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

[Steve Thompson]

Tetrode plate current varies much less with plate voltage than with a
triode so ripple is less likely to appear on the RF signal. Knowing what
sort of amp was being referred to might explain the apparent contradiction.

Steve G8GSQ
On 30/12/2024 01:40, Michael Tope wrote:
> 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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