[ARC5] BC-459 Frequency Jump

[David Stinson]

There are a many things that can cause this.
This is an MOPA transmitter; in addition to power
supply issues, anything which changes the loading
 on either stage can cause the problem.

What I hear in the .mp3 files is a drift, not a "jump."
Jumps are usually caused by, as others have pointed-out,
intermittent connections, dirty output tuning parts, 
corroded grounds etc.

While leaky bypass caps and gassy 1625s have
exhibited this kind of drift, it sounds thermal 
and I'm very accquanted with that issue.  
How are you tuning the output to match an antenna?
If using an external cap and that cap isn't well 
RF rated, it will heat up, change value and that 
will pull the MO frequency as the loading on the 
PA changes.  You don't see it during a QSO because
 the part heats and cools as you key, averaging 
the change.   If you had an "instant reading" 
audio freq counter,  you'd likely see
the changes our ears "average out."

One can spend as much money as one wants on 
good RF caps.  Seen them for $75 and for $5.
I've found the ones from Eastern Europe
and Russia to be excellent and cheap.  
I use these in series with the antenna lead 
for 80 Mtrs with good results:
http://www.ebay.com/itm/271738088165
It will also work on 40 meters but 50 pF is better.
For 40 meters, I like to use some little green 
doorknobs from Bulgaria.  I don't see them listed 
right now but they show-up fairly often.  
I've had no thermal drift issues with these caps.  

73 DE Dave AB5S