I too have noticed that directly ground the grids lowers the drive
requirement. The amplifier is also more stable after conversion to QSK.
My amplifier was the original 10-80 meter version. I left the stock
suppressors in.
73
Jim W7RY
-----Original Message-----
From: Paul Baldock
Sent: Saturday, June 15, 2013 12:47 PM
To: amps@contesting.com
Subject: [Amps] SB200 Anti Parasitic Chokes
A few weeks ago I posted asking if anyone new the optimum
Anti-parasitic chokes (APCs) to use when modifying an SB200 for 6
Meters. I received some interesting comments but no definitive
answer. So I thought I would share with you what I came up.
I experiment with many different combination or R and L and came up
with something very similar to the original used in the SB200. The
original SB200 APC is a 47Ohm/2W Carbon Comp in parallel with about
.08uH. This actually works well a 6M except the resistor get quite
hot. In fact I disassembled the original APCs and found the resistors
actually measured around 65Ohms probably due to age and heat stress.
Based on the higher value working well I finished up with 2 x
150Ohm/3W low inductance metal film resistors in parallel with .08uH.
I tried 3 in parallel and it did not make any difference so I went
back to 2. These run only slightly warm
If anybody wants any info on doing the SB200 6M conversion feel free
to contact me directly. No secrets here!
BTW I did remove the chokes and caps between the Grids and Ground on
the 572Bs and replaced them with a direct short to ground resulting
in more output power and less drive required. No flames about this please.
- Paul KW7Y
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