[Amps] 4CX350A Cathode Driven HF amp strange symptom

[Victor Rosenthal 4X6GP]

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
>>>
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