[Top] [All Lists]

[AMPS] Homebrew 3-500 need help

To: <>
Subject: [AMPS] Homebrew 3-500 need help
From: (
Date: Sat, 6 Feb 1999 14:16:29 -0500

On Sat, 06 Feb 1999 08:38:53 -0500 Scott Gordon <>
>Here is some background.  The amp is running two 3-500Z.  I just 
>out the power supply from 110v to 220v.  Plate voltage two tubes 
>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 
>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 
>nearly 1500 Watts out.  But this never last very long.  It keeps 
>back to 1000 to 1100 watts with two tubes.
>Now I understand I am really driving that one tube with 100 watts 
>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 
>watts or so. So straighten me out?  Why am I seeing 1400 to 1500 at 
>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
>FAQ on WWW:     
>Administrative requests:

You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at
or call Juno at (800) 654-JUNO [654-5866]

FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>