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

[bandersen]

Cable type, probe type, lead tress, termination...all this stuff is essential when doing an alignment.

RF out at 1 volt on the meter or did you actually measure the output level on a scope?
1 volt is HUGE by the way. We're usually working in uV or mV volts at this level.

[Chris K]

That really helped a lot. Cleared up about 75% of the "fuzziness". Image blanking of course with the camera.

[Chris K]

This is clear enough that I can actually see something I can understand. The discriminator response is supposed to look like one cycle of a sine wave with 21.25mc exactly at the Y=0 origin. There's supposed to be 360 kc between the peak and trough of the wave or 180kc on either side of 21.25mc. Those marker points of 21.07mc and 21.43mc are exactly at the high and low peaks. The issue now is no matter what I do to T-113 to adjust, I can't get the curve to come back up to Y=0 after the 21.43mc marker to complete the wave symmetrically. It just sorta tails off.

[Chris K]

Originally Posted by bandersen

Cable type, probe type, lead tress, termination...all this stuff is essential when doing an alignment.

RF out at 1 volt on the meter or did you actually measure the output level on a scope?
1 volt is HUGE by the way. We're usually working in uV or mV volts at this level.

Learning a lot here. Thank you for being so generous with your time and knowledge.

[bandersen]

I suggest you move on to the other stages of the sound IF and come back to this. If the other stages are off it would effect the discriminator response. I usually do this last or come back to it again for a final touch up.

[Chris K]

Originally Posted by bandersen

I suggest you move on to the other stages of the sound IF and come back to this. If the other stages are off it would effect the discriminator response. I usually do this last or come back to it again for a final touch up.

OK I'll play around with it a bit. BTW, the sweep/gen was set for 300mV output and not 1.0 volts. Just trying how to figure out how to read and adjust this.

[bandersen]

Just use a low enough level you get a decent waveform on the scope. The reason termination is important is because the sweep gen samples the output to maintain a constant amplitude as it sweeps across frequencies. It's expecting a certain load (usually 50 ohms) for this to work properly.

[Penthode]

It would be useful what step in the alignment you are at. I believe it is a KCS28 chassis and the alignment should be the same at the 8T241.

[Chris K]

Starting Sunday 9/1 I’m going right back to the start with the VTVM based adjustments on T-113. I’m going to post step by step. Hope it doesn’t get too tedious!

[Chris K]

Where it says to inject a signal of 21.25mc at 100mV, can I use the sweep generator in CW mode and use the power meter to set the voltage or will it not do that? I do have another signal generator, one of those old Heathkit generators but I can’t get the signal strength to less than 300mV. This is for nulling out both sides of T-113 using the VTVM.

[Penthode]

Originally Posted by Chris K

Where it says to inject a signal of 21.25mc at 100mV, can I use the sweep generator in CW mode and use the power meter to set the voltage or will it not do that? I do have another signal generator, one of those old Heathkit generators but I can’t get the signal strength to less than 300mV. This is for nulling out both sides of T-113 using the VTVM.

Yes the 8601a in CW mode is a fixed frequency signal generator. You use the 8600a to set frequecy and a VTVM or scope to adjust for a maximum or minimum voltage as required.

Let's g thru the alignment step by step. Again, the RCA alignment notes should be followed to the letter and if a result cannot be achieved at a given step, it is either the equipment set up of a fault in the receiver. In either case, it must be correct before you move to the next step.

[Penthode]

Originally Posted by Chris K

This is for nulling out both sides of T-113 using the VTVM.

You are not following the instructions correctly. You are supposed to detune the secondary (bottom) then adjust the primary (top) for maximum. Then to proceed to adjust the bottom not for minimum but for zero. The VTVM needle will swing positive and negative. You must adjust for zero.

I do not understand why you want to null out both primary and secondary? That is not how a Foster-Seeley discriminator works.

[Chris K]

Yes that’s what I thought. I didn’t have a chance to sit down with it today…family stuff and a 94 year old dad in a geriatric center. Life is pretty complicated these days! Thanks for clarifying what I’m supposed to do in this first step

[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?

[Chris K]

Cram? VTVM stupid autocorrect