Glen Zook wrote:
>I am in the process of building a single band linear for 160 meters
>using a pair of GI-7bT tubes. The reason for single band is that I
>have 3 other linear amplifiers that cover 80 through 10 but none of
>them cover 160 meters.
>
>Looking at various circuits (gleaned from the Internet) I notice one
>common factor and that is none of them, at least that I have found,
>have any provision for monitoring grid current. Also, unless I am
>overlooking something, I don't find any specifications for maximum grid
>current for the GI-7b or GI-7bT.
>
>My 160 meter exciter puts out a maximum of about 80 watts which
>definitely should be plenty to drive a pair of GI-7bT tubes. Anyway,
>does anyone have any suggestions or information on if I should have any
>worries about this. I am well aware of grid restrictions on tubes like
>the 811A, 572B, 3-500Z, etc. But, this is my first venture using the
>GI-7bT tubes.
>
This page is a central resource for information about Russian tubes:
<http://www.nd2x.net/base-1.html>
Half-way down, there are tables of designs for various triodes and
tetrodes including the GI-7B. YU1AW's schematics suggest the following:
Va = 1800=2000V
IA0 = 30-50mA*
IA = 350-400mA*
Vb = 12-15V
Pdr = 15-20W*
Po = 400-450W*
Igmax = 50-100mA*
*per tube
The suggested figures vary between different schematics, and the grid
current will be strongly dependent on the drive level, output loading
and anode voltage.
Don't worry about grid dissipation. The GI-7B, GS-31B and GS-35B are
'planar' triodes, originally intended for UHF operation, and their
construction is much more rugged than the other tubes that you mentioned
above. The grids are massively built from reinforced mesh and can take a
lot of abuse:
<www.ifwtech.co.uk/g3sek/misc/gs35g.jpg>
--
73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek
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