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Old 5th Feb 2023, 12:41 pm   #81
Katar83
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Default Re: What did I get myself into? Murphy A40C.

Ah yes, that was it! Thank you! The mechanism was turning smoothly but I did remember it was initially slightly 'clicking' into position before the cord snapped and I had it temp fixed so I checked that by moving it manually and it does get into each band position and tuning is then much easier. I've got replacement cord here so will look into replacing it eventually but want to do it as the last step so not to get it dirty
So on SW I get lots of stations(mainly foreign it seems) on the lower bands and barely anything on the higher ones right now.
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Old 5th Feb 2023, 1:29 pm   #82
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Default Re: What did I get myself into? Murphy A40C.

The answer is really very simple and it seems you are fundamentally failing to understand how this set works.

You select the short wave BAND you wish to tune across with the small SW dial and then you tune across that BAND with the main MW dial.

It's really not that difficult.
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Old 5th Feb 2023, 2:28 pm   #83
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Default Re: What did I get myself into? Murphy A40C.

Yes, I'm aware how this suppose to work but was confused by the fault in this set which Bill explained earlier a few posts up, I can assure you that for someone that never operated a pre war set and with a fault like this it is anything but easy to figure out
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Old 5th Feb 2023, 3:09 pm   #84
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Default Re: What did I get myself into? Murphy A40C.

Pre-war radios are no different to post-war ones. The only difference here is how Murphy went about it - ironically, to make short wave tuning easier to use.

It was reviewed in the Wireless World along with a description of how it works. I think you would be well advised to seek that review out.
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Old 5th Feb 2023, 4:41 pm   #85
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Default Re: What did I get myself into? Murphy A40C.

I'm young enough to be amazed and confused at the same time by kilocycles and dials and setups like this, all radios I ever used have simple buttons and a horizontal dial, completely different to this one
I do have that pdf but neither of articles I've read or posts on this forum explained the fault I have with my set until Bill did(thanks again!). Effectively if you don't 'click' into a specific SW band(which with my set is impossible by turning the knob), you're not going to get anywhere with the main dial.
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Old 9th Feb 2023, 1:24 am   #86
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Default Re: What did I get myself into? Murphy A40C.

Right, half completed now, it's a lot of work, tidied up some original wiring, found more OC resistors, replaced lots of waxies. Got one question.
I have a number of resistors that are 20-25% off its spec, eg 10k ohms is now 12k, 150k is 185k. Leave or replace?
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Old 9th Feb 2023, 4:48 am   #87
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Default Re: What did I get myself into? Murphy A40C.

Quote:
Originally Posted by Katar83 View Post
Right, half completed now, its a lot of work, tidied up some original wiring, found more OC resistors, replaced lots of waxies. Got one question.
I have a number of resistors that are 20-25% off its spec, eg 10k ohms is now 12k, 150k is 185k. Leave or replace?
It does to a certain extent depend on where they are in the circuit. But in general such over-spec values will not cause any noticeable effect. Valves were designed to work over a fairly wide range of voltages (i.e. 150 - 200 volts on the anode or more), and the normal effect of an over-value resistor in the anode circuit or cathode circuit (automatic bias) will be a bit less gain.

You will normally be able to hear if an out of spec resistor is causing any issues. Distortion especially on loud sound may be due to a badly out of spec resistor (higher voltage drop causing the valve to be operated outside of its characteristic).
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Old 9th Feb 2023, 9:51 am   #88
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Default Re: What did I get myself into? Murphy A40C.

A lot of resistors are 20% tolerance remember, just check the colour codes or I think lack of for 20%.
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Old 9th Feb 2023, 11:46 am   #89
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Default Re: What did I get myself into? Murphy A40C.

Yeah, pretty sure majority of these have 20% tolerance and the ones I was referring to are mainly around 25% so a bit over spec. I will leave them unless I'll have a replacement on hand.
Pic for reference, it's a rat's nest with a number of 'improvements' made ~50 years ago that need fixing now.
Slowly getting there, got just two bottom panels to do today and then the cans.
Also fitted 8uF caps for rectifier, 82uF caps for output valves and a 100W resistor instead of 50W one, that shouldn't hopefully overheat.
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Old 9th Feb 2023, 12:03 pm   #90
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Default Re: What did I get myself into? Murphy A40C.

Quote:
Originally Posted by HamishBoxer View Post
A lot of resistors are 20% tolerance remember, just check the colour codes or I think lack of for 20%.
20% tolerance has no colour code.

It was silver = 10%, gold = 5%.
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Old 9th Feb 2023, 5:19 pm   #91
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Default Re: What did I get myself into? Murphy A40C.

Wow. Pre war sets don't usually worry me, but that is something else!!
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Old 9th Feb 2023, 8:17 pm   #92
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Default Re: What did I get myself into? Murphy A40C.

Let this be a WARNING!

HT voltage in this radio can be deadly!

Back to fitting these new grommets...
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Old 10th Feb 2023, 1:49 am   #93
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Default Re: What did I get myself into? Murphy A40C.

Spent another whole evening trying to decipher panel 4 and 5, 4 all sorted now, started with panel 5 and realised that I'm missing one old big electrolytic can and previous guy just fitted wrong caps everywhere. Slowly getting through this but I think I'll have at least 50 hours spent on this by the time I finish
Did not expect that!
Also, replaced all rubber grommets holding tuning capacitors. 4 worth of halfords grommets and 2 for rubber spacers from B&Q. Was extremely fiddly job and required a long flat screwdriver.
I'll also need some metallised paint as the screens are peeling on couple of valves
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Old 10th Feb 2023, 8:35 am   #94
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Default Re: What did I get myself into? Murphy A40C.

I wouldn't worry too much about repainting the valves unless you intend to do a complete refurbishment on them. It won't make much difference performance wise (assuming the metalising's earth wire is in contact) and it won't look too good just 'patched up'. There are threads on here about re-doing valve metalising, but it's a big(ish) job.

It's coming on great BTW!
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Old 11th Feb 2023, 5:01 pm   #95
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Default Re: What did I get myself into? Murphy A40C.

Think I have some silver varnish in the garage so I might just touch it up where the paint already peeled just to stop further peeling, just need to find it.

Spent another evening on this, all the panels are now sorted, might just need to go over silver mica caps but its not a big issue for now.

The one waxie in one of the IF cans was an absolute ball ache to get to

Started condenser block today and have to say, there should be a warning for these somewhere, its an extremely messy job, but needs doing as it was shot.
Got it all out, cleaned it as best as I could and I'll think I'll rebuild it mounting all new caps and two resistors that were outside of the can inside it, solder it all to the tags inside the can and then add spade connectors so its easier to get it out in the future if needs be.
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Old 12th Feb 2023, 1:30 am   #96
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Default Re: What did I get myself into? Murphy A40C.

A couple of pics of how I did mine. May be of some help
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Old 12th Feb 2023, 5:25 pm   #97
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Default Re: What did I get myself into? Murphy A40C.

That looks great, had something similar in mind.
Is that a 4uF AC capacitor though? I take it capacity isn't crucial here and using standard 4.7uf cap won't be an issue?
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Old 12th Feb 2023, 6:44 pm   #98
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Default Re: What did I get myself into? Murphy A40C.

4.7uF should be fine.
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Old 16th Feb 2023, 11:24 pm   #99
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Default Re: What did I get myself into? Murphy A40C.

Right, finished condenser block, not the prettiest job but it will work.
Can was just lightly sanded and given a coat of clear, generally chassis will stay as is as I want to preserve its 'patina'
Now need to connect it all back and then should be finally ready to troubleshoot it.
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Old 17th Feb 2023, 8:42 am   #100
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Default Re: What did I get myself into? Murphy A40C.

Looking good!
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