The all-important IF alignment of the AM - Tube Radio Restoration Back to Basics part 10

[@DavidTipton101]

You're a covid magnet Manuel. Well done once again and under duress this time 🙂

[@electronicsoldandnew]

I do my duty to society: by attracting the virus to my body, I prevent it from getting to others 😊

[@andrewblack4100]

The best channel of its type. Thanks very much for your excellent teaching.

[@electronicsoldandnew]

Thank you for your support. Happy to know it’s appreciated

[@ralphj4012]

Very informative, easy to follow. Looking forward to the alignment by taste method (2:32).

[@electronicsoldandnew]

Yes, though tip of the tongue to anode of power tube 😊 Thank God for Google translate

[@tubeDude48]

Thia should help anyone that are wondering why a little more basic equipment is needed to work with this hobby. 👍

[@electronicsoldandnew]

👍

[@josephmagedanz4070]

Thanks for walking us through this. Much appreciated!

[@electronicsoldandnew]

My pleasure

[@erikdenhouter]

As far as I understand, the wobbulator uses the 1/60 (or 1/50) of a second because it is an easy to get trigger signal from the mains. But for sweeping sake, the lower the better. If you can do it on 1/2 of a second, it is better, but... older analogue scopes would not give you a solid lit line to look at, only a very slow tracing dot which is hard to read from. For you, with a digital storage scope (I think you have), you can 'remember' slow tracing dots, and for that easily use slow sweeping. Only thing is the reaction time is a bit clunky. The problem with faster sweeping is that your tuned tank circuit(s) reacts on the extra AC signal of higher sweep frequencies, and with that distort the shape.

[@erikdenhouter]

I see I was impatient, later in the video you sort of get into what I tried to bring over 👍

[@electronicsoldandnew]

👍

[@JonRig]

Great video, as always, and a great series. Well done in getting this one out while battling covid. Hope you get over it quickly and it hasn't blasted through the household!

[@electronicsoldandnew]

It’s hit the two of us. Our daughter has escaped so far.

[@Radiotechnika-Z.Ch.]

Hello. As usual, you explained everything very well in this video. However, in my opinion you should emphasize that the entire theoretical consideration of tuning an AM intermediate frequency amplifier that you presented here applies to a radio receiver with bandpass filters that are not supercritically coupled to each other. Because if the primary and secondary circuits of the bandpass filter are supercritically coupled, when they are tuned using a regular generator method, we have to suppress the circuit that is currently not tuned. Of course, when using the vobuloscopic method, this is not necessary because we can see the shape of the transfer curve of the intermediate frequency amplifier on an ongoing basis. Best regards from Poland.

[@electronicsoldandnew]

👍

[@tennesseered586]

Well explained. Thank you.

[@electronicsoldandnew]

Pleasure

[@Leo6009]

You get well Manuel!

[@electronicsoldandnew]

👍

[@karstenhubert568]

Hello, one point I didn’t catch: which setting you use on the oscilloscope to get a bell curve which is just a line. On my oscilloscope I have a double bell curve, up and down, which is completely colored in. Means I see all frequencies of the sweep. Thank you for nice explanation of alignment!

[@electronicsoldandnew]

You’re measuring the signal before the detector. I measure at the agc capacitor, after it’s gone through the detector diode.

[@karstenhubert568]

Thank you for your answer. Actually I don’t measure on a radio but for trial on a Saba filter. I can see the bell curve and do the setting on the filter. Let me try to show you a picture of what I see.

[@petersdelucaaa2vg306]

Another excellent video. I would assume a 4th method would be watching the magic eye tube assuming all was well with the tube and circuit. Do you think that a 100ms setting (sweep of 1.2 or 1.4 seconds) will always give the capacitor time to discharge and should be used for AM AGC and the FM discriminator alignments? Get well soon!

[@electronicsoldandnew]

The magic eye is effectively displaying the AGC voltage anyway, so that would work. The longer the sweep the better, but it becomes difficult to actually make adjustments as the lag between that adjustment and the visual result is long.

[@EJP286CRSKW]

You want the sweep interval to be much longer than the AGC time constant, in this case formed by (R161+R`11)*C116. Otherwise it looks like audio and gets filtered out in the AGC line.

[@electronicsoldandnew]

True, the longer the sweep the better. However, when the sweep is too long, it no longer becomes possible to actually adjust it live as the time it takes to see the effect is too long.

[@pbaemedan]

Outstanding video, thank you. But by changing the shape of the sensitivity curve you have changed the selectivity (out-of-band rejection). If you are in an area with few number of stations near your frequency, this will not be much of a problem, but if you have a strong station , it can prevent reception of the weaker station. Selectivity testing might be required. It will be a compromise between sensitivity and selectivity.

[@electronicsoldandnew]

That is always the trade-off

[@pbaemedan]

@@electronicsoldandnew we had installed a new radio in our cargo plane, we went out on a check flight, on our way back we selected the tower frequency and the local radio station wiped out the tower channel. It was just not a nuisance issue, but a safety of flight issue. We later found out that proper sensitivity alignment was throwing off our out of band rejection which was found during our EMI Test.

[@electronicsoldandnew]

That could be critical

[@daveturner5305]

What would be interesting to round this out would be some method of demonstrating whether the cores were in the same position or not for each alignment method. In an ideal world they would be, but of course we don't live in an ideal world. If the methods produce equivalent results then aligning using one method should show that any tweak using another method would 'detune' the original. In my naïve way I think that the measurement taken at the output stage would cause less potential interference/burden to the circuit than that taken at the AGC capacitor. Any constructive comments are appreciated. Cheers

[@electronicsoldandnew]

The AGC voltage is measured with a high impedance circuit (the 10X scope input), so should not affect the reading. I’ve done comparative adjustment in the past, just to check, and very little difference can be noted.

[@mackfisher4487]

Nice job Prof. your goal of increasing the number of radio restoration hobbyists is probably going to happen, the downside is eBay prices will go up on old tube type receivers. Sorry that you got the virus again, paradise must be contaminated by all those tourists.

[@electronicsoldandnew]

😊 I think WE probably contaminate the tourists 😊 as for eBay prices, they have already climbed up over the past couple of years.

[@mackfisher4487]

@@electronicsoldandnew Yes Manuel prices have gone up, and its your fault for being so successful in the restoration hobby. (Couldn't resist poking fun) go sit on the balcony and pet the cat, take time to enjoy the summer weather.

[@electronicsoldandnew]

Orrrrr… maybe I’ll sit on the verandas searching for more radios, so that I can stock up on this scarce commodity for my retirement 😊

[@BKGoldDetecting]

Is the actual IF frequency subject to tolerances. I mean is it possible that a set with an IF of 460kHz could actually be 459 or 461 or even further off? If so is it possible to determine the actual IF first so you know what to set your signal generator to, or would it make so little difference it’s not worth considering?

[@electronicsoldandnew]

Yes, you can actually have the IF shifted quite a bit and it’ll work well. The dial accuracy will be off, though. That aspect is explained in my latest video on RF alignment. To see where it is peaking, just inject a modulated signal at 460, and monitor the output strength. Then shift down and up from the 460 to see where it peaks.

[@DavidSmith-zx7wz]

Take care of yourself!!

[@electronicsoldandnew]

👍

[@BobAndersson]

Covid again. 😨 You do seem to have been unlucky (an island thing?) but great news that it hasn't been too bad and that you're recovering.

[@electronicsoldandnew]

Yes, this is the third time (I think) that I’ve had it. Fortunately it seems to be getting weaker.

[@milantrcka121]

@@electronicsoldandnew Building immunity step by step by actual exposure to pathogen. Vaccination?

[@electronicsoldandnew]

Had them all. Just gaining experience 😊

[@TheEmbeddedHobbyist]

Using the scope method you can't easily see that the peak is on the if frequency. Peaking it at the correct centre frequency should give you the best output. Just checking but is trace 4 trigger the start of the sweap and not the if frequency so you don't want to peak at the trigger point?

[@electronicsoldandnew]

The trigger signal is set to show the entire sweep from left to right. The center frequency is therefore right in the middle, as it’s a linear sweep.

[@TheEmbeddedHobbyist]

@@electronicsoldandnew so trigger going high to low is at the centre of the sweep? Just checking as I was expecting a pulse and not a square wave from the trigger. Still very interesting.

[@electronicsoldandnew]

Yes, you can change the trigger setting on the scope, and also the trigger sense on the signal generator.

[@kennethiman2691]

Get well soon!

[@electronicsoldandnew]

👍

[@eddys.3524]

What did you say about using two ears?? My AI messed up making it readable... LOL

[@electronicsoldandnew]

AI algorithms don’t use their ears either 😊

[@paulpaulzadeh6172]

Neef FM too