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Broken R36 B5K 5K Logarithmic potentiometer #parts

bernd@...
 

I am currently assembling a QCX 80m, when realized my R36 potentiometer is broken. Now I am looking for a replacement at my local dealer.

1. I need to know how much power [W] the potentiometer should be able to endure.

2. Is it truly a log potentiometer. On the part i see a lable "b5k" which usually refers to linear potentiometer, but i might be wrong.

Any help would be appreciated. Links to dealers delivering in Germany would be very great.

Regards,

Bernd, DO5BX

ajparent1/KB1GMX
 

1. I need to know how much power [W] the potentiometer should be able to endure.

A very very small fraction of a milliwatt.  A part that can withstand 1/10th watt is adequate.

2. Is it truly a log potentiometer. On the part i see a lable "b5k" which usually refers to linear potentiometer, but i might be wrong.

Log and audio taper are approximately the same and in practice are the same.

A5K would be linear taper.  B5K is normal audio or log taper.  There are other tapers like reverse log..

Can't help much with vendors over there.  Sorry.

Allison

Peter GM0EUL
 

Hi Bernd
Its a 5K linear pot and it has to endure only a tiny bit of power.  I replace mine with miniature pots with an integrated power switch and mount them off the board.

I've got a batch from D&M Components Ebay shop they are good, relatively inexpensive and they will post to Germany

https://www.ebay.co.uk/itm/1-2-5-10-20-50-100-200-500-K-M-Ohm-Potentiometers-Lin-Log-Switched-Single-Dual/110857852314?hash=item19cfa4959a:m:mKtFMLgvEhuWQ4AsBoCbjHg&var=410103853788

73, Peter GM0EUL

Peter GM0EUL
 

Hi Allison
I posted my reply before seeing yours.  I'm sure its the other way round, A5K is the audio/log version and B5K is linear.

73, Peter GM0EUL

Chris Smith <me@...>
 

This is one of those standardisation messes unfortunately which I learned about the hard way a few times. The reason no one agrees is that it actually depends on the region and vendor. Some examples from my notes I've stumbled across:

1. American / Far East manufacturers use B for linear and A for log.
2. European manufacturers use A for linear and C for log
3. Omeg mark their linears as A and log as B (this is the one I tripped over).
4. Vishay mark linear as A and log as L even though they're an American company.
5. There's also anti-log but I have no idea what they were but probably overlap with the above unhelpfully.

Through mergers and all sorts of business deals which are unmanagably complex to reverse engineer such as Vishay buying out European and US pot manufactuers and spending years selling a mix, it's a drag working out what is what.

Ergo, if in doubt, always consult the manufacturer's datasheet if it exists and/or measure it!  On top of that it's quite hard to make log pots cheaply so the cheap ones (under $5-8 a go) are basically two linear tracks stuck end to end and arranged not to offend the ears so much so this makes measurement somewhat flawed if you're not careful.

Getting back to the original point, if it's made by WL like my QCX, this is Far East which the B is linear. These are known as 16mm "alpha style" pots. Suitable cheap equivalent source is Tayda's Taiwan Alpha pots which are quite good really: https://www.taydaelectronics.com/5k-ohm-linear-taper-potentiometer.html 

I'm going to bed now and will probably dream of potentiometers :(

--
73 Chris M0XTE.


On Thu, 21 Feb 2019, at 22:45, Peter GM0EUL wrote:
Hi Allison
I posted my reply before seeing yours.  I'm sure its the other way round, A5K is the audio/log version and B5K is linear.

73, Peter GM0EUL

bernd@...
 

Thanks a lot. I think i will be able to fix this now <3

Richard G4TGJ
 

Why not ask QRP Labs for a replacement?
--
73
Richard
G4TGJ

Zdenek OK2BQN
 

ohwenzelph
 

The potentiometer is quite delicate.”
on my first qcx it literally fell to pieces when I picked it up.
substituted a junk box 5k pot that (just barely) fit

Hans Summers
 

Hi all
 
The potentiometer is quite delicate.”
on my first qcx it literally fell to pieces when I picked it up.
substituted a junk box 5k pot that (just barely) fit

I do hear of broken potentiometers sometimes. The exposed tabs made from SRPB material are probably not exactly easily broken, but certainly more easy than the other components in the kit.  I doubt that they are broken in the final shipment from QRP Labs to you, because the QCX kits are always packed in bubble-wrap and then in the cardboard boxes. Damage probably occurs earlier in the supply chain somewhere so it's hard for us to prevent. But, the instance of broken pots does seem to be very rare. 

Of course if anyone has a broken pot then contact me and I will send you a replacement. 

73 Hans G0UPL
http://qrp-labs.com