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

[Ken Harada <jo1vrk@hayama.net>]

Hi,

It was indeed an oscillation.  I have then given up Ground Grid / 
Cathode driven circuit, and modified it to GK/Grid Driven with input 
load resistor.  It works perfectly fine & stable, with driving power as 
low as 5W.  FL2100Z chassis and transformer provides good platform for 
4CX350A.

Regards,

Ken Harada - JO1VRK

On 2023/05/24 21:51, Victor Rosenthal 4X6GP wrote:
> Yes, it could be at VHF or even LF.
>
> 73,
> Victor, 4X6GP
> Rehovot, Israel
> Formerly K2VCO
> CWops no. 5
> http://www.qsl.net/k2vco/
>
> On 24/05/2023 15:42, Ken Harada wrote:
> > 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
> > > >
> > > > _______________________________________________
> > > > Amps mailing list
> > > > Amps@contesting.com
> > > > http://lists.contesting.com/mailman/listinfo/amps
> > > _______________________________________________
> > > Amps mailing list
> > > Amps@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/amps
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps