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[AMPS] Homebrew 3-500 need help

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Subject: [AMPS] Homebrew 3-500 need help
From: (Scott Gordon)
Date: Sat, 06 Feb 1999 08:38:53 -0500
Here is some background.  The amp is running two 3-500Z.  I just changed

out the power supply from 110v to 220v.  Plate voltage two tubes 2800v
idle 2500 volt key down.
Let's take 40 meters into a dummy load:
I thought I may have a soft tube, but now I don't think so..
1 - Tube installed driving from the Kenwood TS-570 100 watts of power
using the auto tuner for my tuned inputs.. 1100 Watts out on 40 m
I can put the other tube in and replace this one and get the same
thing.  I key down and talked for 20 min in the dummy load on each tube
and they hung in there at 1100 watts.  I have since tried each tube
seperatley in both sockets.  Same thing 1100 Watts.
If I put two tubes in there retune the the auto tuner and the amp, I get

nearly 1500 Watts out.  But this never last very long.  It keeps falling

back to 1000 to 1100 watts with two tubes.
Now I understand I am really driving that one tube with 100 watts less
some percent of loss via the auto tuner.  And when I put two tubes in
there impedence changes and now I am only driving each tube half the 100

watts or so. So straighten me out?  Why am I seeing 1400 to 1500 at the
beginning and
then it falls back with two tubes?  But with one tube it stays pretty
constant at 1100?
Any info would be appreciated,

Scott 73's KQ8RP

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