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Post subject: Blues Deville 410 (USA made) Adjustable bist install?
Posted: Thu Oct 11, 2012 2:44 pm
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Joined: Thu Oct 11, 2012 2:42 pm
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I want to add an adjustable bias pot on my old Blues Deville. Does anyone have any information on how I would do it? I know torresengineering.com sells a kit, but I don't really want to spend $30 for $5 in parts. Plus, I have been reading mixed reviews about his stuff.

Any help is appreciated! Thanks!


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Post subject: Re: Blues Deville 410 (USA made) Adjustable bist install?
Posted: Thu Oct 11, 2012 7:53 pm
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Joined: Tue Jun 29, 2010 1:20 pm
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Location: Indiana
Hi Geosh,

Basically, replace R87 with a 15K ohm resistor in series with a 25K ohm pot, both resistor and pot 1/4 watt or higher. This will give you a good range of adjustment for most any type of tubes. You can mount a full sized pot and resistor on the chassis by drilling a hole in the chassis close to R87, but not too far away as to introduce noise, being sure that the pot case is well clear of the tubes and circuit board. Or, solder a smaller multi-turn pot and resistor to the circuit board. To mount to the circuit board, you might have to drill some small holes in the board near the resistor, and use a touch of hot glue to secure the pot firmly to the board, delicate work, and you have to be sure to clear the other circuit traces on the back of the board if drilling holes.

If mounting to the circuit board, use a pot like this and you can just glue it to the board without having to drill holes.
http://www.mouser.com/ProductDetail/Bourns/RJ26FP253/?qs=sGAEpiMZZMvygUB3GLcD7oYQkxX9lDAfyoKCKyjcTik%3d

Or, use this type if you want to drill holes in the board for a more secure mount.
http://www.mouser.com/ProductDetail/Bourns/3299Y-1-503/?qs=sGAEpiMZZMuz2E8dTn0VFfo4R8fTsagshrcvCSgT0EA%3d

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Post subject: Re: Blues Deville 410 (USA made) Adjustable bist install?
Posted: Fri Oct 12, 2012 12:49 am
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+1 shimmilou,

Multiturn pots are the best for bias use . They can't turn by itself. Normal pot with less than one turn can move and change bias.


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