Topics

Air filters for 500 series.

greenboxmaven
 

I have obtained some 500 series scopes in the last month or so. One of them, a 585 is absolutely filthy but shows signs of life. Needless to say, the aluminum mesh filter is gone and has been gone for years. How effective are those filters when properly cleaned and treated? I have seen people use the foam filter material from air conditioners, but wonder if they are effective. I am considering getting a small fine particle trapping furnace filter and cutting and refitting it's cardboard rim to fit the scope's filter frame. What experiences have others had with filters?

Bruce Gentry, KA2IVY

Chuck Harris
 

It is not a very big fan, and these scopes make a lot of
heat.

If you can't see through the filter, it is probably going
to be too restrictive. A pleated furnace filter will certainly
be too restrictive.

Also, many of the scopes that originally had the aluminum mesh
filters, don't have a fan protection screen to keep the filter
from impinging on the fan's space.

All of those that used the plastic mesh type filters (which turned
to black crumbles over time) did have an aluminum diamond mesh
screen to keep the filter material from being drawn into the fan.

The aluminum mesh filters were phased out before the 545B and 547
were released, but were always a part of the 585, and later 585A.

-Chuck Harris

greenboxmaven via Groups.Io wrote:

I have obtained some 500 series scopes in the last month or so. One of them, a 585 is
absolutely filthy but shows signs of life. Needless to say, the aluminum mesh
filter is gone and has been gone for years. How effective are those filters when
properly cleaned and treated? I have seen people use the foam filter material from
air conditioners, but wonder if they are effective. I am considering getting a small
fine particle trapping furnace filter and cutting and refitting it's cardboard rim to
fit the scope's filter frame. What experiences have others had with filters?

Bruce Gentry, KA2IVY




John Williams
 

The mesh filters were used to eliminate or at least reduce emr emissions from the scope, which could seriously effect lab equipment. They also filtered air to some degree. Later Tektronix switched to foam filters. They then had to put a metal screen over the opening to reduce emr, as well as to prevent the foam from being sucked into the fan. The mesh filters were basically stove fan filters, and various sizes of these are readily available at the Depot of course.

I reason this way: The scopes may have been used in very dusty dirty environments and therefore needed an air filter. However most of us are running them in the house or garage. As the air in those locations is usually fit to breath, I don’t think a filter is necessary, unless the noise or emr is objectionable. I have used portions of furnace filters, but gave it up as too much of a hassle. So I have some scopes with filters, some without. I have not noticed any appreciable difference. However, maybe if I had a cat or dog (lab cat.?) I would find some hair in the scope or my nose.

I guess the scope is not fully restored unless it has the correct filter with Tektronix label on it. But what the hell.

Stephen Hanselman
 

They were also sprayed with filter-coat which sucked up dust, for a while

Steve

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of John Williams
Sent: Friday, November 15, 2019 12:48 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Air filters for 500 series.

The mesh filters were used to eliminate or at least reduce emr emissions from the scope, which could seriously effect lab equipment. They also filtered air to some degree. Later Tektronix switched to foam filters. They then had to put a metal screen over the opening to reduce emr, as well as to prevent the foam from being sucked into the fan. The mesh filters were basically stove fan filters, and various sizes of these are readily available at the Depot of course.

I reason this way: The scopes may have been used in very dusty dirty environments and therefore needed an air filter. However most of us are running them in the house or garage. As the air in those locations is usually fit to breath, I don’t think a filter is necessary, unless the noise or emr is objectionable. I have used portions of furnace filters, but gave it up as too much of a hassle. So I have some scopes with filters, some without. I have not noticed any appreciable difference. However, maybe if I had a cat or dog (lab cat.?) I would find some hair in the scope or my nose.

I guess the scope is not fully restored unless it has the correct filter with Tektronix label on it. But what the hell.

John Williams
 

Yes I still use the same oil coating on the k&n filters in my motorcycles and car. Good for motors, not sure if it’s good for lungs.

Robert Simpson
 

Fans in scopes seem to be fairly weak compared to other fans. For example kitchen exhaust fans, house fans etc. Try blowing through a regular house filter and you can see how restrictive they are. One member in an earlier post indicted flow was more important than filtering.
Bob

Keith
 

My 5 series Tek appears to use a very typical 45w Howard Industries fan. These are nothing but glorified refrigerator evaporator fans, and equivalent models are still commonly available.

It looks to me like it would be easy to up the motor wattage a notch while staying in the same frame size. One could then pitch the OEM aluminum fan blades a little steeper by hand (not that hard to do - I've done it on other fans) and maybe tighten up the dimension of the fan flange with some plastic trim or something similar. (That's where the efficiency of these fans really suffers, and the tighter the fit, the better the efficiency. Of course, if the bushings get loose, a tight tolerance fan will hit, but hey...that's why you're supposed to replace those bushings when they "become worn" just as it says in the manual. :-)

FWIW, if anyone is experiencing inadequate airflow, IMO it would be pretty easy to gain 15-20% airflow increases while keeping an original look by doing these or similar steps.

Filter oil - yeah, ditto on the K&N oil. Works great as long as it lasts, which is quite a while in reasonably clean environments.

Finally, similar shredded wheat metal filter material is available from restaurant supply houses. (Grease traps use a similar material) and the C channel that makes up the filter frame is common as well. This, just in case someone wants to fabricate a "near correct" filter for their 5 series. FWIW

Cheers

Chuck Harris
 

Overheating of the 500 series scopes, including the 555, was not
a problem. Not at all.

Overheating of the lab the scope was in, well that was a different
story.

Why fix it if it isn't broken?

Your mod may increase the airflow, assuming the filter isn't so
restrictive that the fan is working up against a wall, but it
will also increase the noise. Something most people don't need or
want.

You say that the fan is nothing but a glorified refrigerator
evaporator fan, given that tek spec'd these fans in the late 1940's,
and late 1940's refrigerators didn't have evaporator fans, are
you sure that refrigerator evaporator fans aren't really nothing
but glorified oscilloscope fans? ;-)

-Chuck Harris

coolblueglow@... wrote:

My 5 series Tek appears to use a very typical 45w Howard Industries fan. These are nothing but glorified refrigerator evaporator fans, and equivalent models are still commonly available.

It looks to me like it would be easy to up the motor wattage a notch while staying in the same frame size. One could then pitch the OEM aluminum fan blades a little steeper by hand (not that hard to do - I've done it on other fans) and maybe tighten up the dimension of the fan flange with some plastic trim or something similar. (That's where the efficiency of these fans really suffers, and the tighter the fit, the better the efficiency. Of course, if the bushings get loose, a tight tolerance fan will hit, but hey...that's why you're supposed to replace those bushings when they "become worn" just as it says in the manual. :-)

FWIW, if anyone is experiencing inadequate airflow, IMO it would be pretty easy to gain 15-20% airflow increases while keeping an original look by doing these or similar steps.

Filter oil - yeah, ditto on the K&N oil. Works great as long as it lasts, which is quite a while in reasonably clean environments.

Finally, similar shredded wheat metal filter material is available from restaurant supply houses. (Grease traps use a similar material) and the C channel that makes up the filter frame is common as well. This, just in case someone wants to fabricate a "near correct" filter for their 5 series. FWIW

Cheers



John Williams
 

Right Chuck I agree. Thee biggest reason for overheating was poor maintenance. The filter was often not cleaned properly, but I think that even a dirty filter would still pass enough air to sufficiently cool the scope. More likely was a poorly maintained fan motor. If the motor was not regularly or properly lubricated, that would lead to it gradually slowing until finally seizing. Then the technician would pour oil into the oil holes on the motor but it would be too late. Oil would run down and coat the rear of the scope, which would eventually become a dirt encrusted mess. The only solution is to remove the fan, disassemble the motor and clean the crap out of the bushings. I have worked on some that even this extreme repair didn’t fix. That’s where a few spares come in handy. I also notice the dirtiest scopes are usually only dirty from the top, underneath they are pretty clean. I don’t know why this is, it’s as though they sat in a basement with the covers off.