Need help identifying these Pots!

[Platefire]

I can't tell by what I'm seeing if they are Audio or Liner? By measuring the Ohms I would think they are Liner--because most of the resistance goes away after 12:00 Oclock.

I got two 250K and one 1 meg ALPHA Pots. The 250's have "B250K" and the 1 Meg has "B1M".

I also got a 1 meg that only has the number "0844" on the back and on the front "10A1M"

Thanks, Platefire

[theundeadelvis]

Alpha usually labels their linear pots with the "B," and audio "A." I think this is what most manufacturers do, but feel like it's not necessarily a "standard" (I could be totally wrong).

[Platefire]

Thanks, I went ahead and installed the B 1M AlPHA. It works a lot better than that other 1 Meg I had in there. I could tell just checking it with an Ohm meter that the Alpha was at about 50% at 12:00 Oclock and the other was still at 90% at 12:00 Oclock---couldn't live with that! The Alpha works and sounds a lot better! Plate
 

[RicharD]

B is typically linear and A is typically audio.  The quick test is to set the pot at center.  If the wiper reads 50% of the value it's linear.

[HotBluePlates]

Depending on which end you use as your reference, an audio pot would look like 10% or 90% at half-rotation. For the reference that gives 10% resistance at half rotation, a reverse-audio pot would have 90% using the same reference. The correct reference is the one normally attached to ground when used as a volume pot.

[Platefire]

Well Thanks! After all these years foolen with this I still get cornfused about this  :shocked:

Yeah the first pot I had installed must have been audio because it was 90%(resistance/900K) at 12:00. Couldn't get any volume until after 12:00. When I installed the AlPHA it was 50% at 12:00, much better IMHO. I thought an Audio pot was suppose to have more early volume than Liner?? Plate

[HotBluePlates]

Your description is confusing.

If the pot is a volume pot, you probably want an audio taper pot. That's because hearing is logarithmic, so the taper of the pot is such that the impression is even volume change over the entire range of the volume control. If you measure it correctly, it looks like 10% resistance at half-rotation, or 90% resistance at half for backwards-measuring.

If you install a linear pot, the volume seems to come up quickly, and sounds nice and loud by 2-3 on the knob. The problem is, it sounds like there's almost no change for the rest of the 70-80% of volume rotation.

[bluesbear]

I use Alpha pots exclusively and they definitely use "B" for linear. I don't know about anyone else but I'm sure about Alpha.
Dave

[Platefire]

Well my discripsion may sound confused because I am, har!    This is my concept of how it works: Full counter-clockwise is full resistance(1Meg) and as you turn your pot clockwise the resistance is reduced so more of your preamped signal is released to the power amp. 10% resistance at 12:00 to me would say 10% of 1Meg=100K indicating the that 90%/900K resistance is still in operation. To me 10% of your total output at 12:00 is not enough. I'm not saying my concept is right, it's just what I've been thinking was right. Plate

[HotBluePlates]

Well, the way you're thinking of it makes sense for you, but doesn't jive with standard terminology.

Full counter-clockwise is full resistance(1Meg) and as you turn your pot clockwise the resistance is reduced so more of your preamped signal is released to the power amp.

Clockwise? Full resistance? Viewed from what direction? Measured between what lugs?

For the love of god, don't... whatever you do ... look at the tweed Deluxe to understand a volume control. They are intentionally "backwards".

Imagine a volume control viewed from the back, with the shaft pointing away from you and the lugs pointing up. Number the lugs 1, 2, 3 from left to right. If you rotate the shaft counterclockwise, the wiper (lug 2) moves to lug 1 (usually grounded). In a standard volume control, signal enters lug 3 (always 100% resistance from lug 3 to ground/lug 1), exits on lug 2.

Imagine turning the shaft fully counterclockwise; the wiper has now moved towards lug 1, and resistance between lug 1 and lug 2 is zero (or close). Turn the shaft halfway up. Meausre resistance between lug 1 and lug 2; in an audio taper pot, it's about 10-30%, in a linear taper, it's 50%.

If you measure from the worng reference, or intentionally wire the pot backwards like a 5E3, then things might look strange.

The tweed Deluxe volume control does not make direct sense, so don't try to be sensible with it. It might also explain why you feel a linear taper could work better for you, in that amp (it generally would not work well in a conventional volume control).

[Platefire]

Hay HBP you are assuming 5E3 and you know what they say about ass-u-me, har! 
The amp I'm working on presently with the volume pot acting strange is actually a AA764 champ. Thanks for the explination on the pot operation and I've wired lot of amps and pots in my time and usually don't have these kind of issues--usually don't have to think about it---but when this happens it causes you to start re-looking at everything and figure out what going on. Guess I can blame it on a senior moment! Thanks, Plate

[PRR]

If your audio level is already almost-right (source is very consistent or you use a gain trimmer ahead of the main level pot), and you want consistent output, then Linear may be best.

When your sources range from early DG LPs to local ballgame on AM tuner (a LOT), want to play some loud and some soft, and you just have the one level control, it's gonna be a Audio or it gets too twitchy for loud sources to play soft.

> tweed Deluxe volume control does not make direct sense

The backward loaded linear approximates two ganged linears in cascade: attenuation squared. This is very similar to true-LOG over a good range, and perhaps smoother than the "Audio" taper.

> I thought an Audio pot was suppose to have more early volume than Liner??

Less.

The original function was in AM radio. A local station may be 10,000 times stronger than a distant station. Even after AVC, maybe 100 times stronger. With a Linear volume pot, that strong station would have to be set at "0.1" on a 0-10 scale, and pots just can't be set to ~~1%, too twitchy for human hands. With a 10% Audio taper, "5" is 1/10th and ideally "1" would be 1/100th.... you have 100:1 useful range of source and playback.

I would expect the AA Champ to work either way, though for hot hands at low room volume, Audio taper is much nicer.

It sure sounds like something else is wrong. But the way an AA Champ is supposed to be wired, there isn't much you can get wrong. Even wiring the pot backward 5E3 style should give you something before "5".

[FYL]

I use Alpha pots exclusively and they definitely use "B" for linear. I don't know about anyone else but I'm sure about Alpha.

The situation is quite messy.

The current standard is A for log audio (typ. 15% resistance at 50%), B for linear (typ. 50% at 50%). The old standard was C for log audio, A for linear.

European manufacturers used B for log audio, A for linear. Some still do.

Others use L for linear, A for audio. Or L for audio, A for linear, cf. the enclosed pic depicting available tapers from Vishay/Sfernice. A,F, L, R, S, W tapers: alphabet soup anyone?

Oh, and there's also E for reverse log audio (typ. 25% at 50%), D log (50% at 10%) and RD log (reverse D log).

[Platefire]

Well Thanks Guys for the help. If I get confused about this again I should have three swift kicks (or maybe four) because you've laid it out as plain as the nose on my face. I didn't know that audio taper came from radio operation but it all make sense. More/longer early travel space on audio taper to have more gradual control over quirkey signals. I don't know why either that he ALPHA B, 1 Meg works better than the I-Meg Audio I had in there, it was wired up correct. I double/triple checked everything. I'm satisfied enough with operation that I've got it packed up ready for shipment.

Thanks also for helping me sort out the VOM transformers on this one. I'll not build an amp for someone again unless I can have a hand in selecting the transformers and can know the specs and wiring in advance. Plate