Not entirely true!! The CT of the filaments is tied in between the two tubes
back the the filament transformer. If one filament opens up the other tube
will stay lit. Check the schematic. By connecting the CT like they do any
imbalance current flows back so that one tube doesn’t drawn more current. The
problem is if one tube goes out it puts a large current on the CT and it can
overheat L20, therefore it is not a good idea to run the amp with only one
tube. The filament transformer can be smaller and lighter with 10volts.
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On Wednesday, July 15, 2020, Jim Thomson <jim.thom@telus.net> wrote:
Date: Wed, 15 Jul 2020 03:52:26 -0400
From: Artek Manuals <Manuals@ArtekManuals.com>
To: "amps@Contesting.com" <amps@contesting.com>
Subject: Re: [Amps] Tl- 922
<Ahh I see now that there ( at least) three R7's on the schematic one on
<HV Rectifier Stack X43-1290-01 and one on the Meter Shunt board
<X54-1300-10 and one on the main chassis !
<As a previous poster noted remove the tubes one at a time
<Dave
<NR1DX
## Problem is... the fils are wired in SERIES ! Remove either tube, and the
remaining tube will not light up.
Henry radio did the same thing on their 2 x 3-500Z amps. Fils in series is
not a smart idea. And for what, so they can use
14 gauge magnet wire..instead of 10 gauge on the bifilar fil choke. They
saved all of a few pennies.
## That grid to fil short happens..after the fil has heated up. You wont see
the short, with tube out of socket.
## The TL-9222 uses a 10 V @ 15A fil xfmr. So dont short out one
fil...or the remaining tube will have a full 10 V on it.
Jim VE7RF
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