TECH: Tektronix 7633 frame and accs....

[Mark (UK)]

Hi all!

I just picked up a SUPERB condition Tek 7633 storage frame with a
timebase and a few amps.

It's all working perfectly, but I've got one issue, it may be me, maybe
the scope has a small problem, or maybe they're like this......

When the intensity of the display is turned up to 9/10, it is fine,
reasonably bright - not as bright as a more modern scope, but I'll
accept that from a 30 year old workhorse - however, when I turn it up
that last 1/10, it goes out of focus. Are they meant to do that to
protect the tube or something? Or is it because it's an old persistance
analog storage tube that maybe it's a quirk of the design?

Or do I have a fault?

Any advice is appreciated.

Yours, Mark.

 

[Jim Yanik]

"Mark (UK)" <jumbos.bazzar@btopenworld.com> wrote in
news:ccv4sr$oj9$1@sparta.btinternet.com:

Hi all!

I just picked up a SUPERB condition Tek 7633 storage frame with a
timebase and a few amps.

It's all working perfectly, but I've got one issue, it may be me, maybe
the scope has a small problem, or maybe they're like this......

When the intensity of the display is turned up to 9/10, it is fine,
reasonably bright - not as bright as a more modern scope, but I'll
accept that from a 30 year old workhorse - however, when I turn it up
that last 1/10, it goes out of focus. Are they meant to do that to
protect the tube or something? Or is it because it's an old persistance
analog storage tube that maybe it's a quirk of the design?

Or do I have a fault?

Any advice is appreciated.

Yours, Mark.

It sounds reasonable.The older a CRT gets,the weaker the cathode gets,and
it takes more beam current to get a trace,but it emits from a wider cathode
area,defocusing the beam.Those storage tubes also use a mesh lens after the
horiz deflection plates that make for a less sharp beam.

BTW,you can tell the approximate age of your scope by checking date codes
on various items;the format is for example;4380,would be week 43,year
1980.Don't just read one IC and figure that's it,look at some big items
like the power transformer,etc.If you get one PCB with date codes not
consistent with the other PCBs and power xfmr,then boards have been
swapped/replaced.

--
Jim Yanik
jyanik-at-kua.net

 

[Mark (UK)]

Hi!

Thanks for that reply, I didn't expect supersharpness, but for the age
of it, it's very good.

The PCBs inside the frame have (c)1973 on them - would that be the year
it was designed or the year it was made?

It looks like everything is original, as it all matches for stickers
inside the plugins.

Yours, Mark.

Jim Yanik wrote:

"Mark (UK)" <jumbos.bazzar@btopenworld.com> wrote in
news:ccv4sr$oj9$1@sparta.btinternet.com:


Hi all!

I just picked up a SUPERB condition Tek 7633 storage frame with a
timebase and a few amps.

It's all working perfectly, but I've got one issue, it may be me, maybe
the scope has a small problem, or maybe they're like this......

When the intensity of the display is turned up to 9/10, it is fine,
reasonably bright - not as bright as a more modern scope, but I'll
accept that from a 30 year old workhorse - however, when I turn it up
that last 1/10, it goes out of focus. Are they meant to do that to
protect the tube or something? Or is it because it's an old persistance
analog storage tube that maybe it's a quirk of the design?

Or do I have a fault?

Any advice is appreciated.

Yours, Mark.




It sounds reasonable.The older a CRT gets,the weaker the cathode gets,and
it takes more beam current to get a trace,but it emits from a wider cathode
area,defocusing the beam.Those storage tubes also use a mesh lens after the
horiz deflection plates that make for a less sharp beam.

BTW,you can tell the approximate age of your scope by checking date codes
on various items;the format is for example;4380,would be week 43,year
1980.Don't just read one IC and figure that's it,look at some big items
like the power transformer,etc.If you get one PCB with date codes not
consistent with the other PCBs and power xfmr,then boards have been
swapped/replaced.

 

[Jim Yanik]

"Mark (UK)" <jumbos.bazzar@btopenworld.com> wrote in
news:ccvr5b$jn6$1@sparta.btinternet.com:

Hi!

Thanks for that reply, I didn't expect supersharpness, but for the age
of it, it's very good.

The PCBs inside the frame have (c)1973 on them - would that be the
year it was designed or the year it was made?

It looks like everything is original, as it all matches for stickers
inside the plugins.

Yours, Mark.

Jim Yanik wrote:

BTW,you can tell the approximate age of your scope by checking date
codes on various items;the format is for example;4380,would be week
43,year 1980.Don't just read one IC and figure that's it,look at some
big items like the power transformer,etc.If you get one PCB with date
codes not consistent with the other PCBs and power xfmr,then boards
have been swapped/replaced.

Look for date codes on components,not the PCB date,that's the date the PCB
was designed,IIRC.

--
Jim Yanik
jyanik-at-kua.net