I have read the theory about RF and IF alignment, but never tweaked a radio.
Using a Signal generator and Frequency Counter, this old Classic TM5 radio seems to be aligned to 449kHz IF, as determined by measuring max AGC voltage. But a few turns of the primary core of IF2 increases the AGC voltage substantially. After 3 turns and no 'peak', I ran out of courage and decided to consult the experts to ask if my technique is okay.
As a first attempt, I intended to leave the IF at 449kHz (so I don't have to worry about re-aligning the oscillator), and to tweak the IF cores from IF2 secondary backwards. Once I know more about it, I had intended to align the IF to 455kHz as per the circuit diagram, then tune oscillator to the IF.
Does this sound correct?? I had been expecting to find a tuning peak in less than 3 turns of the core. Could the IF be a fair way out of alignment, or is my technique incorrect??

The IF & oscillator are two seperate animals despite the oscillator being the generator of the frequency that creates the 455 kHz (and mulltiples). (additive & subtractive hetrodynes)

Catch 22 says that the frequency counter must be correct..

If you feed a modulated signal into the Frequency Counter to calibrate the sig gen. It will be wrong in most cases.

When adjusting 455kHz IF's you start at the last IF & work backwards: That's ok. Astor has information on their units, often in AORSM's and there are other sources.

Normally one monitors the unit at the plate of the Output valve. Mettering the AGC unless specified in the sets method may adversly affect the RF section. Normally I use a CRO as I can see what the coil is doing and also see the resonant point as the coils couple at resonance.

The oscillator coil is normally set at around 600kHz..

Some sig gens have provision for a crystal to calibrate them & you can cross reference then to the sig gen. If you have a short wave set ( or Comms reciever ) tune it to WWVH then "Zero beat" the sig gen to it then note the frequency counters reading. 2.5, 5, 10, 12MHz

Marc

Thanks Marc. Understand your points..... mostly.
**Switched modulation of Signal generator on/off and frequency changed, ~0.4kHz. Another lesson learnt!
**Using my AGC method, I found a good peak with IF2 primary core, secondary core gives a very broad peak. The AGC voltage is now about double where I started; radio still works well, phew!!
**Can you please elaborate on the use of your CRO? Which signal do you monitor etc??
**Zero beat - ???when sweeping across a fixed frequency with a signal generator, one hears,or sees on CRO, high frequency decreasing to 'zero', then back up again. Sounds like a 'chirp' if one sweeps the frequency quickly?????? At the 'zero' the frequencies are the same??? Not sure how I actually get the signals to beat against each other as yet, but will give it more thought.

The CRO will show the audio signal being recovered.

That is one reason the audio signal in the generator must be good and nothing should be distorted within it.

The CRO will show resonance, over coupling and distortion. Some of the older books have references, drawings & photo's of what should appear.

Zero beating has been around since oscillators. Tune a radio to a station (the ones mentioned are frequency references, not just time) Then set the sig gen (no modulation) to the same frequency.

If the frequency generator is correct, the signal will cancel (null) and nothing will be heard. You can expect a low frequency growl as it nulls or an increasing whisle as the two seperate. Do not go at it like a bull in a china shop as it needs fine adjustment.

You can try this with a transistor radio. Its a good cheap method for spot checking sig gens & frequency counters.

Marc

Hey Marc,

... 'zero beating' ....got it ..... Found the null with both Signal Gen and Counter connected to radio, the frequency reading of Counter was not stable. On disconnecting the radio, frequency stabilised quickly at the frequency of the radio station, spot on each time................ wish I had understood how to do that a long time ago!!

I understand that the oscillator is set at RF plus IF, but not quite sure what you meant with "The oscillator coil is normally set at around 600kHz.." ???

Many thanks for your help.

Forgot to mention. There will be enough radiation from a wire out of the sig gen to feed the radio, when doing this. Best done as transmitter, reciever as in real life.

Valve radio should have an antenna wire of course. You can find the IF frequency using that method... do play.

If you hunt out the Astor data or something else with it. There are various posts on the WEB & in radio sites. Not sure on HRSA site.

You will not that when callibrating the dial (BC band) one should put it on 600Hz then adjust the oscillator coil to coincide with it. You then move to 1500 kHz to adjust the aerial trimmer.

In an autodyne / superhetrodyne the oscillator is set to a frequency that is the (sum of , or less than) the incoming frequency, by the pass frequency of the IF transformers (resonant transformers)

eg with a 455kHz IF: When set to a station at 1500kHz
the oscillator wil be at either 1955kHz or 1045kHz depending on the manufacturers whim.

Theory is good but data like the Astor, is how to do it for real.

Marc

Hi Marc et al,
Followed your advice ......"do play" ......and have this radio tuned up nicely ie signals are much stronger on Broadcast Band and plenty of signals on Short band at night (but I don't understand any of the languages; my aerial is a simple, long wire, east-west).
Found a Quad radio "How to tune IF and RF/Osc" reference, and adapted the methodology to my radio.
More importantly, I am starting to understand how to use some of this test equipment I have been given.
Thanks for your help...