> Mr. Rauch -- 80% of 4000V = 3200V. 90% of 4000V = 3600V. What's the
> problem with 3500V?.
Your normal diversion is to lift things out of context. The rest of my
answer explains the difference.
> >which would translate to 3kV or more across the tank inductance.
> >The exact value depends on tank loaded Q, which sets phase shift across
the
> >inductance. Q's of 10-12 result in about 130-degree shift,
>
> And I thought the phase shift in an inductor was 90?.
You thought wrong.
Phase shift depends on reactance and circuit impedances. A series inductor
only causes a 90-degree shift when the load impedance is zero and the
inductor is infinite in value.
In a pi-network tank system we have shunt capacitive reactances at each end,
and a series inductance. The ratio of those reactances and the termination
impedance of the network determines the phase shift. It is 90-degrees in a
minimum Q network that matches two impedances, because the network behaves
like a 1/4 wl transmission line with a surge impedance equal to the
geometric mean of the load and source impedances. The same formula that
would apply to a 1/4 wl transmission line applies to the CLC or LCL system.
In a pi, that is behaving like a pi, the network is two back-to-back L's.
This allows us to set phase delay over a wide range when matching two
impedances. There is no difference in talking about phase shift or Q. Either
one can be translated into the other.
This is why some engineers baffle people by speaking about phase shift in
tanks. They are really describing Q.
Thank goodness things work the way they do, and not the way you thought
Rich! We would be in big trouble designing tank circuits and variable phase
shift networks!!
> >http://www.w8ji.com/demonstation.htm
>
> "In a 3000V PA stage, this would be 10,000V peak! It should make sense
> that amplifiers arc from grossly excessive drive power." -- Tom Rauch.
>
> - ... but it doesn't. In a worst case test with a SB-220 (a 3000V
> stage), the max peak V across the Tune-C was 3500V - which is c. 100V
> from flashing over. The idea of overdrive producing triple V does not
> make sense since 3-500Zs are emission limited.
Once again you totally miss a very important point.
The capacitor and other components limit the peak voltage, not the tube
emission. A tank is an energy storage system. Unless something removes
energy at a rate faster than which it is applied, the voltage and currents
will increase.
Even a very small low-emission tube could build up extreme voltages if
nothing is draining off the stored energy faster at a higher rate than
energy it is being added.
> >You'd better insulate appropriately for worse-case conditions, which is
the
> >maximum breakdown voltage of the tank tuning capacitor times at least two
or
> >three or whatever other component limits the peak voltage under a fault
> >condiution.
>
> Kenwood used a 6000V Tune C in the TL-922 and the Tune-C does not protect
> the 5000V bandswitch from arc-over. Kenwood apparently sells a heap of
> 922 bandswitches.
Yes, and the reason is explained in my web site. Your idea that emission
limits voltage is wrong. It is breakdown of some component, causing that
component to consume the excess energy, that eventually limits stored energy
in a tank. Either that or the system reaches equalibrium before a failure
occurs, becuase there is something loading the tank (like an antenna).
This is all explained at:
http://www.w8ji.com/Vacuum_tube_amps.htm
where I walk through the PA system step by step.
73 Tom
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