The AM Forum

These two items, I think they may be the same, though they could be marked differently.

They appear to be Collins filters for audio response. The trouble is that the old tape someone put on them, which is older than I am, is a sort that seems to have a plastic cellophane-like top layer, a semi transparent paper layer, and underneath the obligatory glue that is sticking it to the cans. I really want to remove the tape but keep the nomenclature for one thing so i can tell for sure exactly what these are supposed to be.

The under layer of adhesive seems pliable, What appear to be the paper and cellophane, those are brittle. But they won't just come right off.

They should be the usual grey collins cans with the orange printed text or drawings on them, silk screen or paint or whatever was uysed in the 40s and 50s.

I don't want to try MEK, and wonder if WD-40, which usually dissolves tape adhesive, will leave the paint alone.  I'm open to suggestions!

  I've never tried it on anything that ancient, but the stuff called "Goo Gone" seems to work very well. They used it in my old workplace to remove sticker and tape residue from products before shipping, so it had to be at least somewhat paint-friendly. Still, I would suggest testing first with a very small application to start with.

I'm going to try some of that and see. Found out that wetting with WD-40 makes the paper part of the 'tape' transparent enough to read the data through it when lit off-angle.

But the mess still should come off so the things will be presentable. It has not come off, but the paint seems inact.

Looks like a couple of high pass filters to knock the bass off the voice. Tried LTspice and got a curve. The ideal curve for ART-13 modulation transformer use! - and for pushing more watts into a given transformer by reducing the bass.

Not the audio component everyone's looking for, but I like variety. These were not something recently obtained - they were in a cigar box recovered from the unwanted pile at an estate so long ago I don't recall it. There are so many stashed cartons and boxes of stuff that I can't always find what I'm looking for, but then when I look for it, it seems I am finding everything else.

naptha is excellent for removing tape residue and is safe on most surfaces.

Thanks for that!

Naptha sounds like something I can get at a hardware store. Right in between the can of mineral spirits and denatured alcohol LOL and hopefully across the aisle from the Goo-Gone which I have never used but want to try. Now that the data from the filters has been read and immortalized here and in LTspice, there will be little harm in trying the proffered solutions.


On the estimating of canned audio filter responses, not exactly the topic but usually a challenge, I'm driven to make more comment on these filters and using LTspice to poke at their secrets, b/c what I wrote is too incomplete.

I forgot to think about one thing in the above LTspice situation. The inductor's resistance. It's not readily measurable from outside the can due to the .01uF capacitors, and as can be seen below that series resistance property of the inductor affects the curve much. DUH.

So, a test has to be done on these, and it might be fun to do the same on every audio filter here, including measuring the inductor resistance any time the product allows it, for example, in the UTC D-7759 both ends of the inductor are accessible; any blocking caps would be external.

There are a couple handfulls of filters in the box harvested from transmitters and the like over the decades. Thing is, who has that much time?

What did Collins intend?
(what are these even from? Probably military since were dual-sourced)

The soft slope (50K Ohm coil):
-6dB @300Hz ref 1KHz to 10KHz
-20dB @ 100Hz ref 1KHz to 10KHz
~~ or ~~
The sharp cut (5K or 10K Ohm coil):
-27dB @ 100Hz ref 400Hz to 10KHz

With the inductance supposed to be 22H, it's got to have some very very fine wire in there, bespeaking a high resistance.

When judged against the LTspice graph, the written specs on one specimen point at 5K to 10K Ohm coil, but more than 10K would exceed the 3dB mark. The 50K Ohm possibility does not offer enough attenuation at 150Hz and too much at 300Hz. Less than 5K Ohms leads to a lump at the turnover point.

My guess from this round is the curve is the sharper of the two, 5K to 10K resistance, but it will have to wait for testing to confirm the reality.

I had some rock hard tape on the front panel of a Hammarlund receiver.  Googone, WD40 and those usual solutions didn’t touch it.  I stayed away from solvents figuring they would destroy the paint.
With some experimenting using automotive stuff I found that Mcguires #7 would soften the rock hard tape into a goo that Googone could then remove.
The trick with Mcguires #7 is that it needs to be put on heavy and left on for 12-24 hours.  The oils seemed to work into the tape and undermine its grip.
Be sure to test it with any base finish.

I always use lighter fluid, never had any problems.

  That is very useful stuff indeed. Not a smoker, so I've got no need for it in its intended application, but a few containers of it have found their way into my workshop over the years, and I'm glad for it. I had an electrolytic filter cap barf its guts out all over the underside of a chassis once—one hell of a nasty, gooey mess—and that was the only stuff in my shop that would remove that goop. I bought a book in a bookstore, and when I brought it up to the counter, the lady noted that the cover was a bit dingy looking, and she reached behind her and retrieved a can of lighter fluid from a shelf—I got the impression that it was standard equipment there—and proceeded to wipe the book's cover with it. At first I was worried that it would leave the book with an oily feel and odor, but it did neither; just left it shiny and new looking.

Is Coleman camp stove fuel just Naptha/lighter fluid?

  The exact ingredients of each might be proprietary, but I suspect that naptha figures prominently in both, since both are formulated to burn cleanly with minimal smoke and soot. Both make fine cleaners.
  Actually, the MSDS for each is probably out on the web somewhere. I haven't had any naptha in my shop for decades; I forget now exactly what it smelled like.

I use ordinary paint thinner any time naptha is called for, but that doesn't mean it will work here.  It makes a great solvent for cleaning clocks, switches, anything gooey or greasy.
Paper tape of the masking type is the most impossible stuff to get off after its been on long enough to dry out.  Horrible stuff!  If you are trying to get it off and not ruin the paint underneath, it might be more successful to carefully scrape or grind it off.

KD1SH said:It's no longer 'MSDS' it is now SDS courtesy of Europe.

Naptha: https://www.marathonpetroleum.com/content/documents/Operations/Tesoro_SDS/Naphtha_SDS_Tesoro.pdf

Coleman Lantern Fuel: http://ferris.msdssoftware.com/ImageDir/i0121104.pdf

Yeah, they still refer to it as a MSDS. For over 20 years as a HAZMAT Tech, I knew where to look for the data I needed. Then about 10 years ago they switched to the SDS format. Different pictograms, different sections. At least the properties for UN labeling and NFPA Diamond labels have not changed.

MEK— I remember that stuff! When I worked at an aerospace company, we always had several pump-bottles of various solvents on our benches: isopropyl alcohol; trichloroethane; liquid freon; and MEK. When I'd accidentally nick my finger with an Xacto blade or something, I'd often dip the finger into the alcohol pump-bottle, to sterilize it. It smarted just a little, briefly, but no big deal. Sometimes, though, I'd get the bottles confused, and go for the MEK instead. Yow! Liquid fire! Wasp venom!

Ronson and Zippo lighter fluid are predominately naptha, maybe 90% or so with some petro distillates thrown in and work just the same but might leave a little distillate residue where pure naptha evaporates quickly and leaves no residue.

Goop plastic tape remover usully works.

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I found pictures of Meguiar's #7, very popular and sold as a glaze or polish containing oils depending on whom, for show cars - people saying it will remove basically what I've got there stuck on those transformer cans, and all kinds of other stuff without runing paint. Some folks are spelling it "Mcguires" and some "Meguiar's". Probably the same stuff. But they all praise it highly along with the other chemicals mentioned here.

All them chemicals - Hopefully everyone has their flammable cleaning stuff stored safely. A friend had given me some Xylene and MEK in those 1-gallon glass jugs plus some acetone last summer. I felt nervous about having those jugs sitting unprotected in the garage, and the furnace is in the next room over - so it's not acceptable. Shortly after, I got a couple of flammable storage cabinets for cheap at an auction. So all of it was moved to the work shop and the cabinets are locked up. The cabinets are the small '4-gallon' size, about 18" square and 2 FT tall. NFPA/IFC/OSHA approved.

Auction or Fastboog Marketplace is the best way to buy those cabinets - I looked them up before bidding and they are $500 at Grainger. I paid $20 each at the auction, there were many of them and few people wanted them. Just please be safe my friends!

Opcom said:It is very common for chem/pharmaceutical labs to use "jugged solvents" for their mass/gas spec analyzers. Large glass jugs with securely fastened tops, (screwed tops with a seal inside) were ok for storage on a shelf. Usually, open 'squirt bottles' were stored in 'HAZCHEM' lockers with a flame/detonation arrestor on top. If you have such arrestor, remove it once a year and shine a light through to make sure there are no obstructions, (spider webs/nests). If you know of a lab auction you could probably acquire them cheaply. No doubt they should be cleaned and certified for lack of contamination.

I moved all my flammables outdoors years ago. Many which include several gallons of gasoline, various solvents like MEK, acetone, toluene, gas welding stuff and propane tanks live out in the shed out back. Moved various gas powered tools there too.  Master bedroom is over the garage. The only thing to worry about is the EV in the garage.

The technique I used to get masking tape off the front panel of an HQ180 was...
Remove as much as you can by hand then flood the tape residue with Meguiars #7 and let it stay wetted for at least 12 hours.  It turned the rock hard tape residue into goo that would mostly wipe off.  The remainder came off with goo-gone.
I hope it works on whatever tape you are fighting.