[AMRadio] 75TH vs. 75TL (was Class C stuff)

[John Coleman]

The TH does means High Mu, which means it requires less swing in grid
voltage to produce the same swing in plate current.  Conductance is I/E
Transconductance or MU is (delta Ip) / (delta Eg) if a grid voltage swing
from -5 to -3 volts the delta Eg is 2 volts if this causes plate current to
change from 50 ma to 70 ma then the delta Ip = 20 ma, so, .020 amps / 2
volts = .01 mhos or 10,000 micromhos.  The higher the transconductance, the
more the AMPLIFICATION FACTOR is possible with design. In CLASS A or AB1
there is no grid current so no driving power required, but in AB2, B, or C
the grid draws current. The characteristics of the individual tube
determines the amount of grid current or driving power required.  The High
or Low factor in manufacturing is the distance from grid distance from the
cathode or filament and the density of the wire windings that make up the
grid.  High MU means the grid is closer to the cathode in order to have more
effect on the plate current and is generally some what of a tighter grid
mesh this causes more grid current to flow. Lower grid voltage swing and
higher grid current means a requirement for a lower input impedance.

73, John

-----Original Message-----
From: amradio-admin at mailman.qth.net
[mailto:amradio-admin at mailman.qth.net]On Behalf Of w5omr
Sent: Thursday, March 21, 2002 1:12 PM
To: amradio at mailman.qth.net
Subject: Re: [AMRadio] 75TH vs. 75TL (was Class C stuff)


:
: Perhaps I should plug in some 100tl,s and see if the high impedance
: grids do better...270 volt swing on the tl's compared to the
: 150 volt swing on the th's....

huh?

the TH is the Hi-Mu version
TL is the Low-Mu version.

or, am I missing something?  Higher Z, means less driving
requirements for the grids.... right?





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