2N5485 Son of Ben

okstateblues

Active member
Looking to finish a Benson build and need some assistance. I have 2N5485's and just want to double check that they will work if installed according to the silkscreen on the board. Any feedback would be greatly appreciated.
 
Why are you going to use 2n5485 instead of j201? Pinout is the same but parameters are different.
 
I've created SOB ltspice model. Let's assume J201 with Vp 0.76V and 2N5485 with Vp 2V.
Then we check build document - set Q1 trimmer to 2k and Q2/Q3 drain voltage to 4V.
There's Q1 10k drain resistor + 2k (trimmer) so we have 12k total.

With J201 as a Q1 we have 5.6V on a drain. With 2N5485 there's only 0.77V...
Let's move to Q2/Q3. To get 4V on drain with J201 we need around 18k. But with 2N5485 we won't ble able to set 4V even with trimmer set to zero. In order to set 4V with 2N5485 we need only 3k6 (remember - there's already fixed 10k). So you'd have to put 1k resistors (or lower value) or even jumper them (btw - with 50k trimmers resistors are superfluous). Back to Q1. To set the same voltage as with J201 - 5.6V we have to lower overall drain resistance to 2k4 (was 12k).
But voltage is not the only factor here. So let's inject a signal into the circuit. 660Hz, 1V p/p.
And now some simulation results. Blue plot - J201, green plot 2N5485, all controls maxed.

Q1
Q1.jpg

Q2
q2.jpg

Q3
q3.jpg

Output
OUT.jpg

Frequency response
freq.jpg

In my opinion - if you replace J201 with 2N5485 it's not SOB anymore.

T
 
I gotta agree With temol... getting used to the smd adapter boards makes life so much easier and opens doors to lots of projects with j201s and 2n5457s.
 
For these boards (or any SMD transistor footprint), apply a small amount of solder to the pad for the gate. With an ESD tweezers, place the SMD J201 into position while the solder is heated on the gate pad. Wait 30 seconds. Heat the pad and lead for one of the other leads and apply a small amount of solder. Wait and repeat. Then, reflow the gate pad/lead to ensure good connection between the device and pad.
 
For these boards (or any SMD transistor footprint), apply a small amount of solder to the pad for the gate. With an ESD tweezers, place the SMD J201 into position while the solder is heated on the gate pad. Wait 30 seconds. Heat the pad and lead for one of the other leads and apply a small amount of solder. Wait and repeat. Then, reflow the gate pad/lead to ensure good connection between the device and pad.


I will give it another try and report back with my results.
 
For these boards (or any SMD transistor footprint), apply a small amount of solder to the pad for the gate. With an ESD tweezers, place the SMD J201 into position while the solder is heated on the gate pad. Wait 30 seconds. Heat the pad and lead for one of the other leads and apply a small amount of solder. Wait and repeat. Then, reflow the gate pad/lead to ensure good connection between the device and pad.
This is the method I use, makes it super easy. Also, using blue tack to hold the board in place while soldering is extremely helpful and makes the process much less frustrating.
 
I have given it another shot. Hopefully this works for my Benson clone. I think this is what is killing my tone. Here's to hoping!
 
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