--- In ham_amplifiers@..., "ad4hk2004" <ad4hk2004@...>
wrote:
- busily changing out 20K ohm, 100 watt, resistors in a Henry 3K
Ultra PS.... Man a bad PS load resistor can sure contaminate
everything when it decides to go open winding and arcs, sputtering
crap onto other components...
It took a bit of sleuthing to find the correct resistors for
replacing... Turns out Newark has em in Ohmite brand...
### I looked at the 8k/3 k ultra manual I have [same manual does
both amps]. On the 8k they use 5 x 20k-100w resistors. Diss is
a whopping 300 W CCS..... presumably so the resonant choke filter
will work. On the 8 k.. they used a 6000 V xfmr. .9 x 6000 =
5400 vdc no load.
### here's the kicker. IF just one bleeder opens up... the OCV
plate V shoots UP to a whopping 6000 x 1.414 = 8484 V !!!
Now the poor 3CX-3000A7 [rated for 5 kv] won't like it.... nor
anything else in the amp. You are lucking you didn't blow up ur
3k ultra.
### I gave up on choke input HV supplies yrs ago. The
resonant choke idea although a good one... is not so simple to
implement.
## My feeling is one is better off to use a C input filter. The
8 k ultra's plate xfmr is flaky at best. They could have used just a
3800 vac xfmr..... which would require LESS turns on the sec
winding.... which in turn would mean the xfmr coulda used bigger
ga wire in the 1st place.
### Dahl does a roaring business selling a 127 lb 10 kva
replacement xfmr + mating choke for the 8 k ultra. Stock, the
8k is only good for 2 kw out CCS rtty/ 3.5 kw pep cw/ssb....
then in real fine print on the schematic it sez..."200 w in... 5kw+
out".
### IMO... why put a ton of weight.. in the form of a choke in a
HV .... better to put the added weight into the plate xfmr in the
1st place... but that's just my opinion.
### I had some 3 k owners e-mail me a while back.... they were in
the 10m contest [where both cw/ssb modes are used the entire
weekend]. The poor fellow had forgotten to change the plate V
from High... to low... when switching from ssb... to cw. The
HV supply bit the dust shortly afterwards. [smoked plate xfmr]
## Henry has gone through so many plate xfmr manufacturer's, I have
lost count. The last supplier for the 3k/8k was ECA. And just
b4 Henry went "outa business"... they dumped ECA as a plate
xfmr supplier !
## I know several fellows who bought the Henry 16 uf - 7.5 kv
rated oil caps.... used em in 4-1000 amps.... and blew up the caps !
With the proliferation of the newer low esr lytics out there
[loads of em on the surplus market].. for a new hb project, they
can't be beat. The latest bunch I got are 50 miliohm and 10 A
CCS ripple current rating.... small things too.... 2500 uf @ 450
vdc... and just 2" diam x 4" long.
## It just seems nuts to me to suck 300 W ccs of bleeder...
then another 150 ma @ 5200 Vdc on idle [8k] on top of that.
### The 8k drops from 5400 vdc to 4700 vdc with a typ load. It
weighs a whopping 350 lbs too ! Since the alpha 87-A will
do 1.5 kw CCS... and the 8k will do just 2 kw CCS... I'd say
Henry just lost it... in the weight dept.
### BTW... a Dahl 10 KVA CCS xfmr weighs.. "just 127 lbs"
Later......Jim VE7RF
denny / k8do
