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

[Michael Tope]

Yeah, Steve, the L4/L7 is a grounded-grid zero-bias triode (2x 3-500Z). 
The constant current curves for the 3-500Z have significant downward 
slope to them. I looked at constant curves for the 4CX800A (aka GU74B) 
and the 4-400A tetrodes and both have relatively flat constant current 
curves.

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


On 12/30/2024 9:32 AM, Steve Thompson via Amps wrote:
> 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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