Ron & Jim -
Maybe I'm missing something, but according to the documentation I have,
all of the regulators and Zeners seem to have input and output bypass
capacitors.
Bypassing multiple pins of a 723 might be counterproductive, actually
degrading noise reduction on the output. There is fast, high gain
amplification going on in there! This is still one of the best
regulators around.
Most caps seem to be larger than datasheet values, but based on other
Drake gear I assume they are tantalum and so work as well as lower value
caps at the higher frequencies.
I don't have any numbers, but I suspect that a 1 uF tantalum is just as
good (low dissipation and inductance) as a multilayer ceramic.
I haven't worked on a lot of TR-7s, usually find that reseating the
cards "fixes" them! :-) Perhaps early units didn't have these caps?
Doesn't seem likely.
Certainly added caps wouldn't make things worse, with the possible
exception of the 723 "Christmas tree", but I question the value.....
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com>
Jim Shorney wrote:
I did do some of the Zener bypassing, but did not measure the results. It
didn't make things any worse, I will say that, and I have pretty good MDS
numbers on my 7. In addition, I also bypassed the 3-terminal regulator ICs to
manufacturer's spec with some surface mount caps on the legs of the IC right
next to the body. Again, no measurements, but it didn't hurt, and I've learned
over the years that they tell you to put those caps there for some very good
reasons.
I did find it interesting that all of the TR-7s that I have worked on so far
have had the IF gain control maxed out already anyway, in some cases apparently
by the good folks at factory service.
73
-Jim
On Fri, 23 Apr 2010 17:30:55 -0700 (PDT), Ron wrote:
Has anyone actually done and measured the results of bypassing the zener diodes and
regulator chips as discussed on QST Feb 1989? The author had "anecdotal" data
only. Was just wondering if there was any instrument measured data floating around out
there. Not really planning on doing this, just more of a curiosity.
73,
Ron WD8SBB
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