Murphy 146C

[sparkymike]

I have just acquired a Murphy A146 C "bat wing"radio. It is not at my house yet as it was bought from the other side of the country to where I live, but lucky for me, my daughter lworks in same town as the seller.
I have been studying the service sheets and it looks to me like a bit of a hybrid with a mains transformer, but with daisy chained valve heaters. Bearing this in mind, if mains plug was wired in reverse , is chassis live as per AC/DC sets , or would you only get a belt off one end of the valve heater train, say around 75 volts or so ?
At the moment the set was said to just hum when switched on, so main electrolytics will be first thing to check when I get it home.
Mike.

[ms660]

According to the schematic it's a live chassis design.

Lawrence.

[cathoderay57]

Hi Mike, I do not have vis of the service sheet. However, the answer to your question is it depends whether the mains transformer is an auto-transformer which means there will be only one winding connected across the mains with tappings off that same winding for the heater chain and HT to the rectifier, or else an isolated transformer with only the primary winding connected across the mains and an isolated secondary winding (with no direct connection to mains) providing a high voltage source for the heater chain and possibly the HT as well. If of the former type, then reversing the mains plug will make chassis live. If the latter then it wouldn't. If you can post a clip of the circuit showing the mains transformer I can confirm which is the case. Cheers, Jerry. Oops, sorry Lawrence, crossed in the post!

[Cobaltblue]

It's as Lawrence says.

See snip.

Funny I didn't remember that about the set I restored mine 30 years ago and finally sold it 15 years ago I had a complete set of the Murphy Baffle sets at the time my favourite being the A188C.

I now only have the A104 and the A122M both table top models.

Cheers

Mike T

[music-centre]

There is also the A146CM, looks the same but with an isolating mains transformer.
Steve.

https://www.radiomuseum.org/r/murphy_a146ca_146.html

[sparkymike]

Well the set is now at my daughter's house 250 miles from my place, so I will not see it until she comes to visit me in April so I am getting twitchy hands, dying to get cracking on it.!! She managed to lift it out of her car boot on her own, which surprised me as I thought these would be quite weighty. She told me that when she got in the house, the knobs were missing, but lucky for me she found them in the car boot. Are these fixed on with the normal grub screw or are they the type with the spring small ring ?
Mike.

[sparkymike]

What is the purpose of L7 and L8 on the power amp. unit ?
Mike.

[ms660]

Mains filter.

Lawrence.

[sparkymike]

That had crossed my mind Lawrence. Was that addition common in those days?
Do they run hot ? I wondered if it was a substitution for a choke, but I see a choke is still present on the diagram.
Mike.

[ms660]

Some manufactures used them, some didn't, they shouldn't run hot.

Yes, not a substitution for the choke, choke's on the DC side.

Lawrence.

[sparkymike]

The 146CM did not have them. The different mains transformer maybe ?
Mike.

[sparkymike]

At last I now have the Murphy at my place. It has been in storage at my Daughter's house , the other side of the UK,since January, when I bought it.
Daughter brought it over today as it is fathers day.
I am pleased to say it is in much better condition than I thought it would be, just going by photos on the website from where it was bought.
I am just having a visual look see to detect any possible problems, before I make a start. First thing I have noticed is some of the interconnecting wiring between the tuner section and amplifier is very brittle. Some or all will have to be replaced. First question, where can I purchase similar wire ? It is stranded but fairly stiff, so if you bend it, it stays put.
The speaker grill material is shot so I will need suitable cloth for that. Is that man still in the Southend Essex area ? I forget his name.
I have now removed the power amplifier and there are a few points here. The
metal canned capacitors, C40/C41 (50uf/50uf) and C39/C38 (16uf/32uf)
are both bulging, so presume they are past re-forming ?
The PEN 45 output valves have that grey/sliver paint flaking near the bases.
Is it possible to spray HT paint of similar colour to improve their look? (that is if they are both ok.)
So far all parts/cabinet and outer finish look to be very good order so the set must have been well looked after in its past life.
I will post some photos later.
Mike.

[sparkymike]

photos before I started.
Mike

[sparkymike]

Photos of the power amp section.
Totally untouched and not messed about with thank goodness.
I have checked all the resistors and all are pretty close to correct value except R24 which is reading 124K when it should be 100K. The electrolytics need replacing as does the large capacitor (.01uf but reading .004uf.)
So far I am pleased with the purchase.
Mike.

[IanG3XYV]

Mike,
I’ve got the same model in my round tuit pile. Yours is in better condition than mine which was stored in a barn. There is woodworm to contend with and quite a bit of rust but all seems to be present. I’ll be interested to follow your progress.
Ian

[Freya]

Originally Posted by sparkymike

The
metal canned capacitors, C40/C41 (50uf/50uf) and C39/C38 (16uf/32uf)
are both bulging, so presume they are past re-forming ?
.

Those capacitors should reform, the chassis is in good condition and must have been kept in a dry place, its doubtful they need replacing.

[HamishBoxer]

No,I would not attempt to reform any bulging capacitor,if they blow than they will shatter the cabinet.
Thankfully I have only seen it happen once on a newish tv.

Nice easy restoration job.

[sparkymike]

I wonder what the large circular cutout on the chassis was for ?
Mike.

[HamishBoxer]

If they look ok,I would normally run them up slowly or I do have cap reformer ex military.

I just am a bit wary of bulges,I am certainly not a CCC, (compulsive cap changer.

[sparkymike]

I have to replace the two capacitors marked in the photo. C47 .01 uf. (right hand one)
and C43 .05uf (Left hand one.)
In the service manual they are rated at 1000volt.
Is this critical? (peak to peak voltage ?)
Mike.