"Ripple modulation factor" has to do with the inability of a tetrode AB1
amplifier to be plate modulated by changing plate voltage. This goes along
with the fact that changing the plate voltage has very little effect on the
output power of the amp. In other words you can't plate modulate an AB1
amplifier.
73
Gary K4FMX
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of
> Conrad PA5Y
> Sent: Wednesday, May 26, 2021 11:39 AM
> To: jim.thom jim.thom@telus.net; amps@contesting.com
> Subject: Re: [Amps] 300Hz sidebands
>
> Hello Jim, it is a grid driven tetrode in AB1, the G2 supply
> is shunt stabilised and from a separate single-phase
> transformer. I can assure you that the drive level and
> therefore the anode current does not vary the relative
> amplitude of the 300Hz sidebands. This surprised me as well,
> but it is -50dBc.
>
> I would also like to understand the additional ripple reduction.
>
> Regards
>
> Conrad PA5Y
>
> -----Original Message-----
> From: Amps <amps-bounces@contesting.com> On Behalf Of
> jim.thom jim.thom@telus.net
> Sent: 26 May 2021 16:25
> To: amps@contesting.com
> Subject: [Amps] 300Hz sidebands
>
> Date: Sun, 23 May 2021 20:51:52 +0200 (CEST)
> From: "sm0aom@telia.com" <sm0aom@telia.com>
> To: g0ruz@g0ruz.com, amps@contesting.com
> Subject: Re: [Amps] 300Hz sidebands
>
>
> On the schematic a choke, Dr 401, is shown between the
> six-pulse bridge and the filter capacitor.
> It is bridged by an overvoltage protector.
>
> As you do not generate the screen voltage from the plate
> supply, modulation from the screen supply can be ruled out.
>
> Left is the 3-phase supply itself.
>
> Made a "back of the envelope" calculation of the ripple
> reduction that a 5 H choke and a 8?F capacitor is capable of;
> which in the order of 40 dB or 1:100.
>
> Add this to the inherent ripple modulation factor of about -
> 30 dB in an
> AB1 amplifier and you should end up in - 70 dBc or so, The
> Collins gear I worked on during the 90s usually showed a
> total 300 Hz ripple modulation of -70 to -75 dB down at full
> power (10 kW).
>
> 73/
> Karl-Arne
> SM0AOM
>
> ## whoa. With little or no load on the B+ supply, the
> 300 hz ripple
> should be through the floor. Typ 3 phase B+ supplies ( on
> 60 hz) and NO filter, choke, nor cap at all, are typ 5.2%
> ripple ( 360 hz ripple in this case of using 60 hz incoming
> mains). The bigger the load, the ripple gets worse, normal.
>
> ## what do you mean by... the inherent ripple modulation factor of
> -30db in an AB1 amplifier ?? Are you talking about a grid driven,
> class AB1 amp, or also a garden variety GG, cathode
> driven Triode ??
> This is a new one for me. Where is this extra 30 db of ripple
> reduction coming from ????
>
> ## On my oem Drake L4PS supplies, with oem 8 x 200 uf caps, the
> ripple is 207 V peak to peak, = 2.8%... = -31db ripple
> redux. Thats
> what I get on the RF scope. Plane as day with a 1290 watt
> dead cxr on the scope. I since tripled the uf in the drake
> supplies....to 75 uf....and ripple is down to 1%, 69 V
> peak to peak = -40 db.
>
> Jim VE7RF
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