[Amps] Small mystery

[Vic K2VCO]

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/
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>
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-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/