[ARC5] BC-459 Frequency Jump

[J Mcvey]

I second this opinion! Look for or assume dirt/corrosion/loose connections at the variable cap rotor to body interface.
 

    On Saturday, January 2, 2016 11:01 AM, Clare Owens <clare.owens at gmail.com> wrote:
 

 I'm no expert, but in the past this sort of thing has been attributed to poor grounding or poor rotating contacts on the variable caps.  Corrosion can build up even in riveted joints but especially in places where screws were used to fasten caps to the chassis.  Loosening and retifhtning them and applying some good contact re-newer (not just cleaner) can help.  Use it on the spring loaded rotating contacts on the variable caps as well and run the caps up and down some to work it in.  I use Caig products and like them very much for their long lasting results.  Nothing has ever matched the Philips contact cleaner/restorer that was sold in the USA in the 1980's for their oscilloscopes and other test equipment but that is long gone from the market.  I use the Caig R100 in the squeeze bottle with the hypo steel tubing spout and it really works well.  Just used it the other day on the transistor sockets in one of my Zenith R1000 Transoceanics and it did the trick without making a mess all over the chassis.

Clare

On Sat, Jan 2, 2016 at 10:43 AM, Mark K3MSB <mark.k3msb at gmail.com> wrote:

Last year I was having trouble with my BC459A on 40M in that it would jump frequency quite a bit during a QSO.

I (re)cleaned the unit and resoldered every solder joint I could get to.   This greatly helped the problem.

Now, every now and then,  the unit will start to jump in frequency, but a quick "thump" to the front panel clears up the issue nicely.  I can use the radio for hours afterwards with no problem.

Yesterday my friend N3CU called me early in the morning for an SKN QSO.   He recorded part of my transmission:

www.k3msb.com/temp/K3MSB_40M_ARC5_1.mp3

Afterwards, we were chatting on the phone and he said the drift issue was greatly cleared up from the last time he heard my BC459.   I asked him to clarify, and he said there was some frequency change when I initially started.

What I did was slightly readjust my TX frequency before I started sending (which is not on the above audio).  We did some subsequent experiments and apparently there is a slight frequency shift when I initially start transmitting, but not during an exchange.

I asked him to record my transmission when I deliberately went key down for 10 seconds, then sent a normal exchange,  then again went key down for about 10 seconds.   Here is what is sounded like:

www.k3msb.com/temp/K3MSB_40M_ARC5_2.mp3

I'm not sure why there is a frequency change when I go key down for a long time.  I can't hear it during a normal exchange.  My Plate, Screen, and Oscillator voltages show no drop.  I'm using a HB power supply with the typical voltage divider as per the manual (the 28V supply is seperate).

This does not happen on 80M using my BC-696A fed with the same power supply.

Comments welcome!

73 Mark K3MSB


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