Jim, if you look art the curves for any of these tubes you will notice that
the plate voltage swing can't be allowed below four or five hundred volts
without excessive grid current (or screen current in the case of a
tetrode).
That means the total voltage swing is plate voltage minus 500 volts
typically. If you are using 2700 vdc on the plate, the total swing is 2200
volts
which is 81.5% of the plate voltage.
If you run 4000 volts, the plate swing can be 3500 volts or 87.5% of the
plate voltage. The difference between the two voltage levels makes the higher
voltage have about 7% more efficiency.
Of coarse this added efficiency may not actually be available if it makes
the power output exceed our 1500 watt limit.
Also, the higher plate voltage will dictate a higher plate load impedance.
Usually higher load impedances come with a higher loss due to the Q loaded
being higher when compared to Q unloaded. A really good plate inductor will
mitigate this effect to a large extent, especially at higher frequencies.
73,
Gerald K5GW
In a message dated 2/9/2010 8:16:37 P.M. Central Standard Time,
Jim.thom@telus.net writes:
From: "DF3KV" <df3kv@t-online.de>
Subject: Re: [Amps] Water cooled 160 meter amplifier..
To: <amps@contesting.com>
Message-ID: <1Nep7B-0Om3CC0@fwd00.t-online.de>
Content-Type: text/plain; charset="us-ascii"
That is the same efficiency as with a 8877 at that voltage.
It will be much better at higher anode voltage.
73
Peter
## why should the tank eff increase.. with higher B+
voltages applied ?? I can see gain going up a bit.
I can also see more power out. What has B+ level
have to do with tank eff ???
later... Jim VE7RF
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