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Author Topic: Restoring National Knobs  (Read 2838 times)
KB1WSY
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Posts: 805




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« on: July 27, 2012, 03:59:15 PM »

I'm attempting to restore a bunch of National HRS series knobs. The main problem is that the skirts are tarnished with yellow patches. When I tried to remove the tarnish with "Brasso" the yellow patches actually became larger.

See photo:

http://tinyurl.com/br3u7ob

Suggestions? Thanks.

73 de Martin, KB1WSY
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G3RZP
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« Reply #1 on: July 28, 2012, 03:34:09 AM »

What material is the skirt? If it is plain aluminium, I'd try steel wool and a drop of washing up detergent.
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KB1WSY
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« Reply #2 on: July 28, 2012, 06:42:07 AM »

I just tried your suggestion but this, too, resulted in more yellow tarnish rather than less. I think what's happening is that I am removing some kind of plating, thus revealing an underlying gold/yellow colored metal.

One possibility, which I am now tending to favor, is that there are two kinds of National HRS type knobs:

--The older ones, used in National's own radios and often with intricately customized numbering/lettering on the skirts. I have a number of those, and I think they are some kind of *coated* metal, probably not alumin(i)um.

--The newer ones, sold at retail for use in homebrew equipment, with non-coated skirts made of alumin(i)um.

Here's a photo montage where I've illustrated this possibility: http://tinyurl.com/czhtt9v.

If this is the case, I would tend to favo(u)r the newer knobs and perhaps that is why they are so incredibly pricey nowadays! It's the older ones that I've been picking up for peanuts.... perhaps there is a process for re-plating the metal on the old knobs, which would be very niceesthetically speaking -- and presumably very cheap.

This is all in aid of getting a uniform look for the controls on my homebrew equipment, and it happens to coincide exactly with most of the knobs in the ARRL projects pictured in the publications from the mid-1960s. Nothing urgent, since I can easily use any old knobs for the time being....

Brand-new alumin(i)um skirts could probably be homebrewed with a metal stamper, but presumably it would cost a fortune to get the stamp custom-made. (Measuring with my callipers, the skirts are .05" thick, 1.44" diameter, and slightly domed, with a small lip around the outside.)

One issue with the National knobs, as you can see, is that the skirt is electrically connected to the shaft, making the use of insulated couplers mandatory on "live" shafts" for anyone who might otherwise be tempted to trust a knob's own insulation!!

73 de Martin, KB1WSY
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N4NYY
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Posts: 4800




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« Reply #3 on: July 28, 2012, 06:56:06 AM »

Get a small cup of Krud Kutter, and let the knob soak for like 2-3 minutes, then rinse with water and dry.

It will take off all the nicotine and gunk, and then likely leave only only the oxidation.

Most know I have done came clean. A coupl needed the oxidation removed afterwards. I had to do that myself.
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KB1WSY
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« Reply #4 on: July 28, 2012, 07:04:41 AM »

Get a small cup of Krud Kutter....

Haven't ever used Krud Kutter and there are quite a few products with that name. I presume you mean this one:http://tinyurl.com/d2wxz6a? Just asking before I head to the supermarket/hardware store....

TNX ET 73 DE Martin, KB1WSY
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G3RZP
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« Reply #5 on: July 28, 2012, 07:54:26 AM »

Could be brass, Martin. HRO knobs (they're pre WW2) are silvery looking, but brass underneath, so National did have a history of that.

In which case, clean them all up so they look like brass, or carefully paint.....
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KB1WSY
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« Reply #6 on: July 28, 2012, 10:25:14 AM »

Could be brass, Martin. HRO knobs (they're pre WW2) are silvery looking, but brass underneath, so National did have a history of that.
In which case, clean them all up so they look like brass, or carefully paint.....

Yes you must be right. The more I scrub the skirt on the older knobs, the "cleaner" the look but it gets yellower and eventually I get a fairly even, "brassy" look which is nice enough on its own terms; see http://tinyurl.com/bqdl6u6. Probably something the "steampunk" crowd would like....

Now that this seems to be sorted out, time to get back to building coils....

73 DE Martin, KB1WSY
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N4NYY
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« Reply #7 on: July 28, 2012, 05:04:10 PM »

That is the stuff.  You can get krud kutter at lowes or home depot. Spray bottle is about $4.00.
« Last Edit: July 28, 2012, 05:57:53 PM by N4NYY » Logged
W9GB
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Posts: 2626




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« Reply #8 on: July 31, 2012, 05:29:01 PM »

Some National equipment used Raytheon knobs, now EHC.
http://www.ehcknobs.com/index.php?id=CK

The Electromed series looks close

Electronic Hardware Corporation (EHC)
320 Broad Hollow Road
Farmingdale, NY 11735
===
Davies Molding (Daka-Ware) is another frequent supplier
http://www.daviesmolding.com/

Skirted knobs
http://www.daviesmolding.com/standard-products/plastic-knobs/skirted-knob/default.html

Instrument knobs
http://www.daviesmolding.com/standard-products/plastic-knobs/instrument-knobs/default.html

Davies # 8070 and 8090 are w/o skirts.

Davies # 8450 and 8460 should look familiar.
« Last Edit: July 31, 2012, 05:40:54 PM by W9GB » Logged
KB1WSY
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Posts: 805




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« Reply #9 on: July 31, 2012, 06:04:35 PM »

W9GB: many thanks. You are right, there are many close options. I will need to decide whether it's worth branching out in this way. I already have quite a stash of Nationals and you can't mix them (on the same front panel) with your suggested options because they are sufficiently different that it is obvious. OTOH if you used (for instance) Electromed skirted knobs throughout, they would be extremely close in look to the original National knobs and would look very nice. Food for thought.

73 de Martin, KB1WSY
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W9GB
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« Reply #10 on: July 31, 2012, 10:25:18 PM »

Martin,

You can call them.  Davies Molding (Daka-Ware brand name) has been making knobs since 1932.  They moved to Chicago's western suburbs a few decades ago, after a fire in their original building.

Since National was in New England, Raytheon (EHC) would have been a natural regional supplier.
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