Equipment information

Precise Development Corporation 111 Valve characteristic meter
Precise Development Corporation
Model: 111
Date: 1959
Category: Measurement instruments
Group: Valve characteristic meter
Description: Gm and Em Tube Tester

The Model 111 Gm and Em Tube Tester introduced to the
electronics industry the most complete tube evaluation
available, other than by expensive and complicated
laboratory Bridge Systems.

The Model III makes the following general tests:

Gm — Mutual Plate Transconductance.

Em — Plate Emission.

Filament Current.

Leakage and Shorts.




1-	Gm

Gm (Mutual Plate Transconductance) is the ability of the
grid of the tube to control its plate current.
Mathematically it is a small change in plate current divided
by the change in grid voltage required to make the plate
current change. The plate voltage is kept constant. From
this it can be seen that the Gm is a most important
measurement - especially in video, I.F. and power amplifiers.

The Gm test is made by applying pulsating DC voltages as
follows:- Positive to the plate and screen; negative to the
grid. An AC signal voltage is also fed to the grid which
causes an AC increment to appear in the plate current. It is
the measurement of this increment which ascertains the Gm of
the tube. These are actual average Gm measurements and are
not hypothesized.

2-	Em

Em (Plate current measurement) of a tube is, as the name
imnlies, measurement of the tube plate current. Although the
voltages applied to the plate are swept, the measurement is
still primarily static. It is an indication of the cathode
current (which, of course, controls self bias) and also the
plate resistance, etc. In this test separate voltages are
again fed to the plate, screen and arid of the tube. The
voltages are AC, the current is DC since the tube rectifies it.


It may be said that the more tests made, the more correct
the analysis of the condition of a tube. |t is necessary,
however, to occasionally look for a faster means. With this
idea in mind, PRECISE has * (Asterisked) the most important
single test for each tube or section thereof. |f you do not
wish to make both the Gm and Em tests, we recommend that you
select the one with the * in back of its listing on the roll


1-	Select the tube type under the heading marked 'TYPE'
abovo the Roll Chart. Gm tests are indicated by 'Gm' in the
'NOTE' column.

2-	Set the FILAMENT Switch to the same value as shown under
the heading • FI L ’ - The top value listed is the Filament
voltage. The value directly beneath it is the Filament
current. Measuring the current is discussed in a later section.

These manuals are available for the above equipment:

Manual Type: Service Manual Precise-7214-Manual-Page-1-Picture
Pages: 17
Size: 5.95 Mbytes (6241210 Bytes)
Language: english
Date: 1959
Quality: Scanned document, reading partly badly, partly not readable.
Upload date:
MD5: 3c96ecb8ef57af75232f885af5390585
Downloads: 113 since 27 September 2015
Construction Book

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