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Re: [Amps] SB-220 low output on 10 was: SB-220 input problem

To: N4ZR <>,
Subject: Re: [Amps] SB-220 low output on 10 was: SB-220 input problem
From: Jim <>
Date: Sun, 9 Dec 2018 16:45:28 -0600
List-post: <>
The tuned input is a very complicated circuit of varying impedances, so cable length can change the match between the exciter and tubes. Are both tubes glowing?  Key down in RTTY mode. Do both tube get the same color of red? Are you sure the plate voltage measurement is accurate on the meter?

What is the plate voltage?

Jim W7RY

On 12/9/2018 4:04 PM, N4ZR wrote:

I'll be ... I don't understand why, but putting 8-10 feet of RG-8X between the K3 and the amp brought the input SWR down to ~1.5:1.  I'd love to know how come.  Power output is still quite low (~600W.)

Could be these 30-year-old 3-500Zs are finally wearing out.  Does that normally show up on higher bands first?

73, Pete N4ZR
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On 12/8/2018 11:46 PM, Jim wrote:
A 6' cable between the amplifier and the radio is minimum length. I use RG58 or RG8-X.

Then see what the SWR is.

Jim W7RY

On 12/8/2018 7:14 AM, N4ZR wrote:
My SB-220 is showing a relatively high input SWR on 10M (about 2.5:1) - which I just discovered this weekend!

Before I burrow into it, what's the most sensible approach? Acquire the capacitors for the input network and simply replace them all?  Or is there somewhere else I should be looking for my problem?

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