[Amps] On Behalf of K4BOF

[Jim Thomson]

Date: Fri, 25 Nov 2011 08:45:36 -0800
From: Vic K2VCO <k2vco.vic at 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