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Old 9th May 2022, 3:42 pm   #21
Techman
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Default Re: Murphy Type 'M3' RF signal generator

Well, there's the date confirmation!

I've just unbolted the clamp from the two 4uF smoothing capacitors and removed them from the unit and there's the date of September 1946, so that pretty much puts the generator at least firmly in 1947, if not even 1946.

Who would have thought it - no one is more surprised than me!

In the first post on this thread I was firmly in the belief that it was a re-badged E2. I even said this to the chap that I got it from and he agreed. Knowing what I know now I wish I'd asked him if he knew any history of where it came from etc.

I'm very pleased that it's an early one and in fact it's actually the earliest Advance model shown on the Radio Museum website, albeit the one shown is just a 1947 advertisement for the Advance Type 'E' version, which actually seems rarer than the Murphy M3 version.
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Old 12th May 2022, 3:18 pm   #22
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Default Re: Murphy Type 'M3' RF signal generator

The signal generator is now fully working. It looks like we've re-written a bit of the Murphy Radio history regarding their dealer test gear around the late forties. I don't know anything about Muirhead and I could find little about them on-line when I had a quick search, so assume that what's known regarding the pre-Advance re-badging is probably correct.

The low AF output seemed to be caused by a combination of low HT and the cathode resistor of the 6J5 going high in value. The HT after the rectifier is now 148 volts and at the smoother it's 118 volts. The two capacitors and the 3K resistor are the HT filter and no HT is taken off at the reservoir, only after the 3K resistor at the smoothing capacitor, so the actual HT used is 118 volts only - remembering that the voltage selector is set at the 250 volt setting. When I originally mentioned a voltage at the transformer I was assuming that we were looking at a version of the E2, which uses half wave rectification with the anodes of the valve strapped together, whereas the type 'E' uses the rectifier as a full wave type, hence the confusing voltage reading, and my fault for not looking closer at what I actually had in front of me.

Those two 4uF capacitors with the 1946 dates on them are 'historic' so although I'd found a couple of vintage 8uF capacitors to fit in their place under the clamps, the originals had to go back in place. I don't 're-stuff', so for the time being (and probably forever) I've soldered a small tag strip to the now disconnected reservoir capacitor positive tag and used this as the mounting for a replacement 3K resistor and the positive ends of the replacement capacitors (these connections are obviously completely isolated from the original capacitors), the negative ends being connect to the re-connected ends of the original capacitors. The original capacitors can always be re-stuffed with smaller modern parts in the future if so desired. It was noteworthy that neither of those original dated capacitors had a ripple rating, whereas one of the replacements I've fitted as the reservoir now does.

I went round some odd bits of the chassis with the 'Rust Eater' again, then after swabbing off with a wet sponge, near boiling water from a kettle (after making a brew) was carefully poured over the treated parts to fully wash away the acid - brutal, but effective and after leaving to thoroughly dry, no harm was done! I then gave it the oily rag treatment, but just with some WD40. You can fettle around with something like this for ages, but it's not a restoration as such, just a repair and preservation, so time to call it a day.

It's all put back together now and seems to be pretty much bang on frequency and seems to be reasonably stable and possibly better than my 'E2'. The things I'm not happy with are the lack of proper cord grip on the mains lead. For the time being I've made the grommeted area more solid by filling it out with some slices of rubber sheet, forced in so that the cable doesn't tend to twist, also marking the 'top' of the cable near the entry point with a felt marker pen so that I'll know if it does. Many would fit a new cable and perhaps drill the case to attach a clamp, which I would probably do if it were for someone else (with their permission of course), but I like to keep with originality when it comes to my own stuff - it's not as if it's going to be in regular use and being moved around all the time. I lifted the hot end of the 0.005 mains filter cap on the live side of the mains input. I was getting 'tingles' from the metalwork, which stopped when the cap was disconnected, although this could well have been just normal capacitive coupling and it stopped anyway when earthed test equipment such as a 'scope and counter were connected. The fact that there were no bangs and blown fuses proved that the capacitor was holding out, but from what was said in an earlier post these are known to fail suddenly, so it was disconnected. I probably ought to have replaced both of them with modern 'Y' types, but I can always return to it and do this at a later stage.

I treated the cracked leather covered handle with some (probably WW11) ex military Dubbin and left it to soak overnight before giving it a good brush with a shoe polish brush and then wiping off the remainder with a WD40 soaked cloth - it seems to have saved it for the time being.

The only odd thing is that the AF output seems to have risen even further since treating the chassis with WD40. I've no answer to why this is, just one of those little quirks that happens for no apparent reason.

The re-painted and treated bottom of the case can't be seen when the unit is stood in place. I'd rather have not painted it, but I had no choice. I had considered the 'very' oily rag approach, but this would have left it very messy, so Zinc and Hammerite were the best solution for long term preservation and cleanliness.

I'll organise a picture or two sometime later, but for now, that's it!
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Old 12th May 2022, 4:05 pm   #23
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Default Re: Murphy Type 'M3' RF signal generator

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Originally Posted by murphymad View Post
These generators were produced specifically for sale to Murphy Dealers for their service departments...

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.
Thanks for that, I've been harbouring an M1 since it turned up in a local auction about thirty years ago and had wondered how it fitted into the scheme of things, as I can't recall reading of the model anywhere. There don't seem to be many around, so here's mine, with card showing the dial settings for the usual set calibration points and IFs.

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Old 12th May 2022, 4:10 pm   #24
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Default Re: Murphy Type 'M3' RF signal generator

Brilliant!

I think that's the first actual picture of a Murphy badged Muirhead that I've seen. I don't think that any others exist anywhere else on-line that I could find.
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Old 12th May 2022, 5:14 pm   #25
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Default Re: Murphy Type 'M3' RF signal generator

Could be worth a few images of what's inside, then. Built like the proverbial tank and I'd forgotten how it gleams. From left, then above, then right, then below: the KT42 is in the first image, ML4 in the second, and the D4 is in hiding.
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Old 13th May 2022, 11:49 am   #26
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Default Re: Murphy Type 'M3' RF signal generator

The chassis metalwork looks to be galvanized.

Is it in working condition and have you found any actual dates on the main electrolytic capacitors?

So we've got an example of the 'M1', and the 'M3' is the earliest model of the Advance 'E' series, being the 'Type E', this pre-dating the 'E1' even, so I'm wondering what Advance model the 'M2' would have been? That's the one we're missing at the moment.

Well, in running the generator yesterday I found that it performed perfectly on all bands from 100KHz through to 30MHz. However, there is a bit of an issue on the highest frequency band 'A' 30-60MHz. It doesn't strike up until it gets to around 35MHz and then drops out at around 58MHz, it's also reading about half a meg low on the scale on this band only, so something to look into when I get round to returning to it sometime. The 'B' band goes up to around 32.8MHz, so we've got a couple of meg missing in the range and the same at the very top end.

Other than the above, all the bands are within a needles width of being spot on frequency when checked with a counter and with very little drift from warm up - not bad for something dating from late 1936. I think it actually drifts less than my E2, which I've had for decades and could really do with a bit of a service, as I don't remember having ever opened it up - unless I've forgotten! The E2 has got noisy controls, whereas this one didn't need any attention to the pots, other than me applying a small drop of oil to all the spindles, including the switches and tuning controls.

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Old 15th May 2022, 4:32 pm   #27
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Default Re: Murphy Type 'M3' RF signal generator

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not bad for something dating from late 1936.
I expect everyone realised that this was a mistake and what I really meant to put was 1946. I edited that post twice to correct various mistakes and still managed not to spot the most glaring one - typical!

Of course we don't know the turnover of components Advance would have had in those days, so those capacitors may not have been used until just into 1947, but seeing as they were September of '46, then I reckon there's a good chance that it was made and sold in very late 1946. That style of generator are quite streamline and modern looking compared to some (other than the TRF and military style radio receiver type dial) and I think I would be right in saying that they carried on using that case design into the 1960s. I've got the 'AF' only version of that generator dating from around 1960.
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Old 16th May 2022, 6:29 pm   #28
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Default Re: Murphy Type 'M3' RF signal generator

Quote:
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The chassis metalwork looks to be galvanized.

Is it in working condition and have you found any actual dates on the main electrolytic capacitors?
Yes, definitely appears galvanised. I've yet to apply power - preliminary tests and re-forming for sure when or if I do, as it could easily have sat idle for twenty or thirty years in addition to the thirty I know about. Would be interesting to see how far the output has wandered from the hand-written card of possibly 85 years ago. I'll search for any internal dates next time I take the case off.
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