[Amps] GI-7B

[Gary Schafer]

> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]
> On Behalf Of Ron Youvan
> Sent: Saturday, December 05, 2009 8:58 PM
> To: amps
> Subject: Re: [Amps] GI-7B
> 
> > The tube will run at that voltage (it's pulse rated at something like
> 7KV or
> > whatever so the problem of internal arc should not be the factor), but
> in my
> > evaluation of a pair running from 1800v - 3100v, the "sweet spot" of
> > efficiency is around 2500-2650.  I'm not sure why, but voltages much
> above
> > this the tube efficiency seems to drop.  And in my application (RTTY
> > mostly), efficiency is the name of the game because you only have 700w
> of
> > total Pd.
> /*snip*/
> >> GI-7B    just a question about what the true limit of plate voltage
> is??
> 
>    Increasing the plate Voltage allows a tube/s to produce more RF
> power, (once you reach the
> current limit of the tube) within limits.
>    My experience with high power transmitting tubes (IOT-D2100) is; the
> tube runs cooler and lasts
> longer at the lowest supply Voltage that the tube can make the required
> power.
> Higher Voltage at a lower current means the tube is operating at a
> higher average resistance,
> resulting in a greater IR drop across the tube.  Dropping the power
> dissipated in the tube
> increasing the overall efficiency.
> --
>     Ron  KA4INM - The only real problem is death is so final.


I don't think that is so. 
True that a tube can make more power with higher voltage because it has more
room for plate voltage swing before cutoff. 

But how cool a tube runs has nothing to do with IR drop in the tube.  How
cool it runs depends upon how much power is dissipated in the plate. That is
determined by the power input verses efficiency.
Some tubes may be more efficient at certain plate voltages but that is not
normally at lower voltages.

73
Gary  K4FMX