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alignment experts - looking for input

jdurbin1

jdurbin1

Tandberg enthusiast
Subscriber
Another AK member (DCinDC) and I have been kicking back and forth in a thread over on Vintage Solid State the question of whether coils (including open coils, inductors, and variable inductors) change value and need to be adjusted when performing an alignment.

I maintain that they DO change (the variable ones at least) due to impact/vibration and/or being adjusted by someone else prior to it landing on my bench. I see improvement in low frequency sensitivity quite often when I go through that part of the alignment.

DCinDC says not so and to stick with cleaning the capacitor (which I agree with as a first step when it comes to tuners/receivers that have open frame caps). But, he doesn't see value in checking & adjusting the inductors as needed, where to me that is absolutely a necessity if you want to be sure the tuner is 100% aligned.

Comments?

John
 
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You're right, in my opinion.

Yup, low end sensitivity can be peaked by adjusting the amp stage coils.

That's why I hate the front-end in a can. You know those Alps and others, that have the pre-formed coils. I don't think I can peak those, using tooth picks, better than I can using using slugs in adjustable cores.
 
cleaning as i said in the other thread is the starting point .. adjustable coils will need tweaking as other components will drift over time .. fixed coils in my opinion should only be adjusted as a last resort ..and for careful fine tuning .. been a long time since i played with tuners so i may be wrong here ..
accurate signal generator is the right tool for setting things up ..plus a good service manual is a big help ..
 
Yeah, I have run into those in a few pieces: the Tandberg 3031A and 3080A receiver both have preformed coils and one of the Sony ES models I run into occasionally had 'em too, as I recall. I learned to do car decks years ago and the front ends on all of those damned things have them, but of course that's because they are far better at not changing value over time (that part I agree with DCinDC about). You really need that in a car tuner where it's exposed to heat/cold cycles and impact and vibration. However, I am not sure I would say they are all produced with such tight tolerances that you can't find some improvement occasionally by adjustment, but as a rule I leave that kind alone most of the time.

John

Jon_Logan said:
You're right, in my opinion.

Yup, low end sensitivity can be peaked by adjusting the amp stage coils.

That's why I hate the front-end in a can. You know those Alps and others, that have the pre-formed coils. I don't think I can peak those, using tooth picks, better than I can using using slugs in adjustable cores.
Click to expand...
 
I could be wrong, but maybe think of it this way. A capacitor is an electrostatic device and the slightest film of anything other than air will change the capacitance. A few thousandths of an inch of dimensional change will change the capacitance. Everything is highly area and distance sensitive. Being open to the air, tuning caps get subjected to crud from outgassing plastic and wire insulation and who knows what else. On top of everything else, they routinely move, so are subject to wear and misalignment when they hit the stops.

Now, inductors are electromagnetic devices. They tend to be wound and potted, so the only thing that moves much is the slug. Deposits of stuff don't affect them. The slug is usually covered with wax or some such, so it tends not to move even under vibration. Once adjusted, inductors are basically stable for decades. Notice that I use weasel words like "tends". There are no absolute rules and I've certainly see inductors move.

Still, it's almost always a mistake to turn a slug before everything else is right, and even then it should be reasonably close if nobody else has messed with it.

I could be wrong or over stating it to some extent, but if the test setup isn't producing sharp peaks or whatever the procedure specifies, something is wrong. I know I'm in trouble when adjusting a coil or cap if the optimum setting isn't quite obvious on the meter or scope. That's the time to stop and reexamine everything. I adjust all slugs as part of an alignment, but usually only a fraction of a turn. The only time I'd touch an open coil is if the procedure clearly said to do so. I'm just not that smart.

BTW, something I find curious is that every factory hi-fi alignment procedure I've ever seen is incomplete and/or has errors. They seem to write them such that if you don't already know what you're doing, you won't be successful by following the procedure word for word.
 
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jdurbin1 said:
DCinDC says not so and to stick with cleaning the capacitor (which I agree with as a first step when it comes to tuners/receivers that have open frame caps). But, he doesn't see value in checking & adjusting the inductors as needed, where to me that is absolutely a necessity if you want to be sure the tuner is 100% aligned.


John
Click to expand...

Don't put words in my mouth. I never said anything like the italics above. At all.

Here's the thread link you conveniently left out, so you would be explaining my position.

http://www.audiokarma.org/forums/showthread.php?p=5940801#post5940801

I never said not to check. I said they won't need it if the tuning cap is clean. BIG difference.

jdurbin your reading comprehension is poor. You still don't even get what I have said.

First of all, the entire inductor adjusting back and forth was brought about by Terra1's post about different adjustments for above and below 98 mhz.

I replied explaining how it was most likely the tuning cap.

Jdurbin replied with his opinion, which is wrong.

Inductors do not change value.

I recommend everyone interested go read the thread.

I stand by what I said and I'm done this.



ConradH said:
I could be wrong, but maybe think of it this way. A capacitor is an electrostatic device and the slightest film of anything other than air will change the capacitance. A few thousandths of an inch of dimensional change will change the capacitance. Everything is highly area and distance sensitive. Being open to the air, tuning caps get subjected to crud from outgassing plastic and wire insulation and who knows what else. On top of everything else, they routinely move, so are subject to wear and misalignment when they hit the stops.

Now, inductors are electromagnetic devices. They tend to be wound and potted, so the only thing that moves much is the slug. Deposits of stuff don't affect them. The slug is usually covered with wax or some such, so it tends not to move even under vibration. Once adjusted, inductors are basically stable for decades. Notice that I use weasel words like "tends". There are no absolute rules and I've certainly see inductors move.

Still, it's almost always a mistake to turn a slug before everything else is right, and even then it should be reasonably close if nobody else has messed with it.
......
I'm just not that smart.
Click to expand...

Conrad you're smarter than you think. I couldn't have said it better.
 
Sorry, I didn't know the history. I was just answering the question as posed.

Believe me, it's no big deal for me.
 
Sorry, no harm intended in the translation - seriously. I was trying to summarize, not put words in your mouth. I'm not trying to start a range war or do whatever it takes to win an argument here, believe me. I thought we were having a civil discussion that might actually lead to someone learning something. And, I only brought it over here where other people that have some expertise in what we're talking about could comment as well.

Please explain one thing to me:

Your words: "I said they won't need it if the tuning cap is clean. BIG difference."

How is that valid advice IF one of the following applies:

1) The tuner in question doesn't have a tuning cap (I know, the one the OP asked about does).

2) The inductors in the tuner in question have been adjusted at some point in time, i.e. they HAVE changed value since the manufacturer put 'em there, because someone moved them or they moved on their own. I can't think you honestly believe that a variable inductor is 100% immune to the effects of age, temp, vibration and impact etc. Despite what Conrad said, it is not 100% the case that they were sealed with wax or paint; in the stuff I work on (regularly), that is rarely the case in fact.

I could go beyond that but let's just keep it simple.

Edit: your comment to Conrad is not quite accurate; if you'd written "Still, it's almost always a mistake to turn a slug before everything else is right, and even then it should be reasonably close if nobody else has messed with it", we'd probably be having a different discussion. Your words were (and I quote):

"They don't change. You had to adjust them due to a dirty capacitor somewhere.

On countless tuners I've aligned, cleaning the tuning cap and adjusting the trimmer caps was all that was needed. Once the tuning cap is clean and virgin, the alignment falls into place with no inductor adjustment needed.

This is also the reason that the detector slope tuned circuits need to be aligned sometimes. It's not that the inductor changed value. It's because the capacitor connected to the detector coil has changed value. But those aren't variable capacitors. So you adjust the inductor. "

I have NEVER adjusted an inductor to compensate for a dirty or failing cap, on the countless tuners I've aligned adjusting the trimmer caps alone results in less than optimal LF sensitivity, and nothing falls into place in a tuner when the twelve inductors the maker put there to align it are ignored in the process.

I can keep this civil if you can, nobody is being attacked here - ok?

John
 
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Guys,
I do agree that inductors are not likely to change value as long as nobody bends the coils. However, when aligning a tuner it is necessary to adjust the inductors as well as the trim caps in order to get the maximum sensitivity across the dial. There are other things in the circuit that do change with time, I suspect the capacitance from base to collector and base to emitter of the transistors can change, other caps in the circuit will certainly drift over time, the board can probably absorb moisture, or maybe if the flux was left on the board that absorbs moisture. I think when you perform a proper alignment, you are compensating for all these things, rather than the drift of value of the tuning coils.
And, yes, if you don't clean the tuner first, you are wasting your time. Now calm down, or I'll make you go sit on the steps.
 
DCinDC said:
First of all, the entire inductor adjusting back and forth was brought about by Terra1's post about different adjustments for above and below 98 mhz.

I replied explaining how it was most likely the tuning cap.
Click to expand...
And I explained I never disputed that. But also tried to bring it back to be helpful to the OP if they were thinking about purchasing based on whether it would be an easy fix.

I think the point of the thread was what can cause the problem.
And IF it is easily remedied.

They already had one receiver with a similar problem. Does he really want two? So better if he can see if he can fix the first one first to feel more confident.

If 95% of the problem is cleaning and after cleaning they still have a problem, do they want to deal with the 5% solution?

The statements that values don't change are still qualified with IFs of other causes.

If it's not cleaning, it could need adjustments elsewhere. If it's not adjustments, it could be some failed part (ConradH). At least that's what I took from that thread.

That gets back to my premise that most people don't have the skills or interest in adjusting or aligning tuners themselves. It's not like they can transition from cleaning mode to tuner troubleshooting mode just like that. Or even understand half of what was being debated here and there.

So they just need to know the layman possibilities before buying rather than just assuming it's a simple cleaning problem.

If they don't have experience adjusting or troubleshooting tuners, those are big IFs.

That was my point. My interest was what might be helpful for the OP to understand. I have no stake on who is right or wrong about changing values. I just know, that after cleaning, there can be room for adjustment. I guess it's how well do you need to clean? I'm not sure most people know or would even attempt to try any adjustments. Most people would be just happy to get 4.0 on the signal strength and the Stereo indicator to light up.
 
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Found this interesting statement in a design document about the stability of inductors in radios. I don't represent that this is necessarily the same application as the typical FM tuner, and I also seriously doubt it's responsible for the issues of those two receivers in the OP from that thread.

However, it clearly states that inductors do degrade with age, specifically as a function of exposure to sustained heat. Note that there are two effects being discussed, one is a short term change in inductance and Q at higher temp, which isn't relevant to the aging issue, but the second one regarding that change becoming permanent over time seems relevant to me:

Temperature stability

An important characteristic of iron-powder core materials is the outstanding temperature stability. The temperature stability information for each iron powder mix is listed in parts-per-million per degree Celsius (ppm/°C) in Figure 1. As an example, the inductance of a 100 ppm/°C material will change by 1% over a temperature change of 100 °C.

Figures 5 and 6 plot the temperature stability for iron powder materials as a percentage change in inductance and Q factor, respectively. Iron powder core materials have excellent temperature stability from -65 °C up to x125 °C. Ferrite materials are more sensitive to temperature and will exhibit changes in inductance and Q from five to 10 times greater than iron powder over the same temperature range.

In an iron-powder core, inductance will increase gradually as the core material's temperature increases from 25 °C to more than 100 °C. With continuous operation above 100 °C, inductance and Q will begin to degrade with time. The extent of this shift is dependent on time, temperature, and frequency. Iron powder cores tolerate temperatures down to -65 °C with no permanent effects.

Extended periods of elevated temperature will result in a permanent shift in inductance and Q when the assembly is returned to ambient. For temperature-sensitive applications up to 100 °C, this shift can be stabilized by artificially aging the core material at 100 °C for a minimum of 48 hours.​

For reference: http://mobiledevdesign.com/hardware_news/radio_stabile_highq_inductors/

Again, I am merely pointing this out as one source that contradicts the assertion that inductors do not change value. Clearly, they can.

John
 
I'm with Warren and J. Got to be adjusted. Usually not as much affect on the circuit as the capacitance. It's a tuned circuit. You need to compensate for those changes. We are talking front ends here, when you get into IF and Discriminator coils many times these have fixed caps, and or silver/mica plates in the can that change over time and need to be realigned.

Keep it civil..
 
Thanks for the comments Mike & Warren... apologies to DCinDC and anyone else I may have inadvertently irritated in the process of getting this answered.

John
 
OK, here's another take on this subject. The assumption made by most people in this discussion is that the tuner front end was adjusted perfect to start. Why would anyone assume this? It may, or may not be so.

Tuners are consumer items, and in the old days, there was a broad range of models offered by most companies. My experience shows the low and mid end tuners spent very little time on the test and adjustment bench. And even some of the higher end units had the same problem.

Time is money, and a good alignment takes skill, good test instruments, time. Many companies apparently did not take the time, or train / tightly supervise the employees to make sure all tuners were perfect when shipped. And I'm not sure how good the test instruments they used were either.

Doing a great alignment involves first making sure the tuner is up to operating temperature, cover on, (1 hour min) and then iterative adjustments through both the IF and RF front end. I think most companies just made sure it worked "OK" and shipped it. Just my opinion, but I've seen and adjusted a LOT of tuners.
Bob
 
Thanks for that input Bob. I've seen some comments on this elsewhere, in particular with regards to one of the Sony ES models I own (ST-S730ES). I gather there are good ones and those not so good, due to inconsistent factory tuning. Between that and the increasing likelihood over time that someone else has been inside, it certainly always made sense to me to assume everything should be checked and adjusted.

John
 
IMO, at the very least,
you should be expecting and willing to adjust the coils in a front end and know what you're doing enough that if you do get into trouble you can bail yourself out. or you've got no good reason to go adjusting stuff in the front end.
 
After many years of experience, I can say with some certainty that trouble is usually far easier to get into, than to get out of.
 
terra1 said:
Those ferrite slugs can be quite fragile, crack and break.
Click to expand...

Many tuners have air coils that you have to stretch and compress to tune them and if you aren't careful a twitch of the hand can badly distort the shape of the coil.
 
I agree that for the most part, lump inductors will not change inductance as much as lump capacitors change capacitance, over time, if the coils are clean.

A good point brought out was that these receivers/tuners were mass produced, and, with competent adjustments, be made better.

For receiver designs that use ratio or foster seeley FM detectors, you will have to balance the current flow in each leg of the coil's secondary, to minimize audio distortion. You do that by adjusting the core (slug) until both legs are coupled equally into the flux from the primary. The tank caps that complete the secondary current paths are not typically adjustable, only the placement of the core will provide a proper balance. I have not seen these that didn't need some improvement.

With an unmodulated 10.7 MHz IF signal injected, one way to get there is to adj the slug until 0 volts at the center tap of the secondary. Others look at the symmetry of the S curve with a swept 10.7 MHz I/F, or it can be done with a distortion analyzer if the RF input is FM modulated with a highly pure sine wave of say, 400 or 1Khz.
 
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