[Amps] The power of an oversized electrolytic capacitor / howmuch PS filter C is enough?

[Gary Schafer]

> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]
> On Behalf Of Leigh Turner
 
> A large energy storage capacitance on the HV rail makes sense from the
> point
> of view the amplifier load current requirements have a large peak-to-
> average
> ratio in SSB service. A stiff B+ voltage also helps with minimising IMD.

I have seen this bandied about but I have never seen any figures on how much
power supply ripple really affects IMD. It would seem to me that the better
the linearity the amp has the less any plate voltage variations will have on
IMD. I would guess that with the typical amplifier that 10% ripple would
cause immeasurable IMD contribution.

> 
> The tolerable ripple level superimposed on the HV plate supply above
> which
> incidental AM hum sidebands appear on the radiated signal is an
> interesting
> question; the anecdotal experience of Rich's friend with only 2 uF of
> filter
> capacitance suggests there's a large tolerance to ripple on the plate
> supply
> with the tube and tank circuit exhibiting a good PSRR.
> 
> We can note the amplifier in question here uses a 4-1000 tetrode, and
> that
> such tubes exhibit a plate current virtually independent of plate
> voltage,
> i.e. tetrodes are a constant current device. Such a characteristic would
> make it more immune to ripple and noise on the B+ plate supply.
> 
> Leigh
> VK5KLT

A tetrode operated in grounded grid operates as a triode as there is no
interaction between grid and screen.

If the amplifier is operated in class C then any variation (ripple) in plate
voltage would directly modulate the signal. But when operated as a linear
amplifier there is much less chance of mixing to take place which is
necessary to create side bands.

73
Gary  K4FMX