[Amps] An Extra Thank You!

[Gary Schafer]

> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
> Behalf Of Paul M Dunphy
> Sent: Thursday, March 05, 2009 4:34 PM
> To: amps at contesting.com
> Subject: Re: [Amps] An Extra Thank You!
> 
> At 05:22 PM 3/5/2009, you wrote:
> >I didn't add the drive back in on mine, so I'm off by that 20W.
> >
> >I'm not sure I completely understand why the drive is added back.  You
> >could write a thick, thick book with what I don't know about tubes,
> >because when I went to school they weren't taught anymore.
> >
> >Jeff/KD4RBG
> 
> Jeff,
> 
>      I'm pretty sure it's because in a grounded grid amplifier the
> input drive signal is passed straight through, so you get it plus
> whatever the tube(s) squirt out.
> 
>      I'm sure there is a better "electrical engineer" answer, but
> that's how I understand it.
> 
> 73, Paul VE1DX
> 

Yes drive power does need to be considered when figuring efficiency of a
grounded grid amp as part of the drive power does pass thru the amp. But,
not all of the drive power appears in the output of the amp. Part of it is
consumed in driving grid which gets turned into heat and is not passed thru.
Also the input circuit has some losses too. It is not easy to determine the
exact amount of drive power consumed by the tube. A very rough guess would
be around 30%.

73
Gary  K4FMX