[R-390] Sigmapert - Evaluation Results

[Chuck Rippel]

I commented on the Sigmapert R390A replacement items couching my comments
that I had not yet had the opportunity to install and evaluate any of the
items save for 1 set of the electrolytic capacitor replacements.  Just
finished the radio whose owner wanted to install 3 of the now 4 items Kurt
offers and can now offer a few comments based on first hand knowledge.

 

The 3TF7 replacement is in item everyone ought to have.  Ballast tubes fail
and are increasingly becoming more expensive and harder to find.  The
Sigmapert replacement is easily installed and could be plugged right into
the IF deck but for the addition of a ground.  There are 3 grounding options
in the well written instructions.  Ground the case of the 3TF7 replacement,
or ground either pins 1,  9 or both of the existing 3TF7 tube socket.  In
the installation I just completed, I chose to run a small wire from pin #1
on the bottom of the existing 3TF7 tube socket to a nearby ground lug.  This
enabled the owner to either use a standard 3TF7 Ballast Tube or the
Sigmapert replacement as he choose without further modification.  The
Sigmapert replacement was slightly warm to the touch after 1 hours use and
did not overheat.  Fitted with a standard 3TF7 IERC tube shield, I doubt the
casual eye will notice the modification.

 

I was equally impressed with the antenna input balun.  The fit and finish
are to be commended.  The balun compensates for the slight mismatch on the
BALANCED antenna input (some RF decks are factory modified) and isolates the
input on a properly grounded from Common Mode pickup problems to a large
extent.  Simply having a reliable connector which to connect the antenna
lead-in is worth the price of the balun !  I'm going to start suggesting
that owners consider purchasing the balun on for use on radios I will be
working on so that when I align the RF deck, it can be aligned with a balun
installed so the antenna input alignments can be properly done.

 

The capacitors are.. capacitors but well worth the cost.  Aging filter
capacitors are a high failure item in every vintage radio and the R390A is
no exception.  Kurt offers replacements that both have a higher working
voltage and increased temperature tolerance.  Yes, I prefer my rebuilt caps
with Mallory elements on radios I'm working on but Kurts are easy to install
and do the job!

 

I have not yet seen the new 26Z5W replacements but can comment that the
original tubes often fail with sometimes disastrous results to the
transformer !  The Sigmapert units replace the hot running tubes and also
drop the increased B+ voltage which results from changing the tube
rectifiers to solid state.  In the 2nd R390A video, we demonstrate only a +
9VDC increase in solid state rectifiers over tubes but the dropping the
extra voltage is welcome especially when its coupled with getting rid of all
the extra heat generated by the tubes and insulating your radio from the
26Z5's reliability track record.

 

I've asked Kurt to consider also making a quality device by which to dampen
the turn on inrush using something other than thermistors.  With the filter
discussion of late, I also suggested Kurt consider building a replacement
mechanical filter using the Dave Curry design which was an exact replacement
(I have one of the 6KC models in one of my R390A's).  A picture and
technical review were sent to Kurt.

 

Keep 'em glowing !

Chuck Rippel