Cannot resist bringing back to life a radio that was going to the skip. A nice Murphy A262. This chassis came along in the mid ‘50s, just as VHF-FM was just starting in the UK. One of the first chassis that used the newly developed Mullard ECC85 valve in the FM section as a RF amp and oscillator. The thing that lets these sets down and loads of others of that era was the use of HUNTS capdensors. These things were rubbish even when delivered from the factory. Anyway, about 10 of these replaced, the smoothing block emptied and fitted with new electrolytic capdensors and sealed to make things look original.. I.F transformers tweeked and the set worked really well. FM VHF nice a sensitive and loads of volume through a 10” loud speaking speaker, driven by a chubby little 6P1 pentode, that needs to go on a diet. The set makes enough racket to fill a large room. Only problem now, is that the mixer oscillator valve 6C9 is becoming hard to find.
After working every evening for two and a half years, we started to have a few problems. Here we go!
This radio came along a few years ago and I gave it a basic restoration. Been in use almost every evening. The other day it started doing some very strange things. Unstable, bad audio, intermittent hum.
So into the shop for a quick fix. Or what I thought would be a quick fix. With the chassis removed and on the bench, I gave her some power. Dead, dial lights working but no HT. I found the EZ40 had a crack around one of the pins. So, a replacement fitted. Now we had HT, but still no audio. After a lot of time wasting, eventually found that the chassis side of the primary winding on the output transformer had broken off. Shit. Carefully peeled back the insulation and manged to get enough copper wire to solder onto. Now we were back to the bad volume and audio. Looked to see if I had anymore hard drugs in the drawer. No.
During my first repair, I had not replaced the HUNTS capacitors that were awkward to access. So, I chastised myself and replaced all the nasty bits. Audio was a bit better, more sensitive. But, hum and oscillations were still there. For the first time this week, I turned on the oscilloscope. Found that the main HT line had full wave ripple with audio superimposed. I had replaced the electrolytic capacitors in the past. But, one was open circuit! With that replaced the radio worked fantastically. It is incredible how sensitive these FM radios were. Lovely set. Replaced the mains cable with some new old stock cloth covered wire. Looks nice.