[Amps] AL-80B questions

[Tom Rauch]

> As long as I have your attention.  Eimac suggests using a glitch
> resistor in the b+ line, in your opinion do you think I should
> install one.  I don't think the AL80A that I have (SN 0156) has one,
> but I may be wrong, just did not see one there.  Should I put one in
> or leave it alone?

The capacitors have about .5 ohms or more each ESR, so that is about 4 ohms
or more. The choke has 2+ ohms, and the rest of the circuit wiring adds
another ohm or so. You'd need to add at least 10 ohms to make a worthwhile
or noticeable reduction in surge, and even then the change would be
questionable for improving reliability.

The most I've ever seen blown with a fault is the diode that clamps the PS
negative rail.

Historically, Ameritron never used limiting resistors unless the tube had a
somewhat common tendency to flash. You will see all sorts of stuff in the
572B amplifier like MOV's, HV surge-rated resistors, and electrolytic
dampers. Mostly so the amplifier runs even after many hard faults, and the
exciter is protected from tube fault damage. Sometimes 572B's flash from
anode to filament, and it will surge the exciter or ruin the tuned input
capacitors if in the transmit mode! In this case the value of protection vs.
cost is worth adding the extra parts.

You should find a spot on later 80B power supply boards that include pads
for the surge-rated resistors if you want to install them. Ameritron has 10
ohm 10w 175P resistors, they are pulse rated and so won't explode and arc
across during a fault.

I use fault resistors in all my personal amps with large oil-filled
capacitors or supplies over 3-4kV, but generally don't bother with small
supplies using multiple reasonable sized electrolytics.

You can see an example of a big amp scrolling down at:

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

That style amp has 33-ohms of fault limiting, but runs at 8kV. Of course it
has air flow monitoring and other protections like a triac power line dump
during HV faults, and a three strike timer since it is for ISM commercial
applications. I guess the bottom line is if the aggravation and cost exceeds
the benefits or not.

73 Tom