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[Amps] step start

Subject: [Amps] step start
From: "jim.thom" <>
Date: Wed, 4 Oct 2023 09:54:05 -0700
List-post: <>
Date: Wed, 4 Oct 2023 07:31:15 -0400 (EDT)
From: Paul Decker <>
To: "" <>,
        "" <>
Subject: Re: [Amps] step start

<Hello group,
<The take-aways I received so far are:
<1. Absolutely have a Plate soft start esp with 200 - 500 uF in the HV.
<2. Plate regulation is not as critical as screen regulation.
<3. Never apply screen voltage before plate voltage. Safe to apply at the
same time. Best practice <is to apply plate voltage before screen voltage.

<That being said, I can design my soft start to start plate voltage. Once
soft start completes and <switches out the 25 Ohm resistors from the plate
primary lines, it can energize the screen primary <lines to bring the
screen voltage on.


###  Don't forget to bias the amp off...before you apply B+. .  With no cut
off bias, or failed cut off bias,  you will peg the Plate current meter.

##  To really do this right, it should have both screen and plate
overcurrent protection.

## I would use 2 x step start resistors in at least you have
some 2 x 50 ohm resistors in parallel. A  DPST relay
could be used to apply 240 vac.   A 2nd  DPST relay could be used, with one
pole used to shunt the step start resistor assy..and the 2nd pole used to
feed power to the 120 vac  coil of the 3rd DPST  relay..whose contacts  are
used to feed 240 vac  to the  pri of the screen  supply.  Fourth DPST relay
used to shunt out the step start resistors in the screen supply.....and
also perhaps close the key line.

##  IF a HV fuse is used in the B+ (and a 25-50 ohm glitch resistor), and
the HV fuse opened off, you will have screen V  still present.  You then
require a circuit to shut it all down, with no B+ present.  WB2WIK used a
125 vdc coil (11 ma) on a DPDT or 4PDT relay..  and a few resistors in
series with the coil....with top end of resistor string  to the B+...and
other end of coil to the B-.   125 vdc zener across the coil....( in case
coil  failed open, the zener will clamp it to 125 vdc). Without the
safety zener, and if the coil opened up, you would have full  B+ sitting on
the input side of the coil.

##  Relay is always operated with B+ on.  HV fuse blows open, relay drops
out, and the various contacts of the relay can be used to open off the key
line, or open off the TX inhibit on the xcvr, or shut down the screen
supply, turn on a red led / neon etc.

Jim   VE7RF
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