Date: Tue, 23 Feb 2010 20:42:44 -0800
From: "Bill, W6WRT" <dezrat1242@yahoo.com>
Subject: Re: [Amps] 120 hz hum
ORIGINAL MESSAGE:
Carl said...
>
>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.
REPLY:
Maybe, maybe not.
Have you considered that with poor regulation, the amp is more likely
to "flat-top", and especially so when tuned up with a pulser and then
used on voice? We don't really know what the engineers were thinking,
except that they now think that the older values were too low.
73, Bill W6WRT
## IF the pulser uses the same duty cycle as Voice, it shouldn't be
an issue. Back in the 60's and 70's.. the biggest 450 vdc lytic you could buy
was these silly 200 uf things. The biggest thing my local emporium could get
was 200 uf @ 500 vdc. What do you think heath was gonna do... install
2 x strings of 8 x caps, to get 50 uf ? Won't fit, and cab would have to be
really
big. 25 uf = aprx 3% ripple with 2500 vdc under load of 800ma. It works...
just.
## 25 uf @ 3200 vdc = 128 joules. Now with the SB-220 running
2 kw DC INPUT on voice peaks, there is no way in hell, that caps with
just 128 joules [128 watt seconds] is going to provide enough energy
for the few msecs at the top of each syllable. They deplete asap, and b+
sags, pep out is down, and I'm 100% convinced, IMD suffers. With a
'typ' 35% duty cycle on SSB, what's really needed, is 2000 x .35=
700 joules.... = 136 uf.
## a 1500w amp @ 60% eff , requires 1500/.6 = 2500 w dc input
...875 joules = 170 uf.
## 90 % of SS and tube stereo amps over the last 40 years are simple,
high C filters.... and very few used regulated supplies. In 1991, 40,000 uf
was common. These days, it's 100-400 K uf.
later... Jim VE7RF
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