[Amps] An Extra Thank You!

[David Craig]

    Am I wrong here?  I though effiency was: power output in watts / (plate 
voltage under load x plate current).  Is this incorrect?

    73 Dave N3DB


----- Original Message ----- 
From: "Gary Schafer" <garyschafer at comcast.net>
To: "'Paul M Dunphy'" <amplifier at ve1dx.net>; <amps at contesting.com>
Sent: Thursday, March 05, 2009 4:45 PM
Subject: Re: [Amps] An Extra Thank You!


>
>
>> -----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
>
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