It could be any number of things as Garey has already indicated, but here is one unusual problem I caught in my radio. I mention it because my very early R4B is pretty much a late model R4A circuit wise.
My radio had a wiring error. The low value resistor between the two sections of the big can cap that feeds the AF stage had been wired in incorrectly such that it was not contributing to RC filtering, there was only C filtering. Even with new caps under the deck that effectively replaced the can cap, I had some residual hum. Once I found the factory wiring error and corrected it, the hum disappeared. It's an easy thing to trace the RC filter path of the multi-section can cap. Dennis AE6C On Mon, May 11, 2009 at 7:19 AM, Garey Barrell <[email protected]> wrote: > Jim - > > Hard to say without more information. What "else" did you replace except > the filter caps? > > Did you ground the new caps to the same point(s) as the old caps? > > What did you use to replace the twist-lok cap? > > Did you change any other ground points? > > Did you replace any tubes? > > Did you replace or change to another speaker? > > Since it's not affected by the volume control it's narrowed down to the two > AF stages "after" the control. > > 73, Garey - K4OAH > Glen Allen, VA > > Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs > <www.k4oah.com> > > > > > Jim Theisen wrote: > >> Hi Drake Wizards >> >> I have a R-4A 11 tube unit. I rebuilt it a year ago last winter including >> all the filter caps >> >> It works great except for one problem. >> It has a fairly loud hum that is *not affected by the volume control.* >> It is quite annoying and I would not like to listen to it for a long time. >> I installed my old Timewave DSP-9+ unit. It removes all the hum. >> All other radios are turned off including the T-4X transmitter. >> Any idea as to what the hum is coming from and what should I look for. >> Thanks. >> >> Jim WB8REH >> >> >> > _______________________________________________ > Drakelist mailing list > [email protected] > http://mailman.zerobeat.net/mailman/listinfo/drakelist >
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