Date: Wed, 4 Aug 2010 10:34:40 -0500
From: rcm@mail.icnet.net (Randall Mullinax)
Subject: [Amps] TL-922 grid chokes
The grid chokes in my TL-922 were replaced with 10 ohm resistors
by the previous owner. The amp works fine except on 10 M where the
resistors go up in smoke within a few seconds.
This bring up several questions.
1. Is the amplifier oscillating on 10 M?
2. Should I replace the resistors with the factory 470 uH chokes
or directly ground the grids?
3. Where can I get replacement grid chokes?
4. I?ve read about adding/increasing negative feedback. Does anyone
have suggestions?
Thanks for any and all comments.
Randy
AD5RM
## I have worked on a couple of TL-922's yrs ago. I remove the 6 x grid caps
and 2 x chokes..toss em.... and strap all 6 x grid pins to the chassis, with
copper strap,as
wide as practical.
## your drive requirements will drop by 20-25 watts on ALL bands.
The amp will be stable as a rock. Since your xcvr is now operating with
20-25 w less drive.. the xcvr's TX IMD will be much better.
## Overall signal quality will be better. IF you want a real grid fuse,
use a
3agc type.. and insert it in series with the existing grid shunt. [either side]
## I installed a 3agc fuse holder on the rear of my 4 x L4B's... with a FAST
rated 250-300 ma rated fuse. If the grid fuse blows open... there is now
no path for dc grid current. Power output drops to zero. Input swr
will rise to infinity. Xcvr will reduce it's PO..down to nothing. Takes
4 x seconds to change the fuse. I have blown one fuse since 1990.
## If ur hell bent to keep using the 10 ohm grid fuses... then you will have to
increase the value of the stock grid caps. Stock..you have a total of 600 pf.
This has to be increased to a total of 1800 pf. [ per socket] .
## you can do this by adding a pair of 560 pf caps to the existing caps.
[per socket]
later... Jim VE7RF
later....... Jim VE7RF
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