[Amps] TL922A and AL80A

[Tom Rauch]

> The TL922 manual says "DO NOT under any circumstance OPERATE your exciter
in
> CW mode when the linear is in the SSB mode. Failure to head this warning
may
> cause immediate, extensive damage to the amplifier""
>
> "REPEAT: DO NOT OPERATE CW IN THE SSB MODE"

The TL922, like the SB220, was designed when the power limit was 1kw CW DC
plate input power.

Power supplies and cooling systems were designed for power level, plus a
safety factor.

> As long as I am asking questions, the AL80A manual says to tune up to 550
mA
> of Ip and then back off to 400.  I think the 3-500Z max Ip is 400 mA.  Is
it
> really OK to drive it at 550 mA?

Sure. Thoriated tungsten tubes are not damaged even when operated at
emission saturation, which is several amperes peak plate current in a
3-500Z. Tuning it slightly beyond the operating current of 400mA sets tank Q
at designed operating values, and also makes sure the amplifier can handle
any exciter transients or overshoot with arcing.

In IVS modes you can reach the peak current with damage to the tube, and
linearity is still good.

All that was approved by Eimac.

> this level?  Is 400 mA the destructive limit or is it the point at which
> tube aging  will accelerate?  Also, in a grounded grid configuration like

Emission demands do not shorten the life of a 3-500Z. The primary cause of
shortened life is sitting idle for long periods (the seals leak and the
elements inside the tube can outgas), and material and manufacturing defects
in the tube. You can see more at:

http://www.w8ji.com/vacuum_tubes_and_vaccum_tube_failures.htm

> the AL80, at what current would linearity be lost?

Linearity is really lost very quickly when the anode is underloaded, by
tuning or "peaking" output at low anode currents and drive power. That is
the worse possible operating error, since even with just a few dozen mA grid
current and a 100mA anode current a 3-500Z can be very non-linear when the
tank is misadjusted and presents a high load impedance to the tube. It also
increases chances of tank circuit component failures quite drastically when
an amplifier is underloaded, or only loaded at the steady output power you
expect to run.

On the other hand the tube is linear up to and beyond 150mA of grid current,
and 600mA of anode current or more, when the tank is adjusted properly.

It is best to follow the manuals.

73 Tom