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Old 29th Nov 2004, 10:58 pm   #21
ChristianFletcher
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Default Re: Radio alignment and goodness of valve sets

I have done some testing tonight using a regitone A133, I have two of these sets and thought it would be useful to compare the performance since one of them has been aligned by me.

ECH42 EAF42 EBC41 EL41 - August 1951.

I have extended my aerial and many *SW station have come in more strongly, however they are all difficult to tune into as the radio's don't appear to be very selectively on some of the stations and tune in with modulation hum or wining in the background. Both of the A133 sets appear to work in a similar manner.

On long wave the aerial has made no improvements and I just get lots of static and interference I can pick up radio 4 but this is not very loud.


I have also set-up my signal generator and done some test starting on SW. I found that a 5 mv pk-pk input measured at the aerial input to the radio was enough to blow my ears off even with the volume set low.

I did have some fun and games, having set the signal generator *to 10 Mhz using the frequency counter I measured the input at the aerial socket using my digital scope. I was rather surprised to find it indicated 10.5 Mhz at 40 mv pk - pk. I rechecked the output from the generator and this was still 10mhz 5 volt pk-pk.

I figured out after tweaking the controls on the generator without any change at the receiver that I must be looking at the output from the local oscillator. I then plugged my counter into the aerial socket of the radio and was able to measure 10,465 Mhz after previously centring the radio on the 10 Mhz signal from the signal generator.

Is this normal ?

I am going to do some more detail test tomorrow evening. I definitely need some practice with my signal generator. I have a home built PAD / Dummy aerial on the signal generator. I think the output impedance of the pad must be far to high as its completely loaded when connected a radio set. Can anyone suggest a suitable value for dummy load and DC isolating PAD.

Thanks for you patience guys - I will get there eventually, It feels like I'm wearing the Idiot hat this week.

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Old 30th Nov 2004, 12:03 pm   #22
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Default Re: Radio alignment and goodness of valve sets

If it's any consolation Christian, it takes years to gain experience with matters relating to radio. I've been in the trade and repairing radio, TV, video's and other gadgets for over 35 years and still pick up new things.

With regard to the whining noise you experience, if you have a lot of modern electronic stuff around the house, you would be surprised at the amount of 'hash' generated on the mains and through the air. To give some examples, I had a strange pulsing noise appearing at certain points over MW and LW which took me some time to trace. Quite by chance one day I was listening to one of the radio's and this pulsing noise was just faintly audible but it was varying in speed and amplitude. My wife was printing stuff out and the noise was varying with the printer action. It turned out to be the (Canon) printer generating hash on the mains which I cured by fitting a filter plug. This is no longer a problem as I now have a new HP printer which doesn't cause interference.

Another prime cause of interference are the Energy Saver lamps. I have a number of these about the house but find that the cheapo supermarket specials generate loads of noise. I have several good-quality ones that give no problems but one cheapo that I had in the workshop virtually blotted out MW and this one is now banished to the top landing...it's place being taken by a good quality type.

So in your case, I would spend some time stringing up an outside aerial with a good quality feed into the house. Perhaps do some detective work if you still have odd interference noises by just unplugging things. You may be surprised at what you find.

Good luck.

Rich.
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Old 30th Nov 2004, 12:21 pm   #23
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Default Re: Radio alignment and goodness of valve sets

Like Rich, I'm increasingly convinced that your radios are fine and you're just having trouble getting a clean signal. You obviously know your stuff about electronics - you have test gear I can only dream about! - but you would probably benefit from taking a low tech approach. 1950s radios don't vary very much in performance by and large, so if they're all behaving in the way you describe, you need to look outside the radio for the problem.

I've seen the picture of your workshop on your website, and it looks like a stone cellar! If you fill that with lots of digital electronics, flourescent lighting etc. you'll generate a massive level of AM noise. SW selectivity often isn't especailly good with these radios - they're not comms receivers after all, and sometimes SW is 'just like that'. With respect to LW, I'd repeat what I've said before - you need a decent longwire aerial to get good LW performance, and a few metres of wire isn't enough. I'm in Oxford, only about 60 miles from Droitwich with no big hills in the way, and I can only get poor R4 reception with 4m of wire stuck in the back and spread around the room.

HTH, Paul
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Old 30th Nov 2004, 2:05 pm   #24
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Default Re: Radio alignment and goodness of valve sets

I think everything you have said makes sense. I just don't have the experience yet to judge if a set is good or not. That's why at the beginning of the post I was looking for a more formalising fault finding technique that take out the skill factor that only comes from years of experience. Looks like I am going to have to learn the hard way - experience.

I will have to eat a big humble pie about the wonderful world of digital scopes. After spending half the night pushing menu buttons and chasing ghost I retired the fluke digital scope and got out the old HP and things made a little more sense.

What with all this noise to track down I may have to get one off those fancy spectrum analyser. Take my advice if you don't know what your doing buy some expensive test gear it impresses the hell out of the customers.


Thanks Again best regards Christian.
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Old 30th Nov 2004, 2:27 pm   #25
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Default Re: Radio alignment and goodness of valve sets

Christian,

That Pye of mine was sorted out about 4 years ago, and I'm confident it performs as well as a set of it's type can. If you've feeding your radios a few millivolts and getting a clear tone out at decent volume, I think you can assume that they are healthy.

I don't know about the local oscillator leakage, but I recall that the local oscillator amplitude is typically a few volts, so 40mV sounds reasonable. I'll check.

Quote:
Thanks for you patience guys - I will get there eventually, It feels like Im wearing the Idiot hat this week.
Don't be silly. No one knows everything about this game and we all fall into holes sometimes.

The SW tuning on most domestic receivers requires safecracker fingers. It wasn't just a gimmick, but let's say that the sets were optimised for MW/LW and made a fair job of SW. It's certainly usable and you can pick up some interesting things.

Also, as it relies on ever changing ionospheric layers for propagation, SW isn't exactly hi-fi.

Other posters have pointed out that you may have a problem with interference and suggested some likely sources. I'd add , anything with a thyristor control can be incredibly noisy . Flouescent tubes nearing the end of their life throw out a lot of RFI. They are expecially irritating if they belong to someone else who leaves them on all the time.

I'd like a spectrum analyser, but I don't think it would be very useful for tracing interference. Still any excuse .

Pete.
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Old 30th Nov 2004, 3:50 pm   #26
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Default Re: Radio alignment and goodness of valve sets

I've just picked up on this one and can perhaps help a little:

I live in a stone roofed cottage in Hebden Bridge, West Yorks which is has very similar geography to Holmfirth and is also full of teashops and tourists etc.

I have just finished getting a P76F to work nicely on LW/SW and MW

I too spent ages trying to sort out a whine - turned out to be my computer monitor, which I'd not even thought about as it is right next to a 1950's German SABA radio which doesn't seem to mind in the slightest but sends the PYE into paraoxysms of whining and groaning. Also a nasty intermittent cracking turned out to be my girlfriend on the Playstation, the dualshock gamepads must have coils noisier than in the most horrid moped.

I've found that LW and MW don't benefit at all from ariels other than to introduce more noise, even with all other electrical sources turned off, the frame ariel seems to be more than adequate for both but I can't get much more than 4 decent stations on MW although that is definitely a geography thing - my Sony/PLL fancy £170 quid thingy doesn't fair much better either.

In a previous test using a P45 with about 15ft of ariel and a Philips Saturn with a ferrite I could get several more stations on MW and probably about 100 more listenable to on SW on both by moving about a mile North and 900ft vertically to my mother's house on top of the hill instead of in the valley. LW not much difference, just a bit less noise, still get RTE1, Radio4 and the odd foreign station at night.

Christian should be able to get R4 fairly well where he is (I used to listen to it in the cellar at work on LW as long as the radio was placed well away from all the computers on the Pye P45)

On the subject of tuning though...I also wanted to do this and managed to crumble a ferrite core and have given up adjusting the LW on the P76, which seems to be stuck and made of very very soft iron. I've seen the hint on using earex to free it up, what to do about getting the old core out? I don't want to lift the whole coil assembly as this looks like a nightmare of a job, dismantling the waveband selector etc which all works beutifuly should I just drill it and try and salvage another similar one?

Cheers

Dom
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Old 30th Nov 2004, 4:19 pm   #27
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Default Re: Radio alignment and goodness of valve sets

Thanks Dom.

Its good to hear that you have resolved your problems. I think there is a few things working against me., local conditions and screening. The building certain is blocking something but the comments on interference are very valid.

As for removing cores I have found heat from the soldering iron works as it exspands the slug and then contracts freeing off. I have also drilled with my dremel and used a left handed easy-out with WD40. I have never used the ear wax stuff..

Thanks

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Old 30th Nov 2004, 4:41 pm   #28
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Default Re: Radio alignment and goodness of valve sets

Christian:

Using a spectrum analyzer can be fun and is very useful if you are setting up aerials or RF distribution boxes but I don't think it will help in finding localised interference sources. The sort of interference we are refering to is harmonic interference. Most micrprocessor based gear run on crystal clocks from several MHz to tens of MHz. However the harmonics extend above or below these standard frequencies.

Remember that a normal TV timebase runs at 15.625kHz and if you tune over MW at night you will usually find a nice whistle every 15Khz or so. How about the flourecent lights in the workshop? If they are the HF 'quickstart' types rather than the old choke operated ones that flash and flicker before they strike then there can be quite a lot of RF noise generated by them.

This just gives an idea of the sort of everyday things that can generate a lot of interference.

Rich.
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Old 30th Nov 2004, 5:47 pm   #29
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Default Re: Radio alignment and goodness of valve sets

I was not being completely serious about buying a spectrum analyser. It one for the Christmas wish list.

It is mainly for pre complience testing on EMC I am thinking about buying one for.

Thanks Chris
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Old 30th Nov 2004, 9:47 pm   #30
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Default Re: Radio alignment and goodness of valve sets

A useful, simple tip for finding intereference on LW and MW.....

take a small, cheap transistor portable, and tune it to the frequency you want. You can do a certain amount of direction finding just with the ferrite aerial, however, if you hold the set close against your body, you will decrease the sensitivity, and increase the directionality. Now take a walk araound the house.....

I have also used this technique at VHF, for finding interference within office complexes, when even the "pistolgrip" yagi was too big.

Jim.

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Old 30th Nov 2004, 10:19 pm   #31
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Default Re: Radio alignment and goodness of valve sets

Just like to add a few more pointers. I was in a similiar situation to you whilst staying in a holiday cottage in Cornwall. I think it was built of local stone and had a metalic roof as well. AM reception inside the cottage was very poor and effected by all kinds of interference. The solution was to place the portable radio near any window.
So if you can't put up an external aerial try wrapping a few turns of wire around the window frame and an external earth might help as well.
On short waves, as a general rule of thum, during daylight it will be the higher frequency bands such as the 16 or 19 meter bands that will be the busiest but at night most of the activity will be on the lower frequency 41 or 49 meter bands
Just a few more hopefully helpful tips for you, good luck.
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Old 1st Dec 2004, 9:18 am   #32
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Default Re: Radio alignment and goodness of valve sets

Jim

When I worked in electronics in digital design an old radio was a key part of our EMC testing and proved most useful for tracing digital hash. from memory we used to connect the output from the AGC to a volt meter and use this before and after mods to the circuit under test. We also built our own ESD out of a LOPT set to charge up a high voltage capacitor. Not exactly scientific but very useful for precompliance.

I am digressing Chris
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Old 19th Mar 2005, 11:50 am   #33
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Default Re: Radio alignment and goodness of valve sets

Quote:
Originally Posted by ChristianFletcher
Can someone give advice on when radio alignment is necessary and typical faults this exhibits. Or should I just align everything that crosses my bench.

I have now restored quite a few radio sets, some have sounded better than other and alignment has not made any difference to performance. Are there measurement techniques to determine how good a set is, that don't rely on 50+ years of radio experience and a good ear. I am not old enough to know the sound of a new valve radio so its sometime difficult to judge if a set is faulty or just a poor performer. This especially related to distortion and sensitive of any newly acquired radio.

A simple check with wobulator will show whether the alignment is out,and also do a sensitivity check. All sensitivities are quoted for 50mW output,its best to follow manufacturers figures,but roughly for a 4 valve +rect, (full superhet) not exceeding 120uV, last IF 2mV,typical figures are 25uV and 1.5mV,check components first before attempting realignment,since low gain can be due to aged components.
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Old 19th Mar 2005, 10:32 pm   #34
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Default Re: Radio alignment and goodness of valve sets

Christian , it is very odd that all your sets are poor on MW and it might be that you are working in a pretty good approximation of a Faraday cage. It also seems as though you have lots of hash generators in with you. From my memory of Holmfirth I think it is in a valley and this will not help.
As you have a lead to an aerial in the loft, it would be worth trying to get some wire outside your walls and roof. You might then get some stronger signals. I did find that in a stone and slate house a simple length of insulated wire draped over the roof and coming in through a window helped a lot. If you can improvise something like this on a temporary basis, being so close to Moorside edge should give you a signal that would enable you to decide which of your sets could be used as a standard of " goodness".
Best of luck.
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Old 29th Mar 2005, 11:08 am   #35
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Default Re: Radio alignment and goodness of valve sets

Hi John

Thanks for the reply. You are right in that I do live in a valley. I think most of my problems would be solved by a good aerial. I recently bought a cheap all band transistor radio and this also works poorly in my workshop.

Regards Chris
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