Zenith Color Roundie Alignment with B&K 415

[bhegges]

I will plan to replace C20 and C21 with the below parts from DigiKey which have a temp code of XF5 and align with what SAMS specifies for replacements:

• https://www.digikey.com/en/products/...0TSD15/2825257
• https://www.digikey.com/en/products/...0TSD10/2345250

As for the SAMS test point D, that correlates to the Zenith Service Manual test point G. This test point is only used to feed the signal generator in as part of 41.25 trap alignment, for the remining IF alignment steps this test point is unused with nothing connecting to it. Before I order I will double check parts in the IF circuit. I also gambled and purchased on Ebay two claimed NOS 6EJ7 tubes. Thank you, Brad.

[bhegges]

Time for an update. I replaced C16, C20, and C21 which all measured 20+% low. I also spent some time swapping tube and seem to have found the right mix, note I did have a poor performing 6EJ7 tube. I might be getting closer, thoughts on what to try next?

• Does one of the 2 below attempts look ok?
• Are there components I should go back and check?
• It's possible a fresh attempt might yield 100% success.
• I can try again and maybe find a happy middle ground?

Attempt 1
After going through all of the IF alignment steps I was able get the markers and attenuation to match the Service Manual overall response curve at test point C2. But when going back and remeasuring at test point C1 the 41.25mc marker is not at minimum and the response in-between the 39.75mc and 41.25mc markers seems large, not sure if this is concerning. See the image below:



Attempt 2
Next I went back to test point C1 and found adjusting the 41.25mc trap was my best option to minimize the 41.25mc response while not messing up the overall response to bad, note the response in between the 39.75 and 41.25 mc markers is still large. Going back to test point C2 shows the 41.25 marker is not correct. See below:

[bhegges]

For reference here is the SAMS IF circuit schematic with the Zenith Service Manual test points and coil/transformer part numbers. Also here are the abbreviated alignment steps:

1. L4 41.25mc (Bottom Tuned) - set to minimum response
2. L4 41.25mc (Top Null) - set to minimum response
3. Directions say not to go back and adjust L4 (this is what I did to get the option 1 response curve, the response curve in option 2 is closer to correct, but that means other adjustments are needed)
4. T4 Primary & Secondary - adjust to match response curve
5. L1 41.25mc - set to minimum response
6. L2 47.25mc (Bottom Null) - set to minimum response
7. L2 47.25mc (Top Tuned) - adjust to 47.25mc (some interaction may exist)
8. L3 39.75mc - set to minimum response
9. Recheck L1, L2, L3
10. T1 45.75mc - adjust to match response curve
11. T2 45mc - set to maximum response
12. T3 43mc - set to maximum response
13. Recheck to ensure marker locations and attenuations