UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Success Stories


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!

Closed Thread
Thread Tools
Old 31st Jan 2017, 3:48 pm   #1
Leon Crampin
Join Date: Nov 2005
Location: Surrey, UK.
Posts: 1,350
Default Improving the Murphy A272C.

This set is the last of the Murphy floor standing baffle sets with a 10" loudspeaker and has FM. Therefore, a candidate for good sound.

Having had one for some years, I have been aware that the audio HF response is rather poor and that the AF gain is not really sufficient. Having to open up this set to fix an unrelated fault, I set about finding a way to improve the audio.

All circuit references are from the Murphy service data.

A 1nF capacitor (C72) is fitted between the anode of the EABC80 and earth. In view of the source impedance, this kills the audio HF - so I removed it. The Bush DAC90A suffers from exactly the same problem. Some improvement, but not enough.

The AF gain is set by the feedback network R42, R11. Increasing the value of R42 therefore increases the gain, so adding 8k2 in series with R42 (8k2 to the 'speaker) fixed the gain problem.

Murphy give alternative feedback networks for the table and console models, so they obviously went to some trouble to define the AF response - but with their component values, the table model especially, must have sounded like mud. For the A272C console, I added a 4n7 capacitor to the junction of the 8k2 and R42 to earth. This selectively shunts the feedback, reducing it as the frequency rises, giving top lift. Effective above about 4kHz, this modification shows that the single 10" Celestian 'speaker can give a good account of itself without a separate tweeter - which I dislike due to the likelihood of phase distortion.

The new components can be mounted on the output transformer using spare tags. The results are most encouraging, realising the excellent sound quality that the speaker and its baffle are capable of producing.

Footnote: The set had failed on FM due to C7 reducing in value from 5nF to < 100pF. It bootstraps the FM mixer and materially increases the IF gain, which becomes unusably low without it. Other Hunts devices in the set have to be evicted as usual.

Leon Crampin is offline  
Old 31st Jan 2017, 6:06 pm   #2
ukcol's Avatar
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
Default Re: Improving the Murphy A272C.

It has always surprised me that the consul baffle sets that were AM only had amplifiers with push-pull output stages but when Murphy produced this VHF/FM model they settled for a single ended output stage.
Best Regards,
Colin McLaughlin
BVWS Member
ukcol is offline  
Old 31st Jan 2017, 8:07 pm   #3
Nickthedentist's Avatar
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 14,096
Default Re: Improving the Murphy A272C.

That's worth knowing, Leon, thank you.

Originally Posted by ukcol View Post
It has always surprised me that the consul baffle sets that were AM only had amplifiers with push-pull output stages but when Murphy produced this VHF/FM model they settled for a single ended output stage.
The Ekco C273 was the same, though doesn't seem to have suffered as a result:
Nickthedentist is online now  
Old 4th Feb 2017, 2:02 pm   #4
Phil G4SPZ
Phil G4SPZ's Avatar
Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,126
Default Re: Improving the Murphy A272C.

Nice work! Lovely sound quality, yes, but you've got to like the styling. A Murphy baffle set once arrived in our living room, but sadly my wife's screams unnerved me and it went into the shed, until I managed to swap it for a pre-war A30C which I donated to a museum, thus saving our marriage!
Phil (BVWS / BVTVWM / NVM / GQRPC 2101)

Optimist [n]: Someone who is not aware of the full facts
Phil G4SPZ is offline  
Old 4th Feb 2017, 4:19 pm   #5
dave walsh
Join Date: Jan 2006
Location: Ramsbottom (Nr Bury) Lancs or Bexhill (Nr Hastings) Sussex.
Posts: 4,162
Default Re: Improving the Murphy A272C.

Well I suppose it's all a matter of taste and not worth shattering domestic bliss for Phil but I notice that [in a 2008 thread] I mentioned that these Consoles seemed to be getting a bit trendy. I bought a 272 then because I'd never seen one with VHF but the AM 146 in particular [especially with a light finish] always looked quite 1930's to me [even though they are much later]. These seem to look good in a period or perhaps minimalist setting [eg bare brick and oak] so I remain surprise that they don't attract higher prices. As ukcol says the AM model has a pretty good amp. Some people have extracted these from a couple of sets making a good stereo units.

Even though I've got a 146 that is 98/% woodworm I'm not sure about gutting a set for this purpose but the output stages extracted and renovated are of a very high standard! As for the 272, Leon's suggested design improvements seem to be a very good option with minimum disruption to the radio itself. I must admit though that that something about the VHF Console [possibly the larger dial] makes it less stylish than it's older 146 brother.

Dave W
dave walsh is offline  
Old 5th Feb 2017, 4:09 am   #6
MurphyNut's Avatar
Join Date: Apr 2016
Location: Croxley Green, Hertfordshire, UK.
Posts: 492
Default Re: Improving the Murphy A272C.

I have a A272C and a 146C but prefer the later despite being an earlier set without FM. It seems much better made, it sounds remarkably rich and pleasing to the ear.
They're always available on eBay at widely varying prices. I suspect they survive in large numbers possibly because they look so unusual and people have hung onto them because they think they're something rare.
MurphyNut is offline  
Closed Thread

Thread Tools

All times are GMT +1. The time now is 3:45 pm.

All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at
Failure to heed this warning may result in death or serious injury to yourself and/or others.

Powered by vBulletin®
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2018, Paul Stenning.