> I have a nice Titan - works great for the most part even
> with a
> 20 year old tube... however on 10 meters the "peak" on the
> tune
> capacitor is right at the minimum capacitance point above
> about
> 28.1 Mhz. Is there anything I can do, simply, to raise
> this
> just
> enough to know I am tuned properly (i.e. requiring LESS
> capacitance)?
Spread the turns very slightly in the section of the tank
coil for ten meters. You DO want the plate capacitor at
nearly minimum C.
> I contacted TT service - they are a great bunch of people
> for
> the most part... they said
> I spoke to the RF design engineer. If the coil is expanded
> on
> 10
> meters in
> order to use more tune capacitance then the tuning will
> change
> on 15 meters.
> If the tuning is changed on 15 meters then the plate choke
> might
> be damaged.
Nonsense. That's totally false. It can't happen.
> The suck out frequency for the plate choke is near the 15
> meter
> band. As
> long as the tune cap will resonate there is no problem.
Series resonance in the plate has nothing to do with
spreading or squeezing turns in the tank coil. They are
separate issues. A choke goes series resonant because of
distributed capacitance and inductance along the choke. At
some frequency it acts like a group of back-to-back L
networks with nearly equal ratios and this makes it have a
very low series impedance. What you do with impedances
outside the choke has nothing to do with how the choke
behaves internally. The sole exception to this is if
something external to the choke is directly coupled to the
nmagnetic or electric fields. Any rig with a half way decent
tank and choke layout would not have an issue, and the
choke should not be series resonant that close to 15 meters
anyway.
> in manual is 5% of capacitance). Of course I could change
> the
> series cap, 25p to maybe a 20 but finding one might be
> difficult
What 25pF series cap is this? Where is it at?
By the way, watch out for that circuit in the Handbook that
shows an L between the tubes and the plate tuning capacitor.
Unless you have a tube with a very high grid
self-resonance...well up into upper UHF...and very good
feedthrough isolation it will often destabilize the
amplifier. It is often a bit tricky to suppress parasitics
with a large L between the tube and the network input
capacitor.
73 Tom
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