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

[Tom Chesek]

I have a DX-100 and an SB-10 but never really utilized them for SSB except 
for one quick QSO just to see if it worked and I don't even remember what 
band I tried it on.  I have used my DX-100 for AM only but never experienced 
what you have experienced.  I didn't feel that my experiences lent itself to 
sharing "expertise", since I don't have any, therefore I didn't respond to 
any posts.  I am only replying now to let you know that the modification to 
the DX-100 for SB-10 use hasn't effected it negatively.  I do not have the 
SB-10 wired in, I just use the coax jumper between the SO-239s on the back 
panel.  Its been a while since I used my DX-100 but again, never had any 
issues.  I often see SB-10s on eBay so it must have been a popular 
modification in its day.

Tom K3TVC




----- Original Message ----- 
From: "Rick Poole" <wa1rkt at arrl.net>
To: <heathkit at mailman.qth.net>
Sent: Friday, December 09, 2011 8:41 AM
Subject: Re: [Heathkit] SB-10 Modification (was DX-100B on Phone - bad audio 
distortion / oscillation)


>
> Received in private email:
>
> >>>>>
>>It would seem to be possible to remove them temporarily  (or at
>>least until you get hold of this problem) without forever nuking the
>>capability ...by removing the wires at the switch end.
> <<<<<
>
> I can always put it back if I want to, but there are wires that run
> the entire length and depth of the transmitter picking up all manner
> of who-knows-what along the way.
>
> Apparently the combination of DX-100B and SB-10 is rare (the
> TX-1/SB-10 is much more common), as evidenced by the fact that I've
> asked a couple of times on these reflectors and haven't yet found
> anyone who has or has had that combination.  So I don't know for a
> fact that it ever really did work all that well in all of its modes.
>
> >>>>>
>>Also, have you made sure the tank coil and associated connections
>>are solid and unmodified? I've seen that cause similar problems in an amp.
> <<<<<
>
> I have gone over everything in the PA section, except the parasitic
> suppressors and the screen bypass caps.
>
> Part of the SB-10 mod is that the connection between the driver and
> the finals, originally about a 2-inch route through a bulkhead
> feedthrough, now goes from the driver, all the way to the farthest
> corner of the transmitter and out a coax connector, through an
> external jumper to another coax connector, and thence to the grids of
> the final tubes.  Normally the SB-10 connects where the external coax
> jumper is.  Seems to me that, even though (very LARGE) shielded coax
> was used from the output of the driver to the coax connector at the
> far corner, still there is plenty of opportunity to pick up unwanted
> stuff.  So, that'll be the first thing I reverse to see if it makes a
> difference.