1966 Murphy B815 MW/LW 8 transistor

[howard]

Hello again,

My first Murphy restoration ! I bought this Murphy B815 with 'Caroline' on the dial at the Harpenden meet for just £2 It was complete, no cracks in the case with just a couple of minor scratches next to the earphone socket but the grille was scratched and coming off, yet it looked restorable and so I grabbed it. It was totally dead but I had a pretty good idea what was troubling this old Murphy, there are four AF117s lurking in this one ..........

Even though this was built during the Rank Organisation period, the construction of this Murphy bears little resemblance to any Bush radios of the period that I have encountered. The bottom door with two circular latches comes off like the ones on the TR130s but it also accomodates two PP9 batteries and has a couple of rubber straps to hold them in place. The chassis is released by pulling on two spring clips, one either side, and it then lifts out the top. Complete separation from the case requires unsoldering two wires to the external aerial socket and removal of the (very large 8") loudspeaker (four nuts and spring washers). I soon worked out why it wasn't working, one AF117 was shorting so I snipped its screen wire and away she went (no insulation on the AF117 wires curiously). She worked so well I decided not to replace the AF117 but to leave it at that. The three variable capacitor mounting bushes had disintegrated as well so I replaced those with three 1/4 inch grommets, quite a fiddly job as there is a brass cog just above them and so I loosened that (two grub screws) and lifted it slightly to allow removal of the three screws.

I took the grille off by lifting the six metal pins which are heat welded into the inner surface of the case. Three had come away from the chrome surround so I soldered those back on. I took the Murphy badge off the grille (two clips), rubbed down and resprayed the grille with Halfords white paint. I took the handle off (a spring clip either end) and polished that up and then cleaned the entire case in upholstery cleaner with my toothbrush. I then reassembled the radio.

For £2 and a bit of paint, this was a bargain This old Murphy sounds very good too as it has a very large loudspeaker. Its a robustly built radio which is now in very nice condition and a very welcome addition to my collection

Howard

[paulsherwin]

Originally Posted by howard

I soon worked out why it wasn't working, one AF117 was shorting so I snipped its screen wire and away she went (no insulation on the AF117 wires curiously). She worked so well I decided not to replace the AF117 but to leave it at that.

Nice set Howard, you certainly got a bargain there!

If I were you I'd change that AF117, as it obviously has an attack of the tin whiskers and *will* short again at some stage. In fact you should consider changing all of them, since they will have come from the same batch. There are lots of threads on the forum discussing subbing AF11x transistors.

Best regards, Paul

[howard]

Thanks Paul,

It was a bargain but a bit of a wreck when I bought it but I was certain I could restore it into nice condition but it took me three days to complete. Well worth it though cos I'm being rewarded now by one of the best sounding 1960s radios in my collection

I have a pile of AF125s to replace troublesome AF117s and often I do if an AF117 is completely dead, so I guess I ought to replace them cos as you say they can continue to be unreliable. Its a shame the AF125s arent the same size cos I do try and keep my radios as original looking as possible but I dont really fancy trying to put old AF117 cans on top of the AF125s !

Howard

[paulsherwin]

Originally Posted by howard

I have a pile of AF125s to replace troublesome AF117s and often I do if an AF117 is completely dead, so I guess I ought to replace them cos as you say they can continue to be unreliable. Its a shame the AF125s arent the same size cos I do try and keep my radios as original looking as possible but I dont really fancy trying to put old AF117 cans on top of the AF125s !

It might actually be possible to do this if it bothers you. Chop off all the wires and *carefully* drill a hole into the bottom. You should be able to push the AF117 case over the top of the AF125, stabilising it with a bit of glue. I must admit I've never tried this though

Good luck, Paul

[mickjjo]

Well done Howard for getting one of these things going!, I've had a B815 for years and I managed to keep it running by swapping AF117s regularly. The last time it packed up about 10 years ago I gave up when the PCB track started disintegrating around the transistor leads. One day perhaps I'll have another go at it, but I remember it was a good sounding set, spoilt by the AF117 curse.

Regards, Mick.

[Darren-UK]

The B815 is a good performing radio. The one thing to ensure with these, however, is spot-on bias settings at the o/p stage or they will suffer a burnt out resistor and will do so without any too noticeable audio distortion as a warning.

[howard]

Thanks Paul, Mickjjo, Darren,

Ive put in a new fully tested/working AF116 to replace the dodgy AF117 now, a bit of sideways move but to be honest I find AF125-AF127s very fiddly if there's not a lot of room to work in. Works just the same

Howard

[howard]

Hello again,

I always test my radios for some time after restoration to check that they're OK but this Murphy eventually packed up altogether Ron Bryan offered to repair it for me and he found quite a few things had gone wrong with this set

The remaining two AF117s were duly replaced with AF125s. As realignment was started, it was noticed that two of the trimmers (C1 and C13) had had their adjustment nuts pinched so I found a couple in a scrap Roberts RIC2 and they were installed in the Murphy.

The IF, MW, LW and BS stages were all realigned. Ron then noticed that the the mid point voltage and quiescent current on the output stage was far too high on an 18V DC supply, and that the mid point was 14.5V, when it should have only been 8.7V. Replacing the AC127 and OC81D transistors had no effect. It was then noticed that that the 10k mid point adjustment pot (R17) was short circuit, caused by an original solder joint bridging one of the pot connections to an adjacent track. Correcting that improved things a little but the mid point voltage of 8.7V was still not attainable. Some of the AC127 bias resistors (R18 22k and R19 22k and R20 33k) were then removed and their values checked, all were a bit high (a couple more than 20%), but substitution of these didn't make much difference either. The capacitors were then checked, C35 and then C36 were taken out and it was found that C36, the 12uF capacitor from the volume control to the AC127 base was leaky. In went a new 22uF capacitor (from a load I'd just bought from RS) and the correct mid point, and quiescent current of 14.5mA was set up ok. Finally the original OC81D and AC127 transistors were reinstated and the mid point voltage was still fine.

Ron commented on the interesting design of this set, in that it has a separate oscillator transistor (Tr1) instead of a combined mixer/oscillator. It also has tuneable bandspread on the HF end of MW, apparently using a variable capacitor intended for AM/FM sets instead of the standard MW/LW type.

I'm delighted with this repair, this Murphy really performs well now, one of the best sounding MW/LW sets in my collection. Many thanks Ron.

Howard