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

[Penthode]

Originally Posted by Chris K

Got it. I think my VTVM is a bit wonky. One more question...the channel selector is set between channels 2 and 13 but that's not a firm detent correct? I just have it between the two channels.

That is correct. There is no detent.

Historical note: This, the KRK5 RCA tuner replaced the KRK2 tuner used in RCA sets from 1946-48. The KRK2 included Channel 1 and the KRK5 in 1948 was the first RCA tuner to drop channel 1. The blank space is where channel 1 would have gone.

[Penthode]

with regards to the core positioning for maximum. You said the core was unscrewed to get the peak. Unscrewing the core reduces inductance which means you are tuning it higher in frequency. What I think you have done is tune it to the same frequency as another stage and it has introduced oscillation! I mentioned the danger earlier of it breaking into oscillation. I suggest you must fix this before adjusting the traps!

Put the core back close to the original position. The circuit tunes broadly and you should detect a smaller peak near the original position. Also if you do get into a state of oscillation and cannot get out of it, what you do is increase the AGC voltage until the oscillation ceases and try increasing the 8601a input until you see the signal.

Certainly if you are having to adjust any opf the circuits that far away, you are doing something wrong. Becareful and stop and think and ask before making assumptions.

[Chris K]

Originally Posted by Penthode

with regards to the core positioning for maximum. You said the core was unscrewed to get the peak. Unscrewing the core reduces inductance which means you are tuning it higher in frequency. What I think you have done is tune it to the same frequency as another stage and it has introduced oscillation! I mentioned the danger earlier of it breaking into oscillation. I suggest you must fix this before adjusting the traps!

Put the core back close to the original position. The circuit tunes broadly and you should detect a smaller peak near the original position. Also if you do get into a state of oscillation and cannot get out of it, what you do is increase the AGC voltage until the oscillation ceases and try increasing the 8601a input until you see the signal.

Certainly if you are having to adjust any opf the circuits that far away, you are doing something wrong. Becareful and stop and think and ask before making assumptions.

OK I will go back and turn the core back in on T-106 and look for the smaller peak.

[Chris K]

Oh darn darn darn darn darn...I think I may have done something wrong! Now this is how inexperienced and electrostupid I am...but it's good because I'm making mistakes I'm learning from...

I was not paying attention to the VTVM DC voltage position...positive or negative. Obviously, if it was set to DC-, the peak is going to be deflection of the meter to the left correct? I can't account for the position when I did the min/max adjustments so it's back to step 6 once again!!!!!!! Besides getting valuable lessons, I sure am learning this particular chassis and the audio and video circuits!

[Penthode]

Maximum is deflection to the right and minimum is the dip to the left.

The problem here is the careful staggered tuning in order to get the full 4MHz bandwidth. There is a lot of gain in the four stages. You can assume unless someone before has tinkered with it, the stages were close to being correct.

So let's go back. Make sure it is not oscillating. To confirm it is not oscillating, switch the HP8601a off and ensure there is no voltage across the 2nd detector load. By no voltage, I mean less than 100mV. Confirm the traps are correct and then set the preliminary staggered tuning setup prescribed in the manual. The spot frequencies are to get the alignment close before the sweep alignment.

[Chris K]

Originally Posted by Penthode

Maximum is deflection to the right and minimum is the dip to the left.

The problem here is the careful staggered tuning in order to get the full 4MHz bandwidth. There is a lot of gain in the four stages. You can assume unless someone before has tinkered with it, the stages were close to being correct.

So let's go back. Make sure it is not oscillating. To confirm it is not oscillating, switch the HP8601a off and ensure there is no voltage across the 2nd detector load. By no voltage, I mean less than 100mV. Confirm the traps are correct and then set the preliminary staggered tuning setup prescribed in the manual. The spot frequencies are to get the alignment close before the sweep alignment.

Ok I will do that. Gotta shut it down tonight. Be back on it tomorrow evening

[Chris K]

This snip is from a different RCA model alignment set of instructions but the chassis has the same traps and the same frequencies. There's something in here I don't understand...


I see the warning about getting false, resonant peaks and nulls when "running the cores completely through" . I don't understand the next statement..."The correct position is with the cores in the outside ends of the coils". What do they mean by outside ends?