umut1001 said:
It has been known that sharing load on a bank of caps may cause blown caps for the reason that they all differ somewhat on specs and one or two will be getting the beat of the load ( or current through them) plus the fact that you will have a lot of connections thru the bank.
It is better, far better to have smaller decoupling caps right at the circuit rails on the PCB…. Be amazed !
rdk845 said:
I have never tested Jfet with reversed Vds. Your 2SJ74 is considered still okay without any damage because you got 9mA when you switched the reversed Vds to the right Vds.
Nevertheless, I give my strong suspicion to the the input Jfet if I review the problem based on the simple ohm's law . . .
All the best.
>>🙂<<
I took out both JFET and measured the Idss with Gate and Source connected. 19V applied with 1Kohm in series. J74 shows clear saturation at 10ma and K1709 at 8ma. This test seems to say JFETs are working, although in actual cricuit Gate and source is not connected. Any idea?Babowana said:
You are making me sweat . . .
I assume that your resistance values of R4, P2, R16 and TH2 are correct, i.e. 2.2K, 0 to 5K, 2.2K and 4.7K.
I assume that your resistance values of R4, P2, R16 and TH2 are correct, i.e. 2.2K, 0 to 5K, 2.2K and 4.7K.
- First, I adjust P2 to maximum 5K. Then A=R4||P2 is 1.53K.
- Next, I calculate B=R16+TH2 and is 6.9K.
- Next, I calculate A||B and is 1.25K.
[/list=1]
So, when I adjust P2 for 0 to 5K, I get the resistance value of 0 ohms to 1.25K ohms between the (-)rail and the drain of 2SJ74. And, if I get about 5mA bias current from 2SJ74, I would get dc voltages across P2 from 0V to 6.25V.
Here I could put a check list:
- All R4, P2, R16 and TH2 values are correct?
- The dc current through 2SJ74 is about 5mA or more?
[/list=1]
If yes and yes, the amp should work.
If no and yes, the R4, P2, R16 or TH2 values are to be corrected.
If yes and no, a repair around 2SJ74 to be done. What about R2?
Are you sure that your R2 is 10 ohms? Might be 100ohms . . .
Good luck!
>>🙂<<
about cooler
hi..my amp is sounds well with my coolers..it seems hot on my table..i connected one transistor to 1,5kilograms of alumunium cooler..but it is not electrostatical painted..i heard that unpainted aluminium coolers are not effecient..is it enough 50cantimeter of this cooler for one channel ?
hi..my amp is sounds well with my coolers..it seems hot on my table..i connected one transistor to 1,5kilograms of alumunium cooler..but it is not electrostatical painted..i heard that unpainted aluminium coolers are not effecient..is it enough 50cantimeter of this cooler for one channel ?
Attachments
Re: about cooler
The central portion looks as though it might be 4 to 5mm thick.
The backplate can transfer heat efficiently for about ten times it's thickness.
If this is only 5mm thick then a transistor fitted to the middle of a 100mm high length of this cooler will work efficiently.
But a 500mm high version will run very cold at the extremities and will not dissipate 5times as much heat as a 100mm tall sink.
I guess a 500mm section will dissipate less than twice as much heat as a 100mm section.
tell us the Rth s-a of this cooler.umut1001 said:
The central portion looks as though it might be 4 to 5mm thick.
The backplate can transfer heat efficiently for about ten times it's thickness.
If this is only 5mm thick then a transistor fitted to the middle of a 100mm high length of this cooler will work efficiently.
But a 500mm high version will run very cold at the extremities and will not dissipate 5times as much heat as a 100mm tall sink.
I guess a 500mm section will dissipate less than twice as much heat as a 100mm section.
firstly i didnt understand you well 🙂
i asked about differences of cooling effeciency between black painted and unpainted coolers..and i think it has 3,5-4mm thickness max
can you write more basic ? thanks
i asked about differences of cooling effeciency between black painted and unpainted coolers..and i think it has 3,5-4mm thickness max
can you write more basic ? thanks
Natural aluminum Vs (versus) Black aluminum
Generally speaking, black heatsinks (cooler) are at least 10% more efficient.
What Andrew T was trying to explain is that the heatsink profile and thickness are often more important than the lenght or total mass (weight).
In plain words, even if you have a 100 cm long heatsink of that profile, it will not be able to dissipate more heat. The disspation curve is not linear: after a certain lenght, to increase the dimension is useless.
Generally speaking, black heatsinks (cooler) are at least 10% more efficient.
What Andrew T was trying to explain is that the heatsink profile and thickness are often more important than the lenght or total mass (weight).
In plain words, even if you have a 100 cm long heatsink of that profile, it will not be able to dissipate more heat. The disspation curve is not linear: after a certain lenght, to increase the dimension is useless.
ok i see someone says blacks are %50 more effeciency 🙂 its not important %10 for me 🙂
yes i now see that the end sides are not as hot as center of cooler🙂
nelson said if you have big cooler you dont have to use thermistors..i am not using thermistors and ztxs now because i use 50cm cooler for one transistor..but i think i should use thermistors and protector transistors when i connect two transistors to one 50cm block as nelson do...i will built stereo amp.thank you
yes i now see that the end sides are not as hot as center of cooler🙂
nelson said if you have big cooler you dont have to use thermistors..i am not using thermistors and ztxs now because i use 50cm cooler for one transistor..but i think i should use thermistors and protector transistors when i connect two transistors to one 50cm block as nelson do...i will built stereo amp.thank you
50% is probably too much: let's say between 10 - 20%
Simple rule: if you have a 50 cm long heatsink, divide the lenght in 4 parts (50/4=12.50cm) then place the two mosfet 25 cm (12.50 *2) apart. Each one will benefit of half heatsink lenght and you get the maximum heat dissipation. If you put the transistors closer you waste a lot of dissipation power of your heatsink.
Thermistors are not mandatory, but very useful regardless the lenght of the heatsink. I don't remember mr. Pass said what you stated. Most probably he was misunderstood.
Simple rule: if you have a 50 cm long heatsink, divide the lenght in 4 parts (50/4=12.50cm) then place the two mosfet 25 cm (12.50 *2) apart. Each one will benefit of half heatsink lenght and you get the maximum heat dissipation. If you put the transistors closer you waste a lot of dissipation power of your heatsink.
Thermistors are not mandatory, but very useful regardless the lenght of the heatsink. I don't remember mr. Pass said what you stated. Most probably he was misunderstood.
ok i see..but in my pcb the transistors are 10cm far from other 🙂 i will try different pcb and do it 🙂 will you send me a good pcb to my email ? @yahoo.com thanks
Sorry, I cannot help you. I designed my own pcb, but the mosfet are only 15 cm apart (center of the mosfet-to-center). Try to modify your design. Put the mosfets orizontally rather than vertically with the "legs" about 22 cm apart. That should result in 25 cm apart (approximately)
Re: about cooler
It's not the kg of aluminum -- it's the surface area and method of mounting.
Here's an easy test -- take a chassis mountable power resistor -- like a Caddock or Dale -- mount on the heatsink -- I have variously used 10 ohm 50W, 100 ohm 30W etc. -- mount a kitchen thermometer (or a better one if you have it on the heat sink) cook at 10 Watts and chart the temperature vs time. At some point it plateau's. The difference between temperatures divided by the cooking energy (10W) should give you a close approximation of the thermal impedance of the heatsink.
If you look at the F5 article, NP specifies the demanded thermal impedance somewhere towards the back.
umut1001 said:
It's not the kg of aluminum -- it's the surface area and method of mounting.
Here's an easy test -- take a chassis mountable power resistor -- like a Caddock or Dale -- mount on the heatsink -- I have variously used 10 ohm 50W, 100 ohm 30W etc. -- mount a kitchen thermometer (or a better one if you have it on the heat sink) cook at 10 Watts and chart the temperature vs time. At some point it plateau's. The difference between temperatures divided by the cooking energy (10W) should give you a close approximation of the thermal impedance of the heatsink.
If you look at the F5 article, NP specifies the demanded thermal impedance somewhere towards the back.
Sorry...Babowana said:
O.K. it seems I got some possible solution.Babowana said:
R4 P2 R 16 and TH2 values and connections are fine and I directly measured current through 2SJ74 source to ground and it was more than saturation current, which is not right.
BUT when I replaced Fairchild mosfets with IRFP9240 and 240 I had for F4, I was able to get correct voltage!
The fairchild Mosfets seems to work fine, but Vgs at Ids = 0.2A was 5.5V for P-type and 3.4V for N type, a quite large difference compared to those between my 9240 and 240. ( i did not try to test mosfets since I read somewhere in the forum that they don't need to be matched in F5) COULD THIS BE THE SOURCE OF VOLTAGE PROBLEM (which wasted several days of my time 😡 )? If so, where can I get pairs with Vgs closer together?
I had an impression that according to Mr. Pass Fairchild Mosfets may provide better sound quality that 9240 in F5. Is this true?
Have another problem with 9240 / 240. I was able to get ~ 0.6V on R 11 12 and 5mV DC over ground and output. But It seems to be too unstable, I have to keep adjusting even after 1 hour and still then, if I reduce the voltage a little bit, it continues to creep down and vise versa. The thermister may not be completely bonded to mosfets though. Is this normal?
Thanks again for your help!
i built the f5amp with 2sk1530/j201 transistors.it sounds very good.i want to try other mosfets too.what about fqa19n20c fairchild transistors? is it worth to buy them?because the shipping is 12dollars to my country..if performance is better we can group buy fairchild with friends..thanks
The Fairchilds are the part of choice for this, I think, but I have not tried
the Toshibas.
😎
the Toshibas.
😎
what is the reason that you never use japanese mosfets?i think they dont have p channel distortion and sounds very fine
i didnt try 240/9240 because of 9240 has p channel distortion in common collector mode..but i think i will try fairchilds..it is not sold in my country and i will ship them.i ask that is it worth to pay 12dollars shipping?is there anyone tried both of these transistors?fairchild seems more powerful
General questions
I have a couple general questions, but applicable to the F5:
I applaud the industry and craftsmanship of those who make their own PCBs for this and other projects, but right now I don't have the time to learn another skill, nor the interest in spending the $$ to accumulate the equipment and materials. And I suspect my long-suffering wife might have something to say about yet another bunch of "stuff" being brought into the house and taking over the dining room table. But that's another story. . .
With a simple circuit as the F5, is there any potential problem with using "dead bug" contruction -- point to point wiring, or more accurately, lead to lead? 😕
Maybe using a piece of GRP perf board to keep the parts from relying completely on their leads for spacing and mechanical strength.
Related question, prompted by some of the discussion about heat sinks, optimum FET placement, pictures of folks' construction:
Any downside to placing the power FETs at the optimum spacing/location on the heat sinks and using short jumpers to connect them to the rest of the circuit at the perf board? That would solve some problems, though it doesn't have the elegance of mounting them directly to a PCB. 😕
Thanks and seasons greeting to all,
Steve Z
who was taken away for awhile by life, but now is back. . . 😎
I have a couple general questions, but applicable to the F5:
I applaud the industry and craftsmanship of those who make their own PCBs for this and other projects, but right now I don't have the time to learn another skill, nor the interest in spending the $$ to accumulate the equipment and materials. And I suspect my long-suffering wife might have something to say about yet another bunch of "stuff" being brought into the house and taking over the dining room table. But that's another story. . .
With a simple circuit as the F5, is there any potential problem with using "dead bug" contruction -- point to point wiring, or more accurately, lead to lead? 😕
Maybe using a piece of GRP perf board to keep the parts from relying completely on their leads for spacing and mechanical strength.
Related question, prompted by some of the discussion about heat sinks, optimum FET placement, pictures of folks' construction:
Any downside to placing the power FETs at the optimum spacing/location on the heat sinks and using short jumpers to connect them to the rest of the circuit at the perf board? That would solve some problems, though it doesn't have the elegance of mounting them directly to a PCB. 😕
Thanks and seasons greeting to all,
Steve Z
who was taken away for awhile by life, but now is back. . . 😎