SB-104 Driver transistors and 104 Upgrades

[Ray Mack]

I heard from Ron last night and he had gotten the MRF 314's from RF
parts.  We talked at length about the relative merits of various
options in transistors.  The 314's sound like they should work just
fine for the following reasons:

1)  Just about any transistor that is capable of the power level (but
without internal compensation) should work in these applications.
Even the venerable 2N6080 series should work.

2)  They are the correct physical size.

My suggestion for the MRF 412 is wrong.  It should be for the
MRF 412A if it would fit.  The difference is that the 412 is flange
mount and the 412A is stud mount.  Also the 412A is case 145A-10 (0.5
inches in diameter) and the parts on the driver board are the 145A-09
(0.380 diameter).  Ooops.

I have not tried it yet but as I stated above I suspect that the
2N6080 series would also work as replacements since they have the same
physical dimensions and ought to have quite adequate gain at HF.  The
main reason for trying these is cost.

Another option is to use the HF linear trainsistors that are rated for
28V.  These are the MRF 401 and MRF 410A.  These are the only 2 that
come in the 145A-09 case.

Stay tuned.  Putting this rig back on the air for my friend WB5NMH is
my Christmas plant shutdown project.  I'll give the 2N6084 a try and
check out the before and after IMD with the spectrum analyser.  Murray
at Multi-Volti used to work at Heath and told me that these rigs were
tough to get clean.

Since parts for this rig are non-existent in some cases, I am also
putting together some new boards to replace the voltage regulators
(the six pin job thatis pure unobtainium) and a replacement driver and
final board using modern transistors.  What do y'all think?  Do we
stay stock on this rig or practical?

Ray Mack
WD5IFS
mack at mails.imed.com
Friendswood (Houston), TX

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