Use of air/dust filter on linear amplifier air intake?

[K1REX]

I'm reconditioning an Ameritron AL-82 and have cut a piece from a sheet of air conditioner filter stock to cover the air intake of the amp. I'm securing the filter panel with magnets (chassis is steel, not aluminum). I'm wondering how widespread this practice is in order to keep dust out of linear amplifiers (where the base of the plate choke is particularly prone to dust build-up which can lead to arcing).

If anyone else is interested in doing this, A large sheet of air conditioner air filter material is available at Ace Hardware for about $5, and a packet of 8 small, but powerful, magnets is also available at Ace for about $3.50.

I hope this topic spurs some discussion. All comments gratefully accepted.

73,

--Stephen, K1REX
   Amherst, MA

[Pete, WA2CWA]

Similar info is in the Ameritron AL-82 manual:

Use a soft bristle brush dipped in alcohol to clean areas mentioned
previously. In the event that cleaning is required at
frequent intervals, place a low restriction air filter material over
the air inlet holes on the left front side of the cabinet near the
filter capacitors. Most hardware stores stock suitable materials
that are used as replacement filters for window air conditioners.

[MikeKE0ZUinkcmo]

I always pull ceramic tubes and clean the dust from the fins any time I go into an amp.   I never gave much thought to filters because I've never found much dust.   That doesn't mean filters wouldn't be a good addition however.   

Also, with the ever increasing cost of tubes, wouldn't air flow, or temp sensors down stream of ceramic tubes be something to consider adding to your favorite BA amp.

I've never measured the plenum pressure in any amplifier, but it might be an interesting exercise.   I'd think some tube data sheets would have plenum pressure/air flow recommendations, I never looked.

[VE3ELQ]

If anyone else is interested in doing this, A large sheet of air conditioner air filter material is available at Ace Hardware for about $5, and a packet of 8 small, but powerful, magnets is also available at Ace for about $3.50.

I hope this topic spurs some discussion. All comments gratefully accepted.

73,

--Stephen, K1REX
   Amherst, MA

About 8 years ago my good HAM friend Mort W2ATO (now SK) was doing this and told me about it.  Been using a flap of filter material over the fan intake on my linear ever since.  It works very well with no noticeable loss of airflow.  I clean it once a year as it gets quite dusty so it certainly traps the dust FB and inside the linear stays clean.  Great idea.
73s  Nigel

[W1ITT]

Steve..
If you put an air filter on the intake of an amplifier, you are obliged to remember to check and clean it periodically.  The broadcast transmitters I was associated with in years past generally had large flat disposable furnace type filters on them.  They would slowly begin to clog with moths, pollen in season, and dog hair at one installation where one of the other engineers  brought his large mutt to work.
A number of the transmitters had a plenum manometer that would measure pressure drop (and infer filter obstruction) that made it obvious that maintenance was necessary, but I usually eyeballed the filters once a week.
I saw one case in a transmitter where someone had neglected filter maintenance and cooked a 4cx5000 to crusty black before it finally failed.
I believe that intake air filters are a good thing, but you have to remember to inspect them on a regular basis.  At one site, a new engineer, in order to make sure that the filters would be readily available, stacked a couple cases of said filters smack up against the air intakes.  I walked by the manometer and noticed something awry.  We had words.

[flintstone mop]

I have noticed that equipment installed on the floor and the air intake at floor level will suck all of the normal dust and junk at that level. Carpeted floors seem worse for another type of dust input.
A desktop amp may not have that type of floor dust coming into it. Now a smoke filled room is another story.
Equipment in a bedroom setting or near pets will suck in the dander and dust from people, clothing, bedding, etc.
Has anyone ever seen what is in your exhaust fan in the bathroom???
The dust from the TP rolls, towels, ladies drying their hair???

Fred

[WD8BIL]

I use a piece of ScotchBrite over the blower intake on the Viking Bud. It gets cleaned/changed once a year along with blowing out the 4CX250B fins whether they need it or not!

[WQ9E]

I upgraded the pedestal fans in my Johnson Desk KW several years ago and installed a filter on the intake fan.  Prior to that the grid compartment fan in the RF deck needed cleaning every couple of years but the easily replaced filter on the outside keeps the pedestal interior clean now.

In the mid 1990s I bought a Tektronix R-556 scope that came from a facility that maintained everything properly down to cleaning and spraying Filter Kote on the screen type Tektronix filters as called for in the manual.  That scope was pristine inside and it came with a couple of cans of Filter Kote.

[KB2WIG]

"  Has anyone ever seen what is in your exhaust fan in the bathroom??? "

I once had to clean the forced air ventilation system in a  Psychiatric  center *. The bathroom vents were disgusting. The most disgusting set of vents was in the alcoholic walk in unit. Big room with cots. The vents were maybe 6' by 4' tall. Pull the covering screen off. Inside are louvers, spaced apart at around 4", running lengthwise. The louvers were covered with a cake consistency smegma of cigarette smoke, dead skin and Who knows what else. There was maybe a clearance of one inch, ONE inch of space available for the air to pass through. The place had a particular aroma of vomit, body odor and other assorted filth smells. My arms went arm pit length into this plenum of crud until it (the plenum) curved away into the bowels of the building. I cleaned out what I could reach. An incoming nursed commented "What did you guys do?? It doesn't stink."


KLC

* When the Psy Center was built, the designer wanted it to look nice and open, like a mall. Not the dreary institutionalized look. So the main floor had nice wide open circular stairwells opening up to the basement. Maybe 20 feet below. I asked why there were rope nets strung  around the 'wells'. " Guys liked to jump" was the answer.

I guess ya should know something about the people your designing for.

[Pete, WA2CWA]

Any piece of equipment whether it's amplifiers, transceivers, boatanchors, computers, etc. that have air intake fan(s) should be inspected and cleaned at least once a year. Dust, pet hair, smoke, and other air borne stuff will get sucked in and accumulate on the blades, fins, and other surfaces and just build up. A filter definitely will help but the periodic cleaning maintenance is still necessary. 

[w1vtp]

Any piece of equipment whether it's amplifiers, transceivers, boatanchors, computers, etc. that have air intake fan(s) should be inspected and cleaned at least once a year. Dust, pet hair, smoke, and other air borne stuff will get sucked in and accumulate on the blades, fins, and other surfaces and just build up. A filter definitely will help but the periodic cleaning maintenance is still necessary. 

Absolutely agree.  Rosie recently urped on the cover of my AL-82 which would have fairly easy to clean but I took the cover off to avoid getting any stray cleaner inside.  WELL!  I was shocked to see the amount of dust, bits of Rosie hair all over the inside the amplifier.  After unplugging the amp and doing the shorting the HV procedure  to make sure there were no KV's lurking around the innards, I proceeded to vacuum out the really excessive dust.  After that, I used my air compressor to blast out the remainder of the dust.

It's amazing to me I didn't have a ZORCH before.  Regular removal of the cover of your HV supplied equipment really should be on your major to-do list. 

The same rules especially applies to any equipment that has an air intake (has forced ventilation).  Important: if you are going to put a filter at the air intake, you must commit yourself to a regular inspection of the filter and replacement, if necessary.  An absolute must!!  Good points on this thread, I think.

Al

[Pete, WA2CWA]

I inspect and clean most of my active rigs, computers, printers, and that have fans in them at last every 6 months. It's amazing how much dust and crud accumulates on the fan blades, heat sinks, filters, and other hardware. Of course having two Eski's that shed 24/7 doesn't help either.

[flintstone mop]

I inspect and clean most of my active rigs, computers, printers, and that have fans in them at last every 6 months. It's amazing how much dust and crud accumulates on the fan blades, heat sinks, filters, and other hardware. Of course having two Eski's that shed 24/7 doesn't help either.

Hey Pete,
We have the same equipment maintenance hang-up. I do about the same thing once a year with the computers in the house. The white fine dust and even hair that gets into the cooling fins for the CPU is amazing.
Gotta be careful about doing this type of stuff during the winter. The brush hairs can cause ESD and destroy the MOBO. Even using a high pressure air spray to blow out the dust can be harmful. Keeping the heat accumulation down on these components will lengthen the life of any electronic device.
In transmitters and linears it would reduce the chance of arcing from the dust and spiders that like to crawl inside our radios.
Fred