Obsolete Mosfets
- pre65
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#1 Obsolete Mosfets
I was looking at the Tubelab powerdrive circuit, and it seems the 2SK2700 mosfet is obsolete.
I found details of an STP4NA90 which is supposed to be a replacement, but none of the usual suppliers seem to stock it.
I saw a variation of a powerdrive type circuit that uses an IRF820, and some versions of that are still available.
Do you "experts" (Mike H ?) think the IRF820 will comfortably replace an 2SK2700 ?
I found details of an STP4NA90 which is supposed to be a replacement, but none of the usual suppliers seem to stock it.
I saw a variation of a powerdrive type circuit that uses an IRF820, and some versions of that are still available.
Do you "experts" (Mike H ?) think the IRF820 will comfortably replace an 2SK2700 ?
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
- Mike H
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#2 Re: Obsolete Mosfets
Looking at the circuit, what might concern me is the gate threshold Voltage, which seems to be equal. Also the gate capacitance of the IRF820 is about half, which is doubtless an advantage.
Just leaves whether VDS of 500V will be OK for what is needed (compared to 900V), looks like it will be.
Also power rating of the two is comparable. So I would say yes. As usual, only one way to be sure! Try it and see.
.
Just leaves whether VDS of 500V will be OK for what is needed (compared to 900V), looks like it will be.
Also power rating of the two is comparable. So I would say yes. As usual, only one way to be sure! Try it and see.
.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
#3 Re: Obsolete Mosfets
STP3NK90 would be another candidate
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#4 Re: Obsolete Mosfets
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
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#5 Re: Obsolete Mosfets
^ Or what he saidNick wrote:STP3NK90 would be another candidate
http://www.alldatasheet.com/view_datash ... d=STP3NK90
.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
- pre65
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#6 Re: Obsolete Mosfets
Many thanks Mike & Nick.
Most helpful.
Most helpful.
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
#7 Re: Obsolete Mosfets
BTW, I would look at some gate resistance in that circuit, or at least check it with a fast scope.
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#8 Re: Obsolete Mosfets
Great minds think alike (?) I was thinking should I put a resistor in series with the gate, this would be just like a grid stopper resistor for a valve. Don't think it needs be a large value tho, what does Nick reckon?
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
#9 Re: Obsolete Mosfets
I would use at least a 1k carbon, maybe 10k to be safe.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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#10 Re: Obsolete Mosfets
That much, OK then.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
#11 Re: Obsolete Mosfets
Well, the mosfet is working as a source follower, so there won't be that much capacitance looking into the grid as long as the drain keeps away from B+ which it will. So 10k is not going to roll off that low down. Given the driving valve is CCS loaded, the entire thing has great potential for parasitics so best (IMHO) to plan ahead. Its the sort of circuit where I would want to watch it working, there are all sorts of possible dragons that may be lurking but not be easy to spot by listening to the output.
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#12 Re: Obsolete Mosfets
Yep I can see that.
So Phil, bit of 'scope practice might also be prudent.
So Phil, bit of 'scope practice might also be prudent.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."