A monostable pentode circuit used to generate sharp pulses at an adjustable and accurately timed interval after receipt of a triggering signal.



a relaxation oscillator of linearly varying voltage with a low nonlinear distortion factor. Phantastrons may operate in a slave or self-oscillating mode. Phantastrons with large ranges of variable voltage (tens or hundreds of volts [V]) use electron tubes, usually pentodes or pentagrid tubes; those with smaller ranges use bipolar or unipolar field-effect transistors. Solid-state phantastrons are called phantastrans.

Figure 1 shows a circuit diagram of a solid-state phantastron, or phantastran. The complete operating cycle of the phantastran is divided into quiescent, triggered, operating, and regeneration stages. In the quiescent stage, T1 is saturated, T3 is on the threshold of saturation, and T2 is cut off. A phantastran of this type is

Figure 1. Circuit diagram of a solid-state phantastron or phantastran: (R) resistors, (C) capacitors, (P) potentiometer, (T) transistors, (D) diode, (Ec) power supply, (TP) triggering pulse

triggered by a negative voltage pulse that passes through C3, D, and C, arrives at the base of T3, and activates T3; after the device is triggered, T1 is cut off and T2 is enabled. An almost linear discharge of the capacitor C occurs during the operating stage, which ends when the potential at the collector of T2 reaches some critical value (1–2 V). At the end of the operating stage, T1 is enabled and becomes saturated as a result of the ensuing regeneration process, while T2 is cut off. During the regeneration stage, C is charged by the power supply through R3 and the base of T3. The duration of the regeneration stage is τr = 3R3C. The duration of the operating stage, that is, the length of the generated pulses, depends on the circuit parameters and ranges from several microseconds to several tens of seconds. The pulse length can be continuously controlled by a potentiometer P or in discrete increments by the capacitor C.

In radio devices, phantastrons are used for the fine tuning of time delays, as sawtooth generators, and to generate long rectangular pulses. A variant of the phantastron is the sanatron.


Vazhenina, Z. P. Fantastronnye generatory: Teoriia, proektirovanie, raschet. Moscow, 1965.
Spravochnik po impul’snoi tekhnike, 4th ed. Edited by V. N. Iakovlev. Kiev, 1973.
Itskhoki, Ia. S., and N. I. Ovchinnikov. Impul’snye i tsifrovye ustroistva. Moscow, 1972.