I have done some modifications to the shematic, so i have uploaded an
revided shematic.
I can't see the reason for floating the B-, to mesure the current i
would just add an 0.1 ohm resistor between the PSU's - tab and ground.
It sould be easy to mesure the current over that? or is it somting I
have missed?
I also have to order an transformer, since there are just 2 producers
of small transformers, i would have to order an 600V and use an
voltage doubler. I could get an 700VA transformer realy cheap, but is
it enoug? I've read that SSB only has an dutty of about 20%.
73 de Thomas.
--- In ham_amplifiers@..., Tony King - W4ZT
<w4zt-060920@...> wrote:
Hello Thomas,
A couple of suggestions for your amplifier...
First, I would float the B- to make metering of plate and grid current
readily available to you. It takes no more than two resistors and a few
diodes to protect the metering to make this big improvement.
Second, I would suggest that you do not do T/R keying of the bias the
way that is shown on your schematic. That method is similar to the
Clipperton L and a few others. The flaw is that during the
transition of
the contacts the cathode will rise to near full anode potential and
when
you make contact with your bias circuit, you are hitting it with a very
high voltage at that moment. A simple cure for it without changing the
circuit entirely, and this applies to the Clipperton L as well, is to
place a jumper across the wiper and the normally closed contact of the
keying relay. That will keep the cutoff resistor in the circuit all the
time and prevent the cathode voltage from soaring. I would also place a
fuse in series with your bias circuit rated at just over your maximum
expected plate current. Also, a Metal Oxide Varistor or an NE-2 neon
bulb in parallel with the bias circuit will help protect it against
transient voltages. You may want to increase the value of the cutoff
resistor to about 20K to minimize the current in standby.
73, Tony W4ZT
