[AMRadio] SB-10 Modification (was DX-100B on Phone - bad audio distortion / oscillation)

[Rick Poole]

At 07:25 PM 12/9/2011, Mike Sawyer wrote:

 >>>>>
>I've been reading all this about the SB-10 modification and such. If memory
>serves me correctly, the only thing one needs to do is to pipe the output,
>(SSB output) back into the input. The SB-10 needed the VFO frequency but if
>you weren't using SSB, you just put a jumper back in and left it in AM. Is
>it me or am I missing something here?
<<<<<

Good evening, Mike.

What you say is essentially correct but there is considerably more to 
it than that... for one thing, the DX-100 finals run in class C on AM 
and CW but must run in some linear mode (in this case class ABx, 
don't know if it's AB1 or AB2) for SSB.  So you have to switch the 
bias level when switching from AM to SSB.  With this conversion kit, 
that involves a separate piece of bent aluminum with a pot and a copy 
of OB2 VR tubes on it.

Also, breaking the connection between the driver and the finals to 
bring the driver output out the back to drive the SB-10, involves 
removing about a one-inch wire and then running a length of coax all 
the way to the farthest corner of the transmitter to a connector, 
then out that connector to the SB-10, back in another connector, to 
the grids of the finals.  That's where the jumper goes that you 
mention, if you're not using the SB-10.

There is some potential for screw-up there.  And when I removed that 
around-the-block-to-go-around-the-corner coax run, my low grid drive 
went away.  I'm in the process of removing the rest of the mod and 
we'll see if my other problems go away.

I'll end up with two surplus SB-10's in unknown condition if anyone 
is interested (one that came with the DX-100 and the other I bought 
as a parts donor).

Rick WA1RKT