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Finding a replacement transistor for a theremin design

carebare47

Oct 21, 2010
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I am going to try and construct a theremin using the design from this website.
I have redrawn the circuit to better see how it connects together and try and work out a bit more about how it works. The redrawn circuit can be found here.
The problem I have is that Q6 and Q7 on the redrawn circuit, which are both 2N5486 FETs (JFETs I think, the two FETs on the Volume resonant circuit and voltage controlled amplifier of the strangeapparatus.com circuits) seem to be out of production, and all the replacements I've looked for (by googling replacement 2N5486) are out of production too. Does anyone know of a replacement part that is still in production, and which criteria on the datasheet have to be matched up to find the replacement?
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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Those devices are N-channel JFETs. They're used at audio frequency. The first is used as a variable resistor in a variable attenuator; the second is used as an audio signal buffer.

Element 14 (formerly Farnell) have the Fairchild 2N5486 in stock; catalogue number 1387771. The price is NZD 0.61 for me, which is about 40p for you, I think. Their postage charges can be significant though.
 

carebare47

Oct 21, 2010
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Thank you very much for your quick reply, now that I know what they are and what they are doing it will be much easier to find a replacement if I have to. I've had a look on the English Element 14 website and as far as I can tell the item is out of stock indefinitely. I've checked the New Zealand Element 14 website and it says they are out of stock too, but with a 57 day lead time. There is one 2N5486 on ebay that I can find, but it's nearly £4 (about $7.80 NZD). I thought it was obsolete but maybe it isn't. If I can't find another source or a viable replacement then I'll buy the ebay one, but if I can avoid spending that much money on them then I will.
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
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OK. Digikey list the Fairchild 2N5486 but not in stock. They list one from Central Semiconductor as in stock for USD 1.00 (but Digikey add significant shipping charges outside USA in my experience): http://www.digikey.com/product-detail/en/2N5486/2N5486CS-ND/4806920

A US company called NTE (http://www.nteinc.com) make replacements for some old devices. Their cross-reference lists NTE451 as the replacement for the 2N5486 (but check the pinout; it may be different). See http://www.nteinc.com/specs/400to499/pdf/nte451.pdf. It may be easier to find than the 2N5486.
 

Arouse1973

Adam
Dec 18, 2013
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Rochester Electronics have >10,000. But not sure MOQ
Adam
 

Arouse1973

Adam
Dec 18, 2013
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Just did live chat with them, they have actually 1316pcs at $0.19 each but unfortunately $250.00 min spend.
 

carebare47

Oct 21, 2010
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Thank you all for the replies and for looking for me! I'll look for NTE451 too. The project is going to be delayed a couple weeks as my college course is running over into summer, but I'll be starting it soon. Thank you all again for your help :)
 
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