used a roller nearby and nicotine stains on the controls. There was a thick layer of dust inside, but everything intact. Most of the cathode of the EL84 was sputtered onto the inside of the glass – presumably a sign of a fairly hard life – and any rubber cabling (including all of the cabinet wiring) was falling apart. After a good clean, the cabinet wiring was replaced up to the octal connector, and the dial lamps replaced (all blown).
Under the bonnet were loads of horrible brown capacitors, many of which were showing significant distress. The only other rubber wire underneath was the mains feed from the on/off switch to the transformer… another good candidate for replacement. Any grid coupling capacitors (including C58, “that” capacitor) were replaced, along with any others that had undergone internal combustion.
Time for the “bang test”. With a 25W lamp in series, power was applied and after a short wait HT began to rise. On hitting 10V I flipped the power off and HT fell slowly to zero over about 30 seconds… a good sign for the HT electrolytics. Note that this model (built on February 23rd 1956) varies slightly from the Trader sheet. C55 (which is supposed to be part of the single electrolytic can) was instead under the chassis and separate. I wonder whether this suggests a replacement (the can is 2 x 50mF rather than 2 x 50mF, 1 x 20mF). Limiter lamp wattages were gradually increased over an hour or two to let the caps reform. With a 100W lamp and 120V HT I had Long Wave!
On with full mains. LW and MW came up fine, sound was rather wooden, but VHF gave nothing more than hum and the occasional whistle.
Next stage was to rebuild the FM front end. This is held with four screws, and the FM tuning inductor has to be disconnected. L1 had to be (carefully) removed, but L2 could be swung out of place to get access to the components underneath.
However… not only was VHF no better on powering up, I’d now lost Long Wave!! Arrrrgh! Thankfully… turning off the massive twin 2 foot inspection lamp I’d used to see what I was doing brought LW back to life… just no VHF.
Changing the three decoupling caps around the IF amp (V4) was the answer. Probably the most difficult possible capacitors to get to, but with C39, C40 and C41 replaced VHF came in loud and clear. Replacing the tone control capacitors and the sound (esp. speech on R4) is pretty excellent.
All that remained was a damn good clean, including the grill, knobs, and tuning scale, removal of the million little paint flecks, touching up of the scratches, and a good polish.
Not bad for a first attempt… and a nice radio for daily listening.