[AMPS] Parasitic suppressors/another question,

[Jon Ogden]

>	Without access to a spectrum analyzer, how does one determine what
>frequency your new amp has any parasitic oscilations occuring on, if
>any?  I realize that keeping an eye on a TV in the room while the amp is
>running into a dummy load might be one way, but if parasitics ARE
>generated, then don't you run the risk of blowing up switches, etc in
>the "finding" process?
>	What are your suggestions?
>	OOHHHH KAAAAAAHHHH!  Flameproof skivies on!  Let loose the dogs of
>war!!!

Here is what I did:

First of all, if the amp is unstable you can easily make it oscillate.  
You can do this by a couple of ways.  Keeping an eye on a TV is NOT the 
way as you have no idea of what frequency you may be oscillating at 
anyhow.

1.) Key the amp with no signal and no load (open circuited) and the 
bandswitch in the 10M position.  Move tune C thru its full range.  If at 
any time you see any grid current or an increase in plate current above 
its idle value: you have an oscillation

2.) Key the amp manually with no signal.  Then send a number of high 
speed dits from your CW keyer.  Crank it up to the highest speed 
possible.  According to the theory presented by AG6K, this can create VHF 
ringing in your anode circuit.  If the VHF ringing isn't damped properly 
then you will get an oscillation started.  If it is a sustained 
oscillation (which will be likely) then you will see increased plate 
current and grid current when the amp is back at zero signal.

3.) One can also use a neon bulb held on an insulated stick close to the 
anode.  If the bulb glows purple at any time it is an indication of VHF 
energy.  If the bulb glows orange it's an indication of HF energy.  You 
should have NO glow with a zero signal keydown.

I hope this helps.

73,

Jon
KE9NA


--------------------------------------------------------------------------
Jon Ogden

jono@enteract.com
www.qsl.net/ke9na

"A life lived in fear is a life half lived."


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