[Amps] Nichrome

[Alek Petkovic]

G'day Amps Champs

This is just a quick note about Nichrome suppressors. Yeah, I know they've 
been done to death a number of times here and elsewhere. I just want to 
relay my experience.

I have a homebrew amp which runs a pair of 3-500z triodes. I built it quite 
a few years ago and since day one, it has had stability problems, 
particularly on the higher hf bands.

I don't know if the cause was voodoo, parasitics, poor layout, my ugly face 
or any combination of the above. Whatever the cause, it was a pig of an 
amplifier and it only ever got used on 40m with an occasional careful 
outing on 20m.

I've worked on that amp a number of times changing layouts, bandswitches, 
tank coils, coupling and decoupling capacitors etc etc. Nothing would cure 
it's bastard nature.

Well, I've been a member of this mailing list for a few years now and I've 
followed all the arguments with interest. In a last ditch effort to win my 
argument with my amplifier, I sent for the kit from one of the more well 
known subscribers to this list. I got a few mates interested also and we 
got a few more kits at the same time to save on postage costs from the US 
to downunder.

Just as an aside, I don't believe Rich recovers much more than his costs 
from the sale of his items but his service is the best in the world. - 
Thanks Rich.

Did I say this was going to be quick? Sorry, I'm getting carried away aren't I?

Yesterday, I finally found the time to open up the bastard amplifier again 
and I set about fitting the Nichrome parasitic suppression equipment. I 
installed the 4 supplied resistor/Nichrome suppressors and the special dual 
wire suppressor which goes between the plate choke and the plate coupling 
cap. The kit also include glitch resistor, protection diodes, gride fuse 
resistors and coupling caps. I didn't use these as they had already been 
fitted in previous attempts.

I've just returned form my local club shack where I took the amplifier for 
testing into our large dummy load. I am very excited to report that the 
amplifier is no longer a bastard. The change is more dramatic than I could 
have ever imagined or hoped for. It is now stable, predictable and easy to 
tune and operate.

After extensive testing on all bands into the dummy load, I ran the amp 
into real life antennas on the 80m to 10m bands. I also went up and down 
each band on high and low power. The result was the same, stable and smooth 
as silk whatever I did to it.

I now have a very useful amplifier. As to what the science or magic is in 
the Nichrome suppressors, I don't give a rip. I'm just happy they work and 
I'm quite happy to recommend them to anybody.

73, Alek
VK6APK