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

[Leigh Turner]

Yes indeed Dave; linearity will be lost if the B+ plate supply varies due to
excess ripple superimposed on the DC. The degree of that loss depends on
whether the tube is operating in Class C, AB2, AB1, etc, i.e. the inherent
degree of nonlinearity in the tube that produces the requite mixing to
create incidental AM sidebands containing the 120 Hz hum modulation on the
amplifier's output signal.

Yes 3-phase HV power supplies are very nice; hence their universal use in
broadcast transmitters and some high-end ham amplifiers.

73

Leigh
VK5KLT 

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Dr. David Kirkby
Sent: Friday, 11 May 2012 6:50 AM
To: amps at contesting.com
Subject: Re: [Amps] The power of an oversized electrolytic capacitor / how
much PS filter C is enough?

On 05/10/12 12:19 PM, Leigh Turner wrote:

> 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


More immune than what?

Whilst the input current will be fairly independent of voltage, the input
power, and hence output power will change if the HT supply varies. That
leads to a loss of linearity.


If you have the ability, then using a 3 phase transformer could be
considered. 
Even without capacitors, the ripple is quite small, since unlike a single
phase supply, the input voltage is never zero.

I do have a 3 phase supply to my house, but it's not tempting to build an
amp with it, as it restricts severely where you can use it.


Dave
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