Transistor sub question N13T1 mabe a (PUT) ?

[newperson]

Hi,
Can someone tell what modern transistor would replace a NEC N13T1 transistor?  The NTE page suggests their NTE6402 and says it is a PUT - Programmable Unijunction Transistor.  Never heard of this but they say they are for timing circuits.  This one is in an old ADSR circuit.  

I will order the NTE one, but I find their equivalents to be questionable sometimes, and since I know nothing about this type of transistor I figured I would see if anyone know anything about these.

Or will the 2N6027 / 2N6028 be fine?

Thanks,

[R.G.]

No way to really tell without the circuit it's in.

All NTE parts are of questionable ancestry. An NTE part may actually be one of several to many manufacturer's part numbers, chosen to mostly work in the "typical" circuits the original parts would work in. I view NTE as what you do if you can't do the right thing.

However, PUTs have a very wide range of things they can do. It may work fine to use a 6027 or 6028. Or it may need some tinkering, especially on the gate-voltage setting string.

Post the circuit and I can be of more help.

[newperson]

Excellent.  Thank you for looking at this. 

[newperson]

Hopefully the link will work.  here is a hard link.  
https://sites.google.com/site/partquestion/home/part

also 'all npn are 2sc945 unless specified'
and 'all pnp are 2sa733 unless specified'


here is the overall schematic for that pcb

[PRR]

This is the point of a _Programmable_ uni-tran. You bias the side electrode to your desired trigger voltage, ANY voltage you like (within limits). Then when the anode goes higher, it shorts-out to do a thing.



D108 is biased by 2200 and 3300 to 3/5th of the supply voltage. R170 et al charge C126 toward supply voltage. But when it gets to 3/5th, D108 goes very low resistance and dumps the charge off C126. When current flow 'stops', D108 opens again, and the cycle repeats.

Differences among PUTs: maximum voltage and current, and the minimum current below which ON turns to OFF. The max limits are probably not a problem. In this circuit, the minimum (Valley) current has some effect on reset time. Valley point is set by bias impedance and Roland(?) made this large so valley is low. Also reset time is a small part of total time and anyway this is a knob-adjustable LFO so small "error of pitch" is totally used controlled.

The VCO above it, under R137, works similarly except with a different charge source, a smaller cap, and an NPN boosts the cap-dump action, probably to make it more robust against PUT variations.

The only issue I see is that a very leaky PUT might never reset. I don't see any easy way to know in advance, even with a meter. Stick the PUT in and see if it oscillates. If not, see what voltage is on C126.