De bovenregionale repeater PI2NOS wordt ontmanteld. Dat meldt de Stichting Scoop Hobbyfonds op
haar website. Vorige week stopte de ontvanger in Breda. De komende
weken volgen een aantal locaties in het noorden van het land.
Drie redenen
De stichting noemt drie redenen waarom PI2NOS in zijn huidige vorm moet stoppen.
De eerste en belangrijkste reden is dat de
inkomsten van sponsoren en donateurs teruglopen. Ten tweede heeft de
bovenregionale repeater al lange tijd te kampen met frequentiemisbruik.
Sommige mensen verstoren het verkeer op de PI2NOS zodanig dat
goedwillenden afscheid nemen van de repeater. Ondanks extra inspanningen van het Agentschap Telecom
zijn de verstoringen niet gestopt. Tot slot noemt de stichting als
reden dat de kosten van de verschillende opstellocaties voor hun
systemen oplopen.
Het is jammer dat dit unieke project van gekoppelde radiosystemen in zijn huidige vorm niet kan blijven bestaan.
From today’s perspective, vacuum tubes are pretty low tech.
But for a while they were the pinnacle of high tech, and heavy research
followed the promise shown by early vacuum tubes in transmission and
computing. Indeed, as time progressed, tubes became very sophisticated
and difficult to manufacture. After all, they were as ubiquitous as ICs
are today, so it is hardly surprising that they got a lot of R&D.
Prior to 1938, for example, tubes were built as if they were light
bulbs. As the demands on them grew more sophisticated, the traditional
light bulb design wasn’t sufficient. For one, the wire leads’ parasitic
inductance and capacitance would limit the use of the tube in
high-frequency applications. Even the time it took electrons to get from
one part of the tube to another was a bottleneck.
There were several attempts to speed tubes up, including RCA’s acorn tubes, lighthouse tubes,
and Telefunken’s Stahlröhre designs. These generally tried to keep
leads short and tubes small. The Philips company started attacking the
problem in 1934 because they were anticipating demand for television
receivers that would operate at higher frequencies.
Dr. Hans Jonker was the primary developer of the proposed solution
and published his design in an internal technical note describing an
all-glass tube that was easier to manufacture than other solutions. Now
all they needed was an actual application. While they initially thought
the killer app would be television, the E50 would end up helping the
Allies win the war.
Television
In
Britain, there was a single television transmitter at Alexandra Palace —
the start of what would become the BBC. This was not only the first
public television service but also the first fully electronic television
system. Pye Ltd. — a company eventually bought by Philips — made
receivers that were surprisingly successful. The sound was at 41.5 Mhz
and the visual was at 45 MHz — high frequencies for those days.
Spurred by the demand, Pye decided that a set with more range would
create a broader market for receivers. The problem was finding a tube
that could handle the 45 MHz frequency in their tuned radio frequency
(TRF) design.
Pye wrote out the specifications for what they needed, but couldn’t
get them made reliably and cheaply. They turned to Philips who took
Jonker’s ideas and added some items needed for this application,
producing the EF50 — a pentode. The resulting TV set (see page 199) had a range of about five times the older sets.
Construction
Old tubes used a difficult process called pinching to seal the end of
a glass tube with the leads running through it. The pinch formed an
inverted V shape where the bakelite base of the tube fit the wide part
of the V and the wires within entered the tube through the point of the
V.
This
had several problems. As more wires had to pass through the pinch, they
had to get closer together. That increased stray capacitance. Worse,
the distance from the bottom of the V to the top of the V meant wires
had to be relatively long which added inductance. Finally, the size of
the V — often half the total length of the tube — was preventing tubes
from getting smaller, hindering the development of portable equipment.
One way to solve this was to build the tubes from metal instead of
glass, with some connections going through the top of the tube. However,
these tubes were expensive to manufacture in quantity and designers did
not like having to wire to the top of the tube. The Stahlröhre bucked
the trend, putting the tube components in horizontally to decrease
wiring to the base and using no top connections. However, again, the
cost to manufacture was high. The 1934 acorn tube was all glass and used
two parts sealed together with short leads but were also known to be
expensive to produce.
Philips, Pye, and the War
When the Dutch military first asked Philips for tubes around 1918,
they declined; Gerard Philips though radio had little practical value.
It would be 1923 before Philips decided to use its expertise in light
bulbs to produce radio tubes. By 1938, Jonker’s work was circulating and
in 1939 there was even an article about it in Wireless Engineer.
By the time Pye came looking for high-frequency tubes, Philips was
ready due to the earlier work. The Pye receiver used six tubes and
required some tweaking, including the addition of a metal shield.
Meanwhile, there was war. The Battle of Britain was in 1940 and the
military was busy in 1939 working on RADAR that also operated at high
frequencies. This RADAR — and the command and control strategies used
with it — would be key to winning the upcoming battle. The team working
on airborne RADAR apparently only had one receiver good enough to get
results. Then they received a tip that Pye had an excellent receiver
that worked in the same frequency range. This became the basis for
Britain’s RADAR sets through the war. About 60% of all Pye TV IF strips
wound up in British RADAR sets.
The big problem was that by 1940 the Netherlands was in German hands.
The production line needed to be moved to Britain, and when the HMS
Windsor took the escaping Dutch government to England, the Philips
family was also onboard with the diamond dies needed to produce the fine
tungsten wires used in the EF50 tube.
After the war, the EF50 would find a home in many oscilloscopes and
radio receivers. This was both because of its superior frequency ability
and the availability of war surplus. Others would also produce the tube
including Marconi-Osram (as the Z90) and Cossor (63SPT). Mullard
produced the tube using the original Phillips equipment and both Rogers
and Sylvania also produced a version.
Nuvistors
This
type of tube would be the king of the hill for RF work until 1959.
That’s the year RCA introduced the nuvistor — a metal and ceramic tube
assembled in a vacuum chamber. These were nearly as tiny as a
transistor, low noise, and had excellent performance at radio
frequencies. These were found in a lot of gear all the way until the
early 1970s including TV tuners, oscilloscopes, and tape recorders.
If you like the sound of an old tube radio, the medium wave receiver
in the video below uses some EF50s and it sounds great. Want more tube history? Or perhaps you’d rather make your own. Or you can watch how they made similar tubes back in the day.
