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Патент USA US2527407

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Oct. 24, 1950
P. A. DONKER
ANODE AND. GRID BIAS VOLTAGE SYSTEM FOR
2,527,406
cLAss B 0R c AMPLIFIERS _
Filed May 9, 1946
PJFZERADRLAANDOAKER
IN VEN TOR.
Arrow
Patented Oct. 24, 1950
2,527,406
UINI‘TED' STATES ‘PATENT OFFICE
ANODELAND: GRID BIAS? VOLTAGE SYSTEM
FOR CLASS B OR C AMPLIFIERS
Pieter Adriaan Donker, Eindhoven, Netherlands,
assignor, by mesne assignments, to Hartford
National Bank and Trust Company, Hartford,
@onns ‘as-trustee
Applieationli/lay 9, 1946, Serial No. 668,424
In the Netherlands July 4, 1941
'
Section 1, Publi‘c‘Law csamAugust s, 1946
Patent‘ expires July 4, 1961i
5 Claims. (Cl. 179-471)
1
-
2
l
The invention relates to a push pull amplifying
system wherein such a negative bias voltage is
supplied to the control grids of the amplifying
tubes that in uncontrolled condition the anode
current of the amplifying tubes is substantially
suppressed (B-class ampli?er) or wherein use is
made of a larger grid bias voltage-than‘ is required
for the suppression of the anode current (C-class
ampli?er).
With such ampli?ers wherein the anode voltage
is taken from an anode voltage apparatus pro
vided with a supply transformer, it is known to
reduce or to prevent distortion of the ampli?ed
recti?er circuit, the ratio of transformation of
the transformer is so chosen, that the voltage
‘drop produced across the‘ primary windings
thereof is smallwith respect to the output voltage.
The invention will be‘ explained more fully
with reference. to the accompanying drawing
which represents, byway of example, one particu
larly advantageous embodiment of a push-pull
amplifying; system: according to the invention.
10
In the amplifying system shown the, for ex
ample, low-frequency oscillations to be ampli?ed
are supplied to‘ the input terminals l of a pre
ampli?er 2 whose output circuit comprises a
transformer: 5. This transformer has a secondary
oscillations which is caused by the-internal resist
ance of the anode voltage apparatus, by supplying 15 winding e which is divided, into two equal parts
to» the control grids of the amplifying tubes not
which are connected‘ into the control-grid cir
only a ?xed negative bias voltage but also a varia
cuits of two amplifying tubes 5 and 6 respective
ble bias voltage which counter-acts the negative
ly which are connected in push-pull and as B
bias voltage and‘ which depends on the load on the
class. With the aid of an output transformer 1
ampli?er.
20 the ampli?ed oscillations are supplied to the load
With known push-pull amplifying systems the
impedance formed, for example, by a loudspeak
required grid bias voltage which increases with
er 8.
the control of the ampli?er is obtained by con
The anode voltages of the amplifying tubes 5
necting an impedance into the output circuit of
and 6 are taken from an anode voltage apparatus
the ampli?er, by rectifying that portion of the 25 which com-prises a supply transformer 51 which
output energy which is taken therefrom and by ,
is to be connected to.v an alternating current sup
supplying the load-dependent direct-current volt
ply, a full-wave rectifying tube it and a smooth
age thus obtained, after being smoothed, to the
ing ?lter-consisting of condensers l l‘ and a choke
control grids.
'
coil l2. The negative and. positive output termi
It is also known to derive the variable grid bias 30 nals I3. and [4' respectively of the anode-voltage
voltage from the’ anode direct-current voltage it
apparatus are connected to the earthed cathodes
self, in which‘ event the grid bias voltage is o'c
of the amplifying tubes 5 and 6 and to the central
tained by rectifying and smoothing the oscilla
tap on the primary winding of the output trans
tions of an auxiliary oscillator whose anode volt
former 1 respectively.
age is formed by that of the amplifying tubes.
The variable negative grid- bias voltage required
35
Although the last-mentioned method of gen
for the tubes 5, B‘connected as a B~class recti?er
erating the variable grid-bias voltage has the ad
is taken from the alternating current supply with
vantage that now the energy required therefor
the aid of an additional supply transformer‘ 15
is taken, in contradistinction to the ?rst-men
and after being recti?ed by a full-wave rectifying
tioned method, directly from the anode voltage 40 tube t6 and smoothed by’ means of a ?lter l1, it
apparatus, the last-mentioned method has the
is supplied via the halves of the secondary wind
drawback of being comparatively complicated
ing of the input transformer 3 to the control grids
and expensive.
of the amplifying tubes.
The invention aims at avoiding the above
. In order to avoid distortion of the ampli?ed
mentioned drawbacks.
45 oscillations clue to an increase of the internal
According to the invention, the variable grid
voltage drop of the anode-voltage apparatus and
bias voltage is obtained by rectifying and smooth
therefore a decrease of the anode voitage upon
ing. an alternating current or voltage which oc
curs in the anode-voltage apparatus and which
depends on the control of the ampli?er.
an increase of the control of the amplifying tubes
The variable grid-bias. voltage is preferably
taken from the secondary winding of a trans
former whose primary winding is connected in
series with the anode'woltage winding of the sup
ply transformer whilst, in order to reduce the 55
the transformer IE but also a variable bias volt‘
age. which counteracts the said fixed negative
bias and which increases with the load on the
voltage drop thus produced in the‘anode voltage
5, 5‘, the control grids: have supplied to them not
only the ?xed negative’ bias voltage taken from
anode voltage apparatus and therefore with the
‘control of the push-pull ampli?er.
’
According to the invention, this. variable bias
2,527,406
3
voltage is derived from an alternating current or
voltage which occurs in the anode-voltage ap
paratus and which increases with the load on this
apparatus. For example, the variable grid volt
age may be taken from the choke coil by provid
actly in counterphase without particular steps
are taken.
In order to ensure in the circuit ar
rangements shown that the said output voltages
are exactly in counterphase, a condenser 26 con
nected in series with a resistance 2‘! is connected
ing a secondary winding on the core of the said
in parallel to each of the secondary winding
coil and by supplying the alternating voltage oc
halves 23, 24 and a voltage which is exactly in
counterphase with the output voltage of the
transformer I8 and which is out of phase with
curring across the said winding, after being rec
ti?ed and smoothed, to the control grids of the
tubes.
10 respect to the alternating voltage across the
A further possibility of realising the system ac
winding-halves 23, 24 is taken from the re
cording to the invention, which has proved to be
sistance 21.
particularly advantageous, is represented in the
Care should further be taken to prevent the
load on the grid voltage recti?er circuit from be
In this form of construction the variable bias 15 coming excessively high, so that the potentiom
voltage is taken from the secondary winding
eter resistances 28, 29 should be taken of com
of a transformer I8 whose primary winding I8
paratively high values, taking therewith into ac
count that the time constant for the charge and
is connected between the two halves 20 and 2I
in which the secondary winding of the supply
the discharge of the condensers 25, 30, 3| should
transformer 9 is divided in view of the full-wave 20 amount to about 0.1 second in order to be able
recti?er I 0 whilst the central tap on the primary
to follow rapid variations in the load on the am
drawing.
'
s
'
winding I9 forms the negative output terminal
of the anode-voltage apparatus. Through the
pli?er.
primary winding I9 passes consequently the anode -
caused by the grid current of the tubes 5, 6, it is
It may be observed that in view of distortion
current of the rectifying tube III, which current 25 also advantageous to take comparatively large re- _
increases with the increasing load on the anode
sistances 28 and 29, in which event, upon the oc
voltage apparatus. As a result there is induced
currence of a slight grid current, the condensers
30 and 3| are charged to a voltage which ap
in the secondary winding 22 of the transformer
I8, whose secondary winding-halves are oppo
proximately corresponds to the maximum in
sitely connected in series with the secondary 30 stantaneous value of the grid-control voltage
whilst the energy required for charging the con
winding-halves 23, 24 of the transformer I5, an
alternating voltage whose amplitude increases
densers and which is taken from the ?nal or en
ergy amplifying stage of the pre-ampli?er 2 is
with the load on the anode-voltage apparatus.
Since the secondary windings of the trans
only in this case.
A supplementary advantage of the above-men
formers I5 and I8 are oppositely connected in 35
tioned increase of the negative grid-bias voltage
series and therefore the output voltages of both
transformers counteract one another the result
upon the occurrence of grid current is that thus
the production of an inadmissibly high anode
ing tube I6 has a maximum instantaneous value
current in the tubes 5 and 6 is counteracted.
which decreases with an increasing load on the 40
In order to prevent the tubes 5 and 6 from be
ing alternating voltage set up across the rectify
anode-voltage apparatus with the result that
with an increasing load on the anode-voltage
apparatus the negative grid bias voltage supplied
to the ?rst smoothing condenser 25 of the ?lter
ing overloaded, it has furthermore proved to be
advantageous to dimension the transformer I8
from which is taken that part of the total grid
bias voltage which varies with the load, in such
I‘! and consequently to the control grids of the ~15 manner that with the highest admissible load on
tubes 5 and 6 decreases owing to the increasing
the amplifying tubes 5 and 6 the iron of the
control of the push-pull ampli?er, which result
core of the transformer I8 just gets saturated.
was aimed at. In order to be able to adjust
Upon an increase of the load above the highest
the grid-bias voltage in each of the tubes 5 and
admissible load on the amplifying tubes 5 and 6
6 exactly to the desired value, the output voltage 50 the absolute value of the grid-bias voltage no
of the ?lter I1 is supplied, via potentiometers 28
longer decreases with the result that a further
and 29 respectively and after being further
increase of the anode current of the tubes 5 and
6 is not supported.
smoothed with the aid of condenser 30 and 3I
respectively, to the control grid concerned.
In the shown practical example of the system
In order to prevent an unnecessary increase of 55 according to the invention the tubes 5 and 6 are
the internal voltage drop of the anode-voltage
represented as triodes. The invention, may,
apparatus with an increasing load, the voltagev
however, also be applied, of course, to tubes hav
drop occurring in the primary winding I9 is pref
ing more than three electrodes and the effect
erably reduced as far as possible. In view thereof
aimed at may also be obtained by supplying the
it is advantageous to take a high ratio of trans 60 variable grid-bias voltage to auxiliary grids in
stead of to the control grids.
flormation of the transformer I8, for example of
:20.
It may ?nally be observed that the use of full
Besides, in order to restrict the voltage drop
wave recti?er systems for generating the anode
in the primary winding of the transformer I8, it
and grid-bias voltages is not essential for the in
is advantageous to ensure that the output volt 65 vention although, in view of the smoothing of
ages of the transformers I5 and I8 are exactly
the recti?ed alternating voltages, this is to be
in counterphase so that the in?uence exerted by
preferred to the use of half-wave recti?er sys
the alternating voltage taken from the trans
tems.
former I8 on the grid voltages of the tubes is as
What I claim is:
great as possible.
'
70
1. A system for supplying anode and grid bias
Since, as is known in itself, the current in the
voltages to an electronic ampli?er of the class
anode current recti?er circuit is not exactly in
B or C type, said system comprising a ?rst direct
phase with the voltage across the secondary
voltage supply energized from an alternating
winding of the transformer 9, the output voltages
voltage source and furnishing anode potential
of the transformers I5 and I8 are neither ex 75 to said ampli?er, said ampli?er acting as a load
2,527,406
on Said ?rst supply, a second voltage supply
furnishing constant grid bias potential to said
transformer to produce a, control voltage, and
age to produce a control voltage whose magni
tude depends on the changes in the load imposed
means to combine said control voltage with said
constant grid bias potential to produce a result
ant grid bias varying inversely as the load.
4. A system for supplying anode and grid bias
voltages to an electronic ampli?er of the class
B or C type, said system comprising a ?rst volt
age supply furnishing anode potential to said
on said ?rst supply, and means for combining
ampli?er, said ampli?er acting as a load on said
ampli?er, means for deriving an auxiliary alter
nating voltage from said ?rst supply varying in
accordance with changes in the load thereon,
means to rectify and ?lter said auxiliary volt
said control voltage with said constant grid bias 10 ?rst supply, said ?rst supply including a ?rst
transformer having a primary winding for con
potential to produce a resultant grid bias varying
inversely as the load.
2. A system for supplying anode and grid bias
nection to an alternating voltage source and a
pair of secondary windings, a full wave recti
' ?er tube having a pair of anodes connected re
voltages to an electronic ampli?er of the class
B or C type, said system comprising a ?rst volt 15 spectively to one end of each of said secondary
windings and a cathode, a second transformer
age supply furnishing anode potential to said
having a center-tapped primary winding con
ampli?er, said ampli?er acting as a load on said
nected between the other ends of the secondary
?rst supply, said ?rst supply including a trans
windings of said ?rst transformer and a second
former having a primary winding for connection
to an alternating voltage source and a secondary 20 ary winding and a ?lter connected between said
cathode and the center-tap of the primary wind
Winding, a recti?er connected to said secondary
ing of said second transformer to provide said
winding, a ?lter connected to the output of said
anode potential, the voltage developed across the
recti?er to provide said anode potential and an
impedance interposed between said recti?er and
said secondary winding, the alternating voltage
developed across said impedance varying in ac
cordance with said load, a second voltage supply
furnishing constant grid bias potential to said
ampli?er, means to rectify and ?lter the voltage
across said impedance to produce a control volt
age, and means to combine said control voltage
with said constant grid bias potential to pro
duce a resultant grid bias varying inversely as
the load.
3. A system for supplying anode and grid bias .4
voltages to an electronic ampli?er of the class
B or C type, said system comprising a ?rst volt
age supply furnishing anode potential to said
ampli?er, said ampli?er acting as a load on said
secondary winding of said second transformer
varying in accordance with said load, and a sec
ond voltage supply furnishing grid bias potential
to said ampli?er varying inversely as the load,
said second supply including a third transformer
having a primary winding connected in parallel
with the primary winding of said ?rst trans
former and a pair of secondary windings con
nected in series through the secondary winding
of said second transformer, a second full wave
recti?er tube having a pair of anodes connected
to the free ends of the secondary windings of
said third transformer and a cathode and a ?lter
connected between the cathode of the second
tube and the center point of the secondary wind
ing of said second transformer to produce the
?rst supply, said ?rst supply including a ?rst 40 varying grid bias potential.
5. An arrangement as set forth in claim 4 fur
transformer having a primary winding for con
ther including phase shifting means interposed
nection to an alternating voltage source and a
between each anode of said second tube and the
pair of secondary windings, a full wave recti?er
secondary windings of said third transformer.
tube having a pair of anodes connected respec
PIETER ADRIAAN DONKER.
tively to one end of each of said secondary wind
45
ings and a cathode, a second transformer having
REFERENCES CITED
The following references are of record in the
of said ?rst transformer and a secondary wind
?le of this patent:
ing and a ?lter connected between said cathode
UNITED STATES PATENTS
and the center-tap of the primary winding of the 50
Number
Name
Date
said second transformer to provide said anode
1,904,272
Cousins __________ __ Apr. 18, 1933
potential, the voltage developed across the sec
1,985,946
Miessner __________ __ Jan. 1, 1935
ondary winding of said second transformer
2,102,779
Beers ____________ __ Dec. 21, 1937
varying in accordance with said load, a second
Norton ___________ __ Oct. 11, 1938
voltage supply furnishing constant grid bias po 55 2,132,830
‘a center-tapped primary winding connected be
tween the other ends of the secondary windings
tential to said ampli?er, means to rectify and
?lter the voltage in the secondary of said second
2,154,200
Dow ______________ __ Apr. 11, 1939
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