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Old 9th Jul 2004, 12:50 pm   #1
radiosaddo
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Default Aligning without an analogue AVO meter?

I'm new round here, hello

I have been repairing valve radios for a couple of years now and am ofcourse, still learing, and enjoying...

As my work is in instrumentation, we use Fluke DMMS and I use one for my radio repairs.

I keep reading stuff like " ..you must use an AVO... " or " ..using your AVO do this... " mainly with radio alignment.
Maybe I have been lucky, but I have never needed to align anything, and was wondering if an AVO is vital for this purpose. I do own a cheap Micronta analogue meter which sits and gathers dust, would that do??

Sorry for this long and daft question, I have a radio which I think needs alignment, I also own an Advance signal generator, so I have (I think) most of what I need.

I have, ofcourse, read the main website here, and other places on the internet, and it all points to AVO's....

Any comments most welcome from you more experienced hands


 
Old 9th Jul 2004, 1:13 pm   #2
Radio_Dave
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Default Re: Anyone here who doesn't use an analogue AVO me

Hi,

I think you'll get lots of replies to this one! I use a DMM 99% of the time. I have a couple of AVO model 8's which are great pieces of kit but are just not as easy to use as DMM's. I do use them If a DMM gives a strange reading though

You must use an analogue meter for checking output when aligning, I use an AVO but your cheap one will be fine. I use an Advance E2 sig gen and I think it's great, its obviously not as accurate as newer stuff but it's the type of kit that was used to align valve radios so it must be ok

One final point, I would only align a radio as a last resort, check everythig else first, If you do re-align make note of the original positions!

Regards

David
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Old 9th Jul 2004, 5:51 pm   #3
PaulR
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Default Re: Anyone here who doesn't use an analogue AVO me

I am also quite new to this and use a cheap and cheerful Tenma analogue meter which performs well and won't worry me too much if I accidentally connect 250 volts to the 2.5 volt setting. It sometimes gives odd readings where there is a lot of RF about but I imagine an Avo would do the same (or is that heresy?).

I have just done my first alignment to an ailing FM set using it and an Advance signal generator and am pleased with the results. I think it would benefit from another try, but it is much better than it was.

Change those old caps first, though!

Paul
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Old 10th Jul 2004, 1:02 am   #4
radiosaddo
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Default Re: Aligning without an analogue AVO meter?

First of all, apologies to the moderators for changing the name of this thread.
It didn't seem to be attracting much interest, and it is an alignment query,rather than a discussion on the general merits of AVO meters.

Second, thankyou: Gentlemen; for your replys.

I have used AVO meters in the past, but wasn't that keen on them, so have never bothered to buy one, my work make a DMM available to me, so thats what I use.

Also, AVOmeters are very very bulky and expensive.

 
Old 10th Jul 2004, 2:48 am   #5
Alan_Douglas
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Default Re: Aligning without an analogue AVO meter?

Since all you need is an indicator rather than a measuring device, nearly anything will work, even the bar graph on some DVMs. Or you can hang a DC meter on the AVC bus and let the radio do the rectifying. I would probably use an audio voltmeter (Ballantine) or even a scope but I don't align many radios.
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Old 10th Jul 2004, 9:13 am   #6
Paul Stenning
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Default Re: Aligning without an analogue AVO meter?

I usually use a 'scope - simply because I have one in place on a shelf by the bench so it's easier to use that than to dig out my AVO-8.

There is a design for a simple output level meter on my website here http://www.vintage-radio.com/project...ndicator.shtml which would be adequate for the job. All you need is something which makes the peak easily visable.

It can be done with a digital meter by watching the numbers, but that's not easy!
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Old 10th Jul 2004, 11:41 am   #7
Tim
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Default Re: Aligning without an analogue AVO meter?

If you are using a 'scope a good trick is to turn the time base to a small time interval( faster " x " ) until the displayed audio wave form forms broad stripe. This and makes judging peak easier.
An analogue meter is handy, I would recommend you get one. Second hand AVO 8's come up on E-bay now and then ( I have seen them for about £30-40and are often available at radio rallies and such like.). I think most people who have been at this for any length of time use both An and Dig , as they are both good at different things.
Any good quality analogue meter would do, as long as it's AC frequency response is sufficient. Accuracy isn't too important, as in this case you are simply looking for a peak reading.
BTW Most analogue meters will measure audio frequency up to a few KHz
I sometimes use a valve AC millivoltmeter for alignment.These come up sometimes too and are designed for measuring higher than audio frequency.
Cheers
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Old 10th Jul 2004, 11:11 pm   #8
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Default Re: Aligning without an analogue AVO meter?

I use an analogue meter or 'scope for alignment, the meter for quick work, the 'scope if distortion is a problem.

I find the display on DVM's are to slow, even with a bargraph.

Jim.
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Old 12th Jul 2004, 4:12 pm   #9
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Default Re: Aligning without an analogue AVO meter?

Thankyou again; Gentlemen, some interesting comments.

I now see that you are looking for a 'maximum' rather than an actual measurement.

I have my el cheapo Micronta analogue meter, so I think I will have a go with that first

I did see the design for the output meter on the website, but was wondering if I could use what I have to hand.

BTW, I saw the comment about using the AVC (AGC) line. also Mr. Stenning mentions this in his recent repairs.

What is the significance of this? As most alignment procedures I have seen say to connect to the loudspeaker

Maybe I should start another thread " Alignment for Dummies " How about a book someone?

 
Old 12th Jul 2004, 4:42 pm   #10
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Default Re: Aligning without an analogue AVO meter?

I align with the voltmeter set on the 2.5v range, but never let the needle creep over the 0.5v mark as it gets close turn down the output from the generator. If it goes over 0.5v the radio's AGC will start working and give you false readings.

I am no expert at this, I learnt everything from Mr Stennings website,
http://www.vintage-radio.com/repair-...lignment.shtml

the only other thing you need is the service sheet.

I know its daunting for the first time but just take your time and be carefull with the live chassis! As I said before mark the tuning slugs and capacitors before you start

Regards

David
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Old 12th Jul 2004, 4:43 pm   #11
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Default Re: Aligning without an analogue AVO meter?

All you're really doing with AM alignment is maximising gain at a particular frequency. Traditionally this was done by injecting a signal modulated with a tone and adjusting for maximum audio output. Some people can do this accurately by ear, but most will use an analogue meter to measure the audio output. People use Avos because these were *the* standard workshop meter in the valve era, and people are fond of them. You don't need an Avo for this application - a £2 throwaway meter from the Saturday market will do. You can use a digital meter but analogues are generally easier to read.

Alignment is normally done using a low signal which won't activate the AGC, but an alternative approach is to use a stronger signal and measure the AGC voltage. This will obviously increase as the signal increases.

Best regards, Paul
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