Date: Wed, 23 May 2012 20:05:07 +0930
From: "Leigh Turner" <invertech@frontierisp.net.au>
Subject: Re: [Amps] [ham_amplifiers] Re: Sensible filter Cap sizing
"Leigh Turner" <invertech@...> wrote:
>
>
> Nah Jim; although 60 uF is plenty adequate to achieve more than ample
> regulation and low ripple on the B+ plate supply, a 116 uF reservoir
> capacitance is at the upper limit of what I reckon is sensible, and is
> erring on the side of overkill and pandering to the lunatic fringe and
> purists :-)
### leigh, you still dont get it. Uf and ripple are related to RL load Z.
An amp that requires 3 kv @ 3A will require triple the C of an amp that
requires 3 kv @ 1A.
## My stereo amp uses 40,000 uf...and its an unregulated 65 vdc supply.
>
> With a stiff no-sagging AC mains feed from the building's distribution
> panel, the B+ rail DC voltage will hardly quiver at full rated load.
### Then how come he can see the difference between 56uf and 112 uf.
>
> Increasing the C in these amplifiers to the excessive values you suggest
> will yield no practical benefit in these already well designed amplifiers.
## well obviously rudi didn't quite get it right. Remember his fubar tank
circuit fiasco, burned up torroids, the use of braided flex weave for tank coil
taps, band switchs not strapped correctly etc.
>
> By way of comparison we can note the Ameritron flagship AL1500 amp has only
26 uF or 33 uF (depending on year of manufacture) of B+ filter capacitance.
### "flagship amp" that's laughable. I know loads of folks with AL-1500's.
If you double the filter C on an AL-1500, you can HEAR the difference on essb.
Most will at least triple the C. We found caps that would drop right in, with
same c to c spacing. then the oem eq resistors get tossed.. and replaced with
100 k 3 watt mof types...from rich etc.
## the original AL-1500 was made eons ago...when caps were big. The new
style same value caps they use now are tiny things.. but the layout is the
same.. and there is loads of space for a bigger cap.
## richs 560 uf caps and the larger 600-700 uf caps are a favourite for
retrofitting into any amp. A 200 uf cap is silly at best..and only provides
3-4 % ripple. For table top amps like that, stuff the biggest cap in there that
will fit. No more B+ sag..and you get an extra 100 w pep out every time. The
amp is cleaner too. I can hear that on 75m from a 1000 miles away. Ripple is
down to 1%.
>
> Squeezing an extra hundred watts or so Pout in a large multi-kilowatt output
amplifier due to the hugely increased Joules of stored energy and stiffer B+ are
neither here nor there. It's a case of erroneous Fool's Gold logic.
### Multi kw po amp. Been there, done that. There is nothing I can do to
improve the regulation coming in off the street, none. The best I can do is use
big ga cu wire from main 200A panel to the HV supply..and that's it. The big
caps do the brute force regulation for me. And its not 100w either, its one
helluva lot more than that.
## BTW, there is nothing wrong with using a doubler either. the drake L4B uses
a doubler.. and B+ drops from 2650 vdc on RX... down to 2500 vdc on TX..with
a 800 ma solid cxr. The advantage of a doubler is... you only require one
half
the sec voltage. Now you only require one half the turns on the sec. Which
means
way less paper insulation used between winding layers, since less layers used.
And between the less insulation + half as many turns.... you can now make the
wire ga of the sec a heck of a lot bigger ! The only caveat is... you have
to use double the
C since the caps only get charged up..or topped up... 60 times per
sec..instead of 120, like
in a FWB.
## That’s another reason the AL-1500 etc, benefits from increased C.
Jim
>
> Cheers,
>
> Leigh
> VK5KLT
>
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