tube fanatic Posted September 10, 2011 Share Posted September 10, 2011 7.8V no load in the filament circuit is reasonable. As Erik so importantly stressed, be sure that the high voltage electrolytics are discharged before you stick your hands in there (and of course the obvious- be sure the amp is unplugged)!!! Feel free to email me with any questions, or if you want any advice about how to easily and safely discharge them. With all respect for your EE degree, many of the EEs I've known and worked with "cut their teeth" on low voltage circuits and tend to have a bit too cavalier an attitude when working on HV stuff! Having on rare occasion gotten my fingers on the wrong side of a TV horizontal output tube plate circuit running at a few hundred volts, I can tell you that it isn't an experience that I'd recommend to anyone! Quote Link to comment Share on other sites More sharing options...
Marvel Posted September 10, 2011 Share Posted September 10, 2011 Both of the heaters on my 6SN7 sockets are hitting 8.31 vdc. I've got right at 120 vac on the outlets. While living in Chattanooga, I normally had 125 vac, as TVA really gives you the goods. Bruce Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted September 11, 2011 Share Posted September 11, 2011 Both of the heaters on my 6SN7 sockets are hitting 8.31 vdc. I've got right at 120 vac on the outlets. While living in Chattanooga, Inormally had 125 vac, as TVA really gives you the goods. Bruce Have you ever checked the filament voltage with the 6SN7s installed? If it is running at more than 7V, tube life is likely to be considerably shortened. Quote Link to comment Share on other sites More sharing options...
erik2A3 Posted September 11, 2011 Share Posted September 11, 2011 tube fanatic: Please let me know how I can help you with this. I know the entire Moondog circuit by heart, and I can share any aspect of it with you. The AC portion of this filament supply is not on its own, meaning that there is not a separate 6.3 volt filament transformer. I agree that it's highly unlikely that the winding is shorted, but I am uncertain of the quality of connections associated with it. 9 volts on one end and 2 on the other is odd to me, because the filaments should be wired in parallel, and they are connected to the same 6.3 volt source. I would like to know how this voltage has been measured in terms of the positions of the filament pins we've discussed above. Again, please let me know if I can help you troubleshoot in any way in terms of information you'd like regarding the schematic. I'm comfortable sharing that with you because it's obvious to me that you are very familiar with vacuum tube circuits. Bruce: are you measuring this without a load (tubes installed?) 8.31VDC is high, and should be dealt with for longer tube life. Are you familiar with Ohm's law? you can calculate the value of resistance needed to bring that back down to a more appropriate level. I measured the voltages on that amp when I had it here, and they were within spec. at that time. What do you measure with tubes installed? erik Quote Link to comment Share on other sites More sharing options...
Cut-Throat Posted September 11, 2011 Share Posted September 11, 2011 Also, keep in mind that the Amplifier was working fine until Neo adjusted the hum pot. So this says to me that he probably moved the amp somewhat and that may have been what caused the 'straw to break the camels back'. IOW -- a loose connection that was finally un-done. That is why I suggested a visual inspection of the internals of the amp. I have opened up amps and have seen a wire completely undone and 'flapping in the breeze'. Makes troubleshooting a snap! Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted September 11, 2011 Share Posted September 11, 2011 tube fanatic: Please let me know how I can help you with this. I know the entire Moondog circuit by heart, and I can share any aspect of it with you. The AC portion of this filament supply is not on its own, meaning that there is not a separate 6.3 volt filament transformer. I agree that it's highly unlikely that the winding is shorted, but I am uncertain of the quality of connections associated with it. 9 volts on one end and 2 on the other is odd to me, because the filaments should be wired in parallel, and they are connected to the same 6.3 volt source. I would like to know how this voltage has been measured in terms of the positions of the filament pins we've discussed above. Again, please let me know if I can help you troubleshoot in any way in terms of information you'd like regarding the schematic. I'm comfortable sharing that with you because it's obvious to me that you are very familiar with vacuum tube circuits. Bruce: are you measuring this without a load (tubes installed?) 8.31VDC is high, and should be dealt with for longer tube life. Are you familiar with Ohm's law? you can calculate the value of resistance needed to bring that back down to a more appropriate level. I measured the voltages on that amp when I had it here, and they were within spec. at that time. What do you measure with tubes installed? erik Thanks for the gracious offer Erik, but I'm not the guy with the Moondogs! It's Neo33 who is experiencing the technical difficulties. You and I are in agreement on all of this, and I am also waiting for Neo to post again with the results of his under-chassis examination of the wiring etc. Isn't this insanity fun??? Regards- Maynard Quote Link to comment Share on other sites More sharing options...
neo33 Posted September 11, 2011 Author Share Posted September 11, 2011 Also, keep in mind that the Amplifier was working fine until Neo adjusted the hum pot. So this says to me that he probably moved the amp somewhat and that may have been what caused the 'straw to break the camels back'. You're exactly right. The Moondogs have been moved from CA to FL. I haven't got to opening up the bad Moondog to inspect the inside wiring yet. When I measured the filament voltages on the 6SN7 sockets of both Moondogs, I measured them without the tubes on per tube fanatic instruction. Something is very wrong with the bad Moondog when one socket measured 2 Volts and the other 9 Volts. I still can't find the manual yet so can somebody tell me what is the range on the filament voltages without the tubes? Quote Link to comment Share on other sites More sharing options...
deafbykhorns Posted September 11, 2011 Share Posted September 11, 2011 Check the filament pins with a load, just don't leave it on for too long since you have B+ at the tube. You should have 5.5volts That circuit consists of a bridge rectifier then a RC network and then the 6sn7s It's either the diode breaking down, a bad resistor or cold solder joint. Since these were kits, I'm betting on the cold solder joint. If you live near the n Florida area, I'd be happy to help you repair this, it a 10minute job, at best Quote Link to comment Share on other sites More sharing options...
erik2A3 Posted September 11, 2011 Share Posted September 11, 2011 Don't do anything unless you know what you are doing. There are nearly 400VDC present in that amp when it's energized, and if you're not sure what pins are the filaments on a 6SN7, there is a good possibility you will not be sure of where the high voltages reside in the Moondog. deafbykhorns: Just for clarification, the dropping resistor is on one leg of the AC filament supply BEFORE the rectifier, not after it, followed by the rectifier and filter capacitor. Have a good day all. erik Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted September 11, 2011 Share Posted September 11, 2011 Check the filament pins with a load, just don't leave it on for too long since you have B+ at the tube. You should have 5.5volts That circuit consists of a bridge rectifier then a RC network and then the 6sn7s It's either the diode breaking down, a bad resistor or cold solder joint. Since these were kits, I'm betting on the cold solder joint. If you live near the n Florida area, I'd be happy to help you repair this, it a 10minute job, at best Pull the rectifier tube before doing this test to provide a greater safety margin. Doing so will result in a slightly higher reading of the filament voltage since the power xfmr won't be loaded down by the plate current/filament draw of the 2A3, and filament draw of the rectifier. Also, the voltage you measure will depend on the line voltage coming in, so it's worth measuring what's coming out of the wall socket too. For tubes like the 6SN7, you don't want the filament voltage under the worst possible circumstance (i.e. the highest power line voltage that you are likely to experience) to exceed 10% above the rated 6.3V. I'd also check the filament voltage of the rectifier which should be around 5V +/- 10%, and the 2A3 which should be 2.5V +/- 10%. If you find that everything is running too high and don't want to get into modifying the filament circuits, pick up a simple variac and dial down the line voltage a bit to create the needed operating conditions. (Also, when working on powered equipment, it's always a good idea to follow the "one hand in pocket" ritual. It prevents you from accidentally being grounded with one hand while you measure with the other- comes in handy if the measuring hand accidentally slips and touches something inappropriate!). Quote Link to comment Share on other sites More sharing options...
mike stehr Posted September 11, 2011 Share Posted September 11, 2011 Send the imaginary defective Moondog to Craig, and he will do imaginary repairs to it, but not charge you imaginary money. By the way, I received my EE at Stanford University in 1980. [:S][] Quote Link to comment Share on other sites More sharing options...
Marvel Posted September 11, 2011 Share Posted September 11, 2011 Both of the heaters on my 6SN7 sockets are hitting 8.31 vdc. I've got right at 120 vac on the outlets. While living in Chattanooga, I normally had 125 vac, as TVA really gives you the goods. Bruce Have you ever checked the filament voltage with the 6SN7s installed? If it is running at more than 7V, tube life is likely to be considerably shortened. With everything running and plugged in, I'm getting 6.02 vdc on the 6SN7 filaments. Quote Link to comment Share on other sites More sharing options...
erik2A3 Posted September 11, 2011 Share Posted September 11, 2011 Tube fanatic You had been curious about the schematic, so was just mentioning that I know the amp well, and if you needed more info on the circuit could share with you whatever you may want to know. Erik Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted September 11, 2011 Share Posted September 11, 2011 Tube fanatic You had been curious about the schematic, so was just mentioning that I know the amp well, and if you needed more info on the circuit could share with you whatever you may want to know. Erik Thanks Erik, but I did finally find the schematic for it (originally, I thought it was stashed with the schematic of the Laurel 300B). And Bruce, that filament voltage is terrific and should give you extremely long tube life! Well, back to the bench to repair my son-in-law's vintage Sony STR-AV1000 solid state (yuck!!!) receiver. I think he hasn't switched over to tubes just to torture me!!! Maynard Quote Link to comment Share on other sites More sharing options...
erik2A3 Posted September 11, 2011 Share Posted September 11, 2011 Maynard: okay, gotcha. I don't even have my moondog schematic anymore - for some reason. It's a simple amp, though. Bruce has a nice pair, filled Kiwami resistors if I remember it right. After rebuilding a Baldwin organ amp to send to another forum member friend, my current project is also solid state -- an unbuilt Dynaco PAT 4 preamp! I'm heading back towards vinyl, and will use for a bit until I build a tubed phono stage, most likely 12ax7. Good luck with the Sony, erik Quote Link to comment Share on other sites More sharing options...
deafbykhorns Posted September 11, 2011 Share Posted September 11, 2011 Don't do anything unless you know what you are doing. There are nearly 400VDC present in that amp when it's energized, and if you're not sure what pins are the filaments on a 6SN7, there is a good possibility you will not be sure of where the high voltages reside in the Moondog. deafbykhorns: Just for clarification, the dropping resistor is on one leg of the AC filament supply BEFORE the rectifier, not after it, followed by the rectifier and filter capacitor. Have a good day all. erik Eric-- My schematic shows the dropping resistor after the bridge....... I have the PDF schematic, send me a pm if you need one Quote Link to comment Share on other sites More sharing options...
erik2A3 Posted September 11, 2011 Share Posted September 11, 2011 Hey, deafbyklipschorns Well, we have a difference here:) I found the schematic online, actually (which someone had posted) and reconfirmed that the dropping resistor is on one AC leg just before the bridge, which is the case with my own pair of Moondogs. Your point is interesting, though, because there may be some differences in different editions of this amp. In fact, as I'm sure you know, it's more common to drop the voltage after the bridge, via CRC, then the filaments. Thanks, too for offering to help Neo with the problem -- I hope he takes you up on the offer. erik Quote Link to comment Share on other sites More sharing options...
neo33 Posted September 11, 2011 Author Share Posted September 11, 2011 I found my schematic and the dropping resistor is also before the bridge. I also verified this is the case upon opening the unit to inspect the inside wiring. I remeasured the filament voltage with and without a load. Without a load the voltage hit 7.8V and with a load it went down to 5.5V. I had the wall plug going into a line conditioner and the voltage came out of the line conditioner at a constant 121.8V. It turned out to be lose solder joints which I am not sure why. I inspected all of the solder joints and they seemed to be well soldered. Just a few of them came off with no sign of breakage. Anyway, thanks all for helping me restoring my bad Moondog. Quote Link to comment Share on other sites More sharing options...
deafbykhorns Posted September 11, 2011 Share Posted September 11, 2011 I just received this schematic from Ron two weeks ago so it's probably one of the last revisions. NEO, sounds like my hunch was right about the cold solder joint. This is probably the biggest problem with DIY. Practice, practice, practice makes for better soldering. You may want to check all the joints! Quote Link to comment Share on other sites More sharing options...
Marvel Posted September 11, 2011 Share Posted September 11, 2011 So... does that mean you are back up with both amps? [Y] Bruce Quote Link to comment Share on other sites More sharing options...
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