Unknown radio. Identified as a Murphy A34.

[ms660]

Originally Posted by LyntonP

Also the AC2/Pen DD has been substituted with an alternative valve along with some minor rewiring. Is the original valve available? I have looked on the internet without much luck.
Lynton

If all else fails:

https://www.langrex.co.uk/stocklist/

An option for a magic eye would be a 6e5gt or similar, plus valve socket, plus a 6volt transformer for its heater supply if the existing mains transformer doesn't have a 6 volt winding.

Lawrence.

[LyntonP]

Hi Lawrence I have looked on Langrex and it does say that they have a small stock but I cannot confirm the price within their listings. I have scrolled through page after page but cannot find the valve in question. Maybe I am not using the site correctly!
Lynton

[music-centre]

Hello Lynton,
Did you mean the 6E5GT? - if so, they are £25 on Langrex
Steve.

[LyntonP]

Hi Steve no it’s a AC2/Pen DD I am looking for.
Ah I see what you mean now . The magic eye tuning valve. It would be nice to have the facility working but the budget won’t stretch to that at the moment. Thanks for your interest.
Lynton

[cathoderay57]

Hi Lynton, good work with the A34. Re: magic eye, a few years ago I restored an A36 which also uses an AC/ME. I couldn't find an AC/ME but I did get a new-old-stock VME4 off eBay which has the same pin configuration but some valve data specifies a slightly lower target voltage (200 vs 250). On the A36 the target voltage measured 230v so I put a 22k resistor in series with the target HT feed and it worked very well. Mind you, you'll probably struggle to find a VME4 as well! Beware of buying used magic eyes off eBay if untested because, in all probability, the magic eye will be a dud or very dim at best. I have a couple of used AC2/PenDD in store so I'll test them and send you a PM. If your existing output valve produces a good sound, personally I'd leave it as-is but if you want the replacement I should be able to help. Kind regards, Jerry

[LyntonP]

Not sure if I am allowed to make a separate post under success stories but I thought I should upload a few pictures of the finished article in order to show the before and after.
Can I also pass on my thanks to everyone who helped in particular to ms660 who provided assistance all through the project, and cathoderay57 who came up trumps with replacement valves.
It was a thoroughly enjoyable, educational, and satisfying project.
Lynton

[Nanozeugma]

Excellent work - not that you need my approbation, but you have it anyway

[LyntonP]

I have been using the radio for just over a week now and although nothing has gone bang I am sure that the set would benefit from an alignment. Listening to R4 there is a loud background hissing which after a while becomes annoying and impossible to tune around. Some of the MW stations fare a little better but the noise is still there.
I do not have a signal generator in order to follow the makers instructions but have been reading some of the posts on this site for further information. One which caught my eye was to use a SG App which could be downloaded. Are these any good? Does anyone use such a thing? The only device I have for apps is my IPad and I would not be sure how to connect it the way you would a SG.
Has anyone ever tuned a radio by ear? Just listening to a received station for best reception?
Maybe there could be something else in the set that needs changing? If so where would I start?
Thanks
Lynton

[Nuvistor]

Hi Lynton,
That’s a very nice job, looks really good.
Before delving into the radio confirm the noise is not external, there is possibly a lot of hash and interference on MW/LW depending just where you are.

The RF alignment can be done using the stations for the adjustments, the problem with doing that with the IF’s is that it’s easy to get wrong and then the RF side can’t then be adjusted properly.

A link to the SG download would be useful but the ones I have seen are audio frequency only.

[LyntonP]

Hi Frank the link is https://play.google.com/store/apps/d...pqd1fAP6OWEuAY
If that works good luck. The link came from a post on this forum.
I appreciate what you say about location. I don’t have a connection to the G5RV in the lounge so I rigged up an aerial around the picture rail maybe this is not as efficient as it should be. However listening on a small transistor radio with a ferrite rod aerial the hiss is still there but a well tuned signal easily swamps it giving clear reception.
Lynton

[ms660]

Looks like a toy audio generator to me:

https://www.keuwl.com/FunctionGenerator/

Lawrence.

[Nuvistor]

The link is for an audio sg, freq below audio 1mHz to above 22kHz so is no use for alignment, even if it did produce radio frequencies it would be difficult to get them out of the computer/tablet without special hardware. It would be ok for testing audio stages though. Unless there is a version in the Apple App Store that version from Google wouldn’t install on your iPad but there are audio sg in the Apple store.

The noise, if it’s there on your transistor radio it’s external, you may be using the directional properties of the ferrite rod to increase the wanted signal and null the source of interference. It may be the Murphy would be better with alignment but only performing that would prove that point.

Have you a way of measuring frequency, if so knock yourself up a simple oscillator and calibrate it with the frequency meter, that should be enough to check the alignment.

Crossed post with Lawrence, you type faster than I do.

[LyntonP]

Gents thanks for the replies. Ok so the app was too good to be true. No Frank I have no way of measuring frequency other than a radio! What about these Chinese generators that are advertised on sites such as Banggood? They seem very cheap for something that needs to be accurate. I can experiment a little more with the aerial and just keep my eyes open on the forum to see if any SG’s come up for sale at a reasonable price.
In the mean time I will resist any thoughts of ‘twiddling’
Lynton

[Nuvistor]

Caution with some of those cheap SG, they state up to 1MHz but that’s very often the square wave function, the sine wave goes to 100Khz, need to check the specification.
I have never had one so don’t know how well they work but don’t forget it will need a readout, those I have just checked have none.

[crackle]

For a quick and dirty alignment, you can, on some radios* simply peak the IF cans.
Then tune to a radio station at the HF end end of MW and peak the RF by adjusting the aerial capacitor trimmer.
Then tune to another station at the LF end of MW and peak the LF end of the waveband by adjusting the aerial coil.
LW can be done by tuning to R4 then adjusting the LW aerial coil.

* I believe some radios have their IF transformers adjusted slightly offset in order to improve the bandwidth, this simple process may not be good on these sets.

Maybe someone else can confirm on the suitability of this set for a quick and dirty alignment such as above.

Mike

[ms660]

No padders or coils to adjust as far as I can make out for Osc and RF alignment, just trimmers towards the HF end of the bands, preset capacitors for IF adjustment, IF is 119kHz.

EDIT: There's an image suppression circuit on the service sheet I'm looking at but the info I have seems incomplete so I'm not sure if that particular circuit is adjustable or not.

Lawrence.

[Nuvistor]

One possible problem with peaking IF transformers on a station is relying on them being very close to being correct. If one is out of adjustment and the other transformers peaked on the off tune one it can cause problems with the RF tracking.

Edit. LO CO seem to be part of the image suppression and the adjustment is via an ‘Erinoid’ (plastic) screw on top of the secondary band pass coil.

[LyntonP]

Originally Posted by Nuvistor

Hi Lynton,
That’s a very nice job, looks really good.

Thanks for the compliments Frank. Yes I invested a lot of time into this simple old radio, but I enjoyed every minute. Very satisfying when it burst into life. Couldn't have done it without the help of the forum members.
Well chuffed!
Lynton

[cathoderay57]

Hi Lynton, it's probably not a good idea to start tweaking trimmers unless you have some experience of doing alignment. Often it will do more harm than good. If you are fortunate there might be a member of the Forum located near you with a sig gen and freq counter who could help you? Cheers, Jerry

[Nuvistor]

A good write up of alignment, I need to point out the the Murphy uses 119Khz IF.
https://www.vintage-radio.com/repair...alignment.html

SG turn up from time to time, if you don’t have a frequency counter to check it’s accuracy you can zero beat it against a known stations, that should give enough points on a chart to show how good it is.