I'm still betting on supplied lead length of the original caps!! :-)
Yes, RF current is likely the reason for the braid, but if the cap's
leads reached there wouldn't be any more of a current problem.
Yet another wild thought, perhaps the longer cap leads would have caused
an inconvenient series resonance.
Bottom line, it WAS DESIGNED intentionally by some pretty good
engineers, and I would be reluctant to change it without proving I
understood why it was done. It wouldn't have cost much to add that
blank terminal to the switch wafer, probably less than special ordered
caps with longer leads, but neither would have been done without a good
reason.
(Spoken by an RF engineer who has had to defend more than one 'crazy
design decision'.)
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Ron wrote:
The only thing I can see is it may be an RF current issue,
Both capacitors together may create a current carrying issue
which is why Drake used a wire braid jumper from the common
point and the chassis ground lug. I know today they would
be taken directly to the ground lug, but who knows what they
were thinking 30 years ago.
Ron / WB4HFN
-----Original Message-----
From:[email protected]
[mailto:[email protected]] On Behalf Of Garey
Barrell
Sent: Friday, February 04, 2011 3:36 PM
To: drakelist
Subject: Re: [Drakelist] L-75 question
Evan -
OK, I see them. I can't figure out what they were thinking.
There doesn't appear to be any reason for that, unless the
new capacitor leads weren't long enough to reach the ground
lug. Anyway, that's my guess and I'm sticking to it! :-)
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
K9sqg wrote:
Garey,
These are C34 and C36. They are 700 pf disc ceramic.
73,
Evan
-----Original Message-----
From: Garey Barrell<[email protected]>
To: K9sqg<[email protected]>
Sent: Fri, Feb 4, 2011 12:47 pm
Subject: Re: [Drakelist] L-75 question
Evan -
What are the two caps you are referring to?
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com <http://www.k4oah.com>>
K9sqg wrote:
Fellow enthusiasts,
Have a question about S2C in the L-75 linear, it is the
wafer switch
controlled by the lever on the front panel for use on
160 and 80>
meters. The two switchable load capacitors are located
from some>
terminals with one end of each cap going to a "common"
terminal on the
switch, and then a lead from there to ground. However,
that "common"
terminal is not connected electrically to any part of
the circuit.>
Was just curious as to why the ground side of each cap is
connected>
to an unused terminal when in fact there is a ground lug
very close to
that switch that could be used for the ground
termination. I'm going
to be replacing those caps and plan on using the ground
lug rather>
than that electrically isolated switch terminal. But then,
am I>
missing something here? I'm sure Drake had a reason for
doing what>
they did, but I can't figure out what it is. At one time I
thought>
that maybe it would be a simplified manufacturing process
to mount the
caps to the switch before installation but then that
didn't make
sense> since a wire/braid had to be run from that
terminal to the
ground lug> anyway. Your thoughts?
73,
Evan, K9SQG
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