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Mosfet breakdown

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rknize

rknize

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Joined 2009
knizefamily.net/russ/electronics/electron-tube-audio/
If my shooting-from-the-hip calculations are right, a 10k resistor (same as R14/24) in place of the CCS should give you something that roughly works. The gain will be down quite a bit, but at least it would serve as a useful test. The resistor would go across the pads for the A and K terminals. Nothing would connect to where the G terminal was.

http://ixdev.ixys.com/DataSheet/98704.pdf
 
R

RuiR

Member
Joined 2011
rknize said:
If my shooting-from-the-hip calculations are right, a 10k resistor (same as R14/24) in place of the CCS should give you something that roughly works. The gain will be down quite a bit, but at least it would serve as a useful test. The resistor would go across the pads for the A and K terminals. Nothing would connect to where the G terminal was.

Thanks :)

Can i test it only in one channel? I have a 1,1 and a 9,1Kohms resistors which will gave in series 10.2Kohms

One question though, how the 12AT7 will be feed? B+ will at R14/R24 :confused:

http://ixdev.ixys.com/DataSheet/98704.pdf
Click to expand...
 
R

RuiR

Member
Joined 2011
rknize said:
If my shooting-from-the-hip calculations are right, a 10k resistor (same as R14/24) in place of the CCS should give you something that roughly works. The gain will be down quite a bit, but at least it would serve as a useful test. The resistor would go across the pads for the A and K terminals. Nothing would connect to where the G terminal was.

http://ixdev.ixys.com/DataSheet/98704.pdf
Click to expand...

Done it Russ.

I end with a B+ ~460VDC, ~350VDC after R14 and ~250VDC 12AT7 plate

It's the mosfet right?

The 10M45S have this characteristic: "Instantaneously reacting resetable
fuses" Does he shut down to protect himself from high voltages? B+ reach around 490VDC when the rectifier tube is warming up :confused:


thank you
 
rknize

rknize

Member
Joined 2009
knizefamily.net/russ/electronics/electron-tube-audio/
RuiR said:
Done it Russ.

I end with a B+ ~460VDC, ~350VDC after R14 and ~250VDC 12AT7 plate
Click to expand...

~250V on the plate is about right. That channel should play music now, albeit with lower gain than it should.

It's the mosfet right?
Click to expand...

I don't understand this question. You are not using any MOSFETs right now, right?

The 10M45S have this characteristic: "Instantaneously reacting resetable
fuses" Does he shut down to protect himself from high voltages? B+ reach around 490VDC when the rectifier tube is warming up :confused:
Click to expand...

The "Instantaneously reacting resetable fuses" comment is under "applications" and not "features." They are saying that you can make a resetable fuse circuit using this part.

490VDC at startup is pretty normal. Keep in mind that at startup, the tube is cold and not drawing any current. The CCS sees no voltage across it at first because the tube is an open circuit. As the tube starts to conduct, the CCS will want to push 9mA through it so the CCS will have a very small voltage across it. As the tube reaches operating temp, the voltage across the CCS will rise until it reaches 80-100V or so.
 
R

RuiR

Member
Joined 2011
rknize said:
~250V on the plate is about right. That channel should play music now, albeit with lower gain than it should.
Click to expand...

Yes it plays ;)


rknize said:
I don't understand this question. You are not using any MOSFETs right now, right?
Click to expand...

Yes, only in one channel though. Replaced the other one with the resistor you suggested and take the readings.

I was asking if the mosfets are burn/faulty?


rknize said:
The "Instantaneously reacting resetable fuses" comment is under "applications" and not "features." They are saying that you can make a resetable fuse circuit using this part.

490VDC at startup is pretty normal. Keep in mind that at startup, the tube is cold and not drawing any current. The CCS sees no voltage across it at first because the tube is an open circuit. As the tube starts to conduct, the CCS will want to push 9mA through it so the CCS will have a very small voltage across it. As the tube reaches operating temp, the voltage across the CCS will rise until it reaches 80-100V or so.
Click to expand...

Ok, i understood :)

You are being a very good help :up: If it play again i will baptize him with your name :D
 
R

RuiR

Member
Joined 2011
rknize said:
Very simple test for a MOSFET. There are better ways using a small battery instead of the meter to charge the gate. Just Google it.

MOSFET testing

Since the resistor method is working, I am really confused about why your CCSs are failing. :confused:
Click to expand...


It works now, at least for a full week :D

I have to thank you Russ for the help and patiente, the resistors test was essential to see it was a mosfet failure :cool: I order DN2540 ones and installed them. They are working.

I have now 260/270/280VDC (it depends wich valve i use) 12AT7 plate voltage and 2.2VDC cathode... the valve runs at 10mA. A little high but i don't have a more suitable resistors.

Thank you ;)
 
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