Date: Wed, 24 Dec 2014 13:23:12 -0800
From: Paul Baldock <paul@paulbaldock.com>
To: mikflathead@aol.com,amps@contesting.com
Subject: Re: [Amps] L4B biasing
Yes you should add bias. I added 11 diodes in the center tap of the
filament trany. So that would be about 7 volts.
- Paul
## One other quick note. With the oem +130v cut off bias scheme, the center
contacts
on the TR relay will eventually fry. With the contacts in mid air, the
cathode will try and assume
full B+ voltage. You cant open off the B- on a GG amp at any time.
With the 50-100K resistor in the CT of the fil xfmr, you never have that
problem.
The center contacts of the TR relay are simply re-wired so that the 50-100K
resistor is shorted out
on TX. If the oem 3PDT TR relay is being used, the oem half wave rectifier
can be swapped to either
a FWB or a FWD. If swapped to a FWD, you end up with +67 vdc, instead of + 28
vdc.
The tr relay will operate a little faster, but not fast enough for qsk. + 67
vdc will speed up a
26 vdc vac relay nicely. +28 vdc will speed up a 12 vdc vac relay just fine.
Gigavac makes the
popular GH-1 vac relay in either 12 vdc or 26 vdc. A 50 uf cap across the
series drop resistor
will speed up any relay even quicker. Called a RC hot shot circuit.
later.... Jim VE7RF
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