Fred -
I wanted to clear up what we were talking about.
If the issue is on receive, then you need new filter caps in the
receiver. The receiver has it's own power supply, completely separate
from the AC-4 transmitter supply.
Assuming all the caps in the AC-4 have been replaced, there is nothing
wrong with doing that in place of the AC-4R 'upgrade' kit. The kit just
makes it a lot easier to do. All this is making the perhaps rash
assumption that the capacitors the other guy used were good, and not as
old as the originals. They "probably" are fine.
I don't recall whether this is a B or C line. However, there are one,
(or two,) can type caps in the receivers, plus a couple under the
chassis. They should all be replaced since all are well over 30 years
old. One or two may still be fine, but even if they are, they won't
last much longer and can cause very expensive damage to the receiver if
they fail catastrophically, i.e., short.
Simplest approach here is the cap replacement kit from Tom at
hayseedhamfest.com. He supplies all caps that need to be replaced,
along with instructions on how to do it.
As for the speaker cabinet vibrating, yes, there is a big transformer
right underneath the top surface with considerable AC current running
through it that is generating a pretty hefty AC magnetic field. The
MS-4 case is steel, and so acts as a large diafrahm and amplifiy the
hum. It will vibrate more when you transmit because of the heavy currents.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com>
fjmel...@aol.com wrote:
Garey:
Thanks for the reply. The issue is on receive and no I don't use 40
very much and I guess this issue might be one of the reasons and the
other is the band has not been to good until just lately. The audio is
annoying to say the least. I have not had any audio reports that would
indicate the same issue on Transmit. I will ask the next time I am on 40.
I use an inverted vee antenna at 30 feet going through a MN-200 tuner
on 40 . The antenna is cut for 3.972 MHz and I go direct through the
tuner on 75 meters .No matching required for that segment of the
band.The audio is ok on 75 meters but the vibration on the top of the
speaker cabinet is always there whether the audio gain is up or down.
I did hear that there was a new circuit board and caps available for
the power supply and that it is recommended to do the upgrade with
these new parts and circuit board. Not sure if that was done when the
supply was rebuilt. I did get a bag of old parts returned to me when
the rig was repaired. A couple of caps and a few resistors plus some
tubes from the transmitter.
Do you sense any vibration when your power supply is running with both
receiver and transmitter turned on in the receive mode?
Thanks
Fred WD8ADG
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