[Amps] GI-7bT amplifier

[Glen Zook]

Thanks for the information.  I can probably get around 2400 volts under load from the transformer that I plan on using.

Glen, K9STH

Website:  http://k9sth.com


--- On Tue, 1/11/11, Jeff Blaine <keepwalking188 at yahoo.com> wrote:

At this plate voltage of 1800-2000 volts, you will end up having pretty high drive requirements and that means a lot more punishment to the grids - however strong or weak as they may be.
 
The tubes are most happy in the 2300-2500V range as far as I can tell.  And with the higher B+ levels, the Ig really drops of strongly.
 
The only official documentation on grid limits it the 7W on the "datasheet."  The trouble is trying to translate that 7W requirement back into an Ig level for any given amp without a set of characterization curves...  As far as I know, no one has done that.
 
There is an effect on this tube at Ig levels of about 60-70 ma where the Ig will "slide back down" when keying. Some have speculated that this is a physical distortion in the grid due to the drive current - I don't know what the actual case is.
 
However, generally speaking I tried to keep my drive currents under 120-150 mA for the pair.  I ran RTTY with this amp in quite a few contests as well as a huge amount of "boiling the dummy load" bench work and the tubes remained strong.