OSCILLOSCOPE SWEEP CCT
cut-off as grid is biassed well negative.
Capacitor Ct will charge
When grid made much more positive (i.e. +ve pulse)
conducts, capacitor discharges (linearily).
Anode voltage falls; this fall is
fed back thru capacitor Ct which will tend to oppose the original change of grid
This effect means that the grid voltage in fact varies almost
However; the anode voltage falls in a linear fashion until anode bottom
is reached THEREFORE; the voltage decrease is linear because the discharge
current through the capacitor is constant!
Circuit derives its name from
Miller effect (in vacuum tubes) which multiply's grid-plate capacitance by (µ
+1) the actual (small) grid-plate capacitance; (this is nullified by a screen
The operation of the circuit can also be controlled by variation of
the suppressor grid voltage.
Edwin Armstrong discovered in 1915 that
oscillation occurs in triode amplifiers by this inter-electrode capacitance when
the anode load was inductive (and below resonance)
In 1919 John Miller of
the US bureau of standards
presented a mathematical analysis of the phenomina
and the effect that now bears his name!
Suggested schematic is a
development of above.
Cathode follower isolates the anode from capacitance
connection i.e. Hi to Low impedance convertor.
From: A simple all-valve
1-inch oscilloscope by Ian Wilson K3IMW
Dr F.C.Williams was a young wartime radar boffin.
He was well known for
his birdsnest breadboard circuits which often left the board,
the bench, and over the edge.
He was also known to comment on circuits with
"Oh! Very sanitary!" or "Phantastic!"
In those days, time bases and the delay
of pulses tended to depend on an exponential rundown due to the simple RC
He worked on linearising the rundown to improve stability,
by using "Miller" feedback.
His pulse-stretching circuit using 2 pentodes + 2
diodes was named the very sanitary Sanatron
and the single pentode
version became the phantastic Phantastron.
In more sophisticated
(WW II) radar equipment a much more linear timebase was needed and also for
precise and adjustable time delays.
To acheve this BLUMLEIN developed
what is commmonly known as the "Miller Integrator".
His patent 560,527 explains its principles and goes on to give a
sample of each of two applications.
These initiated a whole series of
circuits using diodes as auxiliaries and included the celebrated "phanstastron"
During the war such patents were not published and it seems
the basic circuit was covered by A C Cossor Ltd and J W Whiteley a few months
Actually Blumlein's invention was the earlier, but owing to the
elaborate secrecy procedure some time elapsed before the application could be
Hand-built minature oscilloscope using Miller linear sawtooth sweep oscillator (as detailed above)