[AMPS] Logic v. Magic

[Tom Rauch]

> >Did I say suppressors? I said most of your mods are basically 
> >harmless, but some of your suggested mods are harmful and can 
> >ruin tubes.
> >
> the dodge

No, cars have nothing to do with it.

The biggest goof-up is recommending people fuse grids with 
resistors, and remove electronic protection. Bad idea.

> >>
> >>I'm disappointed to see anyone tell others a 
> >>short absorbs energy.
> >>
> >Ä  It doesn't.  It slows the flywheel
> >
> >I had no idea a short reduced the output 
> >frequency of a PA. I don't think that is correct.
> >
> agreed
> thanks.  
> delete "slows " - replace with "reduces amplitude of ".
 
That's still not true. When the load is removed, even by shorting the 
output port, voltages in the tank can increase.

A typical tank, with the output shorted, reflects a high impedance 
at the anode. That allows the tube to slip into a low-conduction 
angle mode... conducting anode current in bursts. This allows tank 
overshoot, and tank voltages increase until something extracts 
power from the tank or the tube/power supply combo quits adding 
energy to the tank.

That can create a big bang, a burned bandswitch, or a melted air 
variable on the tube side of the tank. If you open the load, the 
loading cap can fail and things on that side of the tank arc.

Of course line length between the amp and the open or short 
affects the type of failure, as well as tank component values do.

The mode of failure depends on phase-shift through the tank and 
the type and value of components.

Open or shorted loads, or underloading of the tank, is the single 
largest cause of tank component failures. 

   

73, Tom W8JI
w8ji@contesting.com

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