As I have an Emtron manual tune amp I can only comment on the FU728F
Tetrode.
I would not run a single one of these tubes at 200-330W output, let
alone a pair.
There are at least 3 versions of the FU728F. The earlier versions tend
to have some problems and the later ones say they have a 1200W plate
dissipation, they really are 1500 watts. Other tubes have had this
change on paper as well.
The FU728F is a relatively inexpensive tube for its power capabilities
as "were" the Chinese 8877s
Like many Tetrodes, when run much below 75% output they may exhibit a
negative screen current. The tubes should be operated in the normal
screen current and tuned for a peak in screen (G2) current, for best
efficiency and linearity keeping at less than the maximum ratings .
IOW, the tube should be tuned for a peak in screen current, NOT for max
output, or max plate current
73., Roger (K8RI)
On 9/15/2019 6:40 PM, Guido Tedeschi wrote:
Thanks Joe,
but the manual says that the amp protection is activated from Grid
current too high...
73 de Guido, ik2bcp
Il 16/09/2019 00:20, Joe Subich, W4TV ha scritto:
On 2019-09-15 4:40 PM, w9bs@w9bs.com wrote:
I was running the OM4000a at 200-300w out (with around 3-4w of
drive), and tuning it as normal to the "carrot" on the tuning
indicator.
--
Roger (K8RI)
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