Tek 545B O'scope Fuse and Power

So, I recently got a Tektronics 545B oscilloscope. It's been sitting in a basement for god knows how long, and I thought it would be cool to see if itworked. well, it doesn't. It's missing it's fuse and fusecap, and it's power cable. I had read in a couple of places that the fuse only affected the high voltage stuff, like the CRT. I might be totally wrong about this, which is why I'm asking you guys Well, with that in mind, I found a newer power cable that seemed to fit the bill, so I tried using that. Nothing. I then tried using a voltage regulator. Still nothing. Now, I'm not sure if it's because of the mysterious missing fuse, or if something else has gone badinside, or if it was the power cable (which I doubt). My next guess was that it was the missing fuse. Holy crap does this thing have a strange fuse. I've looked all over for something with a similar rating and size, but withno luck. I'm not as worried about the fusecap. I searched for a couple weeks online, but I eventually came to the conclusion that the thing would probably never work. Today though, I thought I'd give it a go again.
Back of the oscilloscope: http://i.imgur.com/uM64sfX.jpg
I opened it up to find TONS of gunk and dusk blanketing it's insides. I also found a pdf of its manual (which has slightly more info about the missingfuse). Now I think I got in over my head, because I'm too scared to touch anything. Before I go fiddling with 50 year old electrical components, I want to know if it works or not, what I can do to fix the fuse situation (even if only temporarily), and if I should check for anything else.

So, can anyone help me? I'd REALLY like to get this guy working again, but I need some help (obviously, hehe...)

 

So, I recently got a Tektronics 545B oscilloscope. It's been sitting in a
basement for god knows how long, and I thought it would be cool to see if it
worked. well, it doesn't. It's missing it's fuse and fusecap, and it's power
cable. I had read in a couple of places that the fuse only affected the high
voltage stuff, like the CRT. I might be totally wrong about this, which is
why I'm asking you guys Well, with that in mind, I found a newer power
cable that seemed to fit the bill, so I tried using that. Nothing. I then
tried using a voltage regulator. Still nothing. Now, I'm not sure if it's
because of the mysterious missing fuse, or if something else has gone bad
inside, or if it was the power cable (which I doubt). My next guess was that
it was the missing fuse. Holy crap does this thing have a strange fuse. I've
looked all over for something with a similar rating and size, but with no
luck. I'm not as worried about the fusecap. I searched for a couple weeks
online, but I eventually came to the conclusion that the thing would
probably never work. Today though, I thought I'd give it a go again.
Back of the oscilloscope: http://i.imgur.com/uM64sfX.jpg
I opened it up to find TONS of gunk and dusk blanketing it's insides. I also
found a pdf of its manual (which has slightly more info about the missing
fuse). Now I think I got in over my head, because I'm too scared to touch
anything. Before I go fiddling with 50 year old electrical components, I
want to know if it works or not, what I can do to fix the fuse situation
(even if only temporarily), and if I should check for anything else.

So, can anyone help me? I'd REALLY like to get this guy working again, but I
need some help (obviously, hehe...)


_+_+_+_+_+_+_+_+_+_+_+_+_+_+

There is a Yahoo group dedicated to the old Tektronix scopes. Why don't you
join it and ask there?

http://tech.groups.yahoo.com/group/TekScopes/

Over 6000 members, sure to be someone that can lend you some guidance.

The usual way to clean these scopes out is with soap and hot water. That
subject is covered on the group.


regards,
tm

 

Of course the fuse takes care of the whole thing, it's in the primary to
the power transformer. F601, it's a 6amp fast-blo 3AG fuse for 120vac
operation (3ampts if running off 240v). It's a standard glass fuse, you
should be able to get them anywhere. It goes into the fusecap, then you
screw (or is it turn?) the fusecap into the holder at the back of the
scope. I don't know where the fusecaps can be found these days, I
suddenly find I need one and can't find any among all the junk.

Nothing will happen unless that fuse is in place, and that includes the
fusecap.

There's also a thermal cutout fuese in series to the primary of the power
transformer, but that isnt' even a factor until you get the proper fuse in
there witha fusecap.

I got one 20 years ago, though havent' had it on in about 10 years. It
was working fine when I got it, but I since someobody found it at a
hospital as it was about to be tossed out, I suspect it was still in
operation. It worked for a while, then the trace got bent. It's a
multiple section power supply I wasn't sure which section was the problem,
I found it by taking the probe and touching each of the sections across
their filter capacitor, until the waveform got worse. Changed that filter
capacitor, and all was fine. It is incredibly bulky, which is why I moved
it to the basement and thus it's a lot less useful, so it just sits there.


Michael


I searched for a couple weeks online, but I

 

"Michael Black"

** As marked on the rear of the scope - the fuse needs to be a "slow blow"
type.


It's a standard glass fuse, you should be able to get them anywhere.


** Well, anywhere that has available a good range of fuses for electronic
equipment.

Slow blow fuses are commonly stamped or marked with a "T" before the amp
rating.

So look for a " T6.3A " fuse in 3AG size ( or 32 x 6.3 mm) - though such as
high value seems wrong for a tube scope.

If you use a standard "fast " fuse, it may well blow at switch on.



..... Phil

 

To make a correction, when I got the scope I DID have the fuse. It had fallen out somwhere when I took it home though. I had no luck finding it. The thing is, I haven't been able to find a slow blow fuse with the right Amp/Volt ratio. Currently I just want to see if I can get the power light to turnon. As long as I know it's getting power, I can work from there. It's beenin a pretty dry area (but dirty-ish), so I would be suprised if something was damaged in there. The guy I got it from said it worked when he got it, but that was several years ago...

I also sorta lied about me having to electronics experience, actually. I'm an electronic musician and I've been experimenting with making my own synths. In fact the reason I'm fixing this up is to hook it up to my synths and see the waveforms, just as a way to show it off (and also to keep the housewarm in the winter hehehe). Now that I'm looking at it, it seems to be in pretty good condition! Hmmm... I don't suppose there would be any way to subtitute anything else for the fuse? That is, without blowing it up.

 

"Noel Keith"

The thing is, I haven't been able to find a slow blow fuse with the right
Amp/Volt ratio.

** LOL - there no such thing.

The 3AG fuse you need will be probably be marked:

" T6.3A 125V " OR " T6.3 250V "

Sometimes the T is left off and the slow blow characteristic is identifiable
by having a coil spring or long spiral inside the glass.




..... Phil

 

"Dave M"

** I take it the scope has a fan inside - right ?

Many times I have had to give large power amps a " bath " for the same
reason.

Plus, on one occasion, because the customer's storage shed for his hire
business had been flooded with muddy storm water.


..... Phil

 

I couldn't be bothered going down to the basement to check, the manual was
handy. The parts list says fast-blo. The odd thing about the manual is I
see no photo of the back panel.

Which makes sense, and I just copied what was in the manual. I turn mine
on, and the lights dim. If it was fast, you're right, that kind of inrush
would blow the fuse before the thing had a chance to take off.

Michael

 

"Michael Black"

** So the thick plottens .......

Seems there is disagreement between the manual and the labelling on the
back.

A "T 6.3" amp fuse is too big for a tube scope - but an "F 6.3" amp fuse
would be about right, given the inrush surge of the circa 200VA supply
transformer.



..... Phil

 

ntually came to the conclusion that the thing would probably never work. Today though, I thought I'd give it a go again.

When I was a calibration tech for Collins Radio in Richardson, TX we had
a wash cabinet for washing out dirty electronics equipment. It had a
turntable in it and a spray head to rinse it off. We just sprayed
things with soap solution and rinsed them off, then put them in an
oven set at around 120 degrees over night. Paper covered electrolytics
needed to be wrapped to keep the paper from getting wet.

The scope will probably need to have the filters replaced. If it has
an old fashioned selenium rectifier that will undoubtedly need to be
replaced. Early models had the seleniums, unless I am remembering
the 545A. And there is a fair chance a bunch of tubes will be weak.
This is particularly important for the power supply regulator
tube(s). I don't remember if it had 1 or 2 series regulators. If
you have the manual you can tell easy enough.

Bill

 

Alright, so I was able to find 2 types of fuses that I THINK should work. Only thing is that they're ceramic, and not glass, but it shouldn't matter. 6.3A 250V Slow Blow, and 6.3A 125V Slow Blow. They were cheap so I bought 5of each, just in case I needed a backup for whatever reason. I'm also looking for a F6.3A fuse now too. I did manage to get some life in to it though.. A buddy of mine who works on these things came over and brought a spare fuse from another Tek scope of his and said he wanted to see if it worked. Well, it blew instantly. But...hey! At least I got it to do something, right?...right? Also, the fan turned on for that brief moment of life and was slowly spinning.

 

"Bill Gill".

** Is there some kind of rule that makes Americans refer to all liquid
detergents as "soap " ??

Dish washing liquid ( for hand washing) has no alkali, rinses off
completely, is non-conductive, non corrosive to bare metals and hence safe
for use with electronics.

OTOH, products sold for washing clothes and for use in dish washing
machines generally contain alkalis, the water solution is conductive,
corrodes bare metal and is hard to fully rinse off.

Dish washing liquid is the only one that is proven safe to use.

Liquid hand wash ( soap free & pH balanced ) is probably OK too.

Use any others at your peril.



..... Phil

 

I prefer to use mild solvents actually, like alcohol/acetone. This is mainly for PCBs though, when it comes to cabinetry and shit I dunno, dish soap seems really good.

 

** Acetone sure is NOT mild !!!

** Neither is any good for removing oils, grime or drink spills that contain
sugars or fats from PCBs.

** Dishwashing liquid is ideal for cleaning PCBs of nearly anything -
except non water soluble flux.



.... Phil

 

"A "T 6.3" amp fuse is too big for a tube scope - "

Says it right on there if you look at the picture. IIRC the rule is to go by the marking on the unit if it differs from the manual.

I don't see a 6.25 amp as too big for that thing, I believe that is a body builder model with two handles and probably as many tubes as a 1950s color TV set. They pulled over 300 watts, alot of them almost 400.

I believe that scope is more than 50 tears old, I would say circa 1957. Even without transistors they did get a bit more efficient over the years. My old 561A doesn't pull as much as that dinosaur, and I think the only solid state in the is the rectifiers. not sure. but after some years tubes (valves) wound up with more gain so less of them were needed.

The OP should just put a damn seven amp fuse in it and try it. It does not have a fissionable material in it nor any explosives. If you are paranoid keep it away from the drapes, or hell just do it outside. Respect electriciyyes, but put it in perspective.

If it blows the fuse immediately the first thing is to disconnect all the rectifiers off the secondaries of the transformer to see if that's good. In fact if it powers up and has no trace it could still be the transformer. My561A has leakage to the filament winding which shorts out the HV. I took ahi-pot little 6.3 volt transformer and wired it in, it works fine. Howeveronce insulation is breached.......... The nice thing now though is that the HV is no longer applied to that winding.

I remember that Tekronix had a lifetime warranty on their power transformers. I tried to get a replacement for mine and they would sell it to me but that is all. It's not like they didn''t have them. They basically said that they are no longer under the lifetime warranty. The rep also mention that they had alreacy been to court about it, it was like $150 or go **** off.

Maybe I should look at a Gould next.

 

**Don't be too certain. My second CRO was an Hitachi copy of the Tek
545A. It was a massive, heavy, noisy, hot bugger. So close, was the
copy, that the Tektronix service manual was perfectly suitable for
fault-finding and operational needs. FWIW, the only major difference
between the Hitachi and the Tek was Hitachi's use of 2% tolerance
resistors throughout the entire CRO (except for high precision areas).
Tek used 10% or 20% tolerance resistors throughout. The thing used a
full RLC delay line with 20 or so valves. The vertical amplifier valve
filaments operated in a series string of (as I best recall) 120 Volts
DC. Regulation for various circuits (including heaters) was via 3 X 6080
dual triodes. The thing ate them. It had a 200mm fan in the back and
consumed 500 Watts under normal operation. Great in the workshop during
Winter. Not so good during Summer. My subsequent CRO was all solid state.

A 6.3AT fuse, for 117VAC is within possibility. I've got a manual for it
somewhere. BAMA probably have it for free download if you're interested.

 

ntually came to the conclusion that the thing would probably never work. Today though, I thought I'd give it a go again.

**I had one of these more than 30 years ago. It was hot, noisy, heavy
and an average performer. Do yourself a favour - buy a newer CRO. Even
something as old as a Tek 565b will be a revelation. You'll even be able
to move it about, without a forklift.

 

"Jeff Liebermann"
"Phil Allison"

** Yawnnnnnnnnnnnnnnnnnnnnn................

** It broadly refers to it being non alkalai - ie SOAP FREE !!!!!!!!

That is, it will not irritate the skin on ones hands like ordinary soaps do
and washing liquid is infamous for.

Been using them for 20 years myself.

Work very nicely at cleaning my electric shaver too.



.... Phil

 

"Trevor Wilson"

** Here is a pretty good pic of the insides of a 545B.

http://www.barrytech.com/tektronix/vintage/tek545bright.jpg

The AC tranny looks like it *might* be 500VA - but I expect Tek would use a
conservatively rated unit with a low temp rise.

If the OP would care to measure the primary resistance - I can say for sure.



.... Phil

 

"What benefit does
this alleged balancing act have for the user? Too many unanswered
questions."

Anything too acidic or alkaline would be bad. However that doesn't mean something with the "proper" Ph for skin will be exactly right for this.

Of course if rinsed thoroughly anything from 6 to 8 should be just fine.

over a very narrow range of pH. I don't recall the numbers, but it
specifically avoids the typically pH=5.5 of skin so that it does *NOT*
suds when first applied. Only after dilution with water, or a 2nd
application does the pH of the mix increase to roughly a neutral pH=7,
where it will produce suds. The obvious result is that users use
twice as much shampoo as they would with one that would suds at any pH
value. I suspect that hand and dishwashing soap may be similar, but I
haven't bothered to check.
"

Very interesting.

are bad and that it will need disassembly to replace those anyway.
"

You wouldn't believe how long some of those old caps can last. When was the 561A made ? I had to only replace one. I had to replace one in my 7603.