[Amps] step start

[Victor Rosenthal 4X6GP]

Plate voltage regulation on a tetrode is not very important, because the 
screen voltage has a much greater influence on the plate current. 93 uf 
is quite a lot for the plate supply, imho more than you need.The screen 
regulation is critical with this tube, because the screen current has to 
be kept within narrow limits to protect the screen (it will go negative 
easily). It is also important for reasonable IMD characteristics. You 
should consider using some kind of active regulator circuit in the 
screen circuit.
Soft start is useful to protect diode and relays in the power supply, or 
tube filaments or heaters. It is not relevant to plate or screen voltage.
One important point: NEVER turn on screen voltage before plate voltage! 
Make sure this can't happen by accident. The screen will go up like a 
fireworks display if it does. Either turn them on together, or turn on 
the plate voltage first, followed by the screen. And make sure there is 
a 3-minute delay from when the heater is powered on until plate and 
screen voltages are applied.

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

On 01/10/2023 21:19, Paul Decker 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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