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--- In ham_amplifiers@..., R L Measures <r@...> wrote:

...

RICH SEZ.... A 20kV rated C to block 7000V DC sounds like

over-

engineering since the actual AC potential across the blocker

is

minimal.

####### The AC potential across the cap has nothing to do with
it.

#### Rich... Jenning's engineers tell me when using either

fixed

glass/ceramic vac cap as a PLATE Blocker.... MIN V rating of

the

FIXED vac cap has to be a MINIMUM of 3 X No load plate

V......

other wise u get "whisker's" growing on the OFC plates on the
cap..... which will REDUCE the caps V rating.

RICH SEZ... So why does the statement I quoted in the Jennings

catalog on p.4 about DC operation state otherwise?

#### Dunno. Eimac sez the same thing, de -rate vac caps to
1/3 for plate block use !

RICH SEZ.... I did not read this in any Eimac literature,

#### You don't have friends at Eimac... like me.




RICH SEZ...and it does not make good sense

### sure it does. Apply continuous DC HV to a vac cap.,. and
eventually... DCV rating.. due to whisker growth...
DROPS...hence size the caps DC HV rating at least 3 x the plate
supply's unloaded v to start with. That's what Jenning's sez...
that's what Eimac sez... that's what 11m ops say... or else it's
flash kablamo time ..... end of story.






RICH SEZ...since the prima facie consideration for a DC blocker is
the current rating at 29MHz - since at 10m, the DC blocker
typically carries c. 90% of the tank's RF circulating current.

#### "prima facie consideration" ? Are you OJ's lawyer too ?

### yes... 10m and above is the worst case scenario for a plate
block cap.... that's what I have been saying all along.

The 11m ops also highly agree. The
11m ops tell me if they try and use a 16 kv test rated fixed vac
cap with 10.5 kv dc on it..... it will eventually arc.

RICH SEZ... Probably true since Jennings advises that 60% of the DC

test V is the max WV when using DC + RF.

### what ? Jenning's sez the max AC RF working V is 60%
of the DC test V. They are asuming and also implying you have
employed a plate block cap already. What they are refering too is
using a vac cap as a C1/C2 tune/load cap... or using a vac cap to
pad a tune/load cap. In any event... the AC voltage across a
plate block cap is so low... u can ignore it.... UNLESS you insist
on using really small value plate block caps... then you end up
with high AC voltages across em.... as in plate current X Xc
of plate block cap.

### for 10.5 kv dc no load... you want at least a 25-30 kv test v
rated fixed vac cap.

...

RICH SEZ... I do, Jim. Even 500pF is plenty for a DC blocker at

1.8MHz (XC = 190- ohms) in typical amplifiers since RL is in the
kilo-ohmS range.

#### No way. 500pf = 176 ohms of XC.

RICH SEZ.... The rule of thumb is a 5 to one ratio for a coupling

reactance. 176- ohms of XC and a RL of 176-ohms x 5 = 880-ohms or
higher RL should be okay.

### No way. Where did u cook up this 5 to one ratio ??? Not
in any of my engineering books. Any big metal tube operating
with a 880 ohm plate load Z... is gonna be sucking loads of plate
current. 4-5 A typ. 5 A x 176 ohms XC = 880 vac You just
lost it right there!

#### 100 pf = 884 ohms XC [1.8 mhz] gimme a break !

RICH SEZ... With a pair of 3-500Zs, RL is c. 2k, so 884-ohms would

probably work okay if the Tune-C could tune it out.

#### Now it gets even worse ! 5 A x 884 ohms = 4400 vac dropped
across the plate block cap........ not to mention the 45-63A of RF
flowing through it ..on 10m ! [using a 100 pf plate block cap +
big metal tubes]

### Stick a single 100 pf HT-50/58 cap in any 1500W amp....
run it at 1500 W RTTY/FM on 1.8 mhz for say 20 mins.... and
let us know what happens.

RICH SEZ... > no

#### It would vaporize.... that's why.

### a 100 pf plate block doorknob cap wouldn't last 30 seconds

in a 3x3

RICH SEZ... Why would the capacitor dissipate heat?

#### lemme see. With say 2.5 A of plate current at 5 kv under
load... and on 29 mhz... current through the 100 pf plate block
cap = 32 A. A HT-57 100 pf cap is only rated at 13.7 A @
30 mhz [with 13.7 A, the 100 pf cap's temp is 55-65 deg C...149
deg F..... and well over 100+ deg C.. with 32 A flowing through
it] Use multiple metal tubes on 10m or bigger single metal
tubes with lots of anode to chassis C..... look out.

### with 32 A through a cap rated for 13.7 A = meltdown. [5.5 x
more heat. 32/13.7= 2.34 2.34 squared = 5.5 more trbl] Don't
gimme this nonsense about pulse tuning and SSB being a 15% duty
cycle. The correct component here is 6 x 500 pf HT-57's... or
3-4 x 200pf HT-57's. I use 6 x 500 pf HT-57's.... then it
will have low XC on 160m too.

Later... Jim VE7RF

...
R L Measures, AG6K, 805.386.3734
r@..., rlm@..., www.somis.org

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

RICH SEZ... I did the calculations for the 8170 amplifier with

Ohm's Law. The calc. peak mains current was c. 300A. The
measured result was 1200v- pk into 50-ohms on SSB.

### 1200 V pk equates to 14,396 watts pep output into a 50 ohm
load....14,395.65 /.63 = 22,850 w dc input. Primary VA = 22,850
x 1.22 = 27,877 va 27,877 /240v = 116.155 A .... not
including fil xfmr, blower etc. Peak current is aprx 375A
with big wire and a big C filter... every 8.3 msecs.

### Rich... tell us how you take a steady state plate and grid
current meter readings..... with out blowing ur under rated 40 A
house breaker ???? IE: a dead cxr... for just 3-6
seconds... just long enough to measure grid/plate current + fil V,
loaded plate V, etc. Forget the fil v/ plate v...... focus on
just the plate + grid current.

### If u just pulse tune it...and talk...fine... I do too. Unless
both ur plate/grid meter's are peak reading types.... I can't see
how it's done.

### IMO.. the entire system should be configured to at least
handle a 4-7 second dead cxr.... without blowing breakers,
melting coax, frying tank coils etc.

### For a 8170/8171.... I'd use a 100A breaker... and a bare min
of 2 ga wire... and considering the 300-400A peak current draw
every 8.3 msec..... 3 x 000 CU is the real ticket.... regardless
of length.

### BTW... what's the CCS rating of the SB-220's plate
xfmr ??? I heard it was 1200 va. Now Rich has stated it's only
600Va. I'm sure the smaller SB-200 is 600 va CCS.

### Will a SB-220 stock... in good condition, on low plate
V...be capable of delivering 600W CCS RTTY ??? If so...
the plate xfmr would have to be a 1200 va unit.

Later... Jim VE7RF

#### 3/000 CU from main 200A panel to HV supply is what's
really needed. Snip a few strands to make it fit the 100 A
breaker at EACH end.

later... Jim VE7RF

R L Measures, AG6K, 805.386.3734
r@..., rlm@..., www.somis.org

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

On Nov 19, 2006, at 7:32 AM, pentalab wrote:

--- In ham_amplifiers@..., Tony King - W4ZT <w4zt-
060920@> wrote:

Which MOV's do you use and where do you get them?

### From Mouser... Digi key has em as well... aprx 2" tall x
1/2" thick x 2.75" wide base. Those are the 130 v units.
The closest ones for the 240 V service are 250 V rated. IMO..
250 V rated Mov's are cutting it too close.

RICH SEZ...Perhaps it might be a good idea to read the specs on

the 250v-rated MOV's, Jim.

### I did. And the 250 v rating is for a 250 V max rms CCS
condition. Depending on who makes a MOV.... clamp V is always
way higher than that.... which is why old books always said to use
twice the PIV needed for a FWB. These days it's triple the PIV
needed [at least for commercial recifier assys].

### MOV's are just a series of "grains" inside. The series
grains will start to short out with successive hits from
transients, spikes, surges, etc. The actual V rating of the MOV
will slowly start to go down. That's why 130V rated MOV's
are normally used. A 250 v rated Mov is cutting it too fine
for folks whose line V can reach 247-250 V. A few too many
hits on the MOV.. and it's continuous V rating will drop to the
point where it will conduct.... and short out. UNLESS it's
fused.... it's gonna burn up... or explode. Way too many house
fires caused by MOV's as is.

### Check out Joslyn's website in the USA. They are the number
one maker of commercial MOV assemblies for use in commercial /
industrial environments. You won't see any 250 v rated MOV's
used on any 240 V circuits. Their's come in several
configs.... like 130/135 v MOV's from each hot leg to neutral....
and or... 275 V rated Movs across the 240 V line.... or 225 V
rated Mov's from hot to neutral on a 208 3 phase setup.
Their's are all fused as well as alarmed. The latest versions
all have "event counter's" in em.. with time date stamps, etc.
Some of the ones we use at work are 4" square and 1"
thick...each... amd fused... and alarmed.

### Dahl sells MOV's. Why do you think his large bolt down
ones are ALL 275 v rated ....and not 250 V rated ???

### Rich... you just love to cut corner's and engineer stuff
right to the peg... with zero leeway. Rauch does the same. The
whole beauty of HB stuff is one can build it right the 1st
time.... with no corners cut... and loads of headroom.

Later.... Jim VE7RF

R L Measures, AG6K, 805.386.3734
r@..., rlm@..., www.somis.org

The boards are okay I guess but there is nothing special about the
current trips. All they do is sense a voltage drop across a resistor
with higher current and trigger an opto-couplers LED with it. This is
turn will open a circuit by a relay or transistor circuit.

Another thing I seen in one board is that they sample a little of the
screen or bias voltage and put that into a regulator to get the
control voltage for a relay, etc. That was done to keep from having
another coil on the transformer for low voltage. However, you need
one anyhow for the antenna relay, and others.

I design my own as to me any of the boards I've seen are a little
over-kill and over complicated for my taste. The more components
placed in any circuit raises the likelyhood of failure in the future
expotentially. I can make just as good of a regulator circuit with a
few transistors and zener diodes. This for either a series pass or
shunt regulator.

Best,

Will



--- In ham_amplifiers@..., "pentalab" <jim.thomson@...>
wrote:

--- In ham_amplifiers@..., Tony King - W4ZT <w4zt-
060920@> wrote:

Jim,

Don't you think that if a properly designed fault detection

circuit similar to the triode and tetrode boards available today
would have caused a primary circuit shut down saving the glitch
resistors from becoming a smoking pile?

### Partially agreed. Seems to me the 2 x triode boards
available, are based on using an external 24 vdc DPST RELAY...
whose contact's are in the 240 v primary. I don't see any

24

vdc RELAY's... with contacts rated for 100-400A. AC contactor's
on the other hand are all either DPST-DM or TPST-DM.... the

"DM"

means 'double make'.... IE: essentially each pole is two sets

of

contacts in series.... with an input lug... output lug... and a
huge bar on top that comes crashing down on the input/output.

### The DM arrangement is used [vs a dpst relay] simply cuz a
DM will break the arc into two arcs = essentially zero arc....
[when trying to break a full bore load from a xfmr/motor]

### I never see giant bolt down MOV's across the in/out poles
of any contactor's in commercial service.... but I always install
the big bolt down MOV's across all the poles of my own
contactor's in HV supplies anyway. The MOV's.. if used, should
be fused... in case they short out.... with a 120 v neon between
output side of fuse and neutral... to indicate a blown MOV fuse.

### I suppose one could modify the triode board output
easily.... and use the 24 vdc control circuitry, to
activate/deactivate the INPUT of a opto isolator..... the OUTPUT
side of the opto of course, could then be used to
activate/deactivate a..'normal' 120/240 vac solenoid coil of a
contactor. All that would be needed is an opto with a 24 vdc
input, that u sink or source... and a AC output... rated to

handle

the typ contactor solenoid coil. Most opto's have back emf
protection built into the output side.... still I'd use a mov
across the AC contactor's solenoid coil.

This isn't to minimize the value of a good fuse but to add that a
properly functioning circuit can fault the HV supply off so that

all you have to heat the glitch resistor is the stored energy in
the capacitor bank. This is precisely what G3/GM3SEK and WD7S do
with their boards. That way if you are testing and have one of
those "modified" fuses in the circuit, it will still not melt
anything down.

### agreed. Stored energy from the caps is pretty wicked with
100-300 uf and a 50 ohm glitch R.[and 7900 vdc no load].. IE:

3100-

9300 JOULES Everything else is just .."follow on energy".. from
the plate xfmr/FWB.

### I have seen pix of John Lyles stuff... where they used both
an electronic crowbar on the hv B+ to B- [used since pulse
rated service like YC-156's..rated for 67 A of plate current
means too much V drop across a typ glitch R... hence no glitch R
used in any pulse service amp].... and also electronic fault
detection circuits where by primary AC is removed. Also seen
pix of his HV diode boards.. used in 3 - phase HV pwr supplies...
which resemble charcoal.... when the crowbar failed.... and the
fault detection also failed... or was not fast enough.

### seems to me the 2 x triode boards wouldn't handle 3-4 A of
normal anode current... but might be modified ?

### I just wanted to keep it simple. Any electronic protection
would have to be in addition to properly sized HV fuses and
primary breakers.

### We use these electronic current sense devices at work
for huge HVAC motor loads,compressor's,chiller's, etc.[70 to 120+
kw normal operating load] It was explained to me, they are

used

since the start up current is wicked on this stuff... as in 3-7
x normal running current. So, instead of a breaker... it's a
current sense activated contactor. One of em crapped out
last spring.... causing a huge fire in our main 'motor control
center'... destroying a panel 8' wide x 7' tall. Incinerated
every wire in all 45 x conduits too.. a real mess. Turns out the
motor's were ancient. New motor's all have over temp shut
downs built into em. New [adjustable] current sensors have
redundant copies.. and fail safe modes.

### How do you know that every function on those triodes boards
is gonna function when you need it ? You need some kind of

"fail

safe" on em so if they lose pwr... everything shuts off.... or
perhaps two of em.... with say the outputs driving the
relay/conatctor... are in series... so if either one failed... it
would still shut off the AC primary, etc.

### A fast, CORRECTLY sized HV fuse will work every time.
Heck, you could even put 2 x identical HV fuses in series if
you wanted. As a side note, I have seen where fellow's are

using

2 x 5 kv [5 kv AC...7kv dc] rated Buss sand filled fuses in
series.... in lieu of a single 10 kv [10 kv AC...14 kv dc] 10"

long

HV fuse.... simply cuz they had a ton of 5 kv fuses... and had 10
kv dc HV supplies [for a 3 x 20]

### The 2 x triode boards are a good idea .. as long as any one
or more functions on em don't crap out. IF you had say a

GM3SEK

triode board installed on every amp you owned.... I'd have

one

extra spare board put away... for a 'fast' replacement..if
needed. Then fix the bad board at your leisure.

Later... Jim VE7RF

73, Tony W4ZT

pentalab wrote:

Gents

My buddy was recycling his old sand filled fuses... by

soldering

a single strand of 26 ga wire across the 5" long fuse.

Fine

so far.

Amp was running fine the other night... the next day... BOTH

HV

fuses were blown open..... and amp was off from the previous
night !

A real mystery. He then decided to solder TWO 26 ga wires
across each of the old HV fuses. Next step was adding a

small

resistor to one hot leg of 250 cfm fan.. to slow it down a

bit.

[cools the glitch..... which diss 450 w with a dead cxr...

100

w

on ssb]

At that point all hell breaks loose. The paralleled 100 ohm

225

watt wire wound glitch R's looked like u hit both of em with

a

propane torch for 30 mins each.... charcoal !! We know a

HV

to chassis fault occured... may have been a faulty RFC bypass

cap.

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.

Over sizing a HV fuse is bad enough.... and you guys want

to

operate with NO hv fuse at all ?? nuts.

BTW... that Dahl A-540 hypersil C core 253 lb plate xfmr I
have... has a .01 ohm primary.... and a 6.06 ohm sec [5200 v
tap] You got any idea how much current you can suck from

one of

these things ..... 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 !

later... Jim VE7RF





Yahoo! Groups Links

It sounds to me that Jennings wants things two different ways. First
they say don't momentarily test a vacuum cap with DC, but it's okay
to put one in service as a DC blocking cap, de-rated or not. From
everything I've ever read, the whisker problem is caused over time,
not in one minute of use. A DC blocker cap could be in an amp for a
lifetime. That's a good sales gimmick to sell hipots though. I've
never seen that warning either by Comet, or by any of the Russian
manufactured caps. If the cause is over the copper being too soft
used for the plate cups, it ought to be changed to a hard copper or
an alloy to stop it. I can see soft copper for the bellows, but not
the plate cups.

Thank God Rich and I didn't question the Jennings engineers on the
other list as we would have been sent another e-mail by the unknown
admin chastizing us for ever questioning these professionals with
published papers, etc....


Best,

Will



--- In ham_amplifiers@..., R L Measures <r@...> wrote:

On Nov 19, 2006, at 2:59 AM, pentalab wrote:

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

...
RICH SEZ.... A 20kV rated C to block 7000V DC sounds like over-

engineering since the actual AC potential across the blocker is
minimal.

#### Rich... Jenning's engineers tell me when using either fixed
glass/ceramic vac cap as a PLATE Blocker.... MIN V rating of the
FIXED vac cap has to be a MINIMUM of 3 X No load plate V......
other wise u get "whisker's" growing on the OFC plates on the
cap..... which will REDUCE the caps V rating.

So why does the statement I quoted in the Jennings catalog on p.4
about DC operation state otherwise?

### Ur gonna get "whisker's" anyway in plate block service for
a fixed vac cap.... so the 20 kv cap... will actually be over
time... a lot lower than 20 kv. IF u Hi-pot test a fixed vac cap
that has been used for plate block service.... u will see it no
longer hi pot tests to 20+ kv any more.

### other than 11m ops... I never see fixed vac caps used as plate
blockers.

I do, Jim. Even 500pF is plenty for a DC blocker at 1.8MHz (XC =

190-

ohms) in typical amplifiers since RL is in the kilo-ohms range.

11m ops don't need much C for 11m... 100-250 pf max
is what they typ use. Their requirements are for a plate block cap
that handles LOTS of RF... esp for 4x20's, etc.

Tom Rauch apparently knows a Ham who mistakenly used a 100pF DC
blocker in a homebrew amplifier. The amplifier produced the

expected

output from 1.8 to 28 MHz. Sometime later, when a friend was

being

shown the amplifier, he noticed that there were only twp zeros

after

the 1 on the blocker cap. When a 1000pF cap was substituted for

the

100pF cap, the output did not increase although the tuning changed
slightly on the 1.8MHz band.
...
R L Measures, AG6K, 805.386.3734
r@..., rlm@..., www.somis.org

pentalab wrote:

--- In ham_amplifiers@..., Tony King - W4ZT <w4zt- 060920@...> wrote:

Which MOV's do you use and where do you get them?

### From Mouser... Digi key has em as well... aprx 2" tall x 1/2" thick x 2.75" wide base. Those are the 130 v units. The closest
ones for the 240 V service are 250 V rated. IMO.. 250 V rated
Mov's are cutting it too close.. since my line V has been as high
as 247.2 V in summertime. Instead I use the 275 v rated Mov's
from Dahl.... made by "movistar".... almost same dimensions.

Thanks, wasn't sure which "big" ones you used.

### ACROSS poles of contactor's, you want 250-275 V rated Movs...
and not 130 v ones. IF you use fuses in each leg of the 240 v.... and just one opens... there is 240 v across the open fuse. Same deal with a contactor's poles.

Agreed.

## I install the 130 v rated Mov's between each hot leg and grnd.... right at the plate xfmr primary.... and 2 x 275 v rated mov's, in parallel, directly across the plate xfmr primary.
### You can get MOV's from mouser/digi key up to 1 kv. You can also series / parallel em too. Some will use 6 x series 1 kv mov's across the SEC of a 5200 v plate xfmr. Some commercial diode FWB's.. whether single/3 phase... will use a MOV across each diode..... and no cap/resistor. Most commercial bridges will use 3 x PIV for total number of diodes.

You do all you can and something can still fail but we've gone

from jumpering a fuse with copper wire to worrying about the protection circuit failing.
## yeah, I know. I'd trust a proper size fuse 1st... b4 any protection circuits. Both of em together is the real answer.

We are in agreement! I believe in the protection circuits too... there's
more to discuss about these things... see below.

### seems to me the 2 x triode boards wouldn't handle 3-4 A

of

normal anode current... but might be modified ?

Look at Paul's board... you can set it up with any external shunt

for

detecting a fault. Use the board to control any kind of contactor

you have.
#### I cringe when I see a full bore normal load being opened off
by a relay/contactor. Trying to open off an even bigger load during a fault condition is even more demanding.

True... but if the fuse doesn't open... or if it does, and the fault
doesn't clear, it's best to take the HV supply off line. The control of
the contactors will be slower than the fuse and should not see the huge
load as it opens... that may be a matter of timing.

### Watch the relay/contactor... when opening it off... while sucking 100+ A key down ! Imagine this again.... but with 2-4 x more current during a fault condition. Then toss in a high value C filter for fun. Peak current on the 240 V line every 8.3 msecs is 4-6 x normal operating current as is... never mind a fault condition.

yup... see above.

### I just wanted to keep it simple. Any electronic protection would have to be in addition to properly sized HV fuses and primary breakers.

And if your friend had used a correctly sized fuse, it wouldn't

have been an issue.

Simple is good (KISS) but not best when expensive tubes are at risk.

#### Correct. Which was the whole point of the title in the post. They also ran out of 750 Ma fast grid fuses one night.. and stuffed in some 3 A fuses ! If they had lost HV.... the grid current would peg when driven [normal]. The 750 ma grid fuse woulda blown asap... and input swr rises to infinity... and IPA/Xcvr shut down. With a 3 A grid fuse, they woulda damaged the grid.
### frying a pair of 225 w glitch R's is one thing... frying an expensive tube is another...esp when it's totally unwarranted.

And that is the point of using the triode control board. Note that it
will fault the amp off line, breaking the key line, if you exceed a
preset your grid cutoff current. There is lots to be said for not
transmitting into the amp with no HV on it.

Well, this thread started with your description of a failure caused
by your friend using copper wire instead of a real fuse. There is no device you can install that can second guess someone that is going to drop a copper bar in as a fuse. Everything we do is done with the expectation that the original circuitry will be used as
designed. Once part of it is defeated, then all bets are off! ;)

### agreed. I have no control over my buddy's amp. I can just make a suggestion...that's it. I think once they blow stuff up from oversizing.. that they probably won't do it again. A few spare correct size fuses is cheap insurance. If a fuse blows..... don't put in a bigger one... find the reason it blew !
Later... Jim VE7RF

So true... and even if the electronic protections are there, if one chooses to defeat them they will not help.

Thanks Jim, Tony W4ZT

On Nov 19, 2006, at 6:49 AM, pentalab wrote:

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

On Nov 19, 2006, at 2:59 AM, pentalab wrote:

--- In ham_amplifiers@..., R L Measures <r@...>

wrote:

...
RICH SEZ.... A 20kV rated C to block 7000V DC sounds like over-

engineering since the actual AC potential across the blocker is
minimal.

#### Rich... Jenning's engineers tell me when using either fixed
glass/ceramic vac cap as a PLATE Blocker.... MIN V rating of the
FIXED vac cap has to be a MINIMUM of 3 X No load plate V......
other wise u get "whisker's" growing on the OFC plates on the
cap..... which will REDUCE the caps V rating.

RICH SEZ... So why does the statement I quoted in the Jennings

catalog on p.4 about DC operation state otherwise?

#### Dunno. Eimac sez the same thing, de -rate vac caps to
1/3 for plate block use !

I did not read this in any Eimac literature, and it does not make good sense since the prima facie consideration for a DC blocker is the current rating at 29MHz - since at 10m, the DC blocker typically carries c. 90% of the tank's RF circulating current.

The 11m ops also highly agree. The
11m ops tell me if they try and use a 16 kv test rated fixed vac
cap with 10.5 kv dc on it..... it will eventually arc.

Probably true since Jennings advises that 60% of the DC test V is the max WV when using DC + RF.

...

RICH SEZ... I do, Jim. Even 500pF is plenty for a DC blocker at

1.8MHz (XC = 190- ohms) in typical amplifiers since RL is in the
kilo-ohmS range.

#### No way. 500pf = 176 ohms of XC.

The rule of thumb is a 5 to one ratio for a coupling reactance. 176- ohms of XC and a RL of 176-ohms x 5 = 880-ohms or higher RL should be okay

IF the fixed VAC cap
can handle the RF current at 1.8 mhz.and plate load Z of tube is
HIGH.. and it doesn't screw up the tuning too much... it might
work. Big metal tube amps have plate load Z's of 900-1300 ohms.

At 7500v with 1500v on the screen, an 8171 has a RL of c. 1000-ohms.

...

RICH SEZ... Tom Rauch apparently knows a Ham who mistakenly used a

100pF DC blocker in a homebrew amplifier. The amplifier produced
the expected output from 1.8 to 28 MHz. Sometime later, when a
friend was being shown the amplifier, he noticed that there were
only twp zeros after the 1 on the blocker cap. When a 1000pF cap
was substituted for the 100pF cap, the output did not increase
although the tuning changed slightly on the 1.8MHz band.

#### yeah, I heard the same story.. plus another one...except it
was 150 pf.....and in both stories,it was a ceramic doorknob
cap... NOT a fixed vac cap. I wonder if anyone ACTUALLY measured
it with a LCR meter ?? I have measured doorknob caps that had
measured values out by a factor of 10...compared to the stamped
rating on the cap. So unless Rauch's buddy actually measured
it, we don't know what it was !

Smells kinda like bacon.

#### 100 pf = 884 ohms XC [1.8 mhz] gimme a break !

With a pair of 3-500Zs, RL is c. 2k, so 884-ohms would probably work okay if the Tune-C could tune it out.

### Stick a single 100 pf HT-50/58 cap in any 1500W amp....
run it at 1500 W RTTY/FM on 1.8 mhz for say 20 mins.... and
let us know what happens.

no

### A 3x6 has a 1100 ohm plate load Z.. when run full bore.
You don't wanna use a 100 pf cap.... including a vac cap.

### The plate block cap has to be able to handle the RF current..
without cooking.. so u gotta look at it's CCS rating... vs freq.
Ceramic caps don't handle much RF at 1.8 mhz... then again.. they
don't have that much RF through em on 160m. On 10m, the RF
through em is wicked...

Amen, Jim

esp with metal tubes.. with lotsa stray
anode to chassis C..... or even worse in schemes that use NO C1
cap.. and rely on tube C.

### with big metal tubes... plate load Z is always LOW. You
need plenty of plate block C... simply so u don't screw up the
tuning on 160m..... and also so you have a high enough current
rating on 10m.

### a 100 pf doorknob cap wouldn't last 30 seconds in a 3x3

Why would the capacitor dissipate heat?
...
R L Measures, AG6K, 805.386.3734
r@..., rlm@..., www.somis.org

On Nov 19, 2006, at 7:32 AM, pentalab wrote:

--- In ham_amplifiers@..., Tony King - W4ZT <w4zt-
060920@...> wrote:

Which MOV's do you use and where do you get them?

### From Mouser... Digi key has em as well... aprx 2" tall x
1/2" thick x 2.75" wide base. Those are the 130 v units.
The closest ones for the 240 V service are 250 V rated. IMO..
250 V rated Mov's are cutting it too close.

Perhaps it might be a good idea to read the specs on the 250v-rated MOV's, Jim.

R L Measures, AG6K, 805.386.3734
r@..., rlm@..., www.somis.org

On Nov 19, 2006, at 7:47 AM, pentalab wrote:

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

On Nov 19, 2006, at 5:08 AM, Peter Voelpel wrote:

Since I prefer single capacitors as a blocker,

RICH SEZ...Single cap DC blockers have the advantage of Not

exhibiting a VHF- resonance between two or more paralleled
capacitors.

### which never happens.... IF you parallel em with WIDE AL/CU
plates on both sides. 8 x 200 pf HT-57's exhibits no
problems at all.... ditto with 6 x 500 pf HT-57's. ....or 4 x
500 pf HT-59's.

Are you saying that there is no resonance when two caps are paralleled?, or are you saying that in the amplifiers you built you have never had a problem with such a resonance? I know of a case where two caps were paralleled for the DC blocker where the VHF resonance caused a problem, which is why I brought the subject up.

### I looked at the big Draloric's, and the UK eq. For SOME
layouts... they seemed awkward to mount... cuz of the large
diam. I think the 10 kv - 60A 2000 pf ones I was looking at a
while back were 5" diam. In my case, the HT57/59's were
easily obtainable... and the 57's come in 10/15 kv... the 59's
come in 15/20/25 kv. The 50/58's come in 5/7.5 kv.

HEC makes some reasonable sized 25A or so units.

### Dunno how much safety factor one wants in a plate block
cap.... I'd like 50% min. Use what ever is available.
Dralorics here, surplus and also used... are NOT cheap.

I think I paid c. $120 each for some 25A-rated HEC's.

Later... Jim VE7RF

R L Measures, AG6K, 805.386.3734
r@..., rlm@..., www.somis.org

We had a 37 KVA unit here to support 6 houses. one hot?night when it?popped? they hung a 50 KVA

pentalab wrote:

Bob,

Who is asking for any retractions?

I didn't say to wire anything a certain way, just pointed out the
constraints I face and the considerations given when we wire up
something under the NEC code here.

I know you're lying: Ha, ha! I've seen your QTH.

You've got knob and tube wiring with knife switches and bare aluminum
#16 AWG on ceramic nailed-in insulators on the studs.

(I'm just pulling your leg, here, Bob. Your house will probably not
burn down from octopuses.)

In Kentucky I installed an Appleton plug for the gen set on the side
of the house (200 A) and ran a battery charging outlet with a twist-
loc right above it. However, inside, it's a different story. No ATC,
just two different breakers. I didn't want the gen set kicking in
when I wasn't home: Lemme decide on my own.

As for the shack, I run 60 foot 10/3 SOOW cords on four different
circuits from the sub panel, right through the laundry room and
around the office to the bench. All the grounds and grounding goes
through a wall-mounted MGB that has a 4/0 green stranded going right
out to the SAGB and everything is bonded.

I'm afraid to tear into the walls. I don't know what I'll find.

The gen set's wired similarly: The 4X2 AWG is an SOOW cord, but the
frame is directly bonded to the EGR with a dedicated rod right off
the porch.

We already have an old washing tub on the porch, and a 10 cent Coke
machine from the year Gimel, so the gen set fits right in with the
Tobacco Road decor. Hey, it's Eastern Kentucky.

The main antenna disconnect switch is from a friend's house in Elmira
where he yanked the K&T wiring when he renovated. Ceramic, brass, 5/8
blades: a beauty from 1900.

See ya!

Hal

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

On Nov 19, 2006, at 5:08 AM, Peter Voelpel wrote:

Since I prefer single capacitors as a blocker,

RICH SEZ...Single cap DC blockers have the advantage of Not

exhibiting a VHF- resonance between two or more paralleled
capacitors.

### which never happens.... IF you parallel em with WIDE AL/CU
plates on both sides. 8 x 200 pf HT-57's exhibits no
problems at all.... ditto with 6 x 500 pf HT-57's. ....or 4 x
500 pf HT-59's.

### I looked at the big Draloric's, and the UK eq. For SOME
layouts... they seemed awkward to mount... cuz of the large
diam. I think the 10 kv - 60A 2000 pf ones I was looking at a
while back were 5" diam. In my case, the HT57/59's were
easily obtainable... and the 57's come in 10/15 kv... the 59's
come in 15/20/25 kv. The 50/58's come in 5/7.5 kv.

### Dunno how much safety factor one wants in a plate block
cap.... I'd like 50% min. Use what ever is available.
Dralorics here, surplus and also used... are NOT cheap.

Later... Jim VE7RF

--- In ham_amplifiers@..., Tony King - W4ZT <w4zt-
060920@...> wrote:

Which MOV's do you use and where do you get them?

### From Mouser... Digi key has em as well... aprx 2" tall x
1/2" thick x 2.75" wide base. Those are the 130 v units.
The closest ones for the 240 V service are 250 V rated. IMO..
250 V rated Mov's are cutting it too close.. since my line V has
been as high as 247.2 V in summertime. Instead I use the 275 v
rated Mov's from Dahl.... made by "movistar".... almost same
dimensions.

### ACROSS poles of contactor's, you want 250-275 V rated
Movs... and not 130 v ones. IF you use fuses in each leg of
the 240 v.... and just one opens... there is 240 v across the open
fuse. Same deal with a contactor's poles.

## I install the 130 v rated Mov's between each hot leg and
grnd.... right at the plate xfmr primary.... and 2 x 275 v rated
mov's, in parallel, directly across the plate xfmr primary.

### You can get MOV's from mouser/digi key up to 1 kv. You can
also series / parallel em too. Some will use 6 x series 1 kv
mov's across the SEC of a 5200 v plate xfmr. Some commercial
diode FWB's.. whether single/3 phase... will use a MOV across
each diode..... and no cap/resistor. Most commercial bridges
will use 3 x PIV for total number of diodes.

You do all you can and something can still fail but we've gone

from jumpering a fuse with copper wire to worrying about the
protection circuit failing.

## yeah, I know. I'd trust a proper size fuse 1st... b4 any
protection circuits. Both of em together is the real answer.

### seems to me the 2 x triode boards wouldn't handle 3-4 A

of

normal anode current... but might be modified ?

Look at Paul's board... you can set it up with any external shunt

for

detecting a fault. Use the board to control any kind of contactor

you have.

#### I cringe when I see a full bore normal load being opened
off by a relay/contactor. Trying to open off an even bigger load
during a fault condition is even more demanding.

### Watch the relay/contactor... when opening it off... while
sucking 100+ A key down ! Imagine this again.... but with
2-4 x more current during a fault condition. Then toss in a
high value C filter for fun. Peak current on the 240 V line
every 8.3 msecs is 4-6 x normal operating current as is... never
mind a fault condition.

### I just wanted to keep it simple. Any electronic protection
would have to be in addition to properly sized HV fuses and
primary breakers.

And if your friend had used a correctly sized fuse, it wouldn't

have been an issue.

#### Correct. Which was the whole point of the title in the
post. They also ran out of 750 Ma fast grid fuses one night.. and
stuffed in some 3 A fuses ! If they had lost HV.... the grid
current would peg when driven [normal]. The 750 ma grid
fuse woulda blown asap... and input swr rises to infinity...
and IPA/Xcvr shut down. With a 3 A grid fuse, they
woulda damaged the grid.

### frying a pair of 225 w glitch R's is one thing... frying an
expensive tube is another...esp when it's totally unwarranted.

Well, this thread started with your description of a failure

caused by

your friend using copper wire instead of a real fuse. There is no

device

you can install that can second guess someone that is going to

drop a

copper bar in as a fuse. Everything we do is done with the

expectation

that the original circuitry will be used as designed. Once part of

it is

defeated, then all bets are off! ;)

### agreed. I have no control over my buddy's amp. I can just
make a suggestion...that's it. I think once they blow stuff
up from oversizing.. that they probably won't do it again. A
few spare correct size fuses is cheap insurance. If a fuse
blows..... don't put in a bigger one... find the reason it blew !

Later... Jim VE7RF

73, Tony W4ZT

On Nov 19, 2006, at 5:08 AM, Peter Voelpel wrote:

Since I prefer single capacitors as a blocker,

Single cap DC blockers have the advantage of Not exhibiting a VHF- resonance between two or more paralleled capacitors.

I always use Draloric or Rosenthal caps, they are available at all kind of
capacities and voltages.
The are also very nice caps from Russia on the market with high values of
kvar.
Sometimes I also use mica caps by Jahre which are small and powerful, those
are harder to obtain

73
Peter

________________________________

From: ham_amplifiers@... [mailto:ham_amplifiers@...]
On Behalf Of pentalab

### Me, I just use normal HEC HT-57's.... and HT-59's. I also
have looked at Draloric's and similar HEC block caps... these
ones look like aprx 2000 pf @ 10 kv, 60 A CCS @ 32 mhz....
and are aprx 3-5" diam.
...

R L Measures, AG6K, 805.386.3734
r@..., rlm@..., www.somis.org

On Nov 19, 2006, at 5:13 AM, pentalab wrote:

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

### Why don't u take some of that 4 wire home depot 8 awg...

and parallel em into 2 pairs.... eq ga is then 5ga.

RICH SEZ...And throw away the extant 4ga. wire?

#### The above was a joke. IMO ur 100' length [200' loop] of
4 ga wire is WAY too small for a 4x10.

Jim -- Do you design your amplifiers for A0 or for SSB?

4 ga wire isn't
even rated to handle 110 A.....never mind the 4-6 x that
current.... every 8.3 msecs. Calculate the PEAK current drawn
from the plate xfmr pri on a huge C input HV supply... and you
will see why I use big everything, including wire, contactor's,
etc.... from 200 A main panel to pri of 253 lb Dahl plate
xfmr.

Wouldn't a 900-pounder be better?

Duncan's pwr supply modeler.. PSUD-2 comes in handy for
this stuff. It also has 2 x methods of calculating plate xfmr
pri IMPEDANCE. Z is used to calculate peak pri current drawn...
not simply plate xfmr pri dc resistance.

I did the calculations for the 8170 amplifier with Ohm's Law. The calc. peak mains current was c. 300A. The measured result was 1200v- pk into 50-ohms on SSB.

#### 3/000 CU from main 200A panel to HV supply is what's
really needed. Snip a few strands to make it fit the 100 A
breaker at EACH end.

later... Jim VE7RF

R L Measures, AG6K, 805.386.3734
r@..., rlm@..., www.somis.org

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

On Nov 19, 2006, at 2:59 AM, pentalab wrote:

--- In ham_amplifiers@..., R L Measures <r@...>

wrote:

...
RICH SEZ.... A 20kV rated C to block 7000V DC sounds like over-

engineering since the actual AC potential across the blocker is
minimal.

#### Rich... Jenning's engineers tell me when using either fixed
glass/ceramic vac cap as a PLATE Blocker.... MIN V rating of the
FIXED vac cap has to be a MINIMUM of 3 X No load plate V......
other wise u get "whisker's" growing on the OFC plates on the
cap..... which will REDUCE the caps V rating.

RICH SEZ... So why does the statement I quoted in the Jennings

catalog on p.4 about DC operation state otherwise?

#### Dunno. Eimac sez the same thing, de -rate vac caps to
1/3 for plate block use ! The 11m ops also highly agree. The
11m ops tell me if they try and use a 16 kv test rated fixed vac
cap with 10.5 kv dc on it..... it will eventually arc.

### other than 11m ops... I never see fixed vac caps used as

plate

blockers.

RICH SEZ... I do, Jim. Even 500pF is plenty for a DC blocker at

1.8MHz (XC = 190- ohms) in typical amplifiers since RL is in the
kilo-ohmS range.

#### No way. 500pf = 176 ohms of XC. IF the fixed VAC cap
can handle the RF current at 1.8 mhz.and plate load Z of tube is
HIGH.. and it doesn't screw up the tuning too much... it might
work. Big metal tube amps have plate load Z's of 900-1300 ohms.

11m ops don't need much C for 11m... 100-250 pf max
is what they typ use. Their requirements are for a plate block

cap

that handles LOTS of RF... esp for 4x20's, etc.

RICH SEZ... Tom Rauch apparently knows a Ham who mistakenly used a

100pF DC blocker in a homebrew amplifier. The amplifier produced
the expected output from 1.8 to 28 MHz. Sometime later, when a
friend was being shown the amplifier, he noticed that there were
only twp zeros after the 1 on the blocker cap. When a 1000pF cap
was substituted for the 100pF cap, the output did not increase
although the tuning changed slightly on the 1.8MHz band.

#### yeah, I heard the same story.. plus another one...except it
was 150 pf.....and in both stories,it was a ceramic doorknob
cap... NOT a fixed vac cap. I wonder if anyone ACTUALLY measured
it with a LCR meter ?? I have measured doorknob caps that had
measured values out by a factor of 10... compared to the stamped
rating on the cap. So unless Rauch's buddy actually measured
it, we don't know what it was !


#### 100 pf = 884 ohms XC [1.8 mhz] gimme a break !

### Stick a single 100 pf HT-50/58 cap in any 1500W amp....
run it at 1500 W RTTY/FM on 1.8 mhz for say 20 mins.... and
let us know what happens.





### A 3x6 has a 1100 ohm plate load Z.. when run full bore.
You don't wanna use a 100 pf cap.... including a vac cap.



### The plate block cap has to be able to handle the RF current..
without cooking.. so u gotta look at it's CCS rating... vs freq.
Ceramic caps don't handle much RF at 1.8 mhz... then again.. they
don't have that much RF through em on 160m. On 10m, the RF
through em is wicked...esp with metal tubes.. with lotsa stray
anode to chassis C..... or even worse in schemes that use NO C1
cap.. and rely on tube C.

### with big metal tubes... plate load Z is always LOW. You
need plenty of plate block C... simply so u don't screw up the
tuning on 160m..... and also so you have a high enough current
rating on 10m.

### a 100 pf doorknob cap wouldn't last 30 seconds in a 3x3
amp....try it urself.

later.... Jim VE7RF

...
R L Measures, AG6K, 805.386.3734
r@..., rlm@..., www.somis.org

--- In ham_amplifiers@..., "Robert B. Bonner"
<rbonner@...> wrote:

If I ever do build that 30 x 40 garage I will probably put in a 400

amp panel out there and sub feed the house. That 200 Amp service is
pretty busy.

### My electrician buddy said 240V 400A service was
available...and "no sweat". 400 A = 96 Kva ! 200A = 48 Kva.
I still don't get it. I have "200 A service".... and SO do my
15 neighbours... all hanging from the SAME 50 Kva pole pig ! Some
of my neigbours have a secondary suite in their homes... with a 2nd
elctric stove, etc.

### since we all got natural gas back in 1992... most of the
electric hot water tanks and oil furnaces have gone bye bye...
reducing the overall load..a bit. I still don't see any natural
gas clothes dryers..yet. Back East, they all have em... plus
gas ranges. My hot water tank, fireplace, and furnace all run on
natural gas.

### Bottom line is... when I smoke the pole pig at dinner time one
night..... I guess I can just whine to the pwr co... and say .."I'm
supposed to be getting 200A CCS service... so where is it? "

### The biggest pole mount pole pig I have seen is 100 KVA. But
these were special one off units...designed to drop 25 kv down to
12.5 kv..... then 12.5 kv into our vault xfmr at work... where the
vault xfmr dropped it again to 208/120. This is all 3 phase... and
both the 3 x old 75 kva xfmr's.. and the 3 x new 100 kva xfmr's
are huge... when u see em on the grnd. Every time I see 3 x
75/100 kva xfmr's.. all on the same pole, I cringe........ the
weight is massive.. as in 2 tons.

### anything above 100 KVA per phase... and it then goes
on the grnd.

Later... Jim VE7RF

pentalab wrote:

--- In ham_amplifiers@..., Tony King - W4ZT <w4zt-
060920@...> wrote:

Jim,

Don't you think that if a properly designed fault detection

circuit similar to the triode and tetrode boards available today would have caused a primary circuit shut down saving the glitch resistors from becoming a smoking pile?
### Partially agreed. Seems to me the 2 x triode boards available, are based on using an external 24 vdc DPST RELAY... whose contact's are in the 240 v primary. I don't see any 24 vdc RELAY's... with contacts rated for 100-400A. AC contactor's on the other hand are all either DPST-DM or TPST-DM.... the "DM" means 'double make'.... IE: essentially each pole is two sets of contacts in series.... with an input lug... output lug... and a huge bar on top that comes crashing down on the input/output.

As you said below, simple modifications will control any contactor you want to use.

### The DM arrangement is used [vs a dpst relay] simply cuz a DM will break the arc into two arcs = essentially zero arc....
[when trying to break a full bore load from a xfmr/motor] ### I never see giant bolt down MOV's across the in/out poles of any contactor's in commercial service.... but I always install the big bolt down MOV's across all the poles of my own contactor's in HV supplies anyway. The MOV's.. if used, should be fused... in case they short out.... with a 120 v neon between output side of fuse and neutral... to indicate a blown MOV fuse.

Which MOV's do you use and where do you get them?

### I suppose one could modify the triode board output easily.... and use the 24 vdc control circuitry, to activate/deactivate the INPUT of a opto isolator..... the OUTPUT side of the opto of course, could then be used to activate/deactivate a..'normal' 120/240 vac solenoid coil of a contactor. All that would be needed is an opto with a 24 vdc input, that u sink or source... and a AC output... rated to handle the typ contactor solenoid coil. Most opto's have back emf protection built into the output side.... still I'd use a mov across the AC contactor's solenoid coil.

That's a reasonable solution. Modification is not difficult.

This isn't to minimize the value of a good fuse but to add that a properly functioning circuit can fault the HV supply off so that

all you have to heat the glitch resistor is the stored energy in the capacitor bank. This is precisely what G3/GM3SEK and WD7S do with their boards. That way if you are testing and have one of those "modified" fuses in the circuit, it will still not melt anything down.
### agreed. Stored energy from the caps is pretty wicked with 100-300 uf and a 50 ohm glitch R.[and 7900 vdc no load].. IE: 3100-
9300 JOULES Everything else is just .."follow on energy".. from the plate xfmr/FWB. ### I have seen pix of John Lyles stuff... where they used both an electronic crowbar on the hv B+ to B- [used since pulse rated service like YC-156's..rated for 67 A of plate current means too much V drop across a typ glitch R... hence no glitch R used in any pulse service amp].... and also electronic fault detection circuits where by primary AC is removed. Also seen pix of his HV diode boards.. used in 3 - phase HV pwr supplies... which resemble charcoal.... when the crowbar failed.... and the fault detection also failed... or was not fast enough.

You do all you can and something can still fail but we've gone from jumpering a fuse with copper wire to worrying about the protection circuit failing.

### seems to me the 2 x triode boards wouldn't handle 3-4 A of normal anode current... but might be modified ?

Look at Paul's board... you can set it up with any external shunt for detecting a fault. Use the board to control any kind of contactor you have.

### I just wanted to keep it simple. Any electronic protection would have to be in addition to properly sized HV fuses and primary breakers.

And if your friend had used a correctly sized fuse, it wouldn't have been an issue.

### We use these electronic current sense devices at work for huge HVAC motor loads,compressor's,chiller's, etc.[70 to 120+ kw normal operating load] It was explained to me, they are used since the start up current is wicked on this stuff... as in 3-7 x normal running current. So, instead of a breaker... it's a current sense activated contactor. One of em crapped out last spring.... causing a huge fire in our main 'motor control center'... destroying a panel 8' wide x 7' tall. Incinerated every wire in all 45 x conduits too.. a real mess. Turns out the motor's were ancient. New motor's all have over temp shut downs built into em. New [adjustable] current sensors have redundant copies.. and fail safe modes. ### How do you know that every function on those triodes boards is gonna function when you need it ? You need some kind of "fail safe" on em so if they lose pwr... everything shuts off.... or perhaps two of em.... with say the outputs driving the relay/conatctor... are in series... so if either one failed... it would still shut off the AC primary, etc.

No, you don't know that it will work but if it is used with the fuse you have done what you can to prevent the smoke. I suppose you could put a "test" button on the front panel to trigger the circuit for test but you could carry this too far real easy.

### A fast, CORRECTLY sized HV fuse will work every time. Heck, you could even put 2 x identical HV fuses in series if you wanted. As a side note, I have seen where fellow's are using 2 x 5 kv [5 kv AC...7kv dc] rated Buss sand filled fuses in series.... in lieu of a single 10 kv [10 kv AC...14 kv dc] 10" long HV fuse.... simply cuz they had a ton of 5 kv fuses... and had 10 kv dc HV supplies [for a 3 x 20]

Well, this thread started with your description of a failure caused by your friend using copper wire instead of a real fuse. There is no device you can install that can second guess someone that is going to drop a copper bar in as a fuse. Everything we do is done with the expectation that the original circuitry will be used as designed. Once part of it is defeated, then all bets are off! ;)

### The 2 x triode boards are a good idea .. as long as any one or more functions on em don't crap out. IF you had say a GM3SEK triode board installed on every amp you owned.... I'd have one extra spare board put away... for a 'fast' replacement..if needed. Then fix the bad board at your leisure. Later... Jim VE7RF

Spares are good.

73, Tony W4ZT

73, Tony W4ZT

pentalab wrote:

Gents

My buddy was recycling his old sand filled fuses... by

soldering

a single strand of 26 ga wire across the 5" long fuse.

Fine

so far.
Amp was running fine the other night... the next day... BOTH

HV

fuses were blown open..... and amp was off from the previous night !
A real mystery. He then decided to solder TWO 26 ga wires across each of the old HV fuses. Next step was adding a

small

resistor to one hot leg of 250 cfm fan.. to slow it down a

bit.

[cools the glitch..... which diss 450 w with a dead cxr... 100

w

on ssb]
At that point all hell breaks loose. The paralleled 100 ohm

225

watt wire wound glitch R's looked like u hit both of em with

a

propane torch for 30 mins each.... charcoal !! We know a

HV

to chassis fault occured... may have been a faulty RFC bypass

cap.

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.
Over sizing a HV fuse is bad enough.... and you guys want to operate with NO hv fuse at all ?? nuts.
BTW... that Dahl A-540 hypersil C core 253 lb plate xfmr I have... has a .01 ohm primary.... and a 6.06 ohm sec [5200 v tap] You got any idea how much current you can suck from

one of

these things ..... 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 !
later... Jim VE7RF

--- In ham_amplifiers@..., R L Measures <r@...> wrote:

### Why don't u take some of that 4 wire home depot 8 awg...

and parallel em into 2 pairs.... eq ga is then 5ga.

RICH SEZ...And throw away the extant 4ga. wire?

#### The above was a joke. IMO ur 100' length [200' loop] of
4 ga wire is WAY too small for a 4x10. 4 ga wire isn't
even rated to handle 110 A.....never mind the 4-6 x that
current.... every 8.3 msecs. Calculate the PEAK current drawn
from the plate xfmr pri on a huge C input HV supply... and you
will see why I use big everything, including wire, contactor's,
etc.... from 200 A main panel to pri of 253 lb Dahl plate
xfmr. Duncan's pwr supply modeler.. PSUD-2 comes in handy for
this stuff. It also has 2 x methods of calculating plate xfmr
pri IMPEDANCE. Z is used to calculate peak pri current drawn...
not simply plate xfmr pri dc resistance.

#### 3/000 CU from main 200A panel to HV supply is what's
really needed. Snip a few strands to make it fit the 100 A
breaker at EACH end.

later... Jim VE7RF

Since I prefer single capacitors as a blocker,
I always use Draloric or Rosenthal caps, they are available at all kind of
capacities and voltages.
The are also very nice caps from Russia on the market with high values of
kvar.
Sometimes I also use mica caps by Jahre which are small and powerful, those
are harder to obtain

73
Peter

________________________________

From: ham_amplifiers@... [mailto:ham_amplifiers@...]
On Behalf Of pentalab

### Me, I just use normal HEC HT-57's.... and HT-59's. I also
have looked at Draloric's and similar HEC block caps... these
ones look like aprx 2000 pf @ 10 kv, 60 A CCS @ 32 mhz....
and are aprx 3-5" diam.