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

[Chris K]

Let me describe what's going on with the very first "null" of the top slug of T-103. I have the HP 8601A set as follows. Frequency is 21.25 MHz continuous. The output is 1KHz AM modulated at 10mV. It is being fed through a 1500pf cap into pin 1 of V2. The coaxial ground lead is clamped to the chassis. The VTVM is set to AC 5V range and was zeroed prior to connection. Probe is connected to pin 1 of V106 and grounded to the chassis. The 10mV RF output is the minimum output strength that can be adjusted to 3V AC but strong enough that interference, like touching the coaxial lead, doesn't cause deflection of the VTVM needle. Tuner is between channels 2 and 13.

I've turned the upper slug in T-103 a couple of turns clockwise and counter-clockwise from the initial position is resulting in no change on the VTVM.

I've checked and rechecked the connections and they are all correct. Is the RF output voltage too low? Shouldn't I get some VTVM deflection with those slug adjustments I made?

[Chris K]

...there is another adventure I might propose and I can do it anyway even if this one goes down too many rabbit holes. I have two identical untouched chassis to this one. I might start a separate thread where I take one and do a dim bulb run up to reform the caps and with guidance from Penthode and others, do the minimum to get it working well...or at the least, as well as Penthode says his TV works on mostly original components.

[Penthode]

Because it is a trap, it is sucking energy. Try cranking up the RF level until you see and indication.

It is a good idea to get a signal indication on the VTVM before you touch anything.

[Chris K]

Not sure what's going on here but I'll tell you what I'm seeing...and hearing.
Let's be certain we are on the same page. I'm trying to do step 6 in the alignment table, the adjustment of the top of T-103. I have the VTVM connected to pin 1 of V106 and set to the 5V AC scale. I'm using my AC probe and ground lead from the VTVM. The 8601 is set for a CW of 21.25MHz. I tried what you suggested about turning up the RF gain. At 30mV through 300mV, I hear the 1KHz tone very clearly through the speaker with 100mV being the sweet spot for best undistorted tone. Anything lower than 30mV or higher than 300mV, I hear no tone through the speaker. At none of these RF output voltages can I see deflection on the VTVM of any significance when I turn the slug. What the hell is going on with this possessed thing?

[Chris K]

Oh and just as an infuriating aside...the frequency counting issues previously were NOT the 8600. The switch on the 8601 that changes the frequency scale from 11 to 110 was wonky. I opened that unit and hit the inside of the switch with some contact cleaner and it seems to be stable. I figured this out when the counter was reading 0.000 with the 8601 set to 21.25MHz and for the hell of it I flipped the switch to the 11 scale and got a stable reading of 2.125 on the 8600. I went through all of the frequencies on that scale and it was rock solid. Now the 110 scale seems to be working after the cleaning but who knows what's next with these old components?????

[Penthode]

Don't try to listen to the tone. It is AM. The sound discriminator is for FM.

Is the VTVM set to AC? Is the bias pot set correctly? Is the video IF, video detector and video amplifier working properly? Is the VTVM attached properly? You need to systematically go through things.

When setting up to adjust the traps, slightly mis tune the generator. Look for a deflection on the VTVM that goes up and down when the generator output level is adjust up and down. And the deflection must increase as you increase the RF level. I suspect you are going to have to increase the RF level to see a deflection. Again do not adjust things until you see the needle deflect with signal.

Also make sure you are not overloading. Overloading is as bad as no signal: it will distort your results.

Once you see the needle deflecting with signal, then fine tune to the trap frequency. Adjust the RF level until you see just enough to adjust the trap for a dip.

[Chris K]

Originally Posted by Penthode

Don't try to listen to the tone. It is AM. The sound discriminator is for FM.

Is the VTVM set to AC? Is the bias pot set correctly? Is the video IF, video detector and video amplifier working properly? Is the VTVM attached properly? You need to systematically go through things.

When setting up to adjust the traps, slightly mis tune the generator. Look for a deflection on the VTVM that goes up and down when the generator output level is adjust up and down. And the deflection must increase as you increase the RF level. I suspect you are going to have to increase the RF level to see a deflection. Again do not adjust things until you see the needle deflect with signal.

Also make sure you are not overloading. Overloading is as bad as no signal: it will distort your results.

Once you see the needle deflecting with signal, then fine tune to the trap frequency. Adjust the RF level until you see just enough to adjust the trap for a dip.

Ok I will forget about the tone. I’ll answer your questions one by one…The VTVM is set to AC and the range is set to 5V as you said.
The 250K pot is in place and the voltage at R135/136 was adjusted to -4.5V DC
When I have fed a video signal through the antenna from my pattern generator I get an image. The multiburst pattern is ok but the high resolution bands are not sharp. Anyway I’m assuming this means the video IF circuit is working?
The AC probe of the VTVM is connected to pin 1 of V106. The needle on the VTVM does deflect sharply to being pegged if I raise the frequency on the 8601. I get lost with what you say after that. Should I slightly mistune the generator and then do something after that? I got confused because you started talking about signal gain and levels and not changes based on mistuning.

[Penthode]

Originally Posted by Chris K

Ok I will forget about the tone. I’ll answer your questions one by one…The VTVM is set to AC and the range is set to 5V as you said.
The 250K pot is in place and the voltage at R135/136 was adjusted to -4.5V DC
When I have fed a video signal through the antenna from my pattern generator I get an image. The multiburst pattern is ok but the high resolution bands are not sharp. Anyway I’m assuming this means the video IF circuit is working?
The AC probe of the VTVM is connected to pin 1 of V106. The needle on the VTVM does deflect sharply to being pegged if I raise the frequency on the 8601. I get lost with what you say after that. Should I slightly mistune the generator and then do something after that? I got confused because you started talking about signal gain and levels and not changes based on mistuning.

If you swing the generator away from 21.25MHz and both sides the amplitude increases, then the trap is working. Remember there are two 21.25MHz traps.

You may have to raise the RF signal at the trap frequency sufficiently until you see the nedle deflect. I am only suggesting you slightly swing the generator away from 21.25MHz to test for the trap presence because the trap will cause a big dip. It seems that you are not applying sufficient RF at 21.25MHz to make the adjustment.

[Chris K]

I’ve gone pretty high on the RF signal. I mean several people have posted going to 500mV is a HUGE rf signal. I’ve gone as high as 300mV and can’t get any deflection at T-103. Should I just move on to another trap at another frequency? No deflection adjusting T105 either at 21.25mc. That’s the sound trap correct?
What do you think of my idea of going back to square one with one of the other KCS28 chassis I have and resurrecting it on mostly original components?

[Penthode]

Originally Posted by Chris K

I’ve gone pretty high on the RF signal. I mean several people have posted going to 500mV is a HUGE rf signal. I’ve gone as high as 300mV and can’t get any deflection at T-103. Should I just move on to another trap at another frequency? No deflection adjusting T105 either at 21.25mc. That’s the sound trap correct?
What do you think of my idea of going back to square one with one of the other KCS28 chassis I have and resurrecting it on mostly original components?

Can you get a signal thru at 22MHz? If so then the trap is attenuating. Because you offset the stagger tuned stages, likely there is less gain around 21.25MHz.

Tell us if you get anything at 22, 23 or 24MHz. If so, you are not getting sufficient signal thru at 21.25MHz. raise the signal and reduce the bias from -4.5v. adjust the pot until you get a signal.

How are you injecting the RF out from the HP8601a?

[Chris K]

Signal is being injected from the 8601 rf out through a coax terminating in a red signal alligator clip and a black ground clip. The signal is going through a 1500pf cap into pin 1 of V2. Ground is clipped to the chassis

[Chris K]

Originally Posted by Penthode

Can you get a signal thru at 22MHz? If so then the trap is attenuating. Because you offset the stagger tuned stages, likely there is less gain around 21.25MHz.

Tell us if you get anything at 22, 23 or 24MHz. If so, you are not getting sufficient signal thru at 21.25MHz. raise the signal and reduce the bias from -4.5v. adjust the pot until you get a signal.

How are you injecting the RF out from the HP8601a?

What do you mean by "get anything"? Do you mean deflection on the VTVM or do you mean the ability to tune the trap and see deflection at those alternate frequencies?

[Penthode]

Originally Posted by Chris K

What do you mean by "get anything"? Do you mean deflection on the VTVM or do you mean the ability to tune the trap and see deflection at those alternate frequencies?

I mean can you see the needle deflect if you set the generator to another frequency? Is the signal from the generator getting through at all?

[Chris K]

Originally Posted by Penthode

I mean can you see the needle deflect if you set the generator to another frequency? Is the signal from the generator getting through at all?

Yes it does deflect

[Penthode]

Originally Posted by Chris K

Yes it does deflect

Does the deflection change when you rotate the RF level? If the level changes at 23MHz but not at 21.25MHz, it means the bias is too high and you will have to rotate the bias control to increase the VIF gain.

So now I interpret there is a level at 23MHz and the level goes up if you increase the 8601a output level.