On Sat, 06 Feb 1999 08:38:53 -0500 Scott Gordon <kq8rp@primenet.com>
writes:
>
>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,
>
I would suspect that you are having a case of component drift at the
higher power level. If it is all bands I would start with the plate
blocking cap.
If it is band limited then look at those unique parts, particularly any
fixed value caps.
Something else to consider is a undersized plate choke or RF heating due
to a close resonance.
73 Carl KM1H
>Scott 73's KQ8RP
>
>
>
>
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>
>
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