The following selection of tube portraits is purely subjective and in no way follows any objective system.
Some tubes have simply become dear to my heart. The condition is, however, that I own this tube myself and
have already worked with it as a hobby.
Let's see what treasures are in the various boxes:
The rare audio end pentode P420 of the manufacturer "Radioröhrenwerk E. Schrack, Wien"
was produced before 1930 (until about 1945) in Austria and was made with 5-pin B5 (O5A) socket.
In similar tubes of this time, grid 2 is not designed as a pin in the middle, but more often as an extra side connection. This
directly heated tube is one of the oldest pentode I own and is still functional. The tube system is arranged horizontally
in the glass bulb!
The tube data are the same or similar to the better known tubes RES174d (Telefunken), B443 (Philips),
PP415 (Tungsram) and L415D (Valvo).
The tubes of the company Schrack were sold under the name "Triotron".
The P420 is directly heated with 4V, 0.15A and intended for battery supply. Unfortunately I do not have an original Tritron
data sheet, so use the tube data with care.
The glass bulb of the pentode still has the shape (similar to a incandescent lamp) of the triodes of its time such as the RE134,
B409 or L413. So the tube is not beautiful, but a nice example of the art of engineering from Austria.
In contrast to the RES174d (the letter "d" marks the side connection as fifth pin) the socket is designed as a 5-pin European
socket like the pentode B433.
The glass bulb of the tube is mirrored (metal coating).
The detailed photos show the 5 pin contacts and a view into the tube on the horizontal system ("metal box") with the
right-angled connections on both sides.
The tube has the faintly legible imprint "Triotron P420 Made in Austria" on the top of the glass bulb. On the socket the
imprint "45" is readable at the bottom.
If You have further data (data sheet!) about this P420 tube, please let me know (eMail).
The rare RF pentode NS4 of the manufacturer "Kremenezky Johann",
Vienna (Austria) and Budapest (Hungary), was produced from about 1931.
A 5-pin B5 (O5A) was used as socket. The anode connection of the tube is designed as
a cap with screw connection on top. The special thing about my NS4 tube is the complete
shielding with a two-piece copper sleeve.
The tubes of the company "Kremenezky" were first sold under the brand name "Orion".
The "Watt AG Vienna" (Tungsram) was also involved. From about 1933
the brand name "SATOR" instead of "ORION" was used in Austria.
Orion's first legal predecessor in Hungaria was founded in 1913 by "János Kremeneczky" under
the name "Magyar Wolframlámpagyár". The Orion brand was there established in 1925 and was mainly
engaged in the manufacture of tubes and radio equipment (in 1947, the Hungarian company was transformed
into the Orion Radio and Electricity Company and was nationalized shortly thereafter).
The NS4 tube with copper shielding was for example built into the "ORION 7050" (about 1933) of the
Hungarian company "Orion Radio" as an intermediate frequency amplifier and shown in
company brochures.
In the magazine "Österreichischer Radio Amateur" (ÖRA) the tube NS4 is
already mentioned in 1931.
The tube data are the same or similar to the better known tubes E466 (Philips),
RENS1284 (Telefunken), H4128D (Valvo) and SP4 (Mullard) as well
as HP4100 (Tungsram).
The NS4 is indirectly heated with 4V, 1.1A. Unfortunately I do not have an original Orion
data sheet, so use the tube data with care.
Remarkable is the complete copper shielding of the tube. Unlike similar tubes,
the glass bulb is a straight cylinder so that the copper sleeve fits well on it.
The glass bulb of the tube is inside strongly mirrored (metal coating).
The detailed photos shows the socket pins and the cap with screw connection on top.
The lower part of the copper shielding is fixed to the tube base with a screw. A wire
leads from the screw into the inside of the tube socket (probably connected to the
inside tube shielding).
The tube has the black imprint "ORION NS4 4 VOLT" on the copper sleeve.
On the side the imprint "U20" is readable.
If You have further data (original data sheet, maybe in Hungarian) about this NS4 tube please let me know (eMail).
The AL4 pentode was developed by Telefunken in 1935 and went into series production in 1936. Philips and Tungsram
built the almost identical AL3 at the same time (this was then simply renamed AL4). RCA developed the well-known
Beam Power Tetrode 6L6 at about the same time.
The AL4 is an end pentode for audio applications in single or push-pull circuits with a maximum anode loss
of 9 watts. The anode (plate), the cathode, the control grid G1 and the screen grid G2 are connected to socket
contacts (8 pin external contact socket), the suppressor grid G3 is directly connected to the cathode inside
the tube. The tube is indirectly heated with 4V using bifilar wound filament. It represents a significant advance over
tubes AL1 and AL2 (predecessor tube). The transconductance (9 mA/V) of the tube, which was very high
for that time, makes the AL4 very sensitive and thus results in a much higher voltage amplification in the output stage.
When the AL4 is at full power (3.6 Vrms grid AC voltage), this results in a speaking power of 4.3 Watts at the anode.
This represents a good power reserve for perfect reproduction of volume peaks. Another advantage is that a grid bias
resistor of 1 MΩ is allowed for the AL4, so that the attenuation to the previous stage remains correspondingly low.
The tube was used in receivers in combination with other tubes of the A-series such as AC2, ACH1, AF3, AF7, ABC1,
AB2 and AM2 or as audio amplifier with the AC2.
The AL4 was for that time (from about 1936) a top tube; the technicians of that time did a very good job.
You can feel that and I simply like the AL4.
The AL4 is indirectly heated with 4V, 1.75A. For operation 250V with about 40mA are necessary. In the
simplest case the external circuitry consists of a 150 Ohm cathode resistor (grid bias -6V) and a load
impedance of 7 kOhm (audio transformer) as well as a control grid resistor of 1 MΩ.
The AL4 has 8 side-contacts ("elephant foot") and therefore requires a P8A socket.
The glass housing of the AL4 is designed as an attractive dome case, also called "coke-bottle".
The pictures show original Bakelite P8A sockets from old production which I bought at a ham radio flea market.
The glass bulb of my AL4 is mostly metallized silver-grey inside. As the view from above shows, the
anode is star-shaped. The AL4 was built by different manufacturers and also slightly further developed,
so that not all AL4s are completely identical.
A picture from an old book from 1939 shows the internal structure of the tube.
My AL4 is labeled as follows on the glass bulb: "TELEFUNKEN AL4 D.R.P". The abbreviation D.R.P. means
"Deutsches Reichspatent".
On the edge of the socket "096" is printed and on the bottom "hd e". The Telefunken
code "hd" means the production of my tube in October 1938, the meaning of the "e" below is unknown to me.
The AZ1 is a directly heated full wave rectifier designed for medium power
receivers and with an eight pin side contact base (P8A).
The rectifier tube AZ1 exists in many different designs with small differences and was
manufactured by many different companies. My specimen could be possible from the structure an
(Telefunken) Italian WE55. The operating data of the tube is however completely
identical to the AZ1. In its simplicity the tube is beautiful to look at. The heating filaments
glow very well visible.
The AZ1 has a 4 Volt filament rated at 1.1 Ampere. The maximum anode RMS voltage is 500 Volts. At
this anode Voltage the DC current could be up to 60 mA. At 400 Volts on the anode the output
could rise to 75 mA and with 300 Volts on the anodes the output current could be 100 mA.
The glass bulb of the rectifier has the elongated shape of earlier tube developments of its time.
The last pictures show the appropriate Bakelite P8A sockets for the AZ1.
Unfortunately there is no longer any label on the glass bulb. At the bottom of the
tube are the letters "vs" and "I". This would plausible mean as
Telefunken key the year of manufacture is March 1939. The meaning of the "I"
below is unknown to me.
The anode of the tube is constructed as a mesh anode. The heating filaments of the two
rectifier systems are connected in series and were designed as nickel strips. Its inner
construction is very simple with a small rectangular mica plate on top and no center bar.
The rectangular shape and size of the mica glow-wire holder and the getter vessel
indicate also Telefunken as a probable manufacturer.
