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Old 3rd May 2022, 12:11 am   #1
Techman
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Default Murphy Type 'M3' RF signal generator

I picked up this Murphy re-badged Advance E2 signal generator at the weekend. The chap said make me an offer and I said a couple of quid and he snapped my hand off - I got the feeling that he'd have probably paid me money to take it away!

You could say that it has 'patina', but it looks like it's been stood in a puddle for the last decade, but probably more likely to be the wet floor of a damp garage or shed. This model is different from others in that it has screws all the way around the front panel, so as well as two domed nuts with washers on the back, all the screws have to be removed from around the front before access to the innards can be obtained - the ones along the bottom took a bit to remove due to the rust.

It has the original rubber mains lead, but seeing as it had a 13 amp plug with the correct fuse fitted, although an unsheathed pin version, I concluded that it must have been used within living memory, so it went on the bench and power applied. It works, but several capacitors are obviously shot. The noise that can be seen on the 'scope waveform will be mains ripple - the two smoothers are bulging and leaking corrosion at the ends, although they don't get warm, so probably just dried out and lacking capacitance. There's no modulation or AF output, so likely to be the notorious C12 that can be seen behind the two valves in the picture - BTW, the two valves are 6J5 and 6X5, not looked in the screened part yet. There's obvious circuit differences from what's published in that there's no resistor between the rectifier and the reservoir and the one between the reservoir and smoother is a different value. HT is low at 114 volts (245 volts AC out of the transformer), so may be being dragged down by the bad capacitors, or perhaps the rectifier is a little down on emission, there's around 78 volts at the smoothing capacitor.

I've already got the Advance E2 version of this generator and all the one's I've seen have been immaculate inside, but as can be seen, this one isn't - spot the corrosion on the 250 volt mains tapping on the transformer!

I was surprised to see that this generator had the more unusual (and perhaps earlier) car radio aerial type sockets, rather than the more usual TV Belling type. I know many convert to BNC, but that's not restoration, it's modernisation - my name's not Carlson!

I really like these generators and I'm pleased to get this unusual Murphy badged version. I seem to think I've heard mention of this model 'M3' before somewhere, but can't remember where. Do we know whether these were specially produced for Murphy dealers or were they for use by Murphy radio themselves - or just a 're-badge' for general sale to anyone?
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Old 3rd May 2022, 12:42 am   #2
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Default Re: Murphy Type 'M3' RF signal generator

These generators were produced specifically for sale to Murphy Dealers for their service departments.
The differ from the standard Advance units in way of the sockets, mains connectors etc. but are basically the same as an E2.

In 1932 Murphy specified a Muirhead generator for their dealers which was a modified design on the standard unit of the day.

In 1938 Murphy combined with Muirhead produced the M1 signal generator and also the P1 service Oscilloscope which when combined acted a a wobbulator for visual alignment.

In the early 1950's Murphy re-badged an early version of the Advance E2 and called it the M2. The cabinet was pained red!

Then came the version that you have badged as the M3.

Very early versions of the M3 will show red paint underneath the grey paint if chipped.

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Old 3rd May 2022, 1:36 am   #3
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Default Re: Murphy Type 'M3' RF signal generator

Thanks for that very interesting information, Mike, exactly what I wanted to know.

Was that a Murphy request to have the car radio type sockets, or were they also used on some Advance models of a certain time period?

I've looked closely and I can see no sign of any underlying red paint, so guessing particularly by the fact that it's got the all rubber mains lead, that it probably dates from the mid to late 50s.

That voltage selector cover plate with only one screw holding it on and allowing it to swing open probably hasn't helped with keeping the innards in pristine condition like the Advance models generally are, although it might have helped with the drying out of moisture that had found its way in.

I don't think that the screws around the front panel had ever been removed, but applying the box spanner to the rear nuts found them to be hardly tight and also to have odd washers, so possibly someone had tried to get it apart, but didn't realise that the front screws had to also be removed, so gave up.
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Old 3rd May 2022, 5:50 pm   #4
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Default Re: Murphy Type 'M3' RF signal generator

I have an E2 badged "Advance" with the car aerial sockets fitted. Watch the mains filter capacitors - although looking like high quality mica dielectric components, they go short circuit at the drop of a hat and can make the case live if not earthed. Mine has an EC52 as an RF oscillator in the screened box. Replacements are still available. The other valves are a 6J5 and 6X5 as above. The 6X5 does not enjoy a good reputation for reliability - an EZ80 on an adaptor might be a wise substitute in a frequently used instrument.

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Old 3rd May 2022, 6:01 pm   #5
Denis G4DWC
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Default Re: Murphy Type 'M3' RF signal generator

Well, that brings back some memories.
As an Apprentice in the mid 60s I had one of these Generators on my Bench and I used it a lot. The shop I worked for in Didcot were Murphy appointed Dealers and I recall one of the two Brothers, who ran the shop, worked at Murphy in his younger days. He was the one that gave me his A40 sadly it's here no longer as it was riddled with woodworm.
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Old 3rd May 2022, 7:30 pm   #6
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Default Re: Murphy Type 'M3' RF signal generator

Quote:
Originally Posted by Leon Crampin View Post
I have an E2 badged "Advance" with the car aerial sockets fitted.
I thought that I'd seen an Advance version with that type of socket, hence why I asked the question again.

I'd noted those capacitors on the mains input and also noted the small spark when connecting an earthed test lead Probably just capacitively coupled AC, but it is provoking it just a bit and they ideally need replacing with 'Y' rated types. The old mains lead is a bit nasty where it terminates and the cord grip method allows it to twist round, not sure if that's original - only a matter of time before it goes bang in its present state!

Well it's a lot cleaner inside the screened part and the third valve is an EF50, and I can't help feeling that this generator is earlier than we're at first thinking. Even with a tacked in replacement for C12 (the original was down to 3 meg ohm on test) there's still no AF output. The other capacitor that's normally there with it (forgot its number just now) doesn't exist in that position, so more investigation needed - perhaps it's somewhere else?

Perhaps surprisingly, the smoothing capacitors seem to have recovered while it's been powered up and the mains ripple has cleared up, although the HT is now down to 106 volts from 114 volts, but the capacitors are running as cool as cucumbers, so I don't think that it's leakage within them that's dragging the HT down. As Leon mentioned about the 6X5 not having a good reputation, it could well be this, but more tests needed to verify - current draw etc.

The bottom of the actual outer case is quite rusty, so much so that I did the initial dismantling outside, scraping the rust scales off with a screwdriver before opening the case, as they were dropping everywhere and making a mess. You can see that there's actually been standing water in the bottom of the case at some point.
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Old 3rd May 2022, 7:35 pm   #7
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Default Re: Murphy Type 'M3' RF signal generator

My Advance P1 has a car aerial type socket for the RF out.
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Old 3rd May 2022, 8:54 pm   #8
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Default Re: Murphy Type 'M3' RF signal generator

I have one too, photo is how it came, not what it looks like now! I think the base is an Advance E1 not the E2.

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Old 3rd May 2022, 9:57 pm   #9
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Default Re: Murphy Type 'M3' RF signal generator

Quote:
Originally Posted by Andrewausfa View Post
I think the base is an Advance E1 not the E2.
I'm starting to think that.

There's a lot of things that don't add up. The rectifier is wired as a full wave and not as a half wave with strapped anodes as in the circuit diagram. There's six terminals on the modulation transformer, ok, one is a blank, but the other five all connect to the transformer internals, which is shown on the circuit diagram as one (auto wound) coil with only three connections. One of the connections goes straight to ground, so perhaps it's an electrostatic screen - not shown on the circuit, but that still leaves four connections going to windings instead of the three shown on the diagram. The bad news is that I'm getting some strange readings on the transformer, so it could be duff - I'll have to disconnect it completely to confirm.
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Old 3rd May 2022, 10:18 pm   #10
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Default Re: Murphy Type 'M3' RF signal generator

Also, the E2 has a highest frequency range of 30 to 100MHz, rather than 30 to 60 MHz as shown here- mine has a parallel-connected 6J6 as RF oscillator with 6J5 and 6X5 as modulator and rectifier, but I believe that later models got miniatures in those latter cases.
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Old 3rd May 2022, 10:22 pm   #11
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Default Re: Murphy Type 'M3' RF signal generator

The 60 MHz upper limit matches the E1, the E2 was 100MHz. I have the E1 circuit if you need it.

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Old 3rd May 2022, 10:23 pm   #12
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Default Re: Murphy Type 'M3' RF signal generator

That's it!

I've just downloaded the circuit for the E1 and that's what I've got. The transformer is a transformer with two separate windings and five connections with no screen and one end of one of the windings going to ground. This seems to contradict what's been said regarding this being a version of the E2. So if the M3 is an E1, then what does that make the M2?

Progress, I think!
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Old 3rd May 2022, 10:29 pm   #13
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Default Re: Murphy Type 'M3' RF signal generator

Quote:
Originally Posted by Andrewausfa View Post
The 60 MHz upper limit matches the E1, the E2 was 100MHz. I have the E1 circuit if you need it.

Andrew
Thanks Andrew. Yours and the previous post came while I was typing the last one and as you see, I managed to find an E1 circuit on-line.

I noticed the 60MHz as apposed to 100MHz, but I seemed to think that there were some early E2 generators that had the sixty limit - the E2 that I already had is 100MHz, although I always thought that was a fairly early one.
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Old 3rd May 2022, 10:37 pm   #14
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Default Re: Murphy Type 'M3' RF signal generator

Andrew,

Looking at your M3 you can see from where the cabinet paint has been scratched that yours is an early version with the red painted cabinet underneath the grey paint.

Yes, they are an E1 not an E2 as I said.

The use of car aerial style Belling & Lee plugs are also seen on other Advance equipment and I would not have thought that Murphy requested that they were specifically used.

Murphy would have opted for the PYE plug as they chose those for other Murphy test equipment like the TPG II

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Old 3rd May 2022, 11:00 pm   #15
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Default Re: Murphy Type 'M3' RF signal generator

Quote:
Originally Posted by murphymad View Post
Yes, they are an E1 not an E2 as I said.
Thanks for the confirmation Mike - it's all very complicated, so no wonder there's some confusion. Now I've seen the actual circuit I can work out what's going on around that transformer (saves drawing it out) and it may turn out to be ok after all. I'm even more pleased that this is actually an E1, rather than the E2, which I've already got.

Edit: Do you know what an M2 would be - was it a red coated E1...or perhaps I'm just getting confused now?
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Old 5th May 2022, 7:03 pm   #16
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Default Re: Murphy Type 'M3' RF signal generator

So far the generator is working perfectly on its RF output and is on frequency. The attenuator seems to be functional and hasn't been blown up by a previous user. Having now seen the correct circuit, it confirms that the transformer has two separate windings, so it would seem to be fine, other than although we now have AF output, it seems a bit low at only half a volt. I suppose there could be a shorted turn dragging it down, but some further investigation is still required in this area. I substituted another 6J5 and I've also now confirmed that the rectifier is fine, the low HT being mainly due to the smoothing capacitors lacking capacitance - they're only 4uF anyway, so it doesn't take much loss to make a big difference, temporarily hanging a 16uF across each one brought the HT back up to what would be expected. I shall replace them with 16uF, as the rectifier can easily take this. The 3K resistor between the two has risen to over 3.5K, so this may well be causing issues as well. The voltage selector is set for 250 volts, giving a heater voltage of just under 5 volts, setting it to the next step down of 230 volts, gives a heater voltage of 6.4 volts. This mains tapping adjustment behind the round plate, of course distinguishes this model from the later E2 model which doesn't have this feature.

I've been doing a bit of research and what we actually have would seem to be a Murphy version of the 'Model E' from just post war 1940s. We can tell this as it doesn't have the four bolts on each corner of the front panel like the later E1, or the E2 for that matter, but has the 14 screws around the outside. I tried to find reference to the Murphy M2, but I could find no mention of it. It seems that unlike AVO, there's little information on dating early Advance gear, so I think we're all learning something here - who would have thought that for something that was virtually being given away as scrap, that it would turn out so interesting - well for me anyway! I said the mains cable was a bit nasty regarding its termination, which it is, but mainly due to it not having any sort of restraining clamp to prevent it twisting up against that choke coil. I've looked closely at the cable and it's actually in nearly perfect condition with no perishing of the rubber. It's really way too thick for its intended purpose, more suited for an electric fire, but that's the size of the grommeted hole it passes through, which would seem to be original. looking closely, it's embossed all along its length with 'Johnson & Phillips London Ltd 250 volts' (1875 - 1964 ref. RM page on them, although I see the name still exists today), would this cable be original? Many of us fit replacement mains cables, but on something like this, replace it and history is lost!

Below is a link to a RM page showing an advert in Wireless World dated February 1947 for the Model E, which looks to be identical to the Murphy M3 that I have here, so much earlier than we thought and we can't argue with that date. The pages for the E1 and E2 both say 1951, but they can't both be 51, although one does have a question mark beside the date.
https://www.radiomuseum.org/r/advanc...nerator_e.html
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Old 5th May 2022, 8:42 pm   #17
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Default Re: Murphy Type 'M3' RF signal generator

When I started in 1954 at a Murphy dealers one of these were there and they must have it for some time as they also had a newer sig gen. They didn't spend money so the Murphy which worked well has to be 40's I would think. Nice to see one again.
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Old 8th May 2022, 11:57 pm   #18
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Default Re: Murphy Type 'M3' RF signal generator

I did a bit of sanding of the rust on the bottom of the case and then got out the 'Rust Eater' that I bought around 45 years ago - I've just noticed that there's two different prices on it, 43p on one side of the pack and 55p on the other!

The metal is really deeply pitted and it has to have been stood on the wet floor of either a very wet cellar or a shed for very many years.

The 'Rust Eater' did its job and after washing the case in hot soapy water and then thoroughly rinsing, it was let to dry for a day or so.

The rusty carrying handle hardware was treated with the 'eater' and then popped in a small pot of white vinegar before washing and drying them.
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Old 9th May 2022, 12:12 am   #19
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Default Re: Murphy Type 'M3' RF signal generator

I'm probably not going to re-paint the whole case, so this is a preservation exercise rather than an actual restoration. The bottom was so rusty that it would have just transferred rust onto anything that it would be stood on, particularly under any damp conditions. So just the bottom of the case was sprayed with a thick coat of zinc rich primer, then sealed with a spray coat of silver grey Hammerite. The bad inside part that had showed signs of standing water was also treated with the 'Rust Eater', then zinc and Hammerite sprayed.
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Old 9th May 2022, 12:33 am   #20
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Default Re: Murphy Type 'M3' RF signal generator

The rust eater did a fairly good job of attacking the rust on the outside of the bottom of the case as can be seen in the first picture below, although the pitting was quite bad, to the point that if left it could well have eventually gone through into holes - I forgot to post this picture earlier.

The second picture shows some of the red paint mentioned in previous posts. There's no sign of it at the edges of the case where the lip goes inside the front panel and the grey original overspray ends where you'd expect to see it if it were another colour coat that had been sprayed over. The picture shows it seen under one of the handle fixings where gradual wear by the leather covered handle going in and out has rubbed the grey paint away. This, I believe, is a red oxide or red lead undercoat, sprayed onto the bare metal by the manufacturer when new so as to make a base for the top coat or coats.
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