Hi,
I'm finishing new GU-77b tetrode QRO in passive grid design.
The data of the tube are here: http://www.gstube.com/data/1557/ [1] .
I'm wondering does 200mA of idle current is OK for this tube on plate
voltage 2.2 kV? (at Ug1 -61V, and Ug2 is 300V I get about 1,4kW OUT).
I'm bit supprised on low readings of Ig2 which is less than 10mA at
1.4kW output, the Ig1 is almoust 0 (less than 1mA). The input SWR on
most bands is less than 1,5 when I use fig1 input network design
http://pa0fri.home.xs4all.nl/Lineairs/Frinear1500/FRI1500eng.htm [2]
without input attenuator.
When I use this input network
http://www.qsl.net/yu1aw/Misc/input%20mach%20HF%20sch.jpg [3] the
readings of Ig2 are normal 20 to 30mA, but with this design the input
SWR on 15M and 10M is way to high and I can't reduce it lower.
I tried
using better plate transformer (bigger iron, about 2.5kV Ua) with fig1
input network than I got about 1.9kW, the Ig2 didn't rise much above
10mA, the Ig1 rised litle still less than 2mA. I tried different
positions of coil in PI network, but that is not changing things, so I
gues there is no problem about PI network settings (beeing off resonance
etc.)
How much of Ig1 would you sugget acording to the tube data for
mostly ssb operation for balanced operation settings (linearity,
output...)? I also think might I have a problem at the input network,
the RF voltage is too low and perhaps I should use up step transformer
to rise the drive voltage?
Many thanks,
Branko, S52V
Links:
------
[1] http://www.gstube.com/data/1557/
[2]
http://pa0fri.home.xs4all.nl/Lineairs/Frinear1500/FRI1500eng.htm
[3]
http://www.qsl.net/yu1aw/Misc/input%20mach%20HF%20sch.jpg
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