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

[Chris K]

It worked! Slug is loose and turns easily. I was able to turn the slug 1/4 turn in either direction from the original position where it sits right now. More to come I'll make the first adjustment shortly if it is needed.

[Penthode]

Is the old transformer salvageable? And the transformer you loosened the core is the correct one with the sound takeoff from the tap in the outer trap? T103's dual purpose is the sound take off from the 21.25MHz trap. You will see two wires soldered to the trap: one at the end which connects to the chassis and the other mid point tap which feeds the first sound IF amplifier control grid.

[Chris K]

Originally Posted by Penthode

Is the old transformer salvageable? And the transformer you loosened the core is the correct one with the sound takeoff from the tap in the outer trap? T103's dual purpose is the sound take off from the 21.25MHz trap. You will see two wires soldered to the trap: one at the end which connects to the chassis and the other mid point tap which feeds the first sound IF amplifier control grid.

No I don't think the old T-103 is salvageable at this point but I'll keep it. The slugs are broken at the top where the tool tip goes to adjust it. Yes I can probably find substitute cores but for right now, I'm putting it aside.

I actually treated all three traps and their cores with the mineral spirits because I want to avoid any issues with them being stuck if they need adjustment.

Yes, the one being focused on is the T-103 trap and on install of the one Bob harvested from his chassis and sent to me, I soldered the tabs you described so we're good there.

I'll need to get back to you on this. I think I'm doing something wrong in the way I have step 6, the adjustment of T-103 configured. I'm not getting a DC read on the VTVM that's in the suggested voltage range. I'll be more specific on what's going on in a day or so.

[Chris K]

I'll be back on this later tonight!!! As I said, I need to be on a much higher scale than the 5 volt scale for the T-103 top coil adjustment with the VTVM ground and voltage leads connected across R119. Something isn't right.

[Chris K]

Could the fact my DC probe has an integral 1MOhm resistor in it be causing issues with this nulling measurement? I should be able to center this VTVM no matter what scale I have it on since there's 120V DC on both sides of the resistor correct? BTW, R119 was out of 5% spec at a hair under 6K. I replaced it with a 1% modern resistor at 5.6K

[Chris K]

I think I just cooked this VTVM. Stopped working at all and I opened it, disconnected the meter from the board and tested it for continuity. Nothing. I think I fried it. Is there anything I can't eff up?

[Penthode]

It is not clear what you are trying to do. Can you explain what step in the procedure you are attempting?

[Chris K]

Step 6. 21.25 mhz signal into pin 1 of V-2 through a 1500pf cap. The potentiometer is in place and adjusted so there’s -4.5V at the intersection of R135 and R136. VTVM connected across R119 and wanting to adjust top of T-103 for minimum on the VTVM

[Chris K]

One thing I want to understand. With the DC probe and ground from the VTVM attached to either side of R119, what is it I’m seeing on the meter? I actually read the voltage just for grins on the leads on either side and they are about 7 volts of negative DC apart. One side is -120V DC and the other is -127V DC which I guess is the result of passing through the resistor? But regardless what is it I’m measuring and “minimizing” when the trap is being adjusted?

[Penthode]

What you are measuring is residual 21.25 MHz which managed to get thru to the video detector load resistor. R119 is the load resistor where the demodulated video signal appears. It is this signal voltage which is amplified by the video amplifier and then fed to the kinescope for display.

As I mentioned before, the detector load resistor signal ground is at -120 volts DC. The reason is the video amplifier is DC coupled to bring the DC component to the picture tube. This means a DC restorer tube is not required. You must understand this. If you do not ask further questions.

When you are adjusting the traps, because the signal is being sucked out by the trap, it is should normally be at a very low level when measured at the video detector. That is likely why you cannot see it. The alignment instructions are a only guide and you must understand what this all means. Because it is a trap and you do not see anything on the VTVM, did you try raising the signal level until you saw the needle deflect? Alternatively, if you reduce the -4.5volt bias to provide more gain, that would raise the signal enough so that you would clearly see the null as you adjust.

Let us know if you do not understand.

[Penthode]

Another way to check for signal is to swing the generator either side of 21.25 MHz slightly. As you move each way away from 21.25 MHz, you should find the voltage level rise. That is a good way to check the trap is adjusted properly.

[Chris K]

OK. I'm still trying to understand this. You said what I'm measuring on the VTVM is residual 21.25 MHz signal voltage??? Then there's -120V DC in addition that goes to CRT? I guess I need to know more about how this circuit works and what it does. I'm in uncharted waters. At R119 (or around R119 as I'm looking at the schematic) there's a -120 volt demodulated video signal that goes into the video amp. Along with it, there's residual 21.25 MHz voltage that needs to be "tuned out" by adjustment of T-103? The residual voltage would cause an issue with the demodulated signal going into the amplifier tube??? Or am I WAY off base?

[Penthode]

I see the measurement point is between the first and second video DC coupled amplifier. What is the question regarding the measurement? It looks to be very straightforward.

[Penthode]

Originally Posted by Chris K

OK. I'm still trying to understand this. You said what I'm measuring on the VTVM is residual 21.25 MHz signal voltage??? Then there's -120V DC in addition that goes to CRT? I guess I need to know more about how this circuit works and what it does. I'm in uncharted waters. At R119 (or around R119 as I'm looking at the schematic) there's a -120 volt demodulated video signal that goes into the video amp. Along with it, there's residual 21.25 MHz voltage that needs to be "tuned out" by adjustment of T-103? The residual voltage would cause an issue with the demodulated signal going into the amplifier tube??? Or am I WAY off base?

Look at it this way. This set is designed to include a two stage DC coupled video amplifier. Let's go back to basics: why is there a two stage DC coupled amplifier? Next to provide the two stage DC amplifier, the two stages have to be DC stacked. With regards to the cathode and control grid, the plate is roughly at +120vdc. So to DC couple the two stages, the first stage grid/cathode is at about -120vdc, the plate of the first stage is DC coupled to the second stage grid/ cathose at around 0vdc and the plate of the second stage is coupled to the grid of the picture tube at around +120vdc. This is to couple the DC component. Do you understand this?

[Penthode]

The video signal at the video detector is only about 1v p-p across R119. But the R119 return is connected to the -120vdc supply to facilitate the DC coupled amplifier.

The DC coupled amplifier is to maintain a consistent black level. Do you understand about black level clamping?