Hello,

I have a 2A that I was unable to get the passband tuner setup so that
the pitch of the noise was equal on both sides of the center.

I setup a sweep generator, 0.1v pk-pk, sweeping from 40 - 60 KHz, in
on pin 5 of V4. I setup an oscilloscope on pin 1 of V5. A marker
output on the sweep generator is used as a trigger.

Doing this, I can clearly see a narrow passband that is shifted around
by the twist of the knob. On the 4.8 KHz position, the passband is
greatly widened, as expected.

Now, back to the narrow mode. There is ALOT of ripple on that
passband, and the sides are not symetrical. One side had a slow
rolloff, while the other had a far faster one. That explains the
greater amount of high frequency hissing in one sideband.

I opened the tuner. Four slugs are ganged together and mounted on a
spring machanism. Each slug is mounted on a coiled wire, which is
soldered to the part that moves them all together. Unlike the 2B and
2C, the slugs are not adjustable. I really want the set to work
correctly, so here is what I'm thinking of doing:

Take out the passband tuner, mount it to a wooden board. Take the
front cover off of the tuner, and install a simple nut/bracket to
simulate the action of the tuning knob. Unsolder and free the slugs.
Using the same sweeping mechanism, adjust the slugs for 2.4 KHz, 6dB
voltage, and as flat on the top as possible. Solder back into place,
reinstall into the radio.

BUT! I remember basic troubleshooting. Failures have a cause. WHY did
the passband tuner to out of tune? Caps in the circuit failed? A short
somewhere? I'll find out, but I am wondering if my method here makes
sense.

Comments?

--
David Goncalves
W1EUJ