Re: [Amps] 4CX350A Cathode Driven HF amp strange symptom

[Ken Harada <jo1vrk@hayama.net>]

Then my wiring is not good?  But I don't hear noise on a receiver beside 
the amp - though I should watch different frequency to detect...

On 2023/05/24 21:39, Victor Rosenthal 4X6GP wrote:
> Perhaps it's breaking into oscillation?
>
> 73,
> Victor, 4X6GP
> Rehovot, Israel
> Formerly K2VCO
> CWops no. 5
> http://www.qsl.net/k2vco/
>
> On 24/05/2023 15:20, Ken Harada wrote:
> > Hi Amp enthusiasts,
> >
> > I am building a HF linear amp with 2 x 4CX350A with cathode driven 
> > circuit,  but getting a strange symptom.  Ep=2000V, Esg=300V 
> > (regulated with Zener and FET), Ecg=-50V to -20V (by LM337SP).  
> > Before applying any RF, I try to adjust no signal anode current by 
> > varying the Ecg.  Going up from -40V, it gradually increases from 0 
> > to approx 50mA, and in a sudden it jumps up to 300mA (around at 
> > -30V).  Moving back to deeper Ecg, it remains 300mA and suddenly drop 
> > to 0 - showing hysteresis.
> > I wonder what is happening to the tubes/circuit and where I should 
> > check.  Any suggestion would be greatly appreciated.
> > Regards,
> >
> > Ken /JO1VRK
> >
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