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@jmr.com>
To: "Vic K2VCO" <k2vco.vic@gmail.com>; "Amps reflector" <amps@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@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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--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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