Bias. Could always effect plate current. What it sounds like is tuning
to some harmonic that will find a strNge resonance and draw current.
As this is likely A frequency outside the bands and likely harmfucl it
is good to reduce the gain quickly. The book has some good guidelines
on the rough position of the controls that will prevent this In my
experience a power supply capacitor is not generally an intermittent
issue, it is either bad or good. If wou have a lot of miles on the
power supply it would be good insurrance to clean it up anyway.
Good luck.
Sent from my iPhone
David Assaf, III
On Jan 25, 2010, at 9:22 AM, Garey Barrell <[email protected]> wrote:
Frank -
Interesting!
One thing, tuning the RF TUNE to the "middle of the 80M band"
_segment_ is probably tuning to the IF of 5.645 MHz.
I certainly suspect Bias supply troubles. Is the FInal idle setting
ok at 70 mA? Possibly intermittent loss of Bias which could
partially "key" the transmitter.
I would strongly suggest replacing the Bias supply filter caps at a
minimum. The chances of catastrophic failure with considerable
damage are just too great to ignore.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com>
iz oos wrote:
Hi Folks,
Premise: my AC-4 has still all the original caps, included the bias
ones which I should decide to change.
Weeks ago, I had experienced something very strange with my T-4XB. It
tunes correctly, but, at a particular point of the RF-TUNE in the
middle of the 80 meters band, it absorbed 320mA notwithstanding the
rig was going to be tuned on completely others band such as the
20meters band with the GAIN control set to minimum!!! This scared me.
It happened twice, albeit I was very quick to move the RF tune knob
so
I saw the 320mA just for less than a second or so. It seems that no
apparent damage occurred, as I tuned the rig on the band correctly.
But after that day then I haven't turned the rig on again.
Could it be due to the bias caps or to something else?
73,
Frank IZ2OOOS
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