View Full Version : Early color IF trap settings


DavGoodlin
09-21-2016, 03:16 PM
We should not mess with these I know, but if there was someone who did before, what is your best method?

Im working on RCA's CTC 11, 12 and 16 chassis now and there is excessive noise in the video that the fine-tuning can seem to get rid of. This is not ringing or smeary stuff but possible too much high-frequency video response

And where is the 3.58 mc trap located, as it is merely mentioned in Sencore's VA-48 manual -assuming it varies between models?

dtvmcdonald
09-21-2016, 08:53 PM
If the traps are off, the main alignment probably is too.

In contradiction to what is usually said here, ALL of my postwar sets
have been off in alignment, so a modest amount, some horribly.
There is no cure except good equipment and following instructions.

If you have the rare set where you can't find instructions, you need to
carefully note settings. I count turns on variable caps and measure slug
positions with a vernier caliper. Then carefully tweek. If you don't
have experience, even with instructions, measure first so you can reset if
it gets out of hand (like oscillation).

Interestingly, if my TRK-12 had been a color set ... no alignment would
have been necessary ... it was a textbook-perfect image of the
CT-100 response as I got it. Of course, this had been a research-lab test chassis.

My avatar was only achieved after doing a really careful alignment job.
"Before" you could have seen the problems in that icon-sized image!

Of course traps are easier, since they can be set to an
exact frequency.

DaveWM
09-22-2016, 10:26 AM
BK 415 sweep gen.

DavGoodlin
09-22-2016, 01:12 PM
BK 415 sweep gen.
Is this the one that is in the same bench cabinet as a 1077B Analyst?


Think Ill hook up a scope to the video detector next, run the Sencore in at the tuner-IF link and compare it to the book.

Later Ill try the RCA WR-69 Sweep Generator - of course then clamping the AGC is needed or it will reduce IF gain to minimum.

Sometimes it helps to use the same vintage test equipment, assuming its functioning properly.

DavGoodlin
09-22-2016, 01:17 PM
If the traps are off, the main alignment probably is too.

In contradiction to what is usually said here, ALL of my postwar sets
have been off in alignment. .. I agree, most time the sound IF and discriminator benefit from some tweeking by ear. Unless Im "all-in" on a restoration I leave the IF alone.

Of course, this had been a research-lab test chassis... Just imagine having the test equipment the mfr had AND the benefit of access to the design engineer, who knew what the circuit was supposed to do:sigh:

DaveWM
09-22-2016, 02:10 PM
Is this the one that is in the same bench cabinet as a 1077B Analyst?


Think Ill hook up a scope to the video detector next, run the Sencore in at the tuner-IF link and compare it to the book.

Later Ill try the RCA WR-69 Sweep Generator - of course then clamping the AGC is needed or it will reduce IF gain to minimum.

Sometimes it helps to use the same vintage test equipment, assuming its functioning properly.

the 415 is a dedicated color sweep gen, all SS, lets you turn on multiple markers. Has the curves painted on the front so you can compare to what your scope looks like. Main issue is getting the right probes to impedence match it (they are frequently MIA).