[ARC5] BC-459 Frequency Jump

[Dennis Monticelli]

The long time constant is revealing.  This is either due to having very
high capacitance power supply capacitors that are slowly sagging (your
indicate this is not the case) or it is due to thermal heating of a
localized area which in turn is slowly changing the loading on the
oscillator.

Small contact surfaces where lots of RF current pass through are the likely
suspects.  So the wipers or bearing of the PA tuning cap are suspect.  The
wiper of the roller-ductor is also suspect.  A weak or gassy 1625 can cause
this also (via grid heating).  I have experienced the latter myself.

The suggestions regarding DeOxit cleaning are good.  Don't forget the
roller-ductor.  If you have relay contacts in the PA path clean these too.
If you used small disc caps for antenna loading then these are suspect
(Parallel them up, switch to NPO or use doorknobs).

Finally, don't obsess about it.  Chirp is quaint in an older rig,
especially during a vintage contest.  But if you work DX or contests, it
doesn't play so well.  Helpful hams have stopped their high QSO rates to
tell me my "transceiver" was sick.   When I tell them the rig is an ARC-5,
most of them get confused but a few just laugh their heads off!

Dennis AE6C

On Sat, Jan 2, 2016 at 3:17 PM, arc5 at ix.netcom.com <arc5 at ix.netcom.com>
wrote:

> Try removing the unun and using the variable at about 50 pFd in series to
> a 50 ohm dummy load.  See if it still drifts.  I've had ununs that heat as
> well.
>
>
> Sent from my ain't-so-smartphone.
>
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