Humbucker Pots

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kennyk
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#1 Humbucker Pots

Post by kennyk »

Perhaps a bit of a basic, and dumb question, but here goes...

I'm trying to source some humbucker pots (for DHT amps) the circuit says 20R, but the closest I've found is the 22R Meggitt variety on Hifi Collective. am I worrying over nothing (or 2 ohms)? are there any alternatives I should be looking at? should I increase the resistance on the other triode in the Parallel pair to match the 22R? (by adding 1R in series with each 10R)
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Greg
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#2

Post by Greg »

It's a variable thing. The 22R Meggitts will be just fine.
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izzy wizzy
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#3

Post by izzy wizzy »

I just looked at the price of the Meggit wotnot and nearly fell off my chair. I bought these to give a go http://www.technologysupplies.co.uk/Wir ... eter-20ohm. Only used them briefly so can't comment on long term use but they seem alright.

cheers,

Stephen
Last edited by izzy wizzy on Wed Oct 23, 2013 9:52 pm, edited 2 times in total.
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#4

Post by pre65 »

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#5

Post by JamesD »

The value is not critical so 20R, 22R or 25R will work fine as well and there is no need to match between the parallel pair of 2A3s either as long as the difference between the two is within 1o% or so...

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kennyk
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#6

Post by kennyk »

excellent, thanks. I've been googling 20R 2W potentiometer. since these are 5W it's no wonder I didn't find them. Now I just need to see if they have a minimum order value...
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Mike H
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#7

Post by Mike H »

RS have got or did have low value wirewound pots, which are not to be sneezed at.

Blimey what a struggle, but found them eventually :D


http://uk.rs-online.com/web/c/passive-c ... 675894&h=f

Or go to uk.rs-online.com and search for 1W wirewound pot

For our puposes they've got 10, 25, 50, 100, 250, 500 Ohms, and a few higher values. I have used these as humbuckers, no problems. Only thing is solder tags are a bit soft though, bend easily so beware of them shorting together if wires are pulled. Or insulate with sleeving.

HTH
 
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kennyk
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#8

Post by kennyk »

Mike H wrote:RS have got or did have low value wirewound pots, which are not to be sneezed at.

Blimey what a struggle, but found them eventually :D


http://uk.rs-online.com/web/c/passive-c ... 675894&h=f

Or go to uk.rs-online.com and search for 1W wirewound pot

For our puposes they've got 10, 25, 50, 100, 250, 500 Ohms, and a few higher values. I have used these as humbuckers, no problems. Only thing is solder tags are a bit soft though, bend easily so beware of them shorting together if wires are pulled. Or insulate with sleeving.

HTH
Cheers Mike, I thought it was 2W pots required not 1W?
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#9

Post by simon »

As an alternative Kenny you could use a pair of 10R resistors instead of the humbuckers. This will give you a pseudo midpoint of a 20R pot but without any adjustability obviously. It's worked well for me in the past and is somewhat cheaper (and probably more reliable in the long run) than a pot.

Wattage wise, if you're using say a 2A3 biased at 60mA then you'll have roughly half that through each resistor, so power = 0.030^2 x 10 = 0.009W. Derate by 3x to 5x so a resistor of .25W or .5W would be fine. Personally I'd go for .5W.
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#10

Post by kennyk »

simon wrote:As an alternative Kenny you could use a pair of 10R resistors instead of the humbuckers. This will give you a pseudo midpoint of a 20R pot but without any adjustability obviously. It's worked well for me in the past and is somewhat cheaper (and probably more reliable in the long run) than a pot.

Wattage wise, if you're using say a 2A3 biased at 60mA then you'll have roughly half that through each resistor, so power = 0.030^2 x 10 = 0.009W. Derate by 3x to 5x so a resistor of .25W or .5W would be fine. Personally I'd go for .5W.
Ah. that's starting to make sense. feeling quite silly because I've been getting hung up on / misled by the 7W 1k resistors. using that as a basis, with 50v across them, that means the current draw should be 50mA through each 2A3?
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#11

Post by Mike H »

kennyk wrote:Cheers Mike, I thought it was 2W pots required not 1W?
LOL all I know is you were looking for 2W, the reason I know not :lol:


Have used the 50R RS ones as humbucker for 300B, and I had worked out even if the Ia was 70 mA the power dissipation for the pot is still very low. say >200 mW. A half Watt resistor could handle it.

If you use the 25R ones, then even less.

HTH (?)
 
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#12

Post by simon »

Yep, you got it Kenny. V = I x R and P = I x V. I'd go for a 12W resistor, but I don't like the smell of really hot resistors ;-)
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#13

Post by David »

RS also do the standard carbon humbucker pots, similar to the Meggitt ones but cheaper. I asked HFC about the Neggitts a few months ago and they said they had none in stock because the price had been going through the roof and they would phone me back. They never did, so I bought from RS.
David
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