Tektronix model 453 Oscilloscope
images and remarks
ralphk klimek June 2009
abstract: Defunct Model 453 Oscilloscope repaired, recovered from dumpster
copy left: these images and remarks are copyleft. You are free to use them as you see fit
retrieved this device from a dumpster. Initially I was quite
pleased, as normally, things are not thrown out because they are merely
defective but that they are no longer bright and shiny. Alas, in this
case, it was thrown out because it had ceased to function.
was one of Tektronix' first fully transistorised scopes, apart
from a number of Nuvistor triodes that were used in the circuit where
one might use a FET today. Mine was not functional, it had no
horizontal drive at all. The beam finder revealled that EHT and other
major circuits, including vertical amplifier were working. The
beam finder also showed that some of the horizontal drive and
deflection amplifiers were still partially alive. This was
clearly repairable ! Luckily, the BAMA archive had the service
manual for a device that was closely related , sufficiently close such
that there were very close similarities in the horizontal deflection
circuits that permitted me to debug it. The true Model 453 used
Nuvistor Triodes in selected circuits, my 453 did not use Nuvistors ! must have been a slightly later model.
cause of the fault was fairly clear. The top of the instrument
had some ventilation holes , small enough to keep out dust, and keep in
the hot air, (!) but not small enough to prevent moisture ingress. It
would appear that at some time in its long life both a mystery fluid
"X" and rat urine had contaminated the horizontal deflection
amplifiers. Someone had also immediately sprayed it with WD40,
the sticky residue was still apparent. When I attempted to solder
the board, the unmistakeable odour of rodent urine revealled the
identity of one the the mystery contaminants.
Rat urine ,
after 40 years, does bad things to electronics. Many of the components
showed some corrosion and some had corroded to oblivion. Would I
persist ? The instrument to very close to being fully functional
...as it was... and I had a manual. Without the circuit I would
have certainly permitted this instrument to continue its journey to
landfill, where it could continue its demise by adding to Melbournes'
groundwater toxic heavy metal overburden, but lets not mention that!
I decided to persist.
All the instruments transistors were
mounted in sockets, an anachronistic effort, but consider that
all the other Tektronix products used thermionic valves where this was
the accepted practice. Active devices , including the "new-fangled"
solid state types went into sockets. Some of the sockets had corroded
to pieces. The plastic transistors had not survived, their leads had
corroded away. I dont think the quick application of WD40 at the time
of the original liquid spill had penetrated into the component sockets.
I replaced them with random equivalents. The main
horizontal deflection amplier transistors leads fell off when I tried
to move them, corrosion had completely severed the leads right against
their berylium oxide heatsinks. No problem, I used some old high
speed high voltage video amplifier CRT driver transistors recovered
from a discarded VGA monitor. Some circuits also used the
impossible to replace Tunnel Diodes, but these were still functional.
(whatever happened to the Tunnel Diode? Tinfoil Hat anyone ?)
had only to replace about 5 completely damaged components and the
instrument springs back into life. The horizontal scan is not as linear
as could be but at least it lives and is usuable as it is. Not
bad for something built in 1965, and its vertical amp was rated to
50Mhz too! I was just starting school then.
, as you would expect, from a technology pioneer like Tektronix was
superb. If it were not for the possibility of liquid ingress this scope
would still work in another fifty years. The screen size is very
small. Hewlett Packard had bigger and brighter screens but they had the
patent for a special final mesh accelerator and focussing electrode
geometry. This scope's faceplate had a die cast mounting ring
that I would imagine had been used with an specially attached camera.
The original deflection transistors ran from a 75V supply rail, so the
available deflection voltage was limited. Their older valve based
scopes had bigger screens as they had the ability to amplify higher
I will probably take this scope to work with me,
for the few times that I still need a scope for. Not bad for forty
odd years, eh ?
see also www.chiark.greend.org.uk/scopes
|Not dead yet, Im alive !!! ||side panel with aux controls and outputs||white ceramic (BeO?) heatsinks and my replacement deflection transistors|
|horizontal deflection and triggers and rat's gunk||good old linear PSU||view of vertical amp and crt|
|vertical deflection amp||underside vertical input amp||underside vertical input amp|
|horizontal amps,triggers,timebase||underside vertical input amp||sideview showing cast aluminum chassis|
page created Fri Jun 19 18:54:51 EST 2009