Big old Murphy A170 radio to restore.

[GreasedMonkey]

So, earlier today I was given this beast.

Cosmetically it is in a bit of a state, 2 knobs are missing and the lacquer has most certainly seen better days. Inside seems to be a better story, looks to have a full compliment of components under a good layer of dust.

I would like to get the set into a fully functional state and restore the cabinet also. I would be very grateful for any information anybody has on this set. I may be asking many questions as this is my first valve set to restore. I have other restored vintage electronics but these hale for the 70s and are transistorised.

Probably worth noting also that I have only basic tools and equipment at home. DMMs, 2 Chanel scope, basic sig gen etc and am hoping to complete this task here with these basic facilities.

I have briefly applied power, 2 of the three dials lit up and there is a rather loud hum, I suspect at mains frequency. At this point I removed power and came here to seek advise on how best to proceed.

[Station X]

Service info here:-

https://www.service-data.com/product...98/5117/m13898

Useful info here:-

https://www.vintage-radio.com/repair...ion/index.html

[Leon Crampin]

A good set with variable IF bandwidth.

Watch out for arcing in the wavechange switch where the section which removes HT from some of the front end when switched to "gram" suffers an insulation breakdown. The fix is to disconnect the 2 wires to this section and join them together. Although the front end is then permanently active, there's no radio breakthrough as the AF signal path is adequately switched.

A straightforward set to restore - be careful with the IF core adjusters.

Leon.

[cathoderay57]

The set uses Mazda valves for which there are no direct equivalents in the more common Mullard E-series except for the UU9 rectifier that is the same as an EZ40. Hopefully you won't need replacements but if you do spares are still obtainable. Best of luck with the resto. Murphy sets are well made and sound good. You will be lucky if there is any green glow left in the magic eye; replacements are scarce and expensive but it won't affect the operation of the set. Jerry.

[GreasedMonkey]

Thanks all.

I have downloaded / printed the service info, thanks Graham. I shall sit and read through this before I proceed.

I have not yet done anything else with the radio, my intention is to remove the chassis this evening so that I may hopefully work on that outside of the case. I assume any loudspeaker of 8ohm impedance will suffice for fault finding/test so I could just use a little 2” one while the chassis is out, somebody please say so if this assumption is incorrect.

[Silicon]

The original speaker was 3 Ohms Impedance.

The closest match is a modern 4 Ohm speaker which is used in vehicles.

An 8 Ohm speaker will work for testing.

[GreasedMonkey]

Unfortunately I did not have much time last night, so the chassis remains in the case so far. But I did get a few minutes with the radio. I gently brushed off most of the loose dust and general detritus from the chassis last night and ran the set up for a few minutes.

There is a full compliment of gently glowing valves heaters and a few crackles and pops from the loudspeaker. With a few feet of random wire poked into the aerial socket I had a scan about the wavebands. The tuner control no longer moves the dial pointers but does still move the varicap.
Strangely I found a weak, noisy station from Belfast. This I found odd as I live about a mile from the Droitwich transmitter masts, but there was no sign of radio 4 LW. There is a very prominent hum from the loudspeaker, I guess the smoothing capacitor(s) have seen better days. Should I attempt to reform, or just replace?

Still, there are signs of life and it does, on some level anyway, sort of function as a radio. This at least makes me confident that it is a god candidate for resto. This evening the chassis will hopefully come out for a good clean.

[Station X]

Please don't turn it on again until you've at least changed the audio coupling capacitor C34 (manufacturer's sheet). If it fails you could destroy the mains transformer, output transformer and output valve.

[GreasedMonkey]

Originally Posted by Station X

Please don't turn it on again until you've at least changed the audio coupling capacitor C34 (manufacturer's sheet). If it fails you could destroy the mains transformer, output transformer and output valve.

Duly noted.

Just to clarify, you are talking about C34 0.01uF from the Murphy Radio book and not C34 from Trader Sheet 1041 which looks to be some form of smoothing cap?

To be honest, after 70 years or so, I am expecting quite a few passives to be out of spec. Component ageing is an issue we face at work, and our stuff has a design life of 7-10 years, so anything still alive after several decades will always impress me.

[Station X]

The trader sheet reference is C26.

[GreasedMonkey]

Originally Posted by Station X

The trader sheet reference is C26.

Thanks.

What is the general school of thought with replacements?
Silver Mica?
Ceramic?
Axial Metal Film?

Seems like now is as good a time as any to start my shopping list.

[Nickthedentist]

See here: https://www.vintage-radio.com/repair...apacitors.html

Vishay-Roederstein MKT1813 series is my favourite for replacing anything from 1nF up to about 1uF.

Most capacitors of less than 1nF are best left well alone unless they are definitely faulty (which is rare).

Caps above 1uF are usually electrolytics and will be miles past their design life. However, they can often be "re-formed" rather than replaced.

[telstar]

Hi. I have one of these fine radios in my collection.
Cheers
Mike

[GreasedMonkey]

Not much progress on this project yesterday (I am in no rush), I have ordered a smattering of capacitors and a replacement lamp for the tuning dial.

The controls on this set have been labelled with one of those home label makers that were everywhere in the 80's. I cannot find any images that show clearly how the controls would have been labelled originally. Would anybody happen to have such an image they could share? Would it originally have been done with some kind of transfer ?

[alanmoore]

Hello, as far as I know , the controls on these and many other sets of this era were not labelled.
Regards
Alan.

[Station X]

There's certainly no labels on the set on the radio museum website:-

https://www.radiomuseum.org/r/murphy_a170a_17.html

[Nickthedentist]

Some radios had temporary paper discs behind each knob, which you discarded once you'd learned your way around the set.

Others had engraved legends on each knob, sometimes highlighted with white paint.

But as Alan and Graham had said, yours is correct, except that someone has added DIY "Dymo tape" labels. These can sometimes be very hard to remove without damaging the underlying finish, though may not be too bad if the woodwork was contaminated with furniture polish or just greasy grime before they were applied. https://en.wikipedia.org/wiki/Embossing_tape

The way someone's felt it necessary to label the magic eye is a bit OTT though. Probably somebody testing out their new Christmas present in the 1970s!

[GreasedMonkey]

Ah, this explains why I can find no images clearly showing labels. Also this is good as it saves me a job during the restoration.

As for the magic eye label, the previous owner said she bout the set second hand when she was a young child, so this could explain the over-labelling. I plan to take the case back to wood and re-lacquer anyhow as there are many deep chips and scratches to attend to, so removal of the dymo tape should not be a problem itself.

[Nickthedentist]

Yes, I had fun sticking un-necessary labels on everything with my new Dymo tape printer when I was at primary school age

[GreasedMonkey]

Originally Posted by Nickthedentist

Yes, I had fun sticking un-necessary labels on everything with my new Dymo tape printer when I was at primary school age

Such frivolities were not allowed by my parents. No stickers for us.
I have since grown my own little people and completely understand and wish I had instigated the same rule.

Anyhow, back to topic, there are 2 knobs missing. Anybody know of any likely suppliers, or is it going to be second hand only? Is my best bet just to wander over to the parts wanted section and make a request there?

I have had a look at places like RS and Farnell etc. at the ranges they carry, but nothing similar to the two I have.