Hi all,
I finally got everything playing music yesterday and let things run for a few hours, sinks got pretty warm, but I could keep my hands on them easily so maybe 125 - 130 F. Today I had the chance to sit down for a good listen. It is a really nice amp, lots of detailed and open, vocals are extremely articulate. It certainly does have a different sound than my F5, or my class AB SKA, or Honey Badger amps, it sounds more real and 3D. I am very pleased with it, it is now my favorite amp. Thanks to all for your help and to Jim (6L6) for making it available for us DIYers.
PJN
I finally got everything playing music yesterday and let things run for a few hours, sinks got pretty warm, but I could keep my hands on them easily so maybe 125 - 130 F. Today I had the chance to sit down for a good listen. It is a really nice amp, lots of detailed and open, vocals are extremely articulate. It certainly does have a different sound than my F5, or my class AB SKA, or Honey Badger amps, it sounds more real and 3D. I am very pleased with it, it is now my favorite amp. Thanks to all for your help and to Jim (6L6) for making it available for us DIYers.
PJN
4U Chassis
12B4A has some great pictures at post #81 et seq. They are for an F5/Alpha J build, but I think they address some of your questions.
12B4A has some great pictures at post #81 et seq. They are for an F5/Alpha J build, but I think they address some of your questions.
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That's a certainty. - the risers can bolt into any part of the bottom perforations as well as a few places on the inside of the front panel - and that will add enough real estate to mount whatever you need.
Thanks guys. Looks doable the way 12B4A set it up but I might order some risors to give me a bit of insurance. So many choices!
Max, that's an odd resistor to burn. Can you measure other voltages around it? Is Q3 in oriented correctly? Voltage across R7, and R11-19? Offset voltage? You can measure with the black lead of your meter connected to ground and post the measured voltages on a copy of the schematic, including polarity.
thanks for the replies guys.
the problem is that I can not do measurements because the r13 goes up in smoke after a few seconds after.
first clue is that the q8 heats up quickly
second clue is that what happens on both channels
if I understand it by reading the pattern r13 is a resistance that detemines the bias current of Q3 which is the same that is the output of the q7:
it may be that both the excessive current that passes through the q7?
why is this happening?
thanks
the problem is that I can not do measurements because the r13 goes up in smoke after a few seconds after.
first clue is that the q8 heats up quickly
second clue is that what happens on both channels
if I understand it by reading the pattern r13 is a resistance that detemines the bias current of Q3 which is the same that is the output of the q7:
it may be that both the excessive current that passes through the q7?
why is this happening?
thanks
Unlikely that enough current would flow through R18 and R19 to allow smoking R13. That end is essentially connected to the negative rail through R19. Look to the other end - Is Q3 inserted the wrong direction or shorted C-B? (How is this end getting current?) Is R7 showing signs of stress?
I'd look for a solder bridge(s). If you don't want to pull the boards off the heat sinks yet, check the resistance from the Q3 end of R13 to the rails and ground. Should be 221R to negative and essentially infinite to positive and ground.
The usual close up in focus picture request applies here. Look for any other resistors that have changed color indicating overheating.
I'd look for a solder bridge(s). If you don't want to pull the boards off the heat sinks yet, check the resistance from the Q3 end of R13 to the rails and ground. Should be 221R to negative and essentially infinite to positive and ground.
The usual close up in focus picture request applies here. Look for any other resistors that have changed color indicating overheating.
thank you very much for your help I am grateful.
1) If I misunderstood your message I checked at the entrance to the side of r13 q3, with the gnd but I do not have continuity
2) Also the r12 has changed color
you can help to understand?
the q3 but has been replaced with the series bc550 I had on hand, of course, saw the dataschet and mounted backwards compared to ztx450, but I did this after the r13 has burned.
thanks again
1) If I misunderstood your message I checked at the entrance to the side of r13 q3, with the gnd but I do not have continuity
2) Also the r12 has changed color
you can help to understand?
the q3 but has been replaced with the series bc550 I had on hand, of course, saw the dataschet and mounted backwards compared to ztx450, but I did this after the r13 has burned.
thanks again
Ahh - there's a clue! R12 should never see significant current unless Q8 has a bad gate. Pull Q8 and measure continuity gate to source and drain, I bet you have a short, source to drain as well. If so replace Q8 with another matched to Q7 (or replace the pair)
Thinking on it a minute, check that you have continuity from the drain pin of Q8 to the negative rail before pulling. It should be the same resistance as R19.
Thinking on it a minute, check that you have continuity from the drain pin of Q8 to the negative rail before pulling. It should be the same resistance as R19.
Considering those points are connected the negative rail with a 0R47 3 W resistor something is amiss unless you are really reading 0.555 ohms, not Kohms.
Try measuring across R18 and R19. If these are showing 550R+ it points to a fault in Q7 and Q8 having burned them out. Any discoloration? Did you use the Panasonics on the BOM? They are not available in ~550R. The Dales are available in 402 and 681, neither of which should get close to 550R with tolerance.
At any rate, burned R12 means that Q8 is toast, you need to replace it or the pair if you don't have another match to Q7.
Try measuring across R18 and R19. If these are showing 550R+ it points to a fault in Q7 and Q8 having burned them out. Any discoloration? Did you use the Panasonics on the BOM? They are not available in ~550R. The Dales are available in 402 and 681, neither of which should get close to 550R with tolerance.
At any rate, burned R12 means that Q8 is toast, you need to replace it or the pair if you don't have another match to Q7.
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So you see R18 is cooked or you were given the wrong value.
Oh, I misspoke - it should have been measured source to rail, but drain to rail is interesting since there should be near infinite resistance. Further evidence that Q8 and possibly Q7 are cooked. Pull them and measure Source to Drain resistance with both polarities (change red and black leads around.) Also check Gate to Source and Drain.
Before you replace and burn up another output pair, you need to see if you can figure out why they burned out. Were you monitoring the voltage across R7 or R8 when you powered up? Hard to say what happened, because even if they were commanded hard on, the top half should have limited the current. I'm a bit suspicious of the ACS devices, Q5 and Q6.
Anyone else have any ideas other than ESD damage during the build?
Oh, I misspoke - it should have been measured source to rail, but drain to rail is interesting since there should be near infinite resistance. Further evidence that Q8 and possibly Q7 are cooked. Pull them and measure Source to Drain resistance with both polarities (change red and black leads around.) Also check Gate to Source and Drain.
Before you replace and burn up another output pair, you need to see if you can figure out why they burned out. Were you monitoring the voltage across R7 or R8 when you powered up? Hard to say what happened, because even if they were commanded hard on, the top half should have limited the current. I'm a bit suspicious of the ACS devices, Q5 and Q6.
Anyone else have any ideas other than ESD damage during the build?
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after the RESISTANCE r13 went up in smoke, I noticed that I had not soldered points on the board in the upper face.
I'll explain: the cards hit the slopes on both sides but I had just soldered the components on the underside believing anyway to get the contact of the weld.
could depend on this thing?
thanks
I'll explain: the cards hit the slopes on both sides but I had just soldered the components on the underside believing anyway to get the contact of the weld.
could depend on this thing?
thanks
Wait - R18 was 5R? not R19? Most likely that you got the wrong part from the supplier. (remember 6l6's advice to measure every resistor before installing it?)
You fried Q8 by effectively putting all the bias current through one device. I'm still trying to understand how that would burn up R12 and R13.
You fried Q8 by effectively putting all the bias current through one device. I'm still trying to understand how that would burn up R12 and R13.