[ARC5] BC-459 Frequency Jump

[Mark K3MSB]

Hi Clare

I did clean the spring loaded contacts and ran the caps (after cleaning)
completely through.  I don't know if I loosened the screws though.  I will
try this.

Mark K3MSB

On Sat, Jan 2, 2016 at 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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