if you're now on 50C on heatsinks , then there is no reserve to add more output devices and increase bias
I could take a guess but...
<<<<<<ls 'f5t is refined as aleph j? as you can see they are in love with the sound aleph j >>>>
If you can just hang out for a half the summer I may be able to speak to that after my F5t v2 is built and all the break-in is over...
There is an article in 6 Moons about the family of First Watt amps but you know there is only one way to know how it sounds in your home/system and to your ears...
I started out a couple of decades ago thinking I would discover what the "best gear" was. I read, I listened and I bought...then I read some more, re-sold and re-bought.
Now I know it is a matter of making more deeply informed choices. It is a process of refinement that still takes some serious attention and some time. It is a trip!
The gift of Nelson Pass is not only more information (and someone who's word you can trust 🙂 but the choice to build! This brings deeper understanding and more pride in the finished product. So...read, read, read and then build, build, build. It is actually much faster and more rewarding. 😀
And thank you Nelson Pass!
<<<<<<ls 'f5t is refined as aleph j? as you can see they are in love with the sound aleph j >>>>
If you can just hang out for a half the summer I may be able to speak to that after my F5t v2 is built and all the break-in is over...
There is an article in 6 Moons about the family of First Watt amps but you know there is only one way to know how it sounds in your home/system and to your ears...
I started out a couple of decades ago thinking I would discover what the "best gear" was. I read, I listened and I bought...then I read some more, re-sold and re-bought.
Now I know it is a matter of making more deeply informed choices. It is a process of refinement that still takes some serious attention and some time. It is a trip!
The gift of Nelson Pass is not only more information (and someone who's word you can trust 🙂 but the choice to build! This brings deeper understanding and more pride in the finished product. So...read, read, read and then build, build, build. It is actually much faster and more rewarding. 😀
And thank you Nelson Pass!
<<<<<<ls 'f5t is refined as aleph j? as you can see they are in love with the sound aleph j >>>>
If you can just hang out for a half the summer I may be able to speak to that after my F5t v2 is built and all the break-in is over...
There is an article in 6 Moons about the family of First Watt amps but you know there is only one way to know how it sounds in your home/system and to your ears...
I started out a couple of decades ago thinking I would discover what the "best gear" was. I read, I listened and I bought...then I read some more, re-sold and re-bought.
Now I know it is a matter of making more deeply informed choices. It is a process of refinement that still takes some serious attention and some time. It is a trip!
The gift of Nelson Pass is not only more information (and someone who's word you can trust 🙂 but the choice to build! This brings deeper understanding and more pride in the finished product. So...read, read, read and then build, build, build. It is actually much faster and more rewarding. 😀
And thank you Nelson Pass!
I fully agree with everything that you said and
and also I bow and say thank Nelson everything you do makes you honor
Help, 1 channel dead
I've only got one channel working.
On the bad channel there is a huge dc offset of some 10V on the output. Q7 and Q8 have no current going through them as there is no volt drop across the 0.47R resistors R18 and R19.
There is 8.5V across R8 which suggests that the CCS is putting out 8.5mA.
There is no volt drop across R7 which suggests that the J74 Q1a may be faulty.
I've got -9V to ground on the jumper where R30 should be, i.e. collector of the CCS transistor Q2.
On the good channel R30 reads -7V, R7 has 5V drop and R18,19 have about 420mV across them.
I had a nylon tie wrap holding Q1a and Q1b together, could this have caused them to overheat?
Are Q7 and Q8 the constant current devices?
Does it seem reasonable that the JFET's are knackered?
thanks for any guidance
Kev
I've only got one channel working.
On the bad channel there is a huge dc offset of some 10V on the output. Q7 and Q8 have no current going through them as there is no volt drop across the 0.47R resistors R18 and R19.
There is 8.5V across R8 which suggests that the CCS is putting out 8.5mA.
There is no volt drop across R7 which suggests that the J74 Q1a may be faulty.
I've got -9V to ground on the jumper where R30 should be, i.e. collector of the CCS transistor Q2.
On the good channel R30 reads -7V, R7 has 5V drop and R18,19 have about 420mV across them.
I had a nylon tie wrap holding Q1a and Q1b together, could this have caused them to overheat?
Are Q7 and Q8 the constant current devices?
Does it seem reasonable that the JFET's are knackered?
thanks for any guidance
Kev
With the power off, measure the resistance across R7 and check that R7- (preset) is functioning correctly.
73.1R isn't enough resistance to develop the necessary voltage to bias the output, you need closer to 1K.
With the power off, measure the resistance across R7 and adjust R7- (preset), will it go to ~1K?
With the power off, measure the resistance across R7 and adjust R7- (preset), will it go to ~1K?
You need somewhere between 4 & 5volts across R7//R7-
that would mean the JFET would have to supply ~80mA!
(4.5V/56R=80.357mA)
that would mean the JFET would have to supply ~80mA!
(4.5V/56R=80.357mA)
I'm not saying that it R7 is set to 56 ohms what I'm saying is that because of the circuitry around it it will measure 56 ohms when it's set to 1k.
I've replaced the small signal bjt's.
I removed and tested the J74's. I measured the Ids current at ~11mA each. I assume that because they both measured what I first tested them at then they're OK so I put them back in.
I measured the voltage across the zener at ~9V.
I took out of circuit the 4 IRFP240's and put in another 1 on each side.
I haven't tested every resistance yet, but as it worked for about an hour I assume they're OK
I've still got the problem.
I've no idea what it could be. I'll test the various resistances around the circuit and compare with the good board but I'm at a loss what to do next.
Has anyone got a picture of the boards with the component printed on them. It's difficult to find which components which now that they're populated. The pictures in the store aren't copyable.