On Oct 29, 2006, at 1:43 AM, pentalab wrote:
--- In ham_amplifiers@..., R L Measures <r@...> wrote:
, and replace the RF chokes with fusing resistors.
RICH SEZ... In my experiences, a suitable glitch-R in the HV+
helps prevent grid- filament shorts.
### agreed... when stuff "goes nuts"... the glitch will LIMIT
current..... precede the glitch with a HV fuse... and that combo
is excellent.
RICH SEZ... What failure does the HV fuse protect against with
thoriated tungsten filament tubes?
### Lemme see. 8kv /50 ohm = 160 A Ur typ 240v pri breaker is
way too slow for my liking... even magnetic hydraulic ones... with
the fastest trip curve u can get. Supplement the pri breaker with
fast fuses might work.
Fast fuses pop like popcorn in C-filter power supplies.
The point here is... when "it" goes
nuts.... I want "it" shut down ASAP... NOW ! You stuff 160 A
through a Buss 5 kv 3 A fuse [5" long sandfilled jobs]... and
they open so fast...good enough for me. Last thing I need.. or
anybody else... is having an arc welder going on inside... waiting
for the pri breaker to maybe open. Pop a HV fuse open in the
B+... and you just took the load off the caps, diodes, and plate
xfmr.
Xfmrs and diodes are adequately protected a plain-vanilla circuit breaker. Capacitors need voltage-protection, not current protection.
A 2nd HV sandfilled fuse between one leg of dahl sec...
and diode board completes the protection.
### what have u got against HV fuses Rich?
Do you carry two spare tires in your car? As I see it, overkill is not good engineering - except perhaps on a moon mission if I going.
Greatest thing
invented since sliced bread.
Come glitch time.. it's always limiting , followed
by HV fuse opening....saves all sorts of destruction...
whether
cuzed by parasitics.. or anything else.
RICH SEZ.. A friend went the Henry booth at a Hamvention and
asked one of the Henry engineers why none of the Henry 3-500Z
amplifiers currently had 160m coverage. The reply: 1.8MHz is
below the 3-500Z's low- frequency cutoff.
### LOL. Joke right ??
RICH SEZ no.
### Other than the 3+8 k ultra... I don't think any of their
amps covered 160m. They probably didn't want to have to
redesign their 3-500Z amps to handle 160m and warc bands.....
for the few additional sales it would generate .. a lot of
fellows don't operate 160m.......
160m is the only game in town for <1000km evening communications when 75m gets long during the Winter months.
OR it could be,they didn't have
the engineering "know how"... OR perhaps they actually believed a
3-500 Z wouldn't operate at such a "low freq"...
Probably all of the above, Jim. Anybody who would use a 1000A-pk mercury contactor on a 1500w amplifier is pretty obviously some kind of schlub.
...
RICH SEZ... One step-start R will not work with amplifiers that
are made for dual 120v/240v operation.
### agreed.... but who in their right mind is gonna run an amp on
120V ?? .... unless it's a single 3-500Z.. or a similar 700w
output ..or less amp.
The Henry 2k-4 has a resonant-choke filter -- perfect for 120v operation with virtually no drop in PEP out.
...
RICH SEZ... I disagree. Inductive loads can produce 25x the
operating potential when current stops.
### What kind of inductive load are u talking about here ??
Even electric heaters have L. An ordinary 12vDC relay's coil can produce 400v when the EM field collapses.
......
RICH SEZ... Most of the grid-filament shorted tubes that I have
high- potted were Eimacs.
### All eimac 3=500Z's have a MU= 130 Knock off's are
all MU=200.
RICH SEZ... Then why do RF Parts 3-500s have the same ZSAC as
Eimacs in a SB-220 or TL-922 while Amperex 3-500s exhibit a lower
ZSAC?
### IF they have the same zsac.... they have the same MU...130
IF they lower zsac... they have a mu of 200. The lower zsac
[higher mu] tubes require less bias to get the idle current
[zsac] dialled in right. Higher mu tubes should require
slightly less drive... since you have less bias to overcome.
Agreed, Jim
Later... Jim VE7RF
...end
R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org
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R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org
