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Re: [Amps] 120 hz hum

To: "Jim Thomson" <Jim.thom@telus.net>, <amps@contesting.com>
Subject: Re: [Amps] 120 hz hum
From: "Carl" <km1h@jeremy.mv.com>
Date: Tue, 23 Feb 2010 10:14:12 -0500
List-post: <amps@contesting.com">mailto:amps@contesting.com>
----- Original Message ----- 
From: "Jim Thomson" <Jim.thom@telus.net>
To: <amps@contesting.com>
Sent: Tuesday, February 23, 2010 8:13 AM
Subject: [Amps] 120 hz hum


> Uhh....Im not complaining about the LK-500 regulation, simply stating a
> fact.
>
> Now if you want to look at the classic Alphas of the 7 series, Ameritron,
> Ten Tec, Heath, Dentron, Drake, Swan, etc, etc, you will find them in the
> 17-33uF range....duh.
>
> The latest series of some amps have more C as a result of capacitor
> technology, not engineering brilliance.
>
> Going back further to the 1963 NCL-2000 it is 10uF AS PER THE RCA specs 
> for
> the 8122's. Static regulation at 0 to 2000W is 16%. Dynamic is much better
> for SSB.
>
> Carl
>
> ##  well, I guess RCA  got it wrong !


** RCA was more concerned about energy storage than ripple. They even 
specify a 15 Ohm glitch resistor, the value of the screen electrolytic and 
its glitch resistor. Burle hasnt bothered to change the specs either.

When I had to replace the 80uF filters in the 6M NCL-2000 I mounted 330uF 
450V CDE snap ins on some perf board. Static regulation didnt improve that 
much, the xfmr winding R must be rather high.

Carl



>
> ## yes, cap technology has really improved a whole bunch.
>
> ##  A buddy of mine lucked out, and found some spanky new
> 450 V  lytics....   4800 uf   [ four thousand, eight hundred].. EACH.  ESR 
> on them is
> .025 ohms [25 milli-ohms]
>
> ##  Ripple  current rating is 40A  !     I checked both Hammond's and CD's
> engineering notes, and went through all the math's, and sure enough, with 
> a simple
> C input filter, ripple current = 2.56 x DC plate current.
>
> ## Anybody who doubts the virtue of really high C  filters, just try it. 
> The PEP
> output on the wattmeter is WAY up. Ripple is almost zero. I'm 100% 
> convinced IMD
> is down as well.  For folks who play with ESSB, you can actually hear the 
> difference
> between  stock C value... and  2-6 X  stock C value.
>
> ##  step start procedure is much the same.  The step start resistor value 
> has to be
> reduced in value, and  shorted out after a longer time period. This will 
> eliminate the
> sec surge.  Caps  charged up to only 1/2 normal B+.. will only have  1/4 
> of the energy.
> Joules =  uf  X   [B+  squared] .../  2 million.      Caps  charged up to 
> 71% of normal B+
> only have 1/2 the energy.   So you can see, to minimize the sec surge, you 
> want to charge
> the caps up as high as you can.. just prior to shorting out the step start 
> resistor.. which may
> be several seconds.  A lower value R means less V drop across the same 
> step start R, and
> higher B+..prior to shunting the R.
>
> ##  they never can be fully charged with normal step start R... because 
> the magnetizing current
> in the plate xfmr pri.. is always flowing through the step start R. 
> Another method to step start
> is to use a small variac in the pri, and switch it out of the circuit 
> completely, with a small relay.
> This method allows the caps to be charged up to 99%  of normal B+... and 
> no sec surge.[and
> no pri surge either].
>
> later..... Jim  VE7RF
>
>
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