Hi Bob
Search for
100A 4000W High-Power
Soft Start Circuit Power Board for Class A Amplifier Amp
73, Alek.
On 9/12/2024 10:00 pm, Bob via
groups.io wrote:
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Alek, Angus, I couldn't make those ebay numbers
work but if you do a search on ebay for "NTC resistor" you get
several.
I had to use one in my 50 amp Astron (RS-50) linear power
supply. It would sometimes trip the breaker. at start up The
one I used is...
SL322R025. It solved?the problem. It's been at least 7
years with no problems. Here's a link...
I originally got the info from "repeater builder"?
73, Bob W4JFA
G'day Angus.
Sorry for the delay. I missed your email and I'm just
cleaning up my emails and noticed this one.
Yes, the NTC works. I use them in this form for a lot of
amps that I build. See Ebay Item number 402565661699.
They are compact and work extremely well.
I've never bothered with soft starts for the little
Yaesu amps, as all the Yaesus I've worked on, have
excessive filament voltage at the filament pins when
connected to our AC mains.
A low value of resistance made up of 5W wirewound
resistors in parallel in series with the filaments
brings the volts back from around 6.9 - 7.0V back down
to the nominal 6.3V. This resistance, usually around
0.15 Ohms, also provides a measure of inrush protection
to the filaments. This is very important when using
Chinese valves, which hate excessive volts on the
filament.
Cheers from sunny Binningup, Western Australia.
Alek VK6APK
On 16/11/2024 5:06 am, AngusGM6AGC via wrote:
Hi Alek,
I trust you are well.
Have you done the step start mod ?¡°A
simple but effective delay can be done with an NTC
resistor. The
primary winding of the transformer is only a few
Ohm, so that a 1Ohm/20A NTC is sufficient to limit
the large momentary switching currents of uncharged
HV elco's and cold filaments.¡±
Is
it effective? Other soft step start arrangements seem
more complex.
I
look forward to hearing from you.
Best
wishes
Angus
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