So this morning i turned my amp on and a few seconds later i got a loud pop through the speakers and no power to the amp. I checked and the fuse was blown. I tried swapping the fuse and it blew again as soon as I turned the amp on. I swapped out the recitfier tube and the fuse and again it popped as soon as i turned the power on. I pulled the board and nothing looks obviously damaged. There is some heat discoloration around r6 on the pcb but other than that everything looks normal.
I remembered reading about cogitechs issue that eneded up being his power transformer so i checked mine and Im reading very small resistance across the heater windings but im getting 75ohm across the hv winding. Is this normal or a sign of a potential issue? Im also getting between 70k-120k between the different windings on the secondary windings. The edcor xrpw178 that Im using has always run pretty hot and I wondered if it was a matter of time before it failed.
Im not really sure what else to check on this thing so Im all ears if anyone has any suggestions on where to start the troubleshooting. Thanks
I remembered reading about cogitechs issue that eneded up being his power transformer so i checked mine and Im reading very small resistance across the heater windings but im getting 75ohm across the hv winding. Is this normal or a sign of a potential issue? Im also getting between 70k-120k between the different windings on the secondary windings. The edcor xrpw178 that Im using has always run pretty hot and I wondered if it was a matter of time before it failed.
Im not really sure what else to check on this thing so Im all ears if anyone has any suggestions on where to start the troubleshooting. Thanks
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I don't have any Edcor power transformers, but 75 ohms resistance through the high voltage winding sounds pretty normal.
Sorry I didn't read carefully -
Pull the rectifier tube and see if it still pops the fuse.
If so, it sounds like the problem is in the negative ( bias ) voltage power supply. Look for a bad filter capacitor or bleeder resistor in the negative power supply, that is shorting the B- to ground. If the fuse holds, then the problem is on the B+ side. Look for the same type of bad part on that side.
Sorry I didn't read carefully -
Pull the rectifier tube and see if it still pops the fuse.
If so, it sounds like the problem is in the negative ( bias ) voltage power supply. Look for a bad filter capacitor or bleeder resistor in the negative power supply, that is shorting the B- to ground. If the fuse holds, then the problem is on the B+ side. Look for the same type of bad part on that side.
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so i pulled all tubes and as soon as i powered up the fuse popped again. measured r5, r6, c6, and c7 and they all measure out correctly. Also checked d2 and d3 and they also seem to be working correctly. I started poking around w my DMM and noticed some odd behavior from ic3. I am getting continuity between pins 1 and 2 which is expected but also getting continuity between pins 1 to pins 3, 4 and 5. Also from pin 3 to 4 and 5. Im not sure excactly how the chip is supposed to work but Im thinking that it not normal for multiple pins to be shorted to ground.
Does anyone know the correct way to test ic3?
Does anyone know the correct way to test ic3?
I put together a dim bulb tester and was able to narrow the issue down to the hv winding. I was able to attach the filament windings without issue but when I attached the hv winding the bulb lit up bright and stayed that way until i shut it down.
I went through all of the resistors from b- through to the cathode of the driver tubes and to the input. Everything measured out to spec except for c8 and c10. Would these caps failing cause my issues or should i be looking elsewhere?
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If your board blows fuses or lights the dim bulb tester without a rectifier tube installed, the problem almost has to be diodes D2, D3 or both. A shorted or reversed C6 could do it too, but it will usually fry R5. C6 and C7 do have the positive wire going to ground.
Another builder had an issue with Chip Quick solder that used "water cleanup flux." This stuff can absorb water from the air in damp environments. It might be ok on 5 volt maker boards, but dangerous on a board that can see 700 volts. Make sure the board area around D2, D3 and the rectifier tube are completely clean and dry.
C8 or C10 can not possibly cause a fuse to blow, even if they were totally shorted out or removed from the board. They would only cause distortion, or no sound.
Another builder had an issue with Chip Quick solder that used "water cleanup flux." This stuff can absorb water from the air in damp environments. It might be ok on 5 volt maker boards, but dangerous on a board that can see 700 volts. Make sure the board area around D2, D3 and the rectifier tube are completely clean and dry.
C8 or C10 can not possibly cause a fuse to blow, even if they were totally shorted out or removed from the board. They would only cause distortion, or no sound.
thanks for the info george! i had measured d2 and d3 in circuit and they were both stopping reverse voltage and passing about the same forward voltage so i assumed they were good. After going through everything else, i went back and pulled them and one of the two was reading reisitance in both directions. Luckily I had a spare set here so I swapped em out and were back in buisness! Lesson learned for me and I got some soldering practice so all in all it was a good learning experience.
Any idea what could cause d2 and d3 to fail? Could an arcing rectifier tube do it?
Any idea what could cause d2 and d3 to fail? Could an arcing rectifier tube do it?
What diodes did you use? I have never seen these blow, so I can't say what would cause it. The usual suspects are power line surges. I would lose a diode every year or two when I lived in Florida, but lightning hit the power lines every day where I lived. I guess that an arc in the rectifier tube could create a surge in the power transformer which could zap a diode.
I suppose you know this, but it is not a good idea to turn any tube amp back on within a minute or two of turning it off. Rapidly turning them off and on has been known to blow parts, usually the rectifier tube.
I suppose you know this, but it is not a good idea to turn any tube amp back on within a minute or two of turning it off. Rapidly turning them off and on has been known to blow parts, usually the rectifier tube.
I used which ever ones were specd in the bom. Ive killed my fair share of rectifier tubes with short cycling my amps. This time had been a minute or so which is usually long enough but wasnt. My impatience always gets the best of me. Im just happy I had a few spares laying around so I could get it back up and running quickly. my ss amps just arent the same
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