Ok. Let’s try this again…RCA 9TC240 Alignment

[Yamamaya42]

I'm getting confused just trying to follow all this.
As Penthode said, the -4.5 is set and forget, set at the start, and don't touch, or it will throw all things off, it's meant to suppress some circuits while you do the alignment, you do not need to monitor it.

[Penthode]

Originally Posted by Yamamaya42

I'm getting confused just trying to follow all this.
As Penthode said, the -4.5 is set and forget, set at the start, and don't touch, or it will throw all things off, it's meant to suppress some circuits while you do the alignment, you do not need to monitor it.

Setting it to -4.5v is simply fixing the AGC to a voltage close to normal operating voltage. The reason is that the IF response changes very slightly as you change the bias. Consider that the IF strip comprise of staggered stages employing the same vacuum tubes which have slightly different characteristics in the course of manufacture. In this world, nothing is perfect and engineering is always a practical compromise.

So the -4.5v is not an absolute. Is is a rough approximation of where it normally would be under average reception conditions.

(My philosophy: I often muse that in our digital world today, the display layer is what most now look at which is defined by a series of precise digital words which if is not corrupted in reception provides a closer to perfect ideal. Not so in the world of analog systems and television where the display layer doubles as the transport layer and is subject to vagaries like this.)

[Yamamaya42]

Originally Posted by Penthode

Setting it to -4.5v is simply fixing the AGC to a voltage close to normal operating voltage. The reason is that the IF response changes slightly as you change the bias. So the -4.5v is not an absolute. Is is a rough aproximation of where it normally would be under average reception conditions.

That's what I thought, I did something like that with my Hoffman, the clip lead fell off on try #2, and I had to start all over again!
#3 worked pretty well!

[Penthode]

Now you are making me confused.

The pot is adjusted for setting the -4.5v which is the AGC voltage measured at the junction of R135 and R136 wrt ground.

The RF CW signal is detected or rectified by the 2nd detector. You vary the 8601a signal until you get roughly 2 to 3 volts ACROSS the detector load resistor R119. The -4.5v should not be changing much: how much is it changing?

[Chris K]

Originally Posted by Penthode

Now you are making me confused.

The pot is adjusted for setting the -4.5v which is the AGC voltage measured at the junction of R135 and R136 wrt ground.

The RF CW signal is detected or rectified by the 2nd detector. You vary the 8601a signal until you get roughly 2 to 3 volts ACROSS the detector load resistor R119. The -4.5v should not be changing much: how much is it changing?

It's not...I was varying the output RF voltage way too high messing with it when I had a bad VTVM lead connection. With the latest min/max adjustments it didn't vary much at all

[Chris K]

Originally Posted by Yamamaya42

I'm getting confused just trying to follow all this.
As Penthode said, the -4.5 is set and forget, set at the start, and don't touch, or it will throw all things off, it's meant to suppress some circuits while you do the alignment, you do not need to monitor it.

Hey...me too! I got it about the "set and forget it" -4.5 volts. I'm not sure how Penthode would like to go forward. These settings are critical to the quality of everything going forward and I've gotta get it right. Maybe I'll post what's going on with pictures of each step and look for input from everyone and a consensus all is good before I go on to the next trap adjustment.

I've ordered some mini alligator clips so I can solder up 4-5 330 ohm, easy on/easy off shunts for the transformers in the last 2 steps in the alignment table.

[old_tv_nut]

It means positioned near the top or bottom rather than the center of the coil.
In other words, start with the coil mistuned by having the core too near the end and move towards the center to get the correct tuning, rather than starting with the core near the center and turning to go towards the end.

[old_tv_nut]

Note in both cases the upper and lower coils are each tuned correctly. The only difference is the amount of coupling. Too much coupling will produce a wide double-humped response with low center frequency response.

[Chris K]

Originally Posted by old_tv_nut

Note in both cases the upper and lower coils are each tuned correctly. The only difference is the amount of coupling. Too much coupling will produce a wide double-humped response with low center frequency response.

Wow...thank you so much. Resonance...harmonics etc...these concepts have always been the most challenging things for me. I can understand a vibration stimulating something else at rest to vibrate but at the same frequency. I don't entirely understand the production of other frequencies from the primary one.

So by coupling here you mean frequency or vibrational coupling...one coil and slug stimulated electrically transferring this frequency based energy to an adjacent coil? These traps are tuned to eliminate specific frequencies from the signal circuit resulting in a broader bandwidth. At least that's my understanding from an earlier part of this thread. How does this primary/secondary tuned pair do that? I have an idea as to how but I'm not very eager to put it out there!

[old_tv_nut]

Originally Posted by Chris K

Wow...thank you so much. Resonance...harmonics etc...these concepts have always been the most challenging things for me. I can understand a vibration stimulating something else at rest to vibrate but at the same frequency. I don't entirely understand the production of other frequencies from the primary one.

So by coupling here you mean frequency or vibrational coupling...one coil and slug stimulated electrically transferring this frequency based energy to an adjacent coil? These traps are tuned to eliminate specific frequencies from the signal circuit resulting in a broader bandwidth. At least that's my understanding from an earlier part of this thread. How does this primary/secondary tuned pair do that? I have an idea as to how but I'm not very eager to put it out there!

The coils between IF stages are coupling the output of one stage to the input of the next. But coupled coils can also be used in a trap circuit where one of the coils connects to a circuit that absorbs energy at the trap frequency instead of passing it to a next stage. And sometimes, the coupled coil is both a sound takeoff that sends the sound signal to the audio IF and and also a sound trap in the video path because it sends the sound signal out of the video path and to the sound IF.

Another thing, we are discussing basically linear filter circuits here, which means they (ideally) do not generate harmonics of the incoming signal, but respond with different amplitude to the different frquencies that are present in the incoming signal. This difference in amplitude at different frequencies is seen as the shape of the IF alignment sweep curve.

[Yamamaya42]

It's a magic spell, and you are a mystical witch casting a spell on the set, mixing all the ingredients in your cauldron one at a time VERY carefully, get one wrong or out of order, it's all messed up, and you have to start ALL OVER AGAIN!

[Penthode]

I also wish to point out the coil you were earlier adjust from the bottom was not a trap but a stagger tuned stage. Take heed of the attached warning from the manual. This unfortunately happens when one begins making changes without carefully reasoning through.

[Penthode]

So for the traps, you are to find the null with the core on the outer most postion. The stagger tuned stages should be in the relative position you started with. If it falls into oscillation, as I am sure others have had on the model, then tuning each stage to the correct physical (original) position should eliminate the oscillation. I have only had to resort to increasing the bias to fix stubborn cases and never having to shunt stages. But if you are not careful you may have to resort to that in order to get back where you started.

[Chris K]

I’m trying. I knew I would cause more problems than I solved once I started messing with this.

[Chris K]

Is there something I should know about a staggered tuned IF? I thought an IF was just a gain increasing series of steps through vacuum tubes and stages. Is staggered tuned different from a standard IF sound or video IF?