[Amps] GI-7B

[MIKE DURKIN]

> 
> > -----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.
> 

Ok, the reason this came to me as a question is that i was thinking of replacing my 3-500Z's (one is arcing over - and had destroyed bias circuitry - which im almost done repairing) with a pair or 3 GI-7B's because the filament -with out the dropping resistor installed is what the Gi-7b calls for and im fairly sure that the bias voltage range will be suitable - But the plate voltage i have is in the range of 3600V - 3800V (not measured but im running a transformer meant for 50Hz at 200V on 60Hz at 240V - so i have higher plate voltage) 

Or sell the one GI-7b i have and get a pair of 3-500ZG's from RF parts ..... its some what a cost issue....

Mike
KC7NOA


 		 	   		  
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