26-07-2020, 12:59 PM
(This post was last modified: 26-07-2020, 01:06 PM by Mike Watterson.)
Coils measure OK.
Now got LO on LW & MW and it tunes.
Sensible RF limits on signal generator, but deaf.
The RF coils connect to AGC line rather than earth. Still deaf if C5 is shorted, equals maximum gain.
Now the LO has stopped! Sigh. The coil continuity is still OK.
I think the coils inductances are, by tags:
2 - 4 : 118 uH, probably L5
5 - 6 : 18.9 uH, maybe L8
2 - 3 : 255 uH, probably L7
1 - 6: 8.6 uH, maybe L6
Which might mean that on the circuit diagram L8 goes to C11 (220p) and L6 goes to 0V, i.e. reversed.
I've numbered tags clockwise from top with 3 and 4 either side of the slot.
1 & 3 has a 390 pF, C13. Pin 1 to 0V. Pin 5 is drive via 220pF, 6 is junction of L6 and L8 and doesn't connect anywhere else. Pin 2 is a green wire to the MW position of S1b, which shorts it to 0V, shorting out L7. On LW, L5 and L7 are in series which is 399uH and an additional 95 pF is switched across C10 to 0V. On LW C13 (390pF) is in series with L5 and L7.
Time for lunch. I'll may look at it this evening. Any ideas?
Now got LO on LW & MW and it tunes.
Sensible RF limits on signal generator, but deaf.
The RF coils connect to AGC line rather than earth. Still deaf if C5 is shorted, equals maximum gain.
Now the LO has stopped! Sigh. The coil continuity is still OK.
I think the coils inductances are, by tags:
2 - 4 : 118 uH, probably L5
5 - 6 : 18.9 uH, maybe L8
2 - 3 : 255 uH, probably L7
1 - 6: 8.6 uH, maybe L6
Which might mean that on the circuit diagram L8 goes to C11 (220p) and L6 goes to 0V, i.e. reversed.
I've numbered tags clockwise from top with 3 and 4 either side of the slot.
1 & 3 has a 390 pF, C13. Pin 1 to 0V. Pin 5 is drive via 220pF, 6 is junction of L6 and L8 and doesn't connect anywhere else. Pin 2 is a green wire to the MW position of S1b, which shorts it to 0V, shorting out L7. On LW, L5 and L7 are in series which is 399uH and an additional 95 pF is switched across C10 to 0V. On LW C13 (390pF) is in series with L5 and L7.
Time for lunch. I'll may look at it this evening. Any ideas?
