[R-390] 2nd osc again

[Larry H]

Nice report Dave.  Glad the 2nd osc came up.  Yes, the variance in readings
from 1mc band to another band is normal, although ideally it would not be
that much.  The variance is usually caused by a less active crystal or a
trimmer not peaking correctly.  I'm not sure if the lower frequency
crystals get weaker over time or not.  T401 should be adjusted so that all
the trimmers will peak correctly.  Remember, when T401 is changed all
trimmers need to be adjusted.  Good work Dave.

Regards, Larry

On Mon, Jul 22, 2019 at 6:29 PM dog <agfa at hughes.net> wrote:

> I went through 7 6AK5 tubes today in the 2nd osc. They varied from -2V
> to maybe -4V. Then I tuned T401, things came up a bit. Then I found the
> ant trim didn't peak at 0 any more. Back to the RF alignment. Found a
> few that were off a tiny bit and one that was way off, one of the slugs.
> I ended up going back and forth on the 8MC and 15MC until they didn't
> interact. Then the individual frequencies were off on the 2nd osc.
> Readjusted them. I think I went through the T401, RF alignment and the
> 2nd osc xtals about 3 times. The funny thing is most of the 6AK5 tubes
> seem to work fine in the 1st osc, about 10V worth. But the 2nd osc I get
> anywhere from less than 3V at 8MC to nearly 10V at 31MC. The PTO is
> slightly low on the low end, but I'm not messing with that, I haven't
> tried swapping tubes on the PTO yet. Does this sound about normal or do
> some of the 2nd osc crystals get weak as time goes on, especially the
> low freq ones? There doesn't seem to be any balancing of the T401 to
> adjust for the xtals low to high. The MC bandswitch seems to be stable
> between bands now. This is on the Dittamore RX, #2. But all the modules
> are EAC. At least now I'm getting noise peak on the antenna trim which I
> didn't before.
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