Sounds as though ALC from the amp is causing the transceiver to step
power. One should NOT use ALC from the L-4B to the K3. The ALC circuit
in the L-4B was designed for exciters which did not have precise power
control. The use of ALC to control power in this configuration is
likely to cause rather poor sounding CW notes. Yes, everything you
describe points to an ALC issue with the amp. WHOOP WHOOP WHOOP
73
Bob, K4TAX
On 5/31/2019 6:21 PM, William Stewart wrote:
All,
I am trying to bring a Drake L-4B to life. I have done the power
supply rebuild, the soft-start and other mods. I have also directly
grounded the grids of the 3-500Zs (Eimac brand). In driving it with my
K3 (SN 51XX, software up to date) I find that the RF power stair-steps
to the set power in a hesitating way over a few seconds. This happens
sending Morse code or using the "Tune" button.
The supply voltage, as monitored on the K3 display, is at about 13.4
volts when transmitting.
I have a power/SWR meter between the K3 and the amp and it shows a low
SWR at all times, as does the K3 SWR meter.
The power meter between the K3 and the amp shows the power gradually
increasing. As the K3 increases power out, the amp power out increases
in a similar fashion.
I see no indication of oscillation. The power meters on the output
side of the amp show no power when the amp is keyed but no RF is
supplied. I placed a low-pass filter (41 MHz cutoff) between the K3
and the amp to no effect.
I notice that if I send a series of Morse code characters such that
the K3 transmit delay timer never times out, once the power ramps up
to the set value, it remains solid until the timer expires - when I
start transmitting again, the power step process repeats.
When I put the amp in Standby, the K3 functions normally.
This smells like an oscillation problem, but I see no evidence of one.
Any advice would be appreciated.
Thanks,
Bill K5EMI
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
