[Heathkit] re: sb 200 input mod

[Steve Beveridge]

Hart - if you have a close look at the article "Heathkit SB-200 Input Fix by
NE7X" - web ref provided recently - you will see precisely what changes are
recommended. The article by Tom Boza is excellent. Not only does he go
through the process used to evaluate the Heathkit input values in quite some
detail, but he then provides a very concise summary of changes to ensure
better matching. He has also described the instrumentation used to study the
problem, so that others can repeat the study if they so choose.

Have a look at the table entitled "NE7X Configuration" and compare these
values to the previous table "Default Heathkit SB200 Configuration".

This table indicates that the only changes to be made were to the
capacitance. None of the coils were modified - no turns removed or added. No
changes were required for 40 and 20 M inputs. More capacitance was added for
80, 15 and 10 M. For example, the 66pf factory value for 10 M input was
increased to 100pf. This seems more efficient than running the tuner.

I'm doing a total rebuild on an SB-200 now and will certainly be making
these mods to mine before it goes into service. While I am fortunate enough
to have a sig gen, spec an and tracking generator, I don't think I will need
them to do the job - thanks to Tom.

Cheers
Steve
VK2XWL

----- Original Message -----
From: "Hart" <hartengel at sympatico.ca>
To: <heathkit at mailman.qth.net>
Sent: Sunday, January 22, 2006 1:40 AM
Subject: [Heathkit] re: sb 200 input mod


> How difficult is this mod really to do?
> Some sites say you need a scope and others don't mention a thing.
> Or should I just run a 300w tuner between the amp and the radio for know?
>
> Hart