Too early to tell what parts you should order unless you want to buy them all.
Was R19 5 ohms on both boards?
Have you measured the resistance from both ends of R12 and R13 to ground?
Have you pulled Q7 and Q8 and checked for shorts? At least one of each pair is likely blown. Do you have any other decent matches?
Have you checked both boards for solder bridges?
Are you sure that both rails were connected in the proper polarity?
Where did you get your jfets for the input pair?
Anyone else have any troubleshooting ideas?
Was R19 5 ohms on both boards?
Have you measured the resistance from both ends of R12 and R13 to ground?
Have you pulled Q7 and Q8 and checked for shorts? At least one of each pair is likely blown. Do you have any other decent matches?
Have you checked both boards for solder bridges?
Are you sure that both rails were connected in the proper polarity?
Where did you get your jfets for the input pair?
Anyone else have any troubleshooting ideas?
Do the current and output MOSFET pairs dissipate an equivalent amount of heat? I ask because I have a pair of sinks (heat sink USA's 10.08" profile, 9" long) that is just wide wide enough, if the boards are mounted perpendicular to the fins. The outer mosfets would be really close to the edges.
hello and thanks to all
the measures I have suggested will do this weekend
the jfet I bought them directly to Diy audio
the mosfet I bought them already paired from Germany
I did not put it on fixed resistors on it r7 r8 r27 on it, I put all the trimmer 2k for r7 and r8
and 100 k and I set to 68k before mounting
I am willing to buy back all of the components if necessary
are now at a point of no return I have to make it work at all costs
thanks for the help I will keep you informed about the controls and measurements
you're right big Bobellis:
an initial examination did yesterday is quickly burned r19 is that q8.
everything has a connection with the fact that it burns r13 and r12 has changed color?
it is possible that not having connected varistors (I had yet to arrive), the peak current of the capacitors has damaged some component?
the strange thing is that this happened on both channels
so I guess I will check today with calm good if all the welds and components are in the right place.
in the meantime, is there any suggestion?
example: I can try to replace q8, r19, r13 and r12 and on again or should I try to make some other measure?
if i try to turn on without having to set the mosfet heatsink for a few seconds, just to see if it burns some component may be a problem?
thank you very much
an initial examination did yesterday is quickly burned r19 is that q8.
everything has a connection with the fact that it burns r13 and r12 has changed color?
it is possible that not having connected varistors (I had yet to arrive), the peak current of the capacitors has damaged some component?
the strange thing is that this happened on both channels
so I guess I will check today with calm good if all the welds and components are in the right place.
in the meantime, is there any suggestion?
example: I can try to replace q8, r19, r13 and r12 and on again or should I try to make some other measure?
if i try to turn on without having to set the mosfet heatsink for a few seconds, just to see if it burns some component may be a problem?
thank you very much
No, the only issue not having the CL30 in place would cause is blowing the mains fuse.
Before removing from the heat sinks check for continuity between anything on the board and the chassis. Disconnect the star ground from the chassis when you check. Particularly look at the drain tab of Q8. Did you use isolators and clean the mating surface of debris? Are the leads on the bottom of the board trimmed so that they don't contact anything?
Did your LEDs light when you powered up? Assuming store boards. If they didn't it could be you had the rails reversed.
Do not try to power the boards off of the heat sinks. You'll just burn the output devices. The outputs need to be matched pairs. Unless you have a big supply your chance of finding a match is slim. Assuming that you didn't get anything else from that supplier go ahead and order another pair for each channel.
Yes, you need to replace the burned resistors, R12/13 and R18/19. That 5R has to go. Q3 is probably bad either a bc or ztx is fine.
Do you use a light bulb tester when first powering up? A bulb in series with the mains lights if there is a major fault and sometimes saves parts.
When testing only bring up one channel until it is working then set up the other. Saves blown parts if you make the same mistake on both.
Before removing from the heat sinks check for continuity between anything on the board and the chassis. Disconnect the star ground from the chassis when you check. Particularly look at the drain tab of Q8. Did you use isolators and clean the mating surface of debris? Are the leads on the bottom of the board trimmed so that they don't contact anything?
Did your LEDs light when you powered up? Assuming store boards. If they didn't it could be you had the rails reversed.
Do not try to power the boards off of the heat sinks. You'll just burn the output devices. The outputs need to be matched pairs. Unless you have a big supply your chance of finding a match is slim. Assuming that you didn't get anything else from that supplier go ahead and order another pair for each channel.
Yes, you need to replace the burned resistors, R12/13 and R18/19. That 5R has to go. Q3 is probably bad either a bc or ztx is fine.
Do you use a light bulb tester when first powering up? A bulb in series with the mains lights if there is a major fault and sometimes saves parts.
When testing only bring up one channel until it is working then set up the other. Saves blown parts if you make the same mistake on both.
thank you for your commitment you're really helping
the LEDs light up when I give current and the pcb are those of diy audio store
in the project we are talking about 60 cl while you tell me CL30
here we have a grid voltage of 230v what type of thermistor is more 'suitable?
mosfets can get them already matched by a German dealer then be reordering them as' soon
Tomorrow morning I get back to work following your advice and try to start up a channel using the pieces of the other (8 mosfets are all combined) then order the parts you need for the second channel
thanks
LSJ74 Power Dissipation
HI,
Just going through the numbers on the differential input circuit. At a 0 signal input, correctly biased circuit (as per 6L6 build guide) the power dissipation appears to be Q1A, about 380mW, and Q1B about 480mW.
Both the 2SJ74 and LSJ74 datasheets indicate a maximum Pd of 400mW. Has anyone had issues with meltdowns?
Those numbers are a little high...
HI,
Just going through the numbers on the differential input circuit. At a 0 signal input, correctly biased circuit (as per 6L6 build guide) the power dissipation appears to be Q1A, about 380mW, and Q1B about 480mW.
Both the 2SJ74 and LSJ74 datasheets indicate a maximum Pd of 400mW. Has anyone had issues with meltdowns?
Those numbers are a little high...
hello
I solved the problems of the r13 now no longer burns I think I've discovered some burrs on the threads of the anchor that sent mosfet mosfet to ground
then the advice of BobEllis were excellent (thanks BobEllis)
but unfortunately I do not have time measuring approximately 0.4 r18 v
but 1.1 and adjusting the trimmer r27 no change to my misfortune and the r10 has started smoking
what other problem can there be?
thank you very much and sorry I do not know how else to do for the solution
I solved the problems of the r13 now no longer burns I think I've discovered some burrs on the threads of the anchor that sent mosfet mosfet to ground
then the advice of BobEllis were excellent (thanks BobEllis)
but unfortunately I do not have time measuring approximately 0.4 r18 v
but 1.1 and adjusting the trimmer r27 no change to my misfortune and the r10 has started smoking
what other problem can there be?
thank you very much and sorry I do not know how else to do for the solution
hello
I solved the problems of the r13 now no longer burns I think I've discovered some burrs on the threads of the anchor that sent mosfet mosfet to ground
then the advice of BobEllis were excellent (thanks BobEllis)
but unfortunately I do not have time measuring r18 approximately 0,4v
but 1.1 and adjusting the trimmer r27 no change to my misfortune and the r10 has started smoking
what other problem can there be?
thank you very much and sorry I do not know how else to do for the solution
I solved the problems of the r13 now no longer burns I think I've discovered some burrs on the threads of the anchor that sent mosfet mosfet to ground
then the advice of BobEllis were excellent (thanks BobEllis)
but unfortunately I do not have time measuring r18 approximately 0,4v
but 1.1 and adjusting the trimmer r27 no change to my misfortune and the r10 has started smoking
what other problem can there be?
thank you very much and sorry I do not know how else to do for the solution
Mistake on my part, got it figured out. Sorry to bother and thanks for taking the time to reply.
Grade "A" LSJ74
Has anyone on this thread used the Grade A LSJ74 parts? Since there's no B grade available, just wondering if it's better to go lower...or higher.
Also concerned about buying a lot of 8 pieces and finding that there are none in the upper en of the range. Ditto for the C grade....they may all be in the 15mA or higher. They're just a bit too pricey to play the matching game.
What to do...
Has anyone on this thread used the Grade A LSJ74 parts? Since there's no B grade available, just wondering if it's better to go lower...or higher.
Also concerned about buying a lot of 8 pieces and finding that there are none in the upper en of the range. Ditto for the C grade....they may all be in the 15mA or higher. They're just a bit too pricey to play the matching game.
What to do...
First, many thanks to 6L6 for the detailed build guide. The guide (and this forum) are making this project fairly easy for a noob like me.
One (perhaps dumb) question: what gauge hookup wire is best for this amp? I used 22awg wire in my preamp, but it looks like this board will support some thicker wire. Do I need to use different wire (like Romex) for power connections versus inputs and outputs, or is standard hookup wire fine for all of the connections in the amp?
One (perhaps dumb) question: what gauge hookup wire is best for this amp? I used 22awg wire in my preamp, but it looks like this board will support some thicker wire. Do I need to use different wire (like Romex) for power connections versus inputs and outputs, or is standard hookup wire fine for all of the connections in the amp?
