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[Amps] Amp Supply LK-550 (550) need replace inrush module's resistor

Subject: [Amps] Amp Supply LK-550 (550) need replace inrush module's resistor
From: "jim.thom" <>
Date: Fri, 13 Oct 2023 08:46:17 -0700
List-post: <>
Looks like you have the fix well in hand.  I'll bet the stock carbon
comp. resistor was underrated and eventually gave out.  It took a long
time but it eventually happened.  I tend to engage in overkill in my
fixes because I don't like crap outs.   In my case I installed a
switch that bypasses the in-rush resistor.  None of this automatic
solid state RC time constant stuff here that can crap out again.
Manually bypassing the in-rush resistor after a second on power on is
an additional step but it's no big deal.  And of course I flip the
switch to put the resistor back in when I shut the amp off.

If you are operating a continuous duty mode it doesn't take long to
fry that resistor.  I noticed the squashed trapezoid and smelled
burning epoxy right away.  It was a cold night in January around 10
years ago and I had to heave my amp off the table and put it outside
behind my house for the night, otherwise the house would have stunk
with toxic fumes and I would have had to go to a motel to sleep.  I
will never go through that again.


## 240 / 10 ohms = 24 amps = 5760 watts.   10-11 ohms works good for a
120 vac input.

20 ohms works better for a 240 vac circuit. 240/20 ohms = 12 amps = 2880 watts.

I also use a manually shunted step start resistor setup, done
externally on my drake

 amps. Putting the step start resistor back in the circuit, before
killing the power

for the  night is an excellent method of shutting down.  With the step start

resistor back in the circuit, it will kill all the back EMF.  I  noticed this

effect on my bigger hb amp power supplies  years ago.  Be careful with any MOV

across relay contacts.  If the MOV fails shorted, you will have  problems.

 MOV's should really be fused.

Jim  VE7RF
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