Date: Thu, 15 Apr 2010 10:49:43 -0400
From: "Carl" <km1h@jeremy.mv.com>
Subject: Re: [Amps] HV lytic max V ratings..some notes
> ## any 1.5 kw CCS out amp with 50-60% eff... will require a bare min
> of 3000-3500 va ccs xfmr. You can buy the alpha 3.5 kva CCS xfmr,
> as used in all their recent amps, including the 91/99/87A..from their
> site.
** I wasnt talking about those later amps. I stay far away from
microprocessor crap.
## The ameritrons will do 1.5 kw out, so will qro/command/
palstar/Emtron. they all have 3.5 kva xfmr's in em.
> I can understand 330-560uF
> which still may place a strenuous starting load on stock amps.
> ## install step start....pretty simple.
** More junk to buy, find room for, and eventually blow unless its
overbuilt. The Harbach stuff is marginal in a SB-220. Amp Supply uses step
start in most models.
## The fix for..'not enough room for step start' is to install it outboard.
I use 2 x standard 8" square x 4" tall metal electrical box's. One DPST
P+B relay with 30A contacts applies the 240vac. 2nd Relay is a SPST
P+B 30A relay. Resistor is a 20 ohm-100-150W Arcol, metal finned unit,
bolted directly to box. 240 is hardwired to input of box. Power cable from anp
is hardwired to box as well. One small control cable comes from 8' x 8" box
on floor... up to a tiny mini box on desk.. with 2 x miniature toggles. One
toggle
turns on 1st relay... then wait a few seconds... then hit the 2nd toggle..turns
on
2nd relay. IE: manual step start. Do the reverse sequence when shutting down
for the night. Then no back emf from xfmr, etc.
## this will also step start the fil xfmr at the same time. Then you can also
do cool
stuff, like drop the resistor back into the circuit.. then toggle from CW to
SSB hi-B+
position.. then shunt the step start R out.
## It's either that.. or fry on/off switch's.. and also cw/ssb switchs.
Without
the step start, the peak current is an easy 160-190A through the on/off switch..
albeit for only a split second.
>
** My backup MLA2500 has 330uF Snap Ins. More than enough, run cold and dont
have to be outboard in a plywood box. 8873/74/75's have at least 10-15dB
better IMD than any Class AB rice box, they dont need any more.
## Then get a Class A ricebox. When toggling between Class A.. and AB
the difference is just un-real..esp when listening off freq.. with a 2nd
RX..aprx
4' away. S-9 crud drops to zero.
** Some tubes cant take all that stored energy from your overkill caps
without something better than a glitch resistor. We dont all run YC-156,
3CX3000A7, 3CX6000A7, 4CX10000A, and bigger like your crowd do.
## better imd, far better bang for the buck, rebuildable in most cases. You
can buy any of the above tubes for a lot less, than what it cost to re-tube
a 87-A.
** RCA specifies right on the 8122 spec sheet that above 2200V no more than
10uF output C be used. Thats what the NCL-2000 used with 8X 80uF. My 6M
version now runs 41.25uF ( 8X 330uF) with no damage yet. But the glitch
resistor has gone from the stock 15 Ohms (Yes a glitch resistor in 1963,
long before Measures and Rauch invented it) to 50 Ohms which doesnt help the
regulation. Ive retrofitted a few customer NCL's with 8X 220uF and 25 Ohm
glitch.
## what's the problem with the 8122's and small tetrodes ? Is it arcing from
anode to screen ?? What else can the anode arc to ?? How come the guys
with the big terodes never have a problem, if the anode arcs to the screen ?
They never damage the screen supply either.
## I use 50 ohm, heavy duty glitch R on everything. I also precede it with a
fast,
hv fuse too. Plus a 2nd HV fuse between sec of plate xfmr.. and FWB. And also
a fast mag hydraulic breaker in the 240 line. ..'instant trip'.
IF B+ arcs to anything... HV fuse opens up <2 msecs.
later... Jim VE7RF
Carl
KM1H
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