Where to get Alpha amp pots? Free mini-rant included....

King Fan

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For *amp* use, is there a model of Alpha pot that has a bushing 3/8" in diameter *and* 3/8" in length? The ones I see are mostly 8mm = ~5/16" in diameter and 6.5mm = .25" long. Yes, I can find some with the 3/8" diameter, but they're still really short.

Stretch goal: Is there one that has a brass bushing and nut??? The standard zinc-y hinky-dinky nuts are pretty lame.

My story: I had a couple Alphas sitting around and noted they had a smooth rotation feel and pretty tight tolerances (1M actually measured nearly 1M). But pretty soon I started finding downsides. Doug Hoffman actually sells cute tiny micro washers to fit around the smaller bushing to adapt it to a 3/8” hole. LOL. But wait, OK, AES sells 3/8" diameter ones also, and even a precision-tolerance version that costs somewhat more. But the high-precision ones only come in a few resistance values, and the 3/8" diameter is still really short. For me length is the deal breaker. Heaven forbid you want to run a star washer *and* an acrylic faceplate. Not happening. (FWIW I think their long-shaft guitar-style pots, around ~0.7" total length, would be too long on an amp -- and still have the too-short bushing.)

Here's the star on the outside to illustrate the problem...

IMG_1291.jpeg


And a request. No fighting. I've seen Alpha-v.-CTS threads that lead to ugly micturition contests. I'm not debating quality; I'm not making comparisons. Whether you hate or love either brand, I'm just looking for Alpha dimension info. And yes, I checked their website -- not that helpful.
 
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schmee

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Not sure I totally understand it all but:
-You can get some values in longer bushings. You may have to accept CTS or Alpha. I bought some a few months ago with long bushings. But without knowing what value you want I cant help.
-There are very thin star washers available if that helps, I would say about 1/3 the thickness of the one you show. Not sure where I got them though. Measure about .025" thick.
-Yeah, I like the brass ones too, but have found no deficit in the aluminum ones really.
Pot codes:
CTSpotCodes.jpg

005.JPG
006.JPG
 
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King Fan

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@schmee , good point, hunting for the right resistance value and taper adds a layer to the 'where to buy' issue. I need a series of values: 1M log, of course, but also 250K linear, 100K log, and 25K linear. And *another* hoop you have to jump through is solid shaft -- slotted, nylon, flatted aren't cool for me.

**The skinny star washers are a great idea -- since I already charged ahead and hunted up the Alpha pots. Anybody have a ready source for these?**

And my bad: I now see CTS also makes some with short ¼" shafts -- which would also be too short for a plastic faceplate. Maybe I've not had problems since I've used metal faceplates (or none in my several tweeds).

@Junior Little -- I love hacksaw solutions, but in the long-shaft ones I've seen, the problem is the *bushings* are still short. I admit there are zillions of variants out there....
 

schmee

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I thin
@schmee , good point, hunting for the right resistance value and taper adds a layer to the 'where to buy' issue. I need a series of values: 1M log, of course, but also 250K linear, 100K log, and 25K linear. And *another* hoop you have to jump through is solid shaft -- slotted, nylon, flatted aren't cool for me.

**The skinny star washers are a great idea -- since I already charged ahead and hunted up the Alpha pots. Anybody have a ready source for these?**

And my bad: I now see CTS also makes some with short ¼" shafts -- which would also be too short for a plastic faceplate. Maybe I've not had problems since I've used metal faceplates (or none in my several tweeds).

@Junior Little -- I love hacksaw solutions, but in the long-shaft ones I've seen, the problem is the *bushings* are still short. I admit there are zillions of variants out there....
I think many of us have had issues with bushing length for sure. I'll see if I can figure out where those thin washers come from. BTW, the long bushing pots I bought recently were off Ebay and off Reverb. Yeah, I had to pay a bit more for them. I suppose oddballs end up available there some times.
I have a 25KB Alpha 3/8" bushing in my hand, so they are out there....

These may be the thin washers: https://www.ebay.com/itm/2249157991...mBCH9YNLg0ROsCaJs%3D|ampid:PL_CLK|clp:2047675
 

Phrygian77

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I think nearly all of the 24mm body, 3/8" diameter bushing, CTS and Alpha pots from the usual vendors are going to be 1/4" length bushings. The Alphas have slightly shorter shafts than CTS too.

The one thing I've been frustrated about is the lack of J taper (25-30% taper) pots in 250k. Thankfully AES/Amplified Parts now has some that are an exact match to the brass bushing/shaft Mojotone pots (assuming everyone hasn't bought them all since I did post a thread about it).

I've seriously thought about checking to see what the cost is for 'mod pots', i.e. custom pots from a company like https://potentiometers.com.
 

Phrygian77

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I meant to add in my previous post that I don't think the pots AES says are improved (tolerance) are actually made by Alpha. From what I remember, they don't list the manufacturer.
 
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King Fan

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I meant to add in my previous post that I don't think the pots AES says are improved (tolerance) are actually made by Alpha. From what I remember, they don't list the manufacturer.
Excellent observation. I hadn't caught that, or I figured they just forgot to add the brand name. But no, the dimensional drawing is not Alpha style. And in any case they have the short bushing.

@schmee , thanks for the link to the skinny washers. At 7/16" ID, they might work just fine. And the price is right -- if that's for 20 items.

At the end of the day, I wonder if some folks using plastic faceplates are skipping the star washers. And I'm starting to wonder if a thin faceplate might beat acrylic for my purposes. Saddle up the old swaybacked charger and oil the armor... a new quest beckons.... :)
 
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King Fan

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How thick is your plastic? I can compare to the stuff I use.
Thanks. I haven't picked out plastic, but I see .08 - .10 plexi sheets for sale locally, while the nice faceplates at Precision Design are .06 IIRC... The other joker in the deck is my nice chubby .08 aluminum chassis; galvaneal and SS are likely thinner, right?
 

Phrygian77

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With the 16 guage Mojotone and Zachmdhunter chassis, 1/4" bushing length (and Switchcraft 11/11A jacks) are just long enough with the internal tooth washers and 1.5mm faceplates that I use. There's no room for any flat washers.

I replaced some of the pots in the normal channel of my '76 Twin Reverb with Alpha when I revoiced that channel. They are noticable shorter than the CTS plastic shaft pots from that era. The skirted knobs barely fit with the knob set back slightly from the faceplate.
 

King Fan

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With the 16 guage Mojotone and Zachmdhunter chassis, 1/4" bushing length (and Switchcraft 11/11A jacks) are just long enough with the internal tooth washers and 1.5mm faceplates that I use. There's no room for any flat washers.

I replaced some of the pots in the normal channel of my '76 Twin Reverb with Alpha when I revoiced that channel. They are noticable shorter than the CTS plastic shaft pots from that era. The skirted knobs barely fit with the knob set back slightly from the faceplate.
That's interesting. If I'm right, 16ga steel is .0625", and 1.5mm is .06", so your chassis plus plate totals just about .125 = 1/8". The standard internal-tooth washers I have are very roughly .07"; if yours are too, that would give you a total layer thickness of .195" = ~5mm, so I can see on those short 6.5mm bushings, you wouldn't have much room for a flat washer. Bit tricky sometimes to even get the nut to grab the threads, eh?
My stuff is .03ish when I checked just now.
Thanks, that's interesting too. Any trouble with it cracking? Any special tools for cutting and drilling? Hey wait, aren't you the guy who just bought a graphics company to save a little money on faceplates? :):):)
 
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corliss1

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As long as you don't attack it with anything super high speed, it drills super easy. I have cracked a couple trying to drill too fast, but I learned real quick.
 

King Fan

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As long as you don't attack it with anything super high speed, it drills super easy. I have cracked a couple trying to drill too fast, but I learned real quick.
BTW, do you happen to have a source/brand/type info for the .03 stuff you use? Acrylic, or??? Only if it's handy...
 

SerpentRuss

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I don't particularly care for Bourns pots, but theirs do come in a long shaft with quite a few brass threads. This is the part number for the 1 MEG audio taper.

EDIT: I'm not sure about that link taking you to the right part, but it's fairly easy to parse on mouser. The standard bourns pro-audio pot has 3/8 inches of thread. The extra long shaft pot (very long) makes up it's length with threads instead of just a longer shaft.

BTW, I measured the threads on all my 3/8 inch alpha pots and they're maybe on thread over 1/4 inch. Not much to work with on a thick faceplate.

 
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ahiddentableau

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From what I have seen, they do make a series of brass bushing 3/8" pots, but they are a custom build and meant for guitars, so they only make them in 250k and 500k audio taper (they make them with standard length and Gibson LP length bushings). So not much help for you. Here is the example:


Other than that I don't see anything between the ones you say are too short for you needs and the 15mm long model. (RV24XX-10-15XX - mouser is my source) I imagine that could work but you'd have to be clever with the lockwashers. I guess I kind of prefer having things right without fiddling.
 
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