Brett,
Yes I know that circuit. I looked a lot at some of Bill's circuits when
I
did my first regulator, and what I used has parts in it stolen from Bill. I
found that I got tighter regulation with the 6AH6 error amp tube over the
6AU6. I also had the problem where every time I turned it on, the regulated
B+ was at a different voltage (within a 5 volt range). Once on the voltage
was solid until cycling power, and then it would jump to a new stable value.
Digging through some reference material, I read that the OA2, OB2 are famous
for this, and that is why more precise regulators of that vintage used a
5651 reference tube. I experimented some, and the capacitor I placed across
the OA2 seemed to fix the problem completely, and that regulator holds the
voltage like glue now. There is a maximum value of capacitance that these VR
tubes can handle before they start acting like a RC oscillator.
Another issue is which side of the regulator do you pull current from to
light up the VR tube? I used the output side as it seemed to provide better
regulation (load and line), and lower noise output. The drawback of course
is that the regulator series pass tube must give up some percentage of it's
available current to support the VR tube. I had about a 2X margin of
available current to needed output current, so this was a good compromise in
my instance.
I also played with sampling Vin and Vout at a certain ratio to feed the
bias voltage to G1 of the series pass tube. There seems to be a point where
the ripple rejection of the regulator goes through a peak, and the output
noise nulls. Anyone ever play with that?
I sure like the 6W6 as a series pass tube. I got 5 of them NOS in box
for
$9.99 from a Ebay auction. Look at the plate curves in triode connected
configuration. They are very stout tubes for the size, and money (little
demand for these so they are cheap!).
Brett in your case I wonder what your Vin, and Vout voltages are, and
what
is the minimum Vin - Vout at Maximum load current that the circuit can
accommodate before going open loop (out of regulation)?
Regards,
Jim Candela
WD5JKO
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Behalf Of Brett Gazdzinski
Sent: Wednesday, November 19, 2003 8:41 AM
To: amradio@mailman.qth.net
Subject: RE: [AMRadio] Screen Regulator Circuits, 20a, etc.
I use a circuit out of the Bill Orr handbook that uses a big Vr tube,
some small octal tube, and a big triode (6as7??).
I forget the tube numbers, but the circuit is adjustable voltage output,
I use it on the screens of my 4cx250b modulator tubes.
Works very well, and has been 100% reliable for over 10 years now.
The 4cx250b mod deck is the one of choice for the 813 pair, its very clean
and runs 600 watts in ab1, so the circuit gets a good workout.
Brett
N2DTS
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