[AMRadio] Ferroresonant transformer revisited

John E. Coleman (ARS WA5BXO) wa5bxo2005 at pctechref.com
Wed May 10 16:38:27 EDT 2006

Looks like a nice Xsistor Jeff.  There may be some MOSFETS with 800 or so
break down that would work as well.  I plan on using the ones that Jim put
me on to for the four 813s driver SOME DAY.

I need to design a dynamic regulator of some sort for the screen supply of
the 813s.  (Needs 800V)  As of now I waste 100 watts in a bleeder resistor
to keep the screens steady.  The screen current is low in comparison to the
bleeder current so the voltage is pretty stiff.  I have thought of a charge
regulator for the input capacitor of the pi filter.  And maybe one of those
HV MOSFET would fit the bill.  My theory is to use choke input with high
capacitance on the output and then enable a charging capacitor at the input
of the filter, turning it into a quasi pi section to keep the voltage up
under heavy load.  I have never done this but have thought about it for many

The circuit would look like a pi type filter but the input capacitor would
not go to ground.  Instead the bottom of it would connect to a tube or
MOSFET device that when biased "on" by a reduction of the controlling sample
voltage would allow the input capacitor to charge.  A diode place across the
tube or MOSFET would allow for the capacitors discharge path.

John, WA5BXO   

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of W5OMR/Geoff
Sent: Wednesday, May 10, 2006 3:14 PM
To: Discussion of AM Radio
Subject: Re: [AMRadio] Ferroresonant transformer revisited

John E. Coleman (ARS WA5BXO) wrote:

BTW, ,John - those Transistors I got, and told you about (for the 
solid-state audio driving circuit) are
2SC3461's.  They would probably be a good replacement for the ECG164's, 
for directly driving the grids of a Class B  modulator.


2SC3461    NPN Triple Diffused Planar Type Silicon Transistor 800V/8A 
Switching Regulator Applications    SANYO

NPN Triple Diffused Planar Type Silicon Transistor

800V/8A Switching Regulator Applications
· High breakdown voltage and high reliability. · Fast switching speed 
(tf : 0.1µs typ). · Wide ASO. · Adoption of MBIT process.

Package Dimensions
unit:mm 2022A

Absolute Maximum Ratings at Ta = 25°C
Parameter Collector-to-Base Voltage Collector-to-Emitter Voltage 
Emitter-to-Base Voltage Collector Current Collector Current (Pulse) Base 
Current Collector Dissipation Junction Temperature Storage Temperature 
Tc=25°C PW300µs, Duty Cycle10%

1 : Base 2 : Collector 3 : Emitter SANYO : TO-3PB


Ratings 1100 800 7 8 25 4 140 150 ­55 to +150

Unit V V V A A A W
°C °C

Electrical Characteristics at Ta = 25°C
Parameter Collector Cutoff Current Emitter Cutoff Current DC Current 
Gain Gain-Bandwidth Product Output Capacitance Symbol ICBO IEBO hFE1 
hFE2 fT Cob VCB=800V, IE=0 VEB=5V, IC=0 VCE=5V, IC=0.6A VCE=5V, IC=3A 
VCE=10V, IC=0.6A VCB=10V, f=1MHz 10* 8 15 155 MHz pF Conditions Ratings 
min typ max 10 10 40* Unit µA µA

* : The hFE1 of the 2SC3461 is classified as follows. When specifying 
the hFE1 rank, specify two ranks or more in principle.
10 K 20 15 L 30 20 M 40
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