Help with pot codes
 

Can anyone help identify the manufacturer and production date of this potentiometer? I'm guessing the four digit code refers to a production date of the 38th week of 1951? The far bit of the print which goes out of view simply says Q/A. Is that the taper?

Re: Help with pot codes
 

The manufacturer is Dubilier. I have a similar boxed pot and the box says Dubilier Control, British Made.

My 50k ohm pot has Q/B printed on it and the box says it is a Q type pot with a log law. The spindle is brass, so the /B could be for log law or even /B for brass. As yours is a /A, do you know if it is linear taper (by measuring resistance with angle of rotation)?

My pot does not have any numbers that could be directly interpreted as a data code, although it does have 9J printed on it. There are other permutations, such as shaft length or shaft flat type or flat length and it is not obvious how these were encoded if, at all.

Ron

Re: Help with pot codes
 

Dubilier Condenser Co. perhaps.

Re: Help with pot codes
 

Thanks guys...much appreciated info. In fact it prompted me to get the pots out again and put the meter on them, which indeed confirmed that they're roughly 1k (ish) linear taper. Also, as I was cleaning them up a little to test I noticed the plastic moulded part had a logo impressed, and a two digit number. I'm guessing the number is simply a week code, but the logo is clearly Dubilier as predicted!

Re: Help with pot codes
 

Unfortunately, when it comes to trying to identify particular pot tracks there isn’t one standard worldwide practice as to defining the type of track – it depends in which country the pots are made and who makes them. IE:

Linear:

Asia ‘B’
America ‘B’
Europe ‘A’
Vishay ‘A’

Log:

Asia ‘A’
Europe ‘C’
America ‘A’
Vishay ‘L’

Anti-log (also known as 'inverse log' or 'reverse log'):

Europe ‘F’
America ‘C’
Vishay ‘F’

Thus, depending on which country their pots are sourced from, the same supplier may even use both conventions. 20mm Omeg pots sold by several suppliers, linear are marked ‘A’, and log are marked ‘B’. However, smaller 16mm diam pots of different manufacture have the opposite markings – linear are ‘A’ and log are ‘B’. (That was the case with Maplins).

As an aside, almost all of the so called ‘log’ pots that we encounter aren’t actually true ‘log’ pots – they’re what's sometimes known a ‘commercial log’ because they're made down to a price. Basically they use two sections of linear track, one section of a much lower value than the other, which are joined. Hence, instead of getting a smooth log law track, we get two straight lines with a kink to roughly mimic a true log taper, quite adequate for most purposes. You see this if you attach a paper dial marked in degrees of rotation. Most pots have 270 degrees of rotation, so each tenth of the rotation equate to 27 degrees. When I was doing some experimentation in connection with reverse log pots, I made a paper dial to attach to the bush on the pot shaft, then made a pointer from a paper clip to push onto the pot shaft. I then plotted the resistance versus degrees of rotation on a graph. I've attached the dial below in case it might be of use to someone.

For most of the pots in radios that we encounter, generally, it’s a safe bet that volume controls are log, and tone controls are linear, but that can only be verified by resistance measurements at various points on the track. Unless a pot is stamped 'Lin' or 'Log', that's only way of being sure. The reason I went into this was that I was restoring a Portadyne 'Princess' and a similar 'Noble' set. Both have 'minimalist' circuitry, are almost identical and are TRF sets, but unusually the volume control also acts as the reaction control, making for easy tuning. In each case, the on-off switches, ganged to the pot had failed open circuit.

There's only an R&TV circuit on the Princess (nothing on the 'Noble'), and the pot track isn't mentioned. I saw what I thought was a 'C' on one of the pots, so plotted the resistance v rotation which confirmed that it was anti-log. The originals had been Omeg and I got in touch with them to see if they could supply replacements. They could, but with a minimum order quantity of ten. (Blore Edwards couldn't help). As it was, I managed to dismantle the pots and get the switches to work.

There's an excellent paper entitled 'The Secret Life of Pots' which some members of the forum will be familiar with.

It has lots of interesting facts and graphs to show the different tracks:

http://www.geofex.com/article_folder...s/potscret.htm

Hope the ramblings might be of interest.

Re: Help with pot codes
 

Hello David,

I think that should be:

20mm Omeg pots sold by several suppliers, linear are marked ‘A’, and log are marked ‘B’. However, smaller 16mm diam pots of different manufacture have the opposite markings – linear are ‘B’ and log are ‘A’.

Regards,

Dave.

Re: Help with pot codes
 

Well spotted Dave - thanks for reading my post and correcting the error!

Re: Help with pot codes
 

That’s great information...it’s actually very useful to get a better in depth understanding of some of the technical aspects of components we often don’t scrutinise as much as others 👍

Re: Help with pot codes
 

Older series of Australian pots from IRC, Ducon & Morganite have:-
linear "A"
log "C"
I can't remember what antilog pots were, but it looks like we followed the European model.

I'm not sure when Oz pots ceased to be made, but from the 1960s on, there was a mix of the old coding with imported Japanese, & ultimately other Asian manufactured pots which used your listing of "B" for linear & "A" for log.

Re: Help with pot codes
 

The idiosyncracies of pot marking makes it fun looking through pot stashes, it's a bit like decoded enigma intercepts from the German Navy circa WW2 : )

Andy.