> Just FYI, A Drake L4 amplifier tank circuit and related
> parts will handle
> 2KW OUTPUT. One of our members here has on several
> occasions converted an L4
> to using an 8877 with a new outboard supply of course, but
> the tank circuit
> stuff held up to all that extra power. Pretty good!
People look at this the wrong way. When we look at a
collection of components and think they have a power limit
we often misjudge it.
There are two limits to a tank circuit, current (heat) and
voltage (arcs). Voltage failures are arc-distance and shape
problems. They cause instantaneous failure like an arced
capacitor or arc-burned switch contact. This is the most
common failure mode.
Current limits are a function of duty cycle, airflow, how
hot the part can get, and how much I squared R loss is in
the component. Mostly RTTY or very heavy duty cycle CW ops
notice this limit.
When we keep the same HV and only increase power 30%, we
increase current 30%. It's like increasing dissipation in
components 70%.
When we increase HV, it can be an instant disaster at any
power level or duty cycle. No so with increasing current.
Another thing is the bandswitch. The Radio Switch
Corporation bandswitch that looks so good in pictures has
close spacing in contacts and the contacts are somewhat
pointed. It has about the same voltage breakdown as a
JV-9000 series switch. The thing that saves that switch, or
any switch, is using it with a higher current lower voltage
tube. All the problems come in when the operating voltage is
3500 or 4000 volts, not when the voltage is 2500 or 3000
volts. There are a few cases where contacts overheat but
they generally are when the plate impedance of the tube is
high, air variables are used, and the tube has considerable
output capacitance. Get an amp like that on 15 or 10 meters
and the circulating currents through contacts can be
terrible. With a long duty cycle the contacts can get so hot
they soften and warp.
The amount of high voltage has a lot more to do with
problems than anything else.
73 Tom
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