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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 1st Feb 2016, 9:24 pm   #1
high_vacuum_house
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Smile Murphy B40 back in operation

I had bought a B40 D radio a few years back and was impressed with its performance. When A forum member here offered one FOC missing its valves (Dave Walsh) I thought it would be interesting to get it going and arranged to collect it. It is an early version (B40 A)

I went to a few BVWS events and the Luton radio event looking in the boxes and eventually had a near complete set of valves for it.

The stumbling point was the output valve which appeared to have been modified with a B9a valveholder on a plate over the existing EF50 type base. This confusion concerned me and the set was put away for a time. At the December BVWS RWB event I bought a B41 radio and noticed it had the same modification. I pulled the B40 out from under the table and traced out the output circuitry which matched the B41. With this knowledge I could be confident the B9a output valve I bought would work.

With the new output valve fitted, the set was now complete bar the bulb in the crystal box and I had a look in my tray of dial bulbs and found one which would work.

I tried plugging in a Plessey MK.4 plug into the mains receptacle and noticed someone had in the past soldered some wires to the pins. Nice and safe I don't think!! With the pins cleaned the plug then fitted!!.

I carefully ran it up on the variac and nothing happened, not even a glint from any of the dial lamps. This was traced to the open construction mains switch which was gunged up. With a good clean and checking first with a multimeter then my megger all was well on the mains side. On powering up this time I had light but no sound. This time it was due to poor contact on the loudspeaker switch. With this switch cleaned and whilst the IF unit was out the other switches and everything else was cleaned. On powering up again I was rewarded to noise in the loudspeaker. Twiddling the tuning knob I received an unknown radio station playing Tubas in the moonlight by the Bonzo dog band

Although I could pick things up the reception was very insensitive. I had a couple of NOS CV303'S which I was going to try but found that V101 (CV303) was stone cold and obviously the heater not doing a lot! No wonder the sensitivity was so poor !!!

Wiggling it around whilst the set was powered up there was a plop from the speaker followed a few seconds later with a massive improvement in sensitivity

I also found that a .003uF capacitor disconnected at one end under V104, this had been deliberately desoldered for some reason. This was traced and should have been connected to ground. With a wire and crocodile clips temporarily connected and grounding the capacitor the set worked ok.

With the set basically working I cleaned the rest of the chassis of dust and checked the tuning capacitor as there was a crackle in a few positions. It is unusual as it has a ceramic shaft to operate the moving vanes.

The band change switch was checked and a few contacts adjusted as they were only just making. The detent for the band change mechanism was rather weak and the spring tension can be adjusted by lifting the bolt and turning a knurled nut. This one had been adjusted to its weakest position. With the tension increased the snap action of the band change was much better.

The front panel was tackled next. This was nice and easy and all the knobs came off easily. The front panel was fairly dirty and so this was removed after removing 8 2BA screws. I found whoever had fitted the panel last time had put the panel on with the inner lid of the crystal box open! On reassembly I made sure it was shut!
The panel came up well with some Servisol foaming cleaner and the knobs with

The red lens in the crystal door covering the X was missing. This lights up when the crystal switch below it is switched to the on position. I found that the transparent red packaging that Jaffa cakes comes in makes a good substitute and so this was cut out of the packaging and glued into position

Once everything was reassembled the set looked very respectable and looking as it did when it was on board a navy ship. This is possibly the first time since it came out of the Royal Navy it has worked as it should have.

The pic below shows it mostly restored with the temporary connection grounding the disconnected capacitor.

Christopher Capener
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Last edited by high_vacuum_house; 1st Feb 2016 at 9:53 pm. Reason: Missed the bit about the red crystal lens !!
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Old 2nd Feb 2016, 12:59 am   #2
turretslug
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Default Re: Murphy B40 back in operation

I'm sure there was a post here regarding an official substitution of the 6BW6 for the original EL22 a while back- I had one of these sets where an IO holder and 6V6GT had been substituted, though both these (a 6BW6 is effectively a B9a 6V6) need a suitable cathode resistor change.

I've come across some quite horrifying mains and other bodges with old and very metal military/professional sets that really made me shudder- you do wonder about some people.... Surely acquiring a set made to some of the beautiful and exacting standards that this stuff was would encourage work aspiring to similar quality It seems not always.

I always thought that if only that loktal/loktal-9 series of valves had had pins 1/8" longer combined with better socket contacts, they might not have acquired their bad reputation for iffiness- the EF50 became notorious.

That's looking like an excellent and rewarding job- it should be good for another 60 years. You might need to beef up that wheel-barrow, though....
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Old 6th Feb 2016, 5:36 pm   #3
dave walsh
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Default Re: Murphy B40 back in operation

It's very satisfying to read about such an expert and painstaking effort by Chris. I encouraged him to "Broadcast" his efforts as I know there is a lot of B40 interest around. He was very pleased to discover the set Mod was in fact, an official conversion and not a bodge. The set came from a lady in Plymouth [appropriately enough]. I wouldn't be surprised if it had come straight off the ship and into a Government Surplus shop. She told me that her son had worked in the recording Industry and he removed the valves for other purposes in the sixties. It was dry stored for over thirty years in her garage.

I obtained it quite a few years ago now. It was collected eventually by my brother in law from Bicester who visits his home town Plymouth. Then it resided in Bicester for some time before it carried on to Ramsbottom where it joined some other "Boat Anchors" for another long stretch until Christopher came to wake the sleeping princess! This is the outcome I'd hoped for

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Old 8th Feb 2016, 11:49 am   #4
newlite4
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Default Re: Murphy B40 back in operation

Well done Chris, quite a bit of in-depth detective work there, nothing straight forward about that restoration, only for the dedicated.
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Old 8th Feb 2016, 3:32 pm   #5
high_vacuum_house
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Smile Re: Murphy B40 back in operation

Many thanks for the replies, I certainly enjoyed pulling this radio to bits and restoring it. They are well designed and must have cost a fortune when new. The mechanical assembly alone is particularly solid with ease of maintenance to remove the IF and PSU chassis from the case. Most of the capacitors did not show any leakage at all when meggered. It is surprising with the weight of the receiver it only has 13 valves.

Christopher Capener
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Old 9th Feb 2016, 6:04 pm   #6
Phil G4SPZ
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Default Re: Murphy B40 back in operation

Well done Chris, and a nice write-up too.
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