[Amps] Acceptable ripple on high voltage plate power supply...

[Michael Tope]

That is interesting, Jim. Other's have commented that a class AB 
amplifier should have relatively high anode supply hum rejection. That 
doesn't appear to be the case for your L4/L7 since the 3% RMS ripple you 
measure on the anode supply is producing enough ripple in the RF 
envelope to be visible on a monitor scope. I wonder why that is?

73, Mike W4EF..................

On 12/26/2024 11:52 AM, jim.thom jim.thom at telus.net wrote:
> Date: Mon, 23 Dec 2024 09:39:03 -0500
> From: "Bob D." <ajamas.rn at gmail.com>
> To: amps at contesting.com
> Subject: Re: [Amps] Acceptable ripple on high voltage plate power
>          supply...
>
> <Check my math....
>
> <For 10% P-P 120 Hz(full wave 60Hz rectified) voltage ripple at max current.
>
> <Ballpark math.
>
> <That's 7% RMS.
>
> <Power is proportional to square.
> <Ratio of sideband power will be 0.005
> <That's 5W total for two sidebands at a KW.
>
> <2.5W each. -26dB
>
> <MThis is at peak power. S meter reading  ratio is voltage so will be -52dB
> <on meter.
> <If a CWv signal is more than 40dB(on s meter) above noise, an exceptional
> <ear, that is looking for them, might hear the sidebands.
>
> <I could be wrong. I do recall reading 10% as the max in an old handbook.
>
> <The above us all at max current draw from the supply. Ripple percent goes
> <down with current draw. Power  in ripple sidebands goes down with square of
> <ripple percent.
>
>
> <73, -bob ah7i
>
> I take the peak to peak ripple..... then divide it by 2.828  to arrive at
> the RMS ripple voltage.
>
> Then take the RMS value of ripple, and divide it by the loaded B+,  to
> arrive at the  % ripple.
>
> IE: Drake L4PS supply...(which uses a FWD, with 8 x 200 uf lytics).  2500
> vdc loaded with 800 ma cxr.  207 v P-P  ripple. (25 uf total filter C
> used).
> 207 / 2.828 = 73.55 vrms.
>
> 73.55 vrms / 2500 =  .0294
> .0294 x 100 = 2.94% ripple.
>
> To express the ripple in -db,   I used as follows.
> 20 x  (LOG .0294) =  -30.62 db.
>
> I can relate to ripple when expressed in -XX db, much better than %.
> 2.94% ripple (-30.62 db) is plane as day on any RF monitor scope.   It's
> horrid imo.  Wavy lines  at the top and bottom of the scope...instead of a
> straight line solid bar.
>
> I 1st picked up on all this when using my Array solutions power master pep
> wattmeter's.
> The last segment  would...'dither'... but only when > 700 w cxr.... and got
> worse as PO increased up to the max of 1290 watts.   Normally ( at lower PO
> levels), each bar graph segment would light up, and the next segment would
> slowly light up, until  full brilliance, then the process would just keep
> repeating itself.  ( It also displays PO  numerically).
>
> This...'dithering'  of the last segment  drove me nuts.   Then hooked up
> the scope...and sure enough, loads of ripple, plane to see. ( but NO ripple
> at all with just the 200w xcvr).
>
> The fix is easy, ripple is just inversely proportional to filter C value.
>   With 75 uf in there ( 2 x Harbach boards), one at each end, and with 330
> uf lytics...... ripple is now 1/3.
> It's now just 69 V  P-P or  24.4 v rms = .976%  or  -40.21 db.
>
> Problem solved, and no more dithering segments.  IMO, 1% or less ripple is
> optimum for ripple on SSB.  Dynamic regulation is much improved with more
> filter C.   When a doubler is used, the caps are only charged up (topped
> up)  60 x per second..... vs  120 x per second on a FWB.   The theory is,
> with caps in the doubler only being charged up 60 x per second, they now
> have to hold their charge twice as long.... hence they really need to be
> double the  uf value to begin with.
>
> On my HB  B+ supplies, I'm experimenting with a C-L-C filter setup, with a
> spst-NC  HD Kilovac  ceramic vac relay across the 4H, 127 lb, Dahl
> choke....rated for 3 amps  CCS @ 15 kv.  Also a hb adjustable spark gap
> across the choke for safety purposes.  Choke is in series with the B+...and
> totally electrically isolated.   Choke can be shunted...on the fly, to turn
> it into one big C filter.
>
> It works but is gross overkill. ( buddy across town had gotten the dahl
> choke from the now defunct satellite relay station north of me).  With a
> 2.5 amp CCS load + 6800 vdc, ripple is just a mere  33 millivolts P-P   or
> 11.7 mv rms.
>   (11.7 mv rms / 6800 vdc  =  .0000017270)   or .0001727%   or  -115 db
> ripple.
>
> The 1st (C1) filter cap knocks the ripple way down.....and the following LC
> filter section attenuates at the rate of 12 db per octave... starting with
> the  initial corner freq being just 1.75 hz.
>
> That -115 db is just for the 120 hz ripple. The harmonics of the 120 hz
> ripple, like 240/360/480 hz etc,  are attenuated even more.
>
> It was just an experiment, to see if actual measurements jived with the
> power supply software....(it does).
>
> Using the software, I found out that the C2 cap has to be at least the same
> value as the C1 cap.   When C2 is  much lower in value  vs  C1, all hell
> breaks loose, with wild up/down oscillations for the 1st  500 msecs.
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