[Amps] GS-35B Efficiency Varies with frequency?

[Carl]

That is characteristic of a tired tube and the poor PS regulation doesnt 
help.

Carl
KM1H


----- Original Message ----- 
From: "Paul Baldock" <pbaldock at frontier.com>
To: <amps at contesting.com>
Sent: Monday, December 10, 2012 7:50 PM
Subject: [Amps] GS-35B Efficiency Varies with frequency?


>I am building a GS-35B amplifier. The efficiency drops off a lot between 
>80M and 10M. Although the gain is quite constant. Does any body have 
>suggestions as to why this is or whether this is typical.
>
> The input PI network has a Q of around 2. The PI output has a Q between 10 
> and 20
>
> Here's some results with 70W Drive:
>
> 3.80MHz. Q=10, Output Power 1.1KW, Vp 3000V, Ip .54A, Ig .26A, Eff 68%
> 7.10MHz. Q=13, Output Power 1.1KW, Vp 3000V, Ip .60A, Ig .28A, Eff 61%
> 10.1MHz, Q=20, Output Power 1.0KW, Vp 2900V, Ip .68A, Ig .30A, Eff 51%
> 14.2MHz, Q=13, Output Power 1.1KW, Vp 2900V, Ip .70A, Ig .29A, Eff 54%
> 18.1MHz, Q=16, Output Power 1.0KW, Vp 2850V, Ip .78A, Ig .31A, Eff 45%
> 21.2MHz, Q=13, Output Power 1.0KW, Vp 2800V, Ip .82A, Ig .37A, Eff 43%
> 24.9MHz, Q=19, Output Power 1.0KW, Vp 2850V, Ip .79A, Ig .35A, Eff 44%
> 28.5MHz, Q=16, Output Power 1.1KW, Vp 2750V, Ip .85A, Ig .38A, Eff 47%
>
> You will note as efficiency goes down the Grid current goes up (in 
> general) for the same drive. Is this normal?
>
> Things I have tried:
>
> 1. Checking that the bias voltage is not affected by RF. No signal 
> Vp=3600V, Ip=140mA, Vb=34.5V.
> 2. Rebuilding 10M PI Output in a different configuration. (It is actually 
> an L-PI)
> 3. Checking that the metering is not affected by RF
>
> Any Suggestions?
>
> What is a safe Max Ig for the GS-35B?
>
> Thanks
>
> - Paul KW7Y
>
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