Dennis -
I remembered that, but I've looked at a LOT of R-4A/Bs since you posted
that (4-5 years?) and I've never found another one! Somebody must have
had a really bad day..... :-) Certainly not that hard to do, and
VERY easy to overlook 30-40 years later. I don't have my notes handy,
but I seem to recall that the resistor was in the correct place on the
terminal strip, but the cap lead was tied to the "wrong" end of the
resistor.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>
Dennis Monticelli wrote:
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]
<mailto:[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 <http://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
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