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.
2N5485 Son of Ben
- Thread starter okstateblues
- Start date
Nostradoomus
Well-known member
The pin out is the same as j201, I’d still use sockets though!
okstateblues
Active member
Ok good deal thanks!
okstateblues
Active member
It's all I had on hand
temol
Well-known member
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
Q2
Q3
Output
Frequency response
In my opinion - if you replace J201 with 2N5485 it's not SOB anymore.
T
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
Q2
Q3
Output
Frequency response
In my opinion - if you replace J201 with 2N5485 it's not SOB anymore.
T
okstateblues
Active member
Fair point. I'm in the process of going the surface mount route with 201s so I may swap in the near future.
okstateblues
Active member
Quick zombie revival are j113's suitable replacements for the j201?
Robert
Reverse Engineer
These are a regularly stocked item now:
These are a regularly stocked item now:
cool. Just curious (if you care to share), are you hand soldering these, or ordering them re-flowed from a shop? I don’tknow the cost for that process, but seems it would save a ton of time if making on a large scale.
okstateblues
Active member
J201's are available in SMD - MMBFJ201. So why even bother with substitutes?
I tried the surface mount way and burned legs off a few of them. Its really frustrating.
okstateblues
Active member
These are a regularly stocked item now:
I may go that route. I have the boards and the SMD's but there has the be a trick to getting these miunted and not burn off a leg.
benny_profane
Well-known member
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.
okstateblues
Active member
Robert
Reverse Engineer
Previously they were hand soldered, which is why there were about 20 - 40 available every couple months.
Now they're pick-and-placed, so there's plenty to go around (and better quality soldering).
soothsayer86
Member
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.
okstateblues
Active member
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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