After re-capping, I had just re-aligned the IFs on this Zenith 6d614.

http://www.nostalgiaair.org/PagesByModel/101/M0025101.pdf

I had set my sig generator to 455khz and checked it with my frequency counter and set it to 455khz nearly exactly.
.. then with 400hz audio modulating the 455khz IF signal from the generator..I tweaked away on the trimmers..( just a touch here and there) and all seemed to be playing quite nicely.
BTW..(as recommended...I always peak the 2nd IF first then peak the first last)

Afterwards...however...I realized that these lousy old brittle/cracking crumblng darned rubber wires were in very sore need of replacing ....so I pulled the IF cans to redo the wires.
I did them one at a time ...so I rewired the 2nd IF first and returned it to the radio to test and it works nicely.
.... but later while I still had the other one (1st IF) out laying on the bench...I was kinda curious to see just how well the IFs really were tweaked.

( The Thomas Edison element of my psyche rearing it's ugly head again)

So I thought I'd check it using my scope.
So with no audio modulation...and without changing my signal generator frequency (455khz @ about 50mv pp output level)
... I just connected it directly to the primary input of the IF transformer. Blu & Red wires.

(btw... I also tried it coupled via a .1uf cap and there was no difference either way)

Then I put my scope on the output or 2ndary side (Green & black )and adjusted the scope's vertical input sensitivity down to the appropriate range... about 20mv per/box.

Here comes Question #1:
Well the output was very low... so I started tweaking the 2ndary trimmer cap and wow.... up popped the signal strong and large about 80 mv pp.

(wow!!... I even got about 30mv gain there too... wonder why that is too?? )

But so...Then I wondered why I had to re-tweak it so far to see the signal come up so nice and strong.
... esp because it seemed to be peaked quite nicely while in the radio.
So that's question #1.

Now question #2:
..is why is it that as I watched the 2ndary signal w/my scope... why is it that I can tweak all I want on the primary trimmer cap and yet see absolutely no gain or loss on the 2ndary signal?? You'd think that as I de-tuned the primary there'd be some fall off observed on the 2ndary.
Unless I'm just over-driving the hell out of the primary or something and swamping it to death with a 50mv input signal.

So I then I tried reversing the arrangement and fed the sig gen into the 2ndary side and then put the scope on the primary side... and re-tweaked the primary trimmer...then the signal came up on that side nicely too.. also to about 80mv pp. Why does this happen that way?

Now Question #3:
So now I can see an optimized 80 mv signal on both sides... but does that mean it is now more perfectly tuned then it was in the radio?

Well...I'll be able to tell best of course after I return it to the circuit to see how it operates.... but this certainly seems a little odd on the surface.

Especially curious about why tweaking the primary doesn't show effects on the 2ndary... kind of weird. No?

I rethought this a bit...
I made a simple 4 turn loop of hookup wier and connected that to my sig generator and placed it close to the IF coild and then connected the scope to one side at a time and re-tweaked the trimmers for and even more exacting peak I think now. They didn't need much just a tad.

Using The previous direct connect method..I'm sure the signal gen is loading down the side it was connected to swamping it out.

If these aren't perfect after I return it to the radio.. maybe it's because these tank-circuit IFs ....while connected to the tubes are being affected both capacitively and inductively by the associated circuit elements... no?

Guess I'm talikng to myself here at 3am.
what do I expect....lol
Ok... it's a bit later now.. I put that 1st IF back in now... and fired it up.... Well what perfection!
Remember... I tweaked it with a small wire loop on the sig gen positioned near each coil as I watched the scope.

So... ostensibly they'd be tuned perfectly... AND it seems in fact it is.

I had left the radio tuned to local station at 930kc.
And after replacing the IF and turning it back on, ...that station came in just about perfectly. After a minute warm up I just slightly rocked the tuner a bit to make sure the signal was maxed... and it just needed the slightest touch and I could hear the audio getting a bit better and then max itself. So I felt I was right on the station as far as my ears could tell.

( now 930kc + 455kc = 1385kc right?)

So I put my frequency generator probe close to the local oscillator coil just to see... and..There it was right smack dab on 1385kc!!! ( so it seems that after perfectly tweaking the IF outside the radio... the associated circuit elemnents when back in the radio had no additional loading effect on the IF transformer at all!)

Nice.

Peter, I am doing the exact same thing you are with my 7s582. I want to get precise IF tuning via a scope. Look at last months questions under alignment. You answered one of my questions. I see that a sweep gen. and a scope are only good with multiple IF's. One a single IF the Q of the IF is preset. Does your set have multiple if's? Did you scope align after the set was assembled? I am still trying to figure out how to get a perfect reading (freq counter)on my signal generator.
I need to change the wires up in my cans but am afraid of disrupting things. The wire coating are still on up in the cans so I might just leave them. Keep me updated

Try sleaving the brittle wires with shrink tubing. Sweep generators are more often used in FM or TV alignment where the combined frequency response is more critical. In FM & TV you are dealing with a much broader bandwidth than with AM. In AM just a signal generator and a scope or multimeter usually suffice just fine. In general the lowest possible signal should be used and the least amount of coupling. As the IF is peaked and the signal it passes increases lower the input signal. The combined IF circuit as a whole should be taken into consideration. That is where the IF is functioning so it is best to align it in circuit. Plus it is a lot less hassle to leave it in the circuit if you can. I usually have my generator connected to a frequency counter but as I reduce the signal the counter can no longer read the signal. I just assume that the generator has not shifted in frequency as I attenuated the signal. I also keep the generator on for at least a 1/2 hour before alignment. This is just my "two cents" and should not be taken as an exhaustive rendition of fact.

MRO

Hi Peter

Don't connect the signal generator or scope probe to an IF Transformer. Both will add capacity and change alignment. Measure AVC voltage for the most accurate alignment. You could do this with a scope set on DC input.

Norm

:Try sleaving the brittle wires with shrink tubing. Sweep generators are more often used in FM or TV alignment where the combined frequency response is more critical. In FM & TV you are dealing with a much broader bandwidth than with AM. In AM just a signal generator and a scope or multimeter usually suffice just fine. In general the lowest possible signal should be used and the least amount of coupling. As the IF is peaked and the signal it passes increases lower the input signal. The combined IF circuit as a whole should be taken into consideration. That is where the IF is functioning so it is best to align it in circuit. Plus it is a lot less hassle to leave it in the circuit if you can. I usually have my generator connected to a frequency counter but as I reduce the signal the counter can no longer read the signal. I just assume that the generator has not shifted in frequency as I attenuated the signal. I also keep the generator on for at least a 1/2 hour before alignment. This is just my "two cents" and should not be taken as an exhaustive rendition of fact.
:
:MRO

Thanks all for your interest and helpful feed back guys.
Nice to know I'm not as alone as I felt at 3am yesterday....lol
ok..
I wasn't trying to do the initial IF alignment with the scope and all.
.. I just happened to have the IF can out on the bench while replacing those wires and so I just decided to try tuning it "passively" (as it were) to determine how accurate I had been when I did it conventionally by ear or with a meter on the speaker.
And as it turned out ...I had been off a bit and by re-tweaking it passively, while out on the bench proved to be extremely accurate. In fact I must have truly been mistuned a little doing it by ear prior to this... ....even though I felt I had peaked (by ear) the IF quite well. But there always seemed to be this slight audio distortion yesterday afternoon..that I wasn't certain came from the signal-path or a flaky speaker.
But as soon as I tuned across the dial today after last night's experimental ''passive'' alignment ....I could certainly notice a much cleaner sounding audio.. ...at least I tink it sounds better...lol

As far as slipping sleeving over the wires goes... thanks and yes I have done that here and there but this radio is one that I'm completely refurbishing and re-painting too... Take a peek:
http://www.pbpix.com/consoltone1.jpg

before and after:
http://www.pbpix.com/consoltone2.jpg

...and then I'll campaign it out on Ebay... so I like to deliver a nice looking reasonably thorough job. Besides almost every wire in this thing needs replacing ... so pulling the IF cans and doing it right was reallly very little extra effort.
They aren't so scary... just pop 'em open and fix them.

By the way I forgot to mention... whenever I work on these Zenith's with old rubber coated wires... I find that the majority of the wires are all brittle and cracked and any slight movement causes the insulation to crumble off... however there are some wires that are just as soft flexible and suptle as when they were new!.
Why is this.
I haven't analyzed this yet... but it seems on the surface, that certain wires like B+ will go bad but cathode circuit, antenna signal wires etc all remain soft.
Why do you think that is? Wires that carry higher voltages also seem ( on cloth wire) to collect a white fuzzy powerdy stuff too.

Hi Peter

There might be something to this?? In TV wires which carry high voltage collect dust.

Can't remember seeing this in radios? Most radios have been off for decades so wire hasn't seen voltage during this time.

Norm

:By the way I forgot to mention... whenever I work on these Zenith's with old rubber coated wires... I find that the majority of the wires are all brittle and cracked and any slight movement causes the insulation to crumble off... however there are some wires that are just as soft flexible and suptle as when they were new!.
:Why is this.
:I haven't analyzed this yet... but it seems on the surface, that certain wires like B+ will go bad but cathode circuit, antenna signal wires etc all remain soft.
:Why do you think that is? Wires that carry higher voltages also seem ( on cloth wire) to collect a white fuzzy powerdy stuff too.

Sometimes the dye that was used to color the wires will cause them to be brittle. I have found that black wire tend to get brittle more often than other wires. I did some work with s/o cord last week and the green and white wires were fine but the black wire was crumbling. The black outer jacket was stiff and crumbly.

MRO

Well ... live and learn I guess...

Remember that I aligned the 1st IF can on the bench (passively) by loose coupling my signal generator using a couple of turns of wire...to the tuned transformers and connected my scope to each of the primary and secndarys ....tweaking for max signal as seen on the scope.
After this I re-installed it and tested how it performed audio-wise....without any further tweaking.

then ...I stated here above...that it seems to be perfectly aligned. I assessed this by tuning for a clear stong signal at one particuar freq on the band... then I placed my freq counter probe near the local oscillator and found it to be at exactly 455khz above the station freq. Everything sounded clear sharp and crip... so I concluded that the "passive" adjustment had optimized the IF's performance.
Well... I WAS WRONG..... lol.
Oh eveything did sound clear and sharp. (but that really wasn't enough).... until last night while I was getting ready for final inspection before re-installing in the cabinet... I was tuning across the entire band... and came to a nice (old-time big band)low-power local station at 1160khz... but it was almost obliterated and swamped out by a stronger nearby station on 1130khz.
At first I thought it was just too weak... but after some thought I realized that there must be a problem because the 1130khz station also came in clearly at 1130khz ...but why should it also be so strong 'again' up on 1160khz??
Plus... this Zenith 6D614 is a SIX tube radio providing an extra front-end RF amp/tuner compared to the 5 tubers... so this Zenith should have no problem isolating and bringing in that weaker 1160khz station.
So I cranked up the ole signal generator at 455khz again and fed it into the grid of the converter via a .1uf ... as specified.
I put my digital volt meter on the AVC line and watched for max neg avc voltage as my ears listened for a strong (max) audio peak as well.
Sure enough that 1st IF can was considerably off its "optimum' peak!!!
So as soon as I finised making it right... I tested the radio again for that weaker 1160khz station ...and this time ..there it was!!
It was nice and clear this time and separate from it's neighbors... no swamping out from the 1130khz station.
GREAT! ( thank you Major Armstrong..)

Well so what does this tell me exactly?
I'm not sure why peaking the IF tank circuits "passively" by loose coupling shouldn't also have worked well enough... but it does not... that's for sure.

Peter,
There's a large list of reasons for your experiments failure. Needless to say, "I coulda/shoulda toll u so"

marv

:Well ... live and learn I guess...
:
:Remember that I aligned the 1st IF can on the bench (passively) by loose coupling my signal generator using a couple of turns of wire...to the tuned transformers and connected my scope to each of the primary and secndarys ....tweaking for max signal as seen on the scope.
:After this I re-installed it and tested how it performed audio-wise....without any further tweaking.
:
:then ...I stated here above...that it seems to be perfectly aligned. I assessed this by tuning for a clear stong signal at one particuar freq on the band... then I placed my freq counter probe near the local oscillator and found it to be at exactly 455khz above the station freq. Everything sounded clear sharp and crip... so I concluded that the "passive" adjustment had optimized the IF's performance.
:Well... I WAS WRONG..... lol.
:Oh eveything did sound clear and sharp. (but that really wasn't enough).... until last night while I was getting ready for final inspection before re-installing in the cabinet... I was tuning across the entire band... and came to a nice (old-time big band)low-power local station at 1160khz... but it was almost obliterated and swamped out by a stronger nearby station on 1130khz.
:At first I thought it was just too weak... but after some thought I realized that there must be a problem because the 1130khz station also came in clearly at 1130khz ...but why should it also be so strong 'again' up on 1160khz??
:Plus... this Zenith 6D614 is a SIX tube radio providing an extra front-end RF amp/tuner compared to the 5 tubers... so this Zenith should have no problem isolating and bringing in that weaker 1160khz station.
:So I cranked up the ole signal generator at 455khz again and fed it into the grid of the converter via a .1uf ... as specified.
:I put my digital volt meter on the AVC line and watched for max neg avc voltage as my ears listened for a strong (max) audio peak as well.
:Sure enough that 1st IF can was considerably off its "optimum' peak!!!
:So as soon as I finised making it right... I tested the radio again for that weaker 1160khz station ...and this time ..there it was!!
:It was nice and clear this time and separate from it's neighbors... no swamping out from the 1130khz station.
:GREAT! ( thank you Major Armstrong..)
:
:Well so what does this tell me exactly?
:I'm not sure why peaking the IF tank circuits "passively" by loose coupling shouldn't also have worked well enough... but it does not... that's for sure.
:

Marv:
... I'm listening.. if you have a long list of why passive tuning doesn't work... please elaborate... I'm anxious to know...
I am an avid participant in this forum especially for what I can learn...
so I'm all ears...

Peter,
The best analogy I can come up with is as follows; Don't use Ford parts to fix a Chevy. In other words, the best test of an active/passive device is the circuit that was designed for it's use. As best I know, IF transformers are designed with a primary inductance/impedance to be driven by moderately high impedance of a vacuum tube plate. Your RF generator output is probably 50 ohms, but even a 600 ohm source would swamp the primary. A small cap will isolate the 50 ohms, but now another reactive component has been added, which will further offset the tuning/resonance. How closely does your scope match the grid circuit of the next stage attached to the secondary. Typical scope probes have around 10mmf inherent capacitance, adding another reactive component. The high freq FET probes have 1-3 mmf and several megs series R. Even your loosely coupled loop around the primary is still another reactive component, which will affect the tuning and resonance. And lastly, the obvious mutual coupling acts like a mirror, in that disturbances at either the primary or secondary affects the other.

marv

:Marv:
:... I'm listening.. if you have a long list of why passive tuning doesn't work... please elaborate... I'm anxious to know...
:I am an avid participant in this forum especially for what I can learn...
:so I'm all ears...

Marv:
Well now...of course I wasn't really 'advocating' the ridicously impractical aspects of removing an IF can and "passively" adjusting it on the bench. Not at all.
.. but rather I was just experimenting and trying to see "if" I would be able to "see"(on scope) how close to optimized the previously tweaked IF already was... and to see if it were possible to ever optimize it "passively".
I'm sure you're probably correct about "loading" considerations as the probable cause of imperfect tweaking.
But then in another thought ..I also wonder exactly how the tuned-circuit IF transformer or "band-pass filter" as it were... actually works as it does...
(just Thinking a bit outloud here...)
Each side is an L/C tank-circuit... so when properly tuned ... is each side an "oscillator"?.. that is being modulated by the audio on the incoming RF?.
.. Or does it work differently ...such that it does not ever "oscillate" per se ... but rather the L/C combinations are presenting a low impedance at the desired frequency? I tend to think it's the latter.

When I fed 455kc to each side by loose coupling.. I saw on my scope, connected to each L/C circuit, "when tuned" a stronger large signal (it appeared larger than the input signal as I remember)... so it almost appeared to be oscillating at the applied frequency.

Well whatever..
.... in any case, it's a moot issue as far as tweaking goes.. it certainly would never be practical to tune them "passively" anyway... lol
Just the "Tom Edison-effect" in me doing a bench experiment.

Each side isn't an oscillator, but rather a resonant tank circuit. It prefers a certain frequency just like a certain sized tub is going to slosh water back and forth at a certain rate, etc. Coils pass lower frequencies progressively better than higher ones. The opposite is true for condensers. The two meet half-way (or somewhere else) at a frequency that they both pass well, and this is the resonant frequency. The electricity sloshes back and forth in the condenser-coil loop at a frequency that both pass equally. Well, I guess you could call it an oscillator, but a passive one, not an active one. It's more of a circuit where oscillations (any resonance is an oscillation) take place--back and forth in the coil-condenser loop. It just so happens that the coil also radiates magnetic pulses, which can be picked up by another coil. The second coil, along with its condenser, are tuned for optimum response so that the currents can slosh back and forth in the loop as efficiently as possible. The grid of the next tube "sees" these oscillations. The reason why a tank circuit requires a condenser and a coil, and not a condenser and condenser or coil and coil, is because they must peak at a certain frequency. If it was coil and coil or condenser and condenser, the two items would pass an infinite number of frequencies, progressively getting better as they went down or up, depending on the items selected (condensers or coils). Sure, as frequencies got higher or lower, they'd pass more easily, but there'd be no selected preferred frequency. If you have a bunch of different frequency sloshes happening in a pan of water (if such a thing could happen on its own), they'd just randomly bump into eachother, and couldn't resonate in a uniform manner.

Another aspect to look at is that the tank circuit isn't really creating an oscillation. The oscillation is created elsewhere--in the local oscillator and in the radio transmitter. It is merely vibrating electrically to a frequency that's being sent to it. If your frequency of pushing a swing didn't match the frequency that the swing swung at, sometimes you'd miss the swing, sometimes you'd push it well, and sometimes it'd slam into you. When the length of the swing is tuned to match the rate you wish to push at, then the swing is in resonance with you. The resonance in the electric tank circuit is like that of a swing or pan of water or any other resonance. Currents will oscillate back and forth at a certain frequency until all energy has been spent (probably in undetectable heat). Only if another source of oscillations (the oscillator and transmitter) feeds the circuit, will it continue to oscillate at a constant amplitude.

Thomas

Also, this explains why a coil can be made to resonate at any frequency, say, in an oscillator or antenna circuit, but why radios don't usually use one coil for all frequency ranges. Most good radios have several coils, or one tapped coil for the different bands. One low frequency broadcast coil could be made to resonate at short wave frequencies (in theory), but it would pass high frequencies so poorly that it'd make the tank circuit inefficient. At the same time, the condenser in parallel with it might pass these higher frequencies extremely well. Since one of the two items is operating inefficiently, though, the whole circuit will be an inefficient resonator.

This also explains why certain IF transformers are marked for certain frequencies. In reality, they can be tuned to just about any frequency the trimmers will allow. However, they have been designed so that when the condensers and coils are in resonance, they meet halfway, or at whatever point is optimum for both the coils and the condensers at the required frequency. You may find that if you put 265KC IF transformers into a radio that requires 455KC IFs, and you are able to tune them to 455KC, that they will not perform as well as IFs designed for 455KC. This may also explain why some radios perform better than others. You may not know it if a manufacturer used the wrong kind of IF transformer simply because there was an abundance of the transformer. I don't know if this practice ever actually took place, but it is possible.

Thomas

Thomas,
Please!! I'm getting seasick with all that sloshing.

marv

:Each side isn't an oscillator, but rather a resonant tank circuit. It prefers a certain frequency just like a certain sized tub is going to slosh water back and forth at a certain rate, etc. Coils pass lower frequencies progressively better than higher ones. The opposite is true for condensers. The two meet half-way (or somewhere else) at a frequency that they both pass well, and this is the resonant frequency. The electricity sloshes back and forth in the condenser-coil loop at a frequency that both pass equally. Well, I guess you could call it an oscillator, but a passive one, not an active one. It's more of a circuit where oscillations (any resonance is an oscillation) take place--back and forth in the coil-condenser loop. It just so happens that the coil also radiates magnetic pulses, which can be picked up by another coil. The second coil, along with its condenser, are tuned for optimum response so that the currents can slosh back and forth in the loop as efficiently as possible. The grid of the next tube "sees" these oscillations. The reason why a tank circuit requires a condenser and a coil, and not a condenser and condenser or coil and coil, is because they must peak at a certain frequency. If it was coil and coil or condenser and condenser, the two items would pass an infinite number of frequencies, progressively getting better as they went down or up, depending on the items selected (condensers or coils). Sure, as frequencies got higher or lower, they'd pass more easily, but there'd be no selected preferred frequency. If you have a bunch of different frequency sloshes happening in a pan of water (if such a thing could happen on its own), they'd just randomly bump into eachother, and couldn't resonate in a uniform manner.
:
:Another aspect to look at is that the tank circuit isn't really creating an oscillation. The oscillation is created elsewhere--in the local oscillator and in the radio transmitter. It is merely vibrating electrically to a frequency that's being sent to it. If your frequency of pushing a swing didn't match the frequency that the swing swung at, sometimes you'd miss the swing, sometimes you'd push it well, and sometimes it'd slam into you. When the length of the swing is tuned to match the rate you wish to push at, then the swing is in resonance with you. The resonance in the electric tank circuit is like that of a swing or pan of water or any other resonance. Currents will oscillate back and forth at a certain frequency until all energy has been spent (probably in undetectable heat). Only if another source of oscillations (the oscillator and transmitter) feeds the circuit, will it continue to oscillate at a constant amplitude.
:
:Thomas

I know you're kidding and all....but I used sloshing with electricity just for a visual, even though the electricity oscillates much faster than a slosh in a bucket.

T.

:I know you're kidding and all....but I used sloshing with electricity just for a visual, even though the electricity oscillates much faster than a slosh in a bucket.
:
:T.

Thomas

I thought your description was very good!!

Dave

I hate when tank circuits leak and drible all over the chasis.

...gee and all along I suspected it was those grid leak resistors for those smelly yellow stains...

I just had an idea! Rather than disassembling the cans, how about just usoldering the lead and slipping some shrink tubing over it? Certainly that would be alot safer and less prone to an OOPs!

Peter, I am doing the exact same thing you are with my 7s582. I want to get precise IF tuning via a scope. Look at last months questions under alignment. You answered one of my questions. I see that a sweep gen. and a scope are only good with multiple IF's. One a single IF the Q of the IF is preset. Does your set have multiple if's? Did you scope align after the set was assembled? I am still trying to figure out how to get a perfect reading (freq counter)on my signal generator.
:I need to change the wires up in my cans but am afraid of disrupting things. The wire coating are still on up in the cans so I might just leave them. Keep me updated

It was interseting to read the progress as were were working though that problem by yourself! LOL

I like using a scope on the things as well. Our ears work on a log scale, which could leave you on either side of a peak without pecieving much of a diffence.

The scope gets it EXACT. The less loading you do with generators or scopes, the better the adjustment will stay the same when they are removed.

I put the generator on the grid circuit, not the transformer. I just clip the scope to the isulation of the plate and crank up the gain. This way the cicuit is working more or less in it's "native" state.

Depending on the how fancy the scope probe is, the capacitve loading to the tuned circuit can be significant. Excessive change in the grid cicuit can also affect the plate capacitance seen by the transformer primary!

:Guess I'm talikng to myself here at 3am.
: what do I expect....lol
:Ok... it's a bit later now.. I put that 1st IF back in now... and fired it up.... Well what perfection!
:Remember... I tweaked it with a small wire loop on the sig gen positioned near each coil as I watched the scope.
:
:So... ostensibly they'd be tuned perfectly... AND it seems in fact it is.
:
:I had left the radio tuned to local station at 930kc.
:And after replacing the IF and turning it back on, ...that station came in just about perfectly. After a minute warm up I just slightly rocked the tuner a bit to make sure the signal was maxed... and it just needed the slightest touch and I could hear the audio getting a bit better and then max itself. So I felt I was right on the station as far as my ears could tell.
:
:( now 930kc + 455kc = 1385kc right?)
:
:So I put my frequency generator probe close to the local oscillator coil just to see... and..There it was right smack dab on 1385kc!!! ( so it seems that after perfectly tweaking the IF outside the radio... the associated circuit elemnents when back in the radio had no additional loading effect on the IF transformer at all!)
:
:Nice.
: