Quote:
Originally Posted by Chris K
So what is it I'm stopping by attaching the resistors? Is it the resonant, in circuit coils or the trap coils? I sorta get the statement this makes the video IF stages an untuned amplifier but the statement "This is so you can see independently the tuner over coupled transformer link frequency response when you sweep it"is making my head spin. So when I sweep the input signal symmetrically 10mc with 25mc as the center frequency (from 20-30mc) and pick it up on the scope at the end of its travel through a detuned IF series of stages, I'll see the full bandwidth signal out at the end? If so why is that important to see and what then am I looking for to adjust?
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The resistors temporarily shunting the coils will essentially make the IF amplifier downstream a broadband untuned amplifier. This will allow you to see only the tuner to first IF over-coupled link frequency response without interference. You want to be able to establish a correct response between tuner and first IF before adjusting the remaining stages. So the order of work is:
1. Confirm traps are correct
2. Sweep align the tuner to first IF over-coupled link with resistors shunting the downstream stages
3. Sweep align the entire video IF with the resistor shunts removed.
You should be cognizant of the fact that unless someone has in the past meddled with the tuner-1st IF link transformers, the adjustment should be close. Be aware that if any of the resistors are not connected or loose, it will distort the response you are trying to obtain.
Once the resistors are removed which will raise the gain of the IF amplifier, there is the danger of oscillation which they describe how to handle in the notes. The oscillation will occur if two of the stages are tuned close to the same frequency. The Video IF stages must be properly stagger tuned to be stable.
Here is a Wiki page describing stagger tuning.
https://en.wikipedia.org/wiki/Stagge...reduced%20gain.