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No, the plug in lights to NOT light in a 7603 frame, this was
intentional, but I don't know the orignal thinking that led to it.
7A26 and similar format vertical plug ins don't need it, and the
7B53A (the intended sweep plug in) has white indicator rings around
the pushbuttons, and NO internal lights. so, if yours doesn't light,
that's just what it's supposed to do, but the rationale is now lost
to history.

Miroslav's comments about neon lamps in the older supplies as
transient protection are not correct, they were warning indicators
for lethal voltage, nothing more. This is even explained in the
service manuals. Older unit have no AC transient protection.

Tek really should have incorporated transient protection with it's
switchers, as many were designed before rugged high voltage FETs
existed, and they are easily damaged by transients. I was not
suggesting you buy a crappy $4.95 trasient protector, as I use some
very high end ones here, but it's up to you. Tek (after many field
failures) added this protection to later 2200 series units, and it
seemed to help significantly, they were just single ordinary GE
varistors. If you are really in love with your gear, by an
autocorrecting Liebert UPS, the ultimate in line conditioning.

Leaving it on vs. turning it off. well, this argument has raged for
decades, but I think you need to consider some simple math: the 7K
series runs VERY hot, and it has some definite MTBF limits associated
with capacitor and semiconductor failures caused by this, not to
mention consuming the CRT. if you leave it on, you are wasting 2/3
of that MTBF at night, and when no one is around. I get the thermal
shock argument, but my own long standing experience is that this is
an order of magnitude less of a problem than burning the equipment
for endless hours.

It makes no difference to me what other people do, but to me, the
wasting of so much equipment life is silly, and serves no purpose
whatsoever. When the tube is gone, you can't exactly whittle one
from a block of wood, so think it over carefully. I have often
thought of putting a small NTC or other surge limiter in series with
the filament to reduce thermal shock, but interestingly, the
overwhelming failure mode I have seen from Tek CRTs is going weak or
gassy, NOT filament failure. What do you suppose that means? Not
good statistical support for leaving it on, that's for sure.

all the best,
walter

Miroslav's comments about neon lamps in the older supplies as
transient protection are not correct, they were warning indicators
for lethal voltage, nothing more. This is even explained in the
service manuals. Older unit have no AC transient protection.

Some of the supplies have spark gaps as well as neon lamps - an example is
the 7904. I'm not sure if they are to protect the scope from the power
line, or to protect the power line from the scope's HV in case of disaster.

Hello Dave,

If those gas filled tubes were high voltage indicators, as Walter thinks,
they would not indicate for very long. There are no serial resistors to
limit current, once 'indication' takes place, current would go sky high and
burn them up. I do not think that gas is neon, either. Neon is fine for
indicators, but does not seem capable to support high current density. The
indicator that Walter read about in manual is hung across two caps in
voltage doubler.

Although Tektronix was known to run some caps at the knife edge of voltage
ratings, this setup would be a real stretch. The 'high voltage warning
indicators' were called 230V and caps after rectifier were rated 200V.

I would guess that spark gaps that you are talking about are part of the
caps, so they do not show in schematic, I could not find them. A name
'Capacitor with Sparker' seems to be what cap manufacturers used for them
(another case of foggy memory). The caps which I saw were discs with an
elongation opposite from leads and a radial cut of various width, probably
depending on rating. My guess is that disc cap was leaded with continuos
wire, making a short across the cap. Then, cap was dipped in coating and a
saw cat made desired spark gap width. I have not seen one of those in a long
time.

I am quite sure that sparkers were to protect scope from outside world. I do
not think that to this day there is a requirement to protect line from load.
Someone in this group is in power business, maybe he can tell us if 500 hp
motor would require protection of the line.

Just in case, we should keep quite about that requirement for protecting
line from small loads. If European Union hears about it they might add it to
EC requirements; those boys have been on a regulation binge forever.

Regards
Miroslav Pokorni