[Amps] Small mystery

[Jim W7RY]

You may need higher voltage AC to supply the -140 VDC grid bias 
suggested. Can you replace this transformer or increase it's output AC 
voltage?

73
Jim W7RY


On 10/29/2013 12:02 PM, Vic K2VCO wrote:
> The voltage can be varied by changing a resistor, up to at least -120v 
> if I wanted to. There should be at least 8 ms between the signal to go 
> into TRANSMIT and when the RF drive appears, and the input relay 
> (which switched the bias) operates in less than 3 ms. So there 
> shouldn't be a problem.
>
> On 10/29/2013 10:47 AM, Paul Christensen wrote:
>> Vic,
>>
>> Within some limits, can you vary Eg1?  I think you are using Ian's 
>> board set, but I don't
>> know to what degree Eg1 and Eg2 are adjustable.
>>
>> My first thought is that you've hit a near ideal target on Eg1 since 
>> there's only a small
>> amount of Ip.  I may not want complete cut-off (or below) bias in 
>> ENABLE.  The more
>> negative Eg1 in ENABLE, the more non-linear artifacts you may notice 
>> in fast VOX (or
>> leading edge CW waveform distortion in QSK) on the initial RF 
>> envelope when finally going
>> from the ENABLE to TRANSMIT bias stages.
>>
>> Paul, W9AC
>>
>> ----- Original Message ----- From: "Steven Katz" <stevek at jmr.com>
>> To: "Vic K2VCO" <k2vco.vic at gmail.com>; "Amps reflector" 
>> <amps at contesting.com>
>> Sent: Tuesday, October 29, 2013 1:24 PM
>> Subject: Re: [Amps] Small mystery
>>
>>
>>> I think you need more negative bias (cutoff) on G1 to pull it down 
>>> into complete
>>> non-conduction.  I always used about -140Vdc.
>>>
>>> WB2WIK
>>>
>>> -----Original Message-----
>>> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Vic K2VCO
>>> Sent: Tuesday, October 29, 2013 10:22 AM
>>> To: Amps reflector
>>> Subject: [Amps] Small mystery
>>>
>>> I'm starting to test my 4CX1000A amplifier and I have noticed 
>>> something that I don't
>>> understand.
>>>
>>> The amplifier has three operating states, which I call READY, 
>>> ENABLED and TRANSMIT.
>>>
>>> In READY,
>>> HV = 3400V
>>> G1 = -89V
>>> G2 = 0 (grounded)
>>> Antenna relays disabled
>>>
>>> In ENABLED,
>>> HV = 3400V
>>> G1 = -89V
>>> G2 = 325V
>>> Antenna relays enabled but de-energized
>>>
>>> In TRANSMIT,
>>> HV = 3400V
>>> G1 = -60V
>>> G2 = 325V
>>> Antenna relays energized
>>>
>>> The idea is that the QSK or VOX line switches between ENABLED and 
>>> TRANSMIT. By switching
>>> to READY during long periods of receiving, there is less chance of 
>>> an 'event', or of a
>>> cat stepping on the key and transmitting at full power, etc. Since 
>>> bias switching is all
>>> electronic, it is faster than screen switching, which uses a relay.
>>>
>>> Now here is the mystery. In READY there is no plate or screen 
>>> current. In ENABLED there
>>> is a negative screen current of a few mA and also a plate current of 
>>> a few mA.
>>>
>>> Why is this current flowing?  I understood that secondary emission 
>>> is caused by
>>> electrons hitting the plate and 'bouncing' or causing it to emit 
>>> electrons itself. But
>>> the plate current is very small in this condition.
>>>
>>> I noticed the same phenomenon with much lower plate voltage, 2400V.
>>>
>>> Could the tube be gassy? The tube is a pull, but I don't want to put 
>>> my new one in there
>>> until all initial testing (including with RF) is finished! I ran the 
>>> heater all night to
>>> getter it, if that matters.
>>>
>>> -- 
>>> Vic, K2VCO
>>> Fresno CA
>>> http://www.qsl.net/k2vco/
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>