[Amps] step start

[Victor Rosenthal 4X6GP]

I mentioned the need for a 3 minute delay before turning on plate and 
screen voltages, but Jim is right -- you CAN turn on plate voltage 
immediately. Just keep the bias on so the tube is cut off for at least 3 
minutes.

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/

On 01/10/2023 22:43, 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 w8zr.net 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.
> 73,
> Jim w8zr
> Sent from my iPad
> 
>> On Oct 1, 2023, at 12:19 PM, Paul Decker <kg7hf at comcast.net> wrote:
>>
>> 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.
>>
>> Paul
>> KG7HF
>>
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