Date: Fri, 25 Nov 2011 08:45:36 -0800
From: Vic K2VCO <k2vco.vic@gmail.com>
Subject: Re: [Amps] On Behalf of K4BOF
Yes, that is exactly the way to do it! :-)
I also highly recommend grounding all of the grids directly, as W8JI suggests.
I've been
using a modified 922 for a few months now and am very happy with the way it
performs.
On 11/24/2011 10:15 AM, Jim W7RY wrote:
> Here you go!
>
> http://www.w8ji.com/tl922_mods_parasitic.htm
>
> 73
> Jim W7RY
## a buddy of mine had sparks etc on his TL-922. He installed the nichrome
suppressor
and all was well. I suggested he directly bond all 6 x grid pins to the
chassis with wide CU strap,
and toss the 6 x grid caps and both grid chokes. He did, and it was rock
stable. Plus the drive
requirements dropped by 20-25 watts. Next up, the nichrome suppressor was
removed, and the
original kenwood suppressors were installed. Amp is still rock stable, and
still requires less drive.
## That's the 6th TL-922 that has gone through the exact above scenario . I
also know of a doz SB-220's
and SB-221's that went through the same above process...and dido with henry
amps. IMO, semi floating the
grids with caps is just asking for trbl. One of the fellow's with the sb-221
had severe TVI into his neighbors'
satellite RX, but only when he was on 17M ! One or more grid caps was flaky.
## carl mentions the 25 ohm dc reistance of the 2 x grid chokes on the TL-922
/SB-220/221.
All the grid chokes I have removed from 4 x Drake L4B's all measure .921 ohm
[ all 8 of em].
IMO, pumping dc grid current through the 25 ohm dc resistance of a
heath/kenwood grid choke
just results in both un-wanted extra bias, and also this extra bias is yo-yoing
with the drive.
.150 grid current x 25 ohms = 3.75 vdc of extra bias..on top of the stock 5 vdc
zener. So now
your bias is yo-yoing from 5-8.75 vdc. Strap the grids to chassis, and ur bias
is now rock stable at 5 vdc.
## On most 100w pep xcvr's like a TS-870, etc, when you reduce the power from
100w down to 85w, the
TX imd will drop down a whole bunch. Strap the grids to chassis, reduce the
drive by 20-25 watts, and now
your xcvr is running a cleaner signal as well. Total imd form the amp is now a
lot cleaner. No more
yo-yoing bias either. 5 to 8.75 vdc bias is nothing short of lousy bias
regulation.
later.... Jim VE7RF
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