Date: Thu, 10 Aug 2017 11:47:58 -0400
From: Kelly Taylor <ve4xt@me.com>
To: Radio WC6W <wc6w_amps@yahoo.com>
Cc: amps@contesting.com
Subject: Re: [Amps] Fil transformer
<Hi Russ,
<Thanks. Just to be clear, I do not require a transformer for providing
filament power: it's to fix a design flaw in the Clipperton L, which lacks a
centre tap for the filament windings and instead feeds the filaments with RF on
one side only, introducing hum.
<The fix is to parallel a centre-tapped 6v transformer secondary with the
filament windings on the main transformer and move the RF input to the new
centre tap.
<The Hammond 166j6 is ideal, as it can be added with no metalwork, and you
simply cut off and tape the primary windings.
<73, kelly, ve4xt,
### There is no RF on the CT...... its just the return for the B-.... IE:
DC plate current. But we know what u mean. Seems nuts that dentron would
use a fil xfmr winding that lacks a CT. That will give u gross amounts of 60
hz hum, with the B-
being returned to the extreme left..or extreme right side of the sec winding.
Dentron must have been asleep at the switch when they speced the xfmr.
## I mentioned this b4, a local buddy re-wound a lower V, 28 vac xfmr....
with 10 gauge wire.. plus added a CT.... for his 2 x 3-500Z HB amp. 5 V at
30A under load. Typ they are 5.5 vac with no load. In his case, the loaded
voltage was too high,
so he removed some turns off of the sec... but only at one end of the winding
!! Loaded voltage was now correct, but the CT was effectively shifted off
to one side...producing 60 hz hum. To do it right, he should have removed an
equal number of windings from both ends..so the CT ends up dead center.
## what ever xfmr u end up using for your fix... measure the DC resistance
from CT to each end. They should be the same of course.
## The xfmr used in the dentron Clipperton L is just a single xfmr... that not
only has the high voltage AC for the B+..... it also has a fil winding for
the 4 x directly heated cathodes.... and also a 3rd low vac winding for the TR
relay and misc stuff.
## Dont use a small CT xfmr thats much less than 6 vac. If its too low, like
3-5 vac, there will be a lot more than 120 vac appearing on the un-used 120
vac primary of the retrofitted small xfmr used for the ... fix.
## The hammond xfmr u picked out appears ideal..as it will fit inside the
Dentron amp, How the heck dentron managed to screw up something as basic
as... CT required on a fil xfmr for a GG amp is an... epic failure ! The
only time a CT is not required
is for the case of a grid driven amp..and dentron never made anything other
than GG triode amps. They obviously never tested em properly. In all
fairness though, the RX at the other end would have to be capable of hearing
the 60 hz ac component, which in my local buddys case, was blatantly obvious
for a 800 mile radius...and his CT was over to one side of exact center.. by
just a little bit vs the oem dentron. One would think QST would have
picked up on that fubar in the 1st 10 mins.
Jim VE7RF
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