--- In ham_amplifiers@..., R L Measures <r@...> wrote:
The point here is.... by oversizing the HV fuse.... the load is
then transfered to the 100 A breaker in the 240 v main 200 A
panel.... which of course didn't blow open...... instead the
glitch R's fried themselves... !
You need well over 100 A to open a 100 A panel breaker.
RICH SEZ... Which is why I used a 40A thermal-magnetic breaker for
the 8170 amp.
#### Which will be on the ragged edge of opening... since we
already determined you are sucking 110 A on keydown cxr. Would
be kind of nice to run a dead cxr..for at least 3-7 seconds.. just
to take steady state plate/grid current readings. You can't do
that with a 40 A breaker. With a 2 x pole [50 A per pole]
breaker.. with it's poles wired in parallel.. and tie bar removed...
and 2 x such assys' used... one per hot leg... u can then have all
4 poles activated for dead cxr stuff... and kick one pole off
per breaker... for ragged edge ssb operation. IE: toggle from
a 100 A breaker... down to a 50 A breaker.
BTW... that Dahl A-540 hypersil C core 253 lb plate xfmr I
have... has a .01 ohm primary.
RICH SEZ...How did you measure this?
### with a B+K 875-B... also used a HP DVM [very expensive
box... just back from the cal lab, reads some extra zero's] The
Fluke 87 will only read to 1/10ths of an ohm. Also, low
resistance readings can be even more accurately done using mho's/
siemens. .01 ohm = 100 mho's. .001 ohm = 1000 mho's .0001
ohm = 10,000 mho's. I have gear that will read higher than
10,000 mho's. In all cases... the sec was shorted, when
taking pri readings... and vice versa.. when taking sec readings.
RICH SEZ... Thus, my guess is that the short-circuit current
would be c. 470A-rms. The secondary current under a short would
be 470A / 21.6 = 21.7A-rms.
Jim: Why would a HV fuse in the secondary be better than a
250V fuse in the primary?
### Cuz a 3 A sandfilled fuse.. with 8 kv/50 ohm glitch = 160
A of fault current. 160A of fault current has a tendency to
blow a HV sand fuse in < 2 msecs. Fast 100 A fuses in the
primary would work... but with 470 A... would not open as fast.
Only 1 x HV fuse needed..... VS TWO x 100 A high speed fuses
in 240 v primary.
.... LOADS... as my buddy with the same 253 lb xfmr
just found out. 253 lb xfmr with a core good for 20 KVA
CCS with a 100 A slo breaker... vs lowly glitch R [wound with
nichrome wire no less] .... no contest.... glitch loses every
time........ unless a correct sized HV fuse is used !
RICH SEZ.... When a correct size HV fuse is used and a short is
applied, does the glitch R survive?
### sure. Doesn't even put a dent on the Glitch R. You can
crowbar the thing all day long.
#### We did find out where the HV arc was happening.... was
between OUTPUT of parasitic suppressor globar clip.. and the 20-
17-15m 1/2" tubing tank coil... bad arc. When driven... the
anode V rises to almost double [restored tank sine wave back
feeds through plate block caps to anode.. adds to the existing dc
HV.] Fix was to rotate the coil on it's axis a bit.
## Last time... the arcing was caused by LOOSE strap from C1
vac tune cap to 20-17-15 m tank coil. STRAP had flopped over a
bit.... and arc occured between parasitic suppressor coil and
this loose strap. Of course in both cases.. ALL the tank
components are at chassis grnd... including tune/load
caps/bandswitch/ both tank coils, etc.... due to the HB 45 uh 18
ga solenoid wound safety choke... wired between chassis and hot
side of vac LOAD cap. [45 uh choke wound on 1" diam solid Teflon
rod... bullet proof... also identical to the 45 uh RF choke used in
the 2 x piece plate choke set up 135/180 uh + 45 uh]
### This safety RF choke HAS to be rugged... no place for your
ARRL hand book 2.5 mh 30 ohm 36 ga.... pi wound assy. Those
things will blow into a million pieces when you try and stuff 160
A through em. They also have more than a tendency to blow up..
with NO HV fuse.... and also with no glitch R.... well... use ur
imagination... 8 kv / 1.4 ohms ESR from modern day lytics + plate
choke = 5700 A Actually.. it's not that bad... since the DC
resistance of any floozy RF safety choke will limit current...
then the choke explodes. A 45 uh 18 ga safety choke is
compact... and a snap to make. Drill + tap a 1/4-20 thread into
the base... and it's easy to mount. 2 x Transverse brass threads
terminate the 18 ga magnet wire.
Later... Jim VE7RF
later... Jim VE7RF
R L Measures, AG6K, 805.386.3734
r@..., rlm@..., www.somis.org
