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: [email protected] [mailto:[email protected]] 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:[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 >>> >>> > _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
