SB-400 Low Power and alignment

[Mark Johnson/Ontario/IBM]

Hello everyone,

My sb400 (part of sb300/400 setup) started to show low power recently so
thought I'd dig into it and see what's going on. During a quick tune-up,
(re-peak the driver and plate coils on each band for maximum power out) I
got 100 watts on 80 & 40, 90 watts on 20, 65 watts on 15, and 50 to 15
watts on the 4, 10 meter bands.

On spec I installed new finals (Westinghouse 6146B's, NOS), a new 6CL6
driver, a new mixer (V4) and a new iso amp (V5). No real change so thought
I'd actually get the book out and follow the proper procedure for the
alignment. After doing that,  the results are worse...I suspect that using
the prescribed method of using an RF probe and VTVM, is causing the
problem. I suspect  the probe/VTVM is loading the tuned circuits such that
the alignment is faulty. I've got some work to do, but has anyone used the
prescribed method in the SB400 manual with good results??

Anyone have any starting point suggestions for my low power problem??

Thanks Team!!

Mark V. Johnson
VE3DJU

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