Variable-µ-pentode - Triode
Pentode; gm 2 mA/V; Triode µ 20; Ih 0.2 A.
This is a DARIO ECF-1 / ECF1 tube, NOT a
BELVU. The picture shown
is to give the customer an idea of what the
ECF-1 / ECF1 looks
like and is for a visual display purpose only.
Patented in 1940, the Dario ECF1 was developed to enable
the design, together with an ECH3, an EBL1 and a
rectifier valve, an adequate superhet with six tuned
circuits. The ECH3 is used as the frequency changer, the
triode of the ECF1 as 1st AF stage, its pentode as IF
amplifier, while the diodes of the EBL1 are used for
detection and AVC and the pentode section works as the
AF output stage.
The internal electrode assembly of the ECF1, which was
taken from the ECH3, is interesting. Mica plates,
holding and screening plates and the triode system are
identical, only the grids of the pentode section are
different. It is amazing that this pentode contains four
instead of three grids, of which the second and the
third grid, connected in parallel inside the valve,
serve as screen grids. Couldn't one simply have omitted a
grid when using the ECH3's structure for the ECF1? The
dimensioning of the grids may be different. This is
clearly visible with the outer grid in each case: as the
second screen grid in the ECH3 it has a fine pitch,
while it has a coarse pitch as the suppressor grid in
the ECF1.
Why ECH4 and ECF1?
One may ask oneself, why at the same time and for the
same design of circuit were the ECF1 and the ECH4
released? The answer for this is somewhat complicated:
The heater current of the ECH4 amounts to 0.35 A. Thus
it is suitable only for parallel heaters and so
precludes its use for AC/DC sets. For the latter, a
suitable 100 mA U- series was released, consisting of
UBL1, UCH4 and UY1, but this series was not available in
all countries. A valve complement of 2 x UCH4 + UBL1 +
UY1 needed a heater voltage of 145 V and therefore
offered no advantage for countries with predominantly
110 to 130-V mains (e.g. France, Spain.) The ECF1
however could be used there both with parallel heaters,
as well as for series heaters with the C- series of
valves. A valve line-up for 110-V AC7DC sets was then
ECH3, ECF1, CBL6 and CY2. This, like the alternating
current version with an EBL1 and 1883, was very common
until superseded by the Rimlock series. In countries,
where the ECF1 was established, the ECH4 remained mostly
unknown, conversely, the ECF1 was not to be found in
ECH4- countries.
This article was edited 25.Jun.05 17:32 by Jacob
Roschy.