[ARC5] BC-459 Drift

[Mark K3MSB]

Well, I guess the problem is not licked.

I drove my SCR-274N over the weekend to pick off some remaining states for
my ARC-5 WAS effort.

I was getting drift (on key down) and a  rough note, but not as bad as
before I did the cleaning as mentioned in my earlier post.  Based on one of
the other threads,  I adjusted my variac to bring the plate voltage down
from 550V to 440V, and the situation improved dramatically.

80M Is rock solid as usual at 550V Ep.   The Oscillator tube was replaced
in the 40M TX with a tested good tube, and from restoring the TX a few
years ago, all the resistors are within tolerance,  the bathtub cap was
replaced etc.

I suppose it's time to go in a replace components in the Oscillator section?

73 Mark K3MSB



On Mon, Jun 22, 2015 at 1:56 PM, Mark K3MSB <mark.k3msb at gmail.com> wrote:

> Well, I think I have the problem licked.
>
> I used 600 grit wet/dry sandpaper to clean behind the wiper arms of each
> of the 3 air variable caps, then cleaned with a bit of DeOxit.
>
> I put the transmitter back in the rack and the tone sounded good with no
> drift,  but then I noticed the power output was fluxuating a great
> deal.      I pulled my phones off at that point, and then I heard the sound
> of arcing.   With my vast level of expereince in ARC-5's I deeded this to
> be not good.  So, I played with the tuning and that didn't seem to have
> much effect.  At that point I realized that the arcing was not coming from
> the transmitter, but the the small matching unit I built to connect to my
> 50 ohms antennas (4:1 UNUN and an old HT-37 tuning capacitor).    I removed
> the side panel from the Bud Box that houses my matching unit and my oh my
> was that arcing pretty.    For some reason the rotators are closer to the
> stators than I remember, so I bent the offending rotator plate a bit, and
> the arcing stopped and power output was nominal (about 50W).
>
> I did not notice the drift problem like I originally reported but the tone
> still has more chrip in it than I'd like.   I want to play with it for a
> while and see how it performs.
>
> 73 Mark K3MSB
>