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

[Penthode]

Originally Posted by Chris K

I guess I don’t know what detune means. What am I looking for on the cram when the signal is injected as stated and I’m looking at DC voltage on the meter? Or am I just way off base?

Yes you are looking for a maximum dc. The CW signal is just an unmodulated sinusoidal signal. The discriminator is rectifying it hence dc on the vtvm. It could be a positive maximum or negative maximum with respect to ground. So long as it is maximum.

The s curve will be a positive and negative wrt ground. It will be linear between the two peaks. That is because the discriminator is a frequency to voltage converter.

Yours is a split sound receiver. You must be aware of that because it tunes differently from a later intercarrier sets. When you adjust the fine tuning control, you tune for best sound. You will fine tune the FM sound signal across the s response: as you approach the correct tuning point, the sound will become stronger as you approach the slope of the S, next you will then hit total distortion at the peak or null of the S and then clearest sound when the fm signal is swinging between both peaks. If you tune further you will hit distortion again. So the proper point is between the two distortion points. When the set is properly aligned, the picture should be optimum when you tune for best sound.

Consider what I have said above. If it isn't clear you must question before proceeding with the alignment.

[Chris K]

I don't know what it means to "Detune" the T-113 secondary. I know it's the adjustment on the bottom of the transformer can but I don't understand the term detune. Detune how? What am I looking for that indicates the secondary is "detuned"?

As for the next step with injection of the 21.25mc signal at 100mV into the second sound IF grid (V117 pin 1) when I get a DC voltage read I'm trying to peak, we're talking a maximum of around 30mV. Does that sound reasonable?

[Chris K]

I'm taking the DC voltage at the intersection of R203 and R204 on T-113 (tab C)

[bandersen]

Just turn the slug a few times. You don't need to look at any readings.

[Chris K]

Originally Posted by bandersen

Just turn the slug a few times. You don't need to look at any readings.

Either way? So the idea is to take it out of it's previous setting like spinning the tuning pegs on a guitar string just to start the tuning process all over again?

[bandersen]

Correct

[Penthode]

The reason for detuning is so that you can clearly see the primary peak. Then you proceed to the discriminator zero adjustment. The "null" does not mean minimum. It means zero. The adjustment will swing plus and minus. You want zero. I normally set the vtvm to read zero mid scale so when I adjust the secondary adjustment I can clearly see it swing positive and negative.

Once the discriminator zero adjustment is made, you generally go back to the primary to slightly touch it up to make the discriminator peaks equal amplitude. Then again confirm the discriminator zero adjustment.

[Chris K]

Originally Posted by Penthode

The reason for detuning is so that you can clearly see the primary peak. Then you proceed to the discriminator zero adjustment. The "null" does not mean minimum. It means zero. The adjustment will swing plus and minus. You want zero. I normally set the vtvm to read zero mid scale so when I adjust the secondary adjustment I can clearly see it swing positive and negative.

Once the discriminator zero adjustment is made, you generally go back to the primary to slightly touch it up to make the discriminator peaks equal amplitude. Then again confirm the discriminator zero adjustment.

OK the secondary has been detuned. I know multiple photos are annoying but here is what I have setup to go.

Here is my VTVM. To be honest, reading voltages and resistance is about all I have done with this. Peaking is something I haven't done often. The instructions say a 3 volt scale but all I have in that range is 1.5 volts and 5 volts. It's set for the 1.5 volt range. From your instructions, I'm not concerned with values, just with maximum movement on the needle? I have it zeroed to the bottom scale which is dBm.



Instructions say use a probe in series with a 1 meg resistor. My probe has this resistor built into the probe.


The generator is set for 21.25mc at 100mv. The meter doesn't show this voltage but I confirmed it on my scope.





Here are the input and output to VTVM points. Input is to pin #1 V117 and the DC probe is on the dual resistor (R203 and R204) on terminal C on the secondary.





So I guess I'm asking is does this setup look OK? My biggest concern is am I using the VTVM correctly, arbitrarily zeroed to the midpoint of the scale and tuning the primary for maximum deflection to...what, the left or does it not matter?

[Penthode]

That looks okay. Signal level may be a little low. The important thing is to not be so low you cannot see the peak or too high where it will overload and result in a false reading and adjustment. I would recommend setting the vtvm to the correct range and then adjust the RF generator level until you get an adequate level to adjust on the meter.

FYI the zero discriminator adjustment is part 2 the first is to set the primary t113 (top) to maximum at 21.25MHz.

[Penthode]

The 1.5v range may be too sensitive. I use on my Heath IM-18 the 5 volt range.

[Chris K]

Ok will do

[Chris K]

Does it matter if the maximum is to the right or left of center...on the VTVM?

[bandersen]

No, and you should have your meter zeroed on the left. The only step you zero in the center is nulling the discriminator.
Just flip to + or - DC volts to get it to deflect to the right.

[Chris K]

Originally Posted by bandersen

No, and you should have your meter zeroed on the left. The only step you zero in the center is nulling the discriminator.
Just flip to + or - DC volts to get it to deflect to the right.

OK I did that. Sweet spot looks like a 21.25mc input at 68mV and peaked on the 5V VTVM scale at this point. Any movement of the primary adjustment either way results in a lower reading.



Does this sound and look about right?

[Chris K]

Ok so once I’m confident I have the primary of the transformer peaked, I then zero the VTVM in the center and take the reading from the new spot (not in front of it right now) adjusting the secondary from the bottom for zero volts. Then go back to the primary setup and maximize it again…then to the bottom again and so forth until everything is stable with no additional adjustments?