Alignment troubleshooting?

[Stylo N M]

Hi,

i was just wondering why sometimes when a radio seemingly apears to not have a great deal wrong with it, why it is that sometimes you just cant quite get the alignment right, and why you just cant quite get everything out of it?
Can this be age related in general, or maybee the quallity of the radio in the first place, what have your exsperences been and did you ever find out why, and why does it happen?

thanks,

paul.

[HamishBoxer]

Well my experience is unless the "phantom twiddler" has been at it then alignment in the main rarely goes off.

[Refugee]

If there is no damage to the slugs in the coils it will be the IF decoupling capacitor next in line for replacement.
Here is an example. The electrolyte residue can easily be seen oozing out of a Callins capacitor on the IF board in the photo.

[kalee20]

Cossor 500 tracking on MW isn't very good, aligning as per their instructions results in the RF circuit being off tune where I wanted to tune to. So I just peaked it at that frequency.

I suspect it was never particularly good, even when new. RF / Osc tracking is always a compromise, on some sets the compromise is worse than others.

[turretslug]

If it's tuning scale alignment, the capacitors used for oscillator tuned circuit padding in a superhet ought to be of types that stay on value for yonks- but that doesn't mean that they always will and the values are quite critical if (like me!) you like the scale to be spot-on. There's an Eddystone 750 here that uses three-point tracking on MW (in a way, Eddystone made a bit of a rod for their own back with a relatively highly resolving scale and a wide frequency ratio per band), I find that tweaking the padder capacitor's trimmer at the low end, the coil core at mid-span (in practice, 909kHz!) and the main variable's band trimmer at the high end gets things within a gnat's wotsit all across the range. (Makes sense with a bit of thought, although it's contrary to the manual....)

[Station X]

I've had problems with alignment where sets use coils tuned entirely by capacitors and having no adjustable tuning slugs.

In all cases the coils had lost inductance for some reason and the cure was to solder silvered mica caps of suitable value across the trimmers.

[Skywave]

Originally Posted by kalee20

I suspect tracking was never particularly good, even when new. RF / Osc. tracking is always a compromise. On some sets the compromise it is worse than others.

Apart from resolving a fault condition, I reckon those remarks accurately sum up this situation. Every set manufacturer has cost limits per set, so models aimed at the lower price end of the market will incur more compromises that those sets at the expensive end. But that doesn't mean that things can't be improved on the cheaper models, provided that you are prepared to devote the time (and possible expense on components, etc.) to investigate and experiment. Finally, there is the matter of tolerance: just how accurate do you require the tracking to be? With a given scale-plate, perfection may be impossible. Which brings us back to Kalee20's comment, in particular, "compromise".

Al.

[kalee20]

Generally true. But there are some surprising examples.

The small, economical (I just can't say "cheap") Ferguson 208U, short superhet, just 3 valves plus rectifier, surprisingly on each of its 3 wavebands, has variable inductors and trimmer capacitors... for both oscillator AND RF!

So, on each band, you can get the tuning spot on, at two places on the dial (meaning that other places it's not going to be far out), and then get the tracking spot on, again at two places across the range.

With two points, you can completely define a straight line, and although the tracking isn't quite a straight-line function, it is so much better than single-point tracking where a single point no way defines a straight line. So many, much more upmarket sets, only provide a single adjustment on RF, and some just a single adjustment even of the oscillator on LW!

[Skywave]

To my way of thinking about tracking, I regard one-point tracking as a design failure. Even in the cheapest sets I'd expect two-point tracking. Surely the manufacturing cost between those two is minimal? Of course, three-point tracking is the best arrangement in a conventional superhet. Yes, I do know that the maths. required to achieve that are a bit complicated, but for a production run, once that's been done and low-tolerance capacitors and inductors with adjustable coils have been specified, the necessary tweaking on the production line shouldn't take a great deal of time when in the hands of an experience technician. (I speak from experience in such roles).

Al.

[G6Tanuki]

Components do age... even things like dust-iron cores. I recall a radio where I couldn't get the RF alignment right - there was a peak when tuning the front-end core but it wasn't very sharp or 'peaky' - it seemed that the core had lost some aspect of its magnetic nature and the peak I was seeing was a case of running out of Microhenries despite the core being screwed inro the centre of the coil.

A replacement core from my box of cores and it peaked-up nicely!

Also as has been mentioned, wax (both the classic candlegrease on MW/LW coils and the more-modern plasticky-stuff slathered extensively by the Japanese in the 1970s and 1980s around the local-oscillator coils in VHF radios) can deteriorate and significantly lower the 'Q' - enough in some cases to completely stop local oscillators from oscillating.

[Stylo N M]

Hi.

That's amazing that the ferrite cores can in themselves deteriate, now that's something that you wouldn't always think of looking at.

Paul.

[TrevorG3VLF]

I would think that ferrite cores would not deteriorate. Iron dust though could rust.

[mole42uk]

I have a Leak Troughline that refuses to line up......

[Skywave]

Originally Posted by G6Tanuki

Components do age... even things like dust-iron cores. I recall a radio . . . .

But can you be sure that that defective core was the original one as fitted by the manufacturers? Sometime is the past, it might have been replaced, yes?

Al.

[kalee20]

Ferrite would hardly age, not for a very very long time (Google 'disaccommodation in ferrite').

Iron dust could rust though, as has been pointed out. The two look superficially similar... Though ferrite is hard and brittle, iron dust is rather softer. It deforms in the hands of the phantom fiddler with his screwdriver; ferrite chips and cracks.

[G6Tanuki]

Originally Posted by Skywave

But can you be sure that that defective core was the original one as fitted by the manufacturers? Sometime is the past, it might have been replaced, yes?

In this particular case [a Japanese amateur-radio transceiver popular in the late-1970s] I have no evidence to suggest the cores had in any way been meddled-with before I fixed it.