Ron -
OK, I can accept that. I've never seen an L-75, so stuck with just the
schematic.
Joe Ham would probably yanked those cap leads out by the root if they
were to try and drop the panel.
The capacitor leads went to the switch tag, and then a lower inductance
lead (and flexible) to ground the common.
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:
Well I took another look at my L75 which I have on the bench
anyway. I think I figured out why the braid jumper and
that wiring arrangement is the way it is.
If you look down each side in the front, there are three
screws on each side that hold the front chassis sub-panel,
which the aluminum front is attached. If you remove the
three screws down each side, that whole front assembly will
fold out to gain easy access to the front area of the
chassis along the bottom. That rotor switch is attached
to the front subpanel along with the power switch. When
that panel is folded out that long braided ground strap
allows the panel to come out easily an inch or so. If the
two capacitor were soldered directly to the chassis ground
lug, pull out that front panel assemble would probably pull
loose the wire lead from those two capacitors and damage
them.
I remembered that but it took a while. When you reach my
age the thinking processor runs slow. I repaired an L75 a
few years ago and was perturbed because it was almost
impossible to get down inside the amp in the front. I found
loosing and folding down the front assembly make it a whole
lot easier to work on the amp in the front.
Ron / WB4HFN
-----Original Message-----
From: drakelist-boun...@zerobeat.net
[mailto:drakelist-boun...@zerobeat.net] On Behalf Of Garey
Barrell
Sent: Friday, February 04, 2011 4:14 PM
To: drakelist
Subject: Re: [Drakelist] L-75 question
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:drakelist-boun...@zerobeat.net
[mailto:drakelist-boun...@zerobeat.net] 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<k4...@mindspring.com>
To: K9sqg<k9...@aol.com>
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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