Differences Final Amp's SB-400 & SB-401

[Mark Graalman WB8JKR]

> Hello Heath Team;
> Why does the SB-401 Final Amp have a 680 ohm resisitor (R17 on the
> SB-401)
> between screen grids of the 6146's and B+ and the SB-400 has a
> straight
> connection..no resistor??

  I don't know, but I wouldn't worry about it. I'm betting its
there for decoupling, and 680 ohms at the values of screen
current that flow means nothing at DC and the screens are
bypassed at the tube end anyway. I say its nothing more
than additional decoupling.

>
> I'm into the alignment on my SB-400 again (500th time) as I'm still
> not
> satisfied with the final amp grid current. I can't get it to draw
> "proper"
> levels of grid current like I can with my SB-401. The power output
> is fine
> on all bands, but the level current control is full up on 40 meters
> (low
> end of band) and 10  meters is the same on the band edges.....All
> new
> tubes, voltages fine....etc, etc. etc.....
>

  I'd make sure the 8 Mhz trap adjustment is correct.

Also, make sure the grid metering resistors are within tolerance.


73,  Mark  WB8JKR

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