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Replacement pots for a '50s Magnatone lap steel guitar
Old 13th January 2019
  #1
Here for the gear
 
🎧 5 years
Replacement pots for a '50s Magnatone lap steel guitar

Hello, everyone. I won an auction on eBay for a '50s Magnatone lap steel guitar. A really cool guitar in superb condition that even came in its original cardboard case. The case had some minor damage, but a friend returned it to nearly as new condition. The only other thing that needs attention is the pots. At first they were very sticky and unreliable. Basically all they did was completely cutting the signal at any position of the pot. You might move it a little bit and you had no sound, and move it again a little bit and you'd get full volume. After cleaning them with G22 contact cleaner, they work very smoothly but again they do nothing but completely cut the signal when turned to zero and let it all out in any other position. I guess I have to replace them and so I ordered a pair of 500K Emerson Pro CTS pots from StewMac that are on their way to my house now. Then I wondered if maybe someone out there who knows better about old Magnatone guitars might advice some other option, which is why I send this post. Thanks everyone in advance for any ideas you may give me.
Old 14th January 2019
  #2
Here for the gear
 
🎧 5 years
I send some pictures taken from the eBay listing so you can see the condition the guitar is in and the condition the case was in when I received it. You can also notice the tuners are in such good shape that I doubt they are original.
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Old 15th January 2019
  #3
Lives for gear
 
🎧 10 years
You will need to open it up and have a look - hopefully the pots will have an OHM spec on it's casing. You probably won't go wrong placing a 500K pot in it - but it may a different original spec. It will probably have a single P-90 style pick-up - in which case - many early P-90's style pick-ups used 300 K pots. The 500K pots may make it sounds a little brighter - according to Internet legend.
Old 15th January 2019 | Show parent
  #4
Gear Guru
 
tINY's Avatar
 
1 Review written
🎧 15 years
Quote:
Originally Posted by RBHan ➡️
It will probably have a single P-90 style pick-up - in which case - many early P-90's style pick-ups used 300 K pots. The 500K pots may make it sounds a little brighter - according to Internet legend.

It's more than legend....

The less you load an inductive pickup, the more HF amplitude you get.



-tINY

Old 15th January 2019
  #5
Lives for gear
 
🎧 10 years
Either the pots will have a resistance stamped on them like 250, 300, or 500K or you'll need to measure them with an ohm meter.
You can pretty much bet, if it uses a single coil pickup, its likely to have 250 or 300K pots. If it uses a humbucker (unlikely) it might be as high as 500K.

The pots in guitar are typically Audio taper. Linear taper typically drops all the volume within 25% of the pot turn. Audio has a curved response which is better for the way our ears perceive loudness. You'll hear a 50% volume cut with the volume turned down half way and it will seem to be even to your ears.

If the pots you currently have in there drop in volume all of a sudden then either the wrong pots were installed at one point or the rotors have worn through the resistive pads so there is no resistance to ground the pickups in the center of the turn. Wrong types of cleaners can do this too. The ONLY cleaners you want to use are designed for pots and either contain silicone or mineral oil to lubricate the pots. There are also some audio pots packed with conductive grease to give the pots a smooth feel which should never be cleaned. Old Tapco gear used them. The grease gives then a harder then normal smooth feel when turning. Problem is when that grease dries up it acts like glue. Cleaners make the problem even worse so replacement is the only option.

Most lap steels I've seen are copies of the Fender which all use single coils and 250K pots. Cant tell you if something like a Tele pot would work or not without seeing it. There are a few different shaft types and lengths. You'd obviously want the knobs to fit so you want to measuer the shaft diameter, check and see if its a split splined or solid shaft too.
Old 15th January 2019 | Show parent
  #6
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Mikhael's Avatar
 
🎧 5 years
Quote:
Originally Posted by wrgkmc ➡️
Wrong types of cleaners can do this too. The ONLY cleaners you want to use are designed for pots and either contain silicone or mineral oil to lubricate the pots.
I'll have to disagree with this. I'll NEVER use a cleaner that has lubrication - unnecessary, and that goop collects dust and stuff over time, which will screw it up even worse.
Old 17th January 2019 | Show parent
  #7
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John Eppstein's Avatar
 
58 Reviews written
🎧 10 years
Quote:
Originally Posted by wrgkmc ➡️

If the pots you currently have in there drop in volume all of a sudden then either the wrong pots were installed at one point or the rotors have worn through the resistive pads so there is no resistance to ground the pickups in the center of the turn. Wrong types of cleaners can do this too. The ONLY cleaners you want to use are designed for pots and either contain silicone or mineral oil to lubricate the pots.
Some lubricated cleaners attract dust which eventually makes them noisier than they started before cleaning. If you MUST use a lubricated cleaner use it VERY sparingly. Many techs will use a little bit and then spray it out with a non-lubed cleaner.

Quote:
There are also some audio pots packed with conductive grease to give the pots a smooth feel which should never be cleaned. Old Tapco gear used them. The grease gives then a harder then normal smooth feel when turning. Problem is when that grease dries up it acts like glue. Cleaners make the problem even worse so replacement is the only option.
That stuff you find in old Tapco mixers and other pots from that era is NOT a factory lubricant, it's an aftermarket product called "Blue Stuff". It worked great at first but after a couple of years it dried out and caused severe problems, eventually hardening and gluing the pots so they couldn't turn. It was eventually withdrawn from the market after causing big problems for many repair facilities.

Quote:
Most lap steels I've seen are copies of the Fender which all use single coils and 250K pots.
Magnatones aren't copies of anything. Their better instruments were more expensive than the Fenders.

A lot of old steel guitars have pots that are significantly lower resistance than those used on regular guitars. This was an intentional design feature intended to create that "mellow" steel guitar tone.
Old 23rd January 2019
  #8
Gear Guru
Bourns makes a very high quality 250k or 500 k log conductive plastic guitar pot. It will have less noise and will not cut the tops off like carbon pots do. A no-load tone pot is also a good addition.
Old 17th September 2020
  #9
Here for the gear
 
The pickup on this is actually under the finish and potted directly into the body. There is no way to access the pickup that isn’t destructive. If the pickup is good, do not mess with it. It is legendary and glorious. I’m researching replacing my controls, saving the originals. They are usuallySporting 500k Clarostat Audio Taper potentiometers. Cap and resistor combos seem to vary. This could be due to changes in amp design, since the were sold as a combo for years and through several ownership changes. How has yours turned out?
Old 19th September 2020
  #10
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enorbet2's Avatar
 
🎧 10 years
Personally, and since those old pots are easy to disassemble and reassemble, I'd at least take them apart and inspect them. If the carbon wafer is cracked, ur screwed, but that's rare. It is common especially when they have been stuck or sticky that the wiper(s) will lose tension and are easily re-tensioned for a complete return to usefulness.
Old 19th September 2020 | Show parent
  #11
Gear Guru
 
John Eppstein's Avatar
 
58 Reviews written
🎧 10 years
Quote:
Originally Posted by wrgkmc ➡️
Either the pots will have a resistance stamped on them like 250, 300, or 500K or you'll need to measure them with an ohm meter.
You can pretty much bet, if it uses a single coil pickup, its likely to have 250 or 300K pots. If it uses a humbucker (unlikely) it might be as high as 500K.

The pots in guitar are typically Audio taper. Linear taper typically drops all the volume within 25% of the pot turn. Audio has a curved response which is better for the way our ears perceive loudness. You'll hear a 50% volume cut with the volume turned down half way and it will seem to be even to your ears.

If the pots you currently have in there drop in volume all of a sudden then either the wrong pots were installed at one point or the rotors have worn through the resistive pads so there is no resistance to ground the pickups in the center of the turn. Wrong types of cleaners can do this too. The ONLY cleaners you want to use are designed for pots and either contain silicone or mineral oil to lubricate the pots.

Most lap steels I've seen are copies of the Fender which all use single coils and 250K pots. Cant tell you if something like a Tele pot would work or not without seeing it. There are a few different shaft types and lengths. You'd obviously want the knobs to fit so you want to measuer the shaft diameter, check and see if its a split splined or solid shaft too.
Copies of Fender?

HELL NO!

Magnatone was a major manufacturer of lap steels when Leo was still in his TV shop, IIRC. And their steels were, in general, much higher quality than the corresponding Fenders.

Magnatone also used a much wider coil than the tall coil Fender pickups. The Fender steels lost favor among players by the late '50s/early '60s.

The great Freddie Roulette, master of the blues lap steel, plays an 8 string Magnatone.*

Also, lap steels nearly always used 250K-300K pots - the lower resistance smoothed off the top and contributed to the round lap steel sound. IIRC I've even encountered pots in the 100K-150K range in old Gibsons.

Quote:
There are also some audio pots packed with conductive grease to give the pots a smooth feel which should never be cleaned. Old Tapco gear used them. The grease gives then a harder then normal smooth feel when turning. Problem is when that grease dries up it acts like glue. Cleaners make the problem even worse so replacement is the only option.
I do not believe that Tapco used that grease in their pots, but since for some reason their pots tended to get scratchy pretty quickly many of them got treated with a spray cleaner/lube called "Blue Stuff" which initially worked really well; the problem was that after a relatively short time it dried out and made the pot hard to turn - in many or most cases the pot became totally useless within 3 years or so and needed replacement, as you couldn't clean out the dried Blue Stuff. I remember this well, as it happened around the time (early '70s) that I was just starting to work as a tech. We used a lot of Blue Stuff for about a year until the problems started showing up.I do not believe that Blue Stuff was actually used by the Tapco factory - no reason for it in a new pot.

The volume pots in Tapcos were not faders in the modern sense, they were gain controls and would not shut off completely. It's been a long time and I don't remember for sure, but it's quite possible that the scratchiness was caused by caps in the cheap circuitry becoming leaky - when you apply DC to a pot in the signal patch it causes the pot to seem scratchy.

BTW, Blue Stuff was, in fact, a silicon based product, so not all silicone products are good for pots. You really should not use lubricated sprays in pots anyway, since the lube attracts dirt. Real lubricated pots are lubed at the factory and have sealed backs - if a pot has vents (as most do in guitar gear) you should not lubricate them.


* - I played bass on a gig or two with Freddie back in the '70s when he played with The Honey Davis band. He was like the Jimi Hendrix of steel guitar - really wild at times. Much later his band rehearsed in my living room occasionally. Always left a big pile of peanut shells under his chair.....

Last edited by John Eppstein; 19th September 2020 at 08:59 PM..
Old 19th September 2020 | Show parent
  #12
Gear Guru
 
John Eppstein's Avatar
 
58 Reviews written
🎧 10 years
Quote:
Originally Posted by Jim Williams ➡️
Bourns makes a very high quality 250k or 500 k log conductive plastic guitar pot. It will have less noise and will not cut the tops off like carbon pots do. A no-load tone pot is also a good addition.
Not on lap steel. On a lap steel you WANT to cut the top off.
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