Off-topic, but interesting (Fiorina fired)

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Fri Feb 11 17:32:19 2005

> Tek 555: No idea - I haven't seen the service manual for one of those :)

I was lucky enough to get the manual (I am not sure if it's a user manual
or a service manual, suffice it to say most of it is alignment and
schematics...) with the instrument.

It's one of the best manuals I've seen for any piece of electronic
equipment (FWIW, the other Tekky manuals of the period are as good). It's
clear, easy to follow, and complete.

As regards the instrument. It's big. it's very heavy. There are 2 handles
on the 'indicator' (the bit you'd call the 'scope) and one on the seprate
PSU so that it can be moved. But you don't want to take it very far. It's
a true double-beam instrument with 2 timebases (and separate X and Y
plates for the 2 guns).


The Y-preamplfiers are plug-ins (it can take multiple-trace plug-ins, so
in theory you can have 8 traces on-screen at once!). The main Y
amplifiers are those Tekky Distributed Amplifiers where you have a 2 rows
of pentodes with delay lines along the control grids and anodes. Manages
an honest 33MHz (and can be pushed beyoned that). The timebases are also
plug-ins, but really for servicing. AFAIK there were never any different
timebase modules for it.

Oh yes, the PSU is regulated by a row of 6080 double triodes. And even
the heater supply to the 'indicator' heaters is stabilised (it feeds a
bright-emitter diode from the heater winding, the anode current of that
controls a pentode, which cotnrols a saturable reactor in series with the
heater teansformer primery. Neat thing is that it regulates the RMS value
of the heater supply, exactly what you want).

Oh yes, it was made to be repaird. It's built on ceramic terminal strips
with silver-plated notches that the components are soldered to. You're
supposed to use silve-loaded solder to avoid damaging the plating (the
stuff sold for SMD rework is ideal). Anyway, in the better 'scopes,
including the 555, there's a little reel of solder inside, to be used for
making repairs.

Failures : Not many. The odd capacitor goes short-circuit, I've had to
replace one valve (actually, that was in my 551, which is a
single-timebase duouble-beam 'scope). When I got it, a metal mouting bush
had borken free and was shorting the 350V line to chassis. That burnt out
one resistor. But if the CRT fails, I've got problems. It was only used
in the 555...


> Aren't they the ones you have to use a special silver-bearing solder on? =
> I
> seem to recall reading about Tek putting a small roll of solder inside th=
> e
> chassis of every scope that used the ceramic mountings.

Not every 'scope. It appers only the better models got the free reel of
solder!

> To be honest, I wasn't that impressed when I had a look round a few surpl=
> us
> dealers a while back. I paid =A335 +VAT for my 466 in a liquidation aucti=
> on.
> Also got a rather nice Farnell L30B power supply (=A36 +VAT) and a Fluke =
> DMM
> for =A38 +VAT. Not too bad IMO.

You did well!. I've picked up what I consider to be bargains over the
years too (my Goould logic analyser was 50 quid, back when logic
analysers were very uncommon instruments). I paid \pounds 30 for the 555
with a few plug-ins (and was given many more). Probably the best bargain
was a 1S1 plug-in (1GHz sampler, basically uses aliasing to look at
repetitive high-speed signals) for \pounds 16.00 complete with gen-rad
cable, attenuators, manaul _and a recent calibration certificate_.

The important thing is to know what something is worth and to stick to it

-tony
Received on Fri Feb 11 2005 - 17:32:19 GMT