--- In ham_amplifiers@..., "craxd" <craxd1@...> wrote:
See below,
Jim,
My guess for the reason Henry used a choke input power supply was
that the transformer can be smaller than one for a capacitor input
by a good bit. Most transformer manufacturers give for a choke
input, the rms current is 1.2 x DC current, and for a cap input it
is 1.65 (Hammond only) to 2 X, with most saying 1.8 X.
### I'm assuming you are refering to PRI AC current ?? Dahl
sez for his hypersil C cores... take the DC INPUT power and
multiply by 1.21 to calculate PRI KVA power. [21%]. 11% of
that comes from a power factor of .9 and the other 10% comes
from cores losses. So what's he's telling me is that the ratio
of KVA input power to DC watts is 1.21
### When I measure these old Hammond's [80 lb units designed for
choke input supplies, IE: high reactance types] when used in a C
input filter set up... I typ get pri KVA is always 1.35 x
higher than DC input watts [load of the amp] .
### BTW... all these old hammond xfmr's used a 2 x choke setup....
all of em. The 1st choke was I think, a hammond fixed choke...
followed by 2 x oil caps.... followed by a hammond swinging
choke... followed by another 2 x oil caps.
### These 80 lb Hammonds were typ 3450-0-3450... and had a 0-110-
115-120 V primary. They were all rated at 2.2 KVA . DC wise....
they were rated for 3000 Vdc @ 500 Ma CCS.... and 750 ma
ICAS. Sec DC resistance, end to end was typ 135 ohms.
### One of em... in C input filter... would run hot as hell...
running a single 4-1000 @ 1900 w pep output. Two of em would
work [then u could run em on 240v} Total weight 160 lbs. Two
of em would again run scorching hot.. with a 2 x 4-1000 amp.
### Their biggest drawback is the 3450-0-3450 sec... and the 120
v primary. The turns ratio is a whopping 6900/120= 57.5 !!
The difference is the rms voltage of the choke input transformer
has to be higher than that of a cap input to match the same DC
voltage. A resonant choke has to resonante at the peak current draw,
so the cap and chokes (Lcrit) critical value has to match that
figure. The only problem, there's no resonance at idle current. You
still get the filtering of the choke, it's just not resonant to
where the ac portion would be killed down like it is at the peak
current. So, Lcit has to be selected at the peak current. See a
copy below from a conversation between Peter G3RZP and I from the
Amps archives.
On transformer regulation, the voltage sag I've found on most all
transformers in better built amps runs about 12% to 14% (I always
figure 13%). I've never seen the 10% value listed in most books.
Heathkit had worse regulation than this in a few models starting
at
15%, and one at 30% if I recall. I've never heard of 9% regulation
anywhere. I guess you could reach that, but you'd have to have a
wheelborrow full of caps, and a lot bigger transformer than need
be.
### And big wire to the main panel.. and big contactor's etc.
A lot of this V sag is coming from the HUGE peak current every
8.3 msec x dc resistance of all the wiring, contactor's ,
breaker's,lugs, etc. All that stuff has to be oversized.... or
bye bye V regulation.... never mind the plate xfmr/caps.
You have to watch at sizing transformers by weight as that always
don't hold true since it has to do with the design of the core. If
you have a core with a larger window, one with a smaller, and both
with the same weight, the smaller would have more core area and
thus be capable of more watts out. This holds true especially in C-
cores. I always did wish Bill Orr would have never said something
about using weight for transformers in his book.
### agreed. I wish Orr would have NEVER mentioned the
nonsense about.. "IVS ratings".... Intermittent Voice
Service !!! which was based upon unrealistic low duty cycle
figures of 25 % [ it's 50% average on any plate current meter].
They also factored in.. I talk... then listen for 15 mins....
during a 5 x way roundatable. They also FORGOT the idling
current from the tube[s] ... which throws all the cals out the
window !
### Don't laugh. TEN TEC still brags about their 7 kw IVS
rating of the xfmr in their Centurion 2 x 3-500Z amp. They
rate the xfmr at 3.5 KVA CCS. The amp is one of these "almost
legal limit" jobs by the factory/QST. It will NOT do 1.5 kw
output RTTY. It's designed to do 1.2 kw output PEP on ssb...
that's it.... just like a stock SB-220.
The problem with a bunch of capacitance is when something shorts,
there's a lot of joules of power released at once which can
destroy more stuff than need be.
### Easy fix.... install a 50 ohm glitch R. For a 7900 V
supply with 135 uf filter cap.... and running up to 3 A of
plate current... we used a pair of 100 ohm 225 W CCS wirewound
resistor's in parallel. These are cheap... right outa the
mouser/digikey catalog. The glitch R assy.... is PRECEDED by
a Buss 3 A HV fuse [HVU Sandfilled type]
### I can short the +7900 to chassis.. or anything else.... just a
'minor' flash from the sandfilled fuse. Nothing gets blown up.
We tried it 12 times so far in this latest project.
A ripple factor of 10% or less is all one really needs. If one
sticks with the published formulas by the transformer
manufacturers, you can't really go wrong as they did the
tests to come up with them.
### 10% ripple would sound like crap over the air ! Both Orr
and ARRL always have quoted 5% max ripple for cw... and 3%
for SSB. Those are still the bare minimum's. A L4B is 3%..
at max load.... so is A SB-220 TL-922. Heck, back then the
biggest lytic was only 200 uf @ 450 V.
### You want to shoot for 1 to 1.5% ripple in a C input HV
supply.... then you can also be assured of good dynamic reg.
Quote from Amps;
. I've never used a swinging choke in
a
tuned choke system, though.
### It would NEVER work. You want the choke and resonating cap
to resonate a BIT above 2 F... or aprx 125 hz. You will never
see a swinging choke in a resonant choke set up. John Lyles sez
they actually ship the resonating caps to the choke builder... who
designs/builds the choke around the caps.
. If you get the wrong resonant condition, you
can get enormous voltages built up too, so this is not an
exercise for the guy who isn't experienced in working on HV
circuits. Tom, W8JI, has a frightening story about that, which
you'll find somehwere in the Amps>
### W8JI scrwed up.... and thought for max ripple reduction...
you resonate the entire mess at 120 hz ! If you do that... peak
voltages will soar, and the biggest flash over you will ever
see. The trick was to resonate it slightly above 120 hz...
around 125-128 hz. I read the story. All he had to do was
slightly DECREASE the cap value... the 2nd time around. There was
no 2nd time around.
## You will notice in the 8K/3K manual... they use 3 x resonating
caps in parallel with the choke... when power is 50 hz. When
on 60 hz... one cap is removed... and only two are used.
later Jim VE7RF