Date: Tue, 9 Feb 2010 23:39:19 EST
From: TexasRF@aol.com
Subject: Re: [Amps] water cooled 160m amp.
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.
## are u saying the tank eff will rise 7% ??
## on a L4B, that works out to 73% on low voltage, and 81% on
high voltage. That is a 8% diff. I don't see any 8% increase in eff.
Then again, low V is 625 watts out, high V is 1290 w. Two
x diff power levels.. BUT at least the plate load Z is the same.
## I understand abt the V swing vs curves for tubes... and I
understand what ur saying, and the concept, I just don't
measure it in practice. Are we supposed to be comparing
identical DC input levels... say 2500v @ 800 ma vs
4000 v @ 500 ma ??? [ same plate load Z] or high plate load Z..
VS low plate load Z ??
Of coarse this added efficiency may not actually be available if it makes
the power output exceed our 1500 watt limit.
## measure the power at the ant, not the amp. Assume .5db to 1db
of feed line loss.. [10-20%]
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.
## The 1/4" tubing coil in the L4B runs hot on 20-15-10m. I can
see a higher loaded Q on maybe 10m.. but not 20+15m. The fix for
that is to add a tiny uh coil, b4 the main PI net.. and transform the
plate load Z way down... THEN the main PI net see's a lower loaded Q.
That's easy to do on the GM3SEK PI spreadsheet.
## running high RF current through coils on HF is usually bad news.
tank eff drops, coils cook, and poor band switch takes a beating.
Even if you used bigger tubing coils, you still cook the bandswitch.
High loaded Q = narrow BW as well.
## best combo I can come up with is vac caps, big tubing coils,
small tubing coil b4 vac tune cap... then transform the plate load Z
down to a lower value. The tube C plus extra small coil b4 Pi net,
form a step down LC network. Then eff is up on the high bands. I call
it an L-PI [or a L-PI-L ] On HF anyway, lower loaded Q = better eff.
later... Jim VE7RF
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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