Hi Jim, heavier loading causes more cathode current to flow to the plate and
less to the grid.
Heavier loading implies that the plate load impedance is lower and there
will be more plate current flow as a result. The total cathode current would be
about the same so the grid current would have to decrease as the plate current
increases.
73,
Gerald K5GW
In a message dated 4/16/2007 8:48:26 A.M. Central Daylight Time,
k7rdx@charter.net writes:
Would not loading heavier cause the grid current to be even higher?Jim..
----- Original Message -----
From: <TexasRF@aol.com>
To: <Paul@PaulFerguson.us>; <amps@contesting.com>
Sent: Saturday, April 14, 2007 9:28 AM
Subject: Re: [Amps] HF-2000 amp problem?
>
> Sounds like you need to increase the drive to 50-75w like 20m and load
> heavier (less load C) for maximum output.
>
> If this scares you, load heavier first and then increase the drive power.
>
> 73,
> Gerald K5GW
>
> In a message dated 4/14/2007 10:25:05 A.M. Central Daylight Time,
> Paul@PaulFerguson.us writes:
>
> I have a 10-year-old QRO HF-2000 amp. It has two Amperex 3-500Z
> tubes. You can see info on it at: http://www.qrotec.com/
>
> It used to output 1,000 watts or so on all bands. Now it outputs
> 1,000 watts up to 20 meters, but only about 500 watts on 17 meters
> thru 10 meters.
>
> On 20 meters and lower, grid current runs about 150 ma and plate
> current about 500 ma. Plate voltage is about 2,800. Input power runs
> 50 - 75 watts.
>
> On 17 meters and higher, grid current is about 100 - 150 ma and plate
> current is 250 - 300 ma. A small increase in input power gives a
> large increase in grid current and little additional output power.
> Input power is 30 - 40 watts.
>
> The amps tuned inputs seem OK as the transceiver sees an SWR of 1.1 -
> 1.3.
>
> All measurements were taken using a 50 ohm dummy load.
>
> Any ideas as to what might be the problem?
>
> 73,
> Paul - K5ESW
> Raleigh, NC
>
>
>
>
>
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>
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>
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