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Re: [Amps] step start

Subject: Re: [Amps] step start
From: Alek Petkovic via Amps <>
Reply-to: Alek Petkovic <>
Date: Tue, 3 Oct 2023 08:00:29 +0800
List-post: <>
If you want a great soft start, just go to Ebay and search for

 100A 4000W High-Power Soft Start Circuit

I bought 10 of them and have used them in 3 projects so far. They are very quiet and all self contained on the one small board.

I'm pretty sure they do a 120V model as well.

I'll be using another one in my AL-1500 when I fit the W7RY QSK in the cominging weeks.

73, Alek VK6APK

On 3/10/2023 2:21 am, Val wrote:
Hello Paul,

As you will put the step start circuit in the transformer primary, it will limit the transformer inrush current and thus all the voltages provided by the transformer - filament, screen, grid, plate.

73, Val LZ1VB

На 01-10-23 в 21:19, Paul Decker написа:
Hello all.

I'm building a 4cx1500b amplifier. This is the first tetrode high power amplifier I've tried to do.  I'm using about 300V on the screen and 2500 on the plate.

For my power supply I'm using a 1 Henry choke input on the screen supply dumping into 200uF This seems pretty stiff.  For the plate supply it's a voltage doubler outputting 2700 V dumping into 93uF.  Not quite as stiff, about 300V drop under full load. I have plenty of capacitors, so I can add more capacitance if needed.

Two questions,
1. is the plate voltage regulated enough or do I need more plate regulation and 2. for soft start,  Should the soft start bring both the screen voltage and plate voltage up or should I let the screen voltage be and just soft start the plate voltage.

Thanks for any insights you all might have.


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