What did I get myself into? Murphy A40C.

[Katar83]

Look what late santa just dropped here.

I partially blame this forum for this 'impulse gift'

I take it the upper left is volume, not sure what the upper right one does(moves band indicator, but I've never had a radio with one of these), the lower right is Long/Medium/Short switch and I take it the lower left is power switch but there are 3 settings there, not sure what they do?

I guess finding a standard manual for it will be tricky but I do have a service one for it.

Well, that should certainly keep me busy for a few weeks.

PS

Is there anyone in East Anglia that could eventually help with calibration of this radio?

[Station X]

What's the make and model?

[ms660]

Murphy A40C:

https://www.radiomuseum.org/r/murphy_a40ca_40.html

?

Lawrence.

[high_vacuum_house]

It is a Murphy A40C radio, possibly the best sounding radio ever once restored with plenty of additions compared to a normal pre-war radio. It is built on 2 chassis, the receiver at the top and the power supply and push-pull output stage at the bottom .

Christopher Capener

[Station X]

Originally Posted by ms660

Murphy A40C:

https://www.radiomuseum.org/r/murphy_a40ca_40.html

?

Lawrence.

I knew you'd soon be on the case Lawrence. Thread title updated.

[Katar83]

Originally Posted by high_vacuum_house

It is a Murphy A40C radio, possibly the best sounding radio ever once restored with plenty of additions compared to a normal pre-war radio. It is built on 2 chassis, the receiver at the top and the power supply and push-pull output stage at the bottom .

Christopher Capener

It is indeed a Murphy A40C and your description of it is pretty much a reason for this 'impulse gift'
Love your signature, this is a perfect example of such radio. Barely managed to get it out of the car.

First question. Just had a quick look, its missing two valves, V8 and V9. V8 is Mazda AC/SP1 valve, which apparently is unobtanium.
Is there anyone here that have one of these and dont need it? Alternatively maybe it could be replaced with something more available?
V9 is skipped in the service manual. Any ideas why?

PS

Found a post mentioning Mazda V914 as V9, that's certainly available so will get one which leaves me with Mazda AC/SP1 as the tricky one...

[Cathovisor]

It's also missing the original speaker.

The knobs are, L-R:

Upper row - on/off volume, tuning, SW band preselector
Lower row - bandwidth/tone/noise suppression, waveband.

The SW preselector comes into play when you set the radio to SW: you preset the band you want to listen to using this control, then tune along that band using the main tuning control - this is achieved by feeding the output of the preselector into the main tuning circuits. It's a sort of dual-conversion set as a result but has the advantage that because of how it works, the AFC works on short-wave as well.

At first sight of the circuit the set appears very intimidating but in reality it breaks down into easy blocks; the main receiver, the SW converter (also used in the A36), the side-chain IF and the AFC/noise suppression circuit. From personal experience, the trimmers on these sets have a fixed capacity in parallel with the trimmer and the fixed part has a tendency to wander in value: they are set in a sort of cement in the bases of the coils. However, standing the bases of the coils in methylated spirits dissolves the cement completely.

As always, I would recommend Dave Grant's Murphy Radio website for more information: www.murphy-radio.co.uk

[Katar83]

Thanks! Not sure how the bandwith/tone/noise suppression suppose to work as it's a selector switch?

Yes, the speaker is not the original one, it's a Goodmans Axiom 112 and I think I've seen the original one, was it a Celestion speaker with a cloth at the back? Previous owner had this radio for longer than I'm alive and it wasn't used for as long too. Looking at the chassis speaker, it looks like it was replaced in the sixties before he purchased it. There are still quite a lot of original wax capacitors, along with a few more possibly more modern ones.

Got it all apart now, I suppose I'll start with some cleaning and go from there

Chassis weighs a ton, also I can see the original colour under knobs and it was significantly darker. Think I'll sand it all down and restain it to match original colour.

Chassis itself doesn't scare me, I'll recap the whole thing, check all resistors and replace what's out of spec and hopefully it will spring back to life, that said alignment is out of question, don't have the tools to do it, neither the skill so hopefully I'll find someone to help me with this

[Paul_RK]

As far as I know Murphy made their own speakers - the original is extremely massive, and its magnet bolts to the block on the cabinet floor. If it had to be changed the Goodmans is at least a pretty good substitute.

Paul

[greg_simons]

Lovely radio, double conversion on shortwave and afc control, very rare on consumer products of the period, I've restored a couple in the past, things to note, use only ac/4pen output valves, sound isn't so good with equivalents, the round silver mica caps that tune the if stages can fail Billington valves may have the sp1 valve - at a price, the wiring from the main chassis to the radio deck will probably be perished, and don't whatever you do try and clean the scale, the paint will come off, you may or may not have a good ac/me tuning indicator, I may have a used example if you're stuck, and of course all the waxies will need replacement, including the block on the radio deck that contains several decoupling capacitors, hope I covered everything!, good luck with what will be an epic restoration.
Greg.

[HamishBoxer]

Circuit top right corner from Paul's site.

[Leon Crampin]

There is an official work-around to replace the AC/SP1 with the heptode section of the TH41 or AC/TH1 (same valve, differing bases). A search of the Murphy websites should reveal the details.

In my A28 receiver, the AC/SP1 in the AF stage can be replaced with an AC/VP1, but the AFC reactance valve is critical. Alignment of these sets is an exacting job and a frequency counter is an asset to achieve symmetrical AFC action.

Leon.

[MurphyNut]

Originally Posted by Paul_RK

As far as I know Murphy made their own speakers - the original is extremely massive, and its magnet bolts to the block on the cabinet floor. If it had to be changed the Goodmans is at least a pretty good substitute.

Paul

I have a A40c, it works, but I'm sure it could be a lot better than it currently is. The speaker in the A40c has a Bakelite cone and much bigger than that replacement Goodmans unit. So I think the sound might be compromised.
Mike Barker, might have an original spare.

[Paul_RK]

Originally Posted by MurphyNut

I have a A40c, it works, but I'm sure it could be a lot better than it currently is. The speaker in the A40c has a Bakelite cone and much bigger than that replacement Goodmans unit. So I think the sound might be compromised.

It's a similar story with my A40C - original speaker, in the case of mine several valve bases have been changed to accommodate Mazda Octals, sound quality impressed me greatly as being far in advance of any other 1930s radio I've heard but the set could certainly benefit from an overhaul. The Axiom 112 would be bound to sound different, but whether better or worse (except from the point of view that would say the sound of the original is always to be preferred) I wouldn't hazard a guess, given that it's a full-range (claimed 40-12000 c/s) 12" loudspeaker of good pedigree from the early 1960s.

Paul

[Katar83]

Originally Posted by Leon Crampin

There is an official work-around to replace the AC/SP1 with the heptode section of the TH41 or AC/TH1 (same valve, differing bases). A search of the Murphy websites should reveal the details.

In my A28 receiver, the AC/SP1 in the AF stage can be replaced with an AC/VP1, but the AFC reactance valve is critical. Alignment of these sets is an exacting job and a frequency counter is an asset to achieve symmetrical AFC action.

Leon.

I've read about this on this forum already but neither of the posts mentioning it has any actual instructions and then I couldn't find anything useful on the murphy site either.

I may have found an AC/SP1 and V914 thanks to this amazing forum, thanks all that messaged me! Will be a few days at least before I get both so I've started with the cabinet for now. First I've washed it just to avoid a tetanus shot, then started partial disassembly, removed shelf, front railings and grill and started removing old varnish, this came off very easy, with just a small amount of chipping in a few places that should be easily fixable.
Veneer is in average condition, especially the top but might still be ok, I'll know for sure after further sanding it down.
I'll probably make a new board for the speaker as the existing board has a too large hole for the goodmans speaker and I dont want to stack them up again. Non original speaker doesn't bother me, this one looks good and should hopefully work well.
Railings will be of course repainted and the only thing I'm unsure about is the grill, I wasn't a fan of it originally as it was dirty and just looked wrong but turned out this is actually a copper mesh and it might actually clean up nicely. Alternatively I either get a cloth in there or another copper mesh, what you guys think?

[vinrads]

I restored one of these some twenty years ago, sometimes I wish that I hadn't sold it, the grille if I remember correctly it's a quite heave woven brass, it will clean up nicely, when you have got it nice and shiny give it a couple of coats of clear lacquer. For the bars I used a very close match car paint.

Mick.

[Katar83]

Thanks, started already and the mesh did indeed clean up nicely, needed lots of elbow grease but looks great now and I will definitely give it a coat of clear lacquer. I think I've cleaned up three bars already too, original paint looks like it is lead based so that needs some careful scraping, then some etch primer and a coat of black car paint and lacquer.
Not done any staining just yet, but have the replacement speaker board ready now too, its effectively a copy of the original one with a smaller hole for the goodmans speaker.
Base needed a lot of work and sanding but its ready for paint too now. I think I'll paint the inside at the same time as there was some heat damage to some paint and of course there will be a replacement speaker board in there too.
I've opted for walnut stain for the cabinet, looks closest match to the original colour to me, one way or another should look much better when finished.
Valves should hopefully arrive by the end of the week so cabinet first and then will start on the radio, still lots of fun work to do!
Pics coming soon!

[Cathovisor]

Originally Posted by Katar83

I've opted for walnut stain for the cabinet, looks closest match to the original colour to me, one way or another should look much better when finished.

The cabinets were Bombay Rosewood with the top being Thuya burr.

[Katar83]

Yes, I'm aware, just the original stain colour under knobs seems to be closest to walnut stain. I doubt they used different colour on top thuya burr so the cabinet will get all considerably darker than when I got it, hopefully matching its original colour

[Katar83]

Yay, the unobtanium valve has arrived so the chassis is complete, no excuses now.

Love the manufacturers guarantee of three months on the V914 valve

Got to say I understand now people switching these radios on after they buy them, the urge is there, even though I know it would result in a number of pops and bangs very quickly.