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Re: [Amps] step start

Subject: Re: [Amps] step start
From: Victor Rosenthal 4X6GP <>
Date: Mon, 2 Oct 2023 16:42:10 +0300
List-post: <>
Why do you want a soft start on either plate or screen voltage? What function does it serve?

Victor, 4X6GP
Rehovot, Israel
formerly K2VCO
CWops no. 5

On 02/10/2023 15:14, Paul Decker wrote:
I was thinking the step start could be put onto both the screen and the plate 
voltage transformer. Since the screen dumps into a 1 Henry, it does take some 
time for that to charge so they both should ramp up.

It's easy enough to have the soft start only on plate and when the soft start 
kicks out, turn on the screen voltage.


On 10/01/2023 3:43 PM EDT MU 4CX250B <> wrote:

Nice project, Paul. I built my first tetrode amp a couple of years
ago, and I was dubious I could carry it off, but it worked well and
was fun. I have website at with photos and schematics.

  Re your questions, a 300V drop in plate voltage won’t be a problem.
That’s a pretty typical  voltage drop and isn’t anything to worry
about. Re your soft start question:  for a tetrode amp, you should
always have the plate voltage turned on BEFORE  turning on the screen
voltage. In other words the screen voltage should never be on by
itself. Doing so will quickly destroy your 4cx1500b. To be on the safe
side, I would turn on the plate voltage and the cut-off bias voltage
when the amplifier is powered up and just leave them on. Once the
plate voltage is on, you can then safely turn on the screen voltage.
On my homebrew tetrode amp, I made a little interlock circuit that
monitored the plate voltage and shut off the screen voltage if the
plate voltage dropped out for any reason.
Jim w8zr
Sent from my iPad

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