Share:
Notifications
Clear all

Murphy B485 transistor radio.  

Page 2 / 2
 
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

@katie-bush

'U' was a designation I remember from the cardboard-bodied cells, and later prefixed with 'LP' for the "leak-proof" version.

I think the PP7 deserves an honourable mention here - staple of many a smaller transistor radio. I'm still amazed the flat 1289 batteries are made, which is just as well for those of us with AVO 7s...

ReplyQuote
Posted : 24/10/2020 10:24 am
Till Eulenspiegel
(@till)
Famed V-Ratter Registered

Battery wires traced and connected up to the new battery holders, eight Panasonic cells fitted. Switch on, plenty hiss but no stations coming through. Local oscillator dead, only a few millivolts between the emitter and base of the XA102 transistor. Will try a replacement transistor first, if a Mullard OC44 can be found all well and good. If not a Hitachi 2SA15 will be fitted instead.

Info about the 2SA15: https://www.radiomuseum.org/tubes/tube_2sa15.html

Till Eulenspiegel.

ReplyQuote
Topic starter Posted : 16/11/2020 9:07 pm
irob2345
(@irob2345)
Active V-Ratter Registered

Try a BC557. Trust me, it will work quite well! And last forever....

Yes I know the Vbe is different. But the bulk resistance of a silicon transistor b-e junction is much lower so that compensates.

ReplyQuote
Posted : 16/11/2020 10:59 pm
irob2345
(@irob2345)
Active V-Ratter Registered

Looking at the pictures, it's hard to believe that the B485 was a production design and not just a prototype. So labour-intensive to make and the rework issues must have been significant.

"Don't go to too much trouble. Those new-fangled crystal triodes will never catch on"!

ReplyQuote
Posted : 16/11/2020 11:13 pm
Nuvistor
(@nuvistor)
Famed V-Ratter Registered

@irob2345

Murphy did design some remarkable good TV and radios but around 1960 they seem to have lost their way. I think the last TV range was the 700 series they made, the 600 and 700 series had problems from what I remember, not the quality of the earlier sets. They did look good though.

https://www.radios-tv.co.uk/murphy-bw-tvs/

Things at the company were obviously not right in some way and in the early 60’s were bought by Rank to eventually become RBM, Rank Bush Murphy. The first common chassis was the V800 series, the Bush was the TV125. A decent design that was built on from the Bush TV105 then TV115 series. I found the 105/115 to be marginally more reliable than the 125 but from my point of view it was still a decent chassis.

Radios followed with some similarities between the two marques but they tended to have their own designs. Perhaps this was due to wanting different cabinet designs, the chassis needed to be different. Nevertheless both marques were decent radios coming out of the same factory.

That’s my recollections but of course from a personal perspective. Others my have different information or view point.

Frank

ReplyQuote
Posted : 17/11/2020 8:50 am
Till Eulenspiegel
(@till)
Famed V-Ratter Registered

Hi Frank, this certainly is a strange set.  As well as the XA102 oscillator transistor it turns out the AF117 mixer transistor is also faulty.  Don't have any AF117s in stock, instead a Telefunken AF137 will be used.

The local oscillator does now work, delivering 1V P _ P to the mixer, but only at the high frequency end of the medium waveband. Using different types of transistor doesn't make any difference in the manner the oscillator works.  No LW oscillation whatsoever.

Posted by: @irob2345

Try a BC557. Trust me, it will work quite well! And last forever....

Will give serious though to using a BC557 type of transistor in this set, and others as well.  Germanium transistors are becoming scarce. A few Russian ones still available I'm told.

Till Eulenspiegel.

ReplyQuote
Topic starter Posted : 17/11/2020 6:37 pm
irob2345
(@irob2345)
Active V-Ratter Registered

The BC557 is commonly thought of as an "audio" transistor, but a look at the specs will show it is a good match for vintage germaniums. With an Ft of 150MHz it is useful up to 10MHz and beyond.

20 + years ago I had a UK-made transistor radio to fix for my father-in-law. The OC169 and OC170s (I think - they were those fat cans with 4 leads) in it were dead. I thought I'd fit 3 BC557s as an experiment. The radio came to life with amazing sensitivity but was still completely stable. Didn't even need to align it.

ReplyQuote
Posted : 18/11/2020 11:06 am
Till Eulenspiegel
(@till)
Famed V-Ratter Registered

The BC557 will replace the old OC44 and OC45 transistors which were in common use between 1957 to 1960/61. The only components needing attention will be the neutralising capacitors. It's possible these components could be dispensed with altogether.

Good news about the Murphy B485. The oscillator is working on both wavebands. An electrolytic decoupling capacitor C18 had gone low capacity. Another elco C49 was found to be in the same condition. Both capacitors now replaced. The original XA102 oscillator transistor has been refitted and the AF117 mixer transistor replaced with a TFK AF137.

Murphy B483 mixer osc
Murphy B483 C49
Murphy B483 C18

Till Eulenspiegel.

ReplyQuote
Topic starter Posted : 18/11/2020 3:28 pm
Till Eulenspiegel
(@till)
Famed V-Ratter Registered

The set works very well on the long waveband. BBC Radio 4 coming in loud and clear, in fact just as good as the local medium waveband transmitter on 603Khz.

Till Eulenspiegel.

ReplyQuote
Topic starter Posted : 26/11/2020 8:41 pm
Nuvistor liked
Page 2 / 2