Hi Steve.
What brings you to the conclusion that its a parasitic oscillation?
Have you measured the frequency?
It sounds more like the amp is simply taking off, in which case, no
amount of fiddling with suppressors is going to help you.
Component size, layout and lead lengths, etc, are critical factors at
50MHz. That's where I'd be looking to solve your problem.
Cheers and good luck,
Alek. VK6APK
On 17/07/2015 4:38 AM, Steve London wrote:
Finished the SB-220 6 meter conversion, but it seems to have major
parasitic oscillations.
A little background - I basically followed the 2008 QST article,
except I have the original relay in it. I don't have a source of
nichrome ribbon, so I made parasitic suppressors recommended by
another avid VHF guy - a copper strap U, and a 300 ohm resistor
straddling the U. No difference with or without those parasitic
suppressors. The tuning capacitor is bigger than the one in the
article - Surplus Sales is sold out of the smaller one. However, the
tank does resonate on 6 meters.
Just to be sure, I'll describe the symptoms: engage the T/R relay with
no input signal. Grid current, plate current and RF output ! I can
change the level of these from 0 to potential disaster by adjusting
the tuning capacitor. The RF chokes in the grid circuit have not (yet)
fried.
Sources for small quantities of nichrome ribbon ?
Other suggestions ?
73,
Steve, N2IC
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
--
From Sunny Binningup
---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|