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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