Recently went back inside my 6LU8, as I had had an issue previously where one tube had a much higher triode plate voltage, 170, vs the 155 design. It moved with the tube. So, I bought a new tube, and swapped it out today. While I was in there, I found that the plate resistor on one side was poorly connected, so reflowed that joint. Poked around a bit to see if all voltages were proper etc. When I reconnected the amp to the source and speakers, it sounded better than ever! REally enjoyed about two-three hours of listening. Then the speakers were making loud popping noise. I shut it down, checked all connections, later powered it up, and the popping started right away, shut it down. Later, just now, I put it back on the bench and carefully brought up the mains to about 100vac, and the tubes started conducting, speakers were quiet unless I touched the input, wherein it made a hum. So far so good. Nothing seems out of the ordinary. I cranked up the power to 115vac, and the popping started again, this time I see that one cap is sizzling, and then popped! I shut down immediately. Now this is the cathode bipass capacitor on the right channel. It is also the channel with the new tube. What would make the cap fail? it is a 220uf, 50v cap. It was installed with the correct polarity. I can replace the capacitor, but what should I look for in order to determine what made it fail? How can I do this safelt without damaging anything else? I will place this question in AK tube forum as well, hopefully someone in either of these places can help Thanks in advance, Roger

well, something is or has gone wrong. About the 10-12 hour mark of listening to my 6LU8, I heard a pop sound from the right channel. The pop repeated and increased frequency to about one pop per second or so. Switched speaker leads, it is definitely the right channel. I turned it off, let it rest a bit, and sure enough it comes back right away. Looking at the tubes while this is going on there is no sparking or arcing. I cannot see any hot spot onthe amp components, even the 5W cathode resistors are not hot! So, any 'typical' source of popping? Bad caps? Power supply? any feedback on how to track down would be helpful. I am going to check all the wiring etc. , but I why would it take this ;ong to show itself? The amp had been in use for about an hour or so, having listened to it for at least that long several times now without issue. Update: reviewed a few 'popping' searches on AK, decided likely a tube, so I swapped tubes and pop switched. Saw a small arc during a pop. Not looking forward to buying new pair of tubes.😣 Roger

While asking some questions regarding my 6LU8 build, someone posted a link to the schematic from your web site. The one I used to build my 6LU8. Anyway, someone pointed out that in your schematic the 2.7k resistor should come AFTER the 510k resistor. Now, I have no idea which would or would not be correct, but I went ahead and reviewd your 6BM8 schematic, and the connections from triode plate to pentode grid is different, There the 1k resistor is connected AFTER the 470k. I also reviewed several other single ended schematics, and they all have the grid resistor right before the grid, and the large resistor to ground is BEFORE the small one. I just would like for you or someone else who can help me here to let me know the correct way to wire this interstage. Roger

I have completed my 6LU8 build. I have listened, and it sounds pretty good through my very small desktop speakers. Anyway, I seemto have a very significant disparity between tubes' triode plate voltages. One is about 160vdc, the other is about 145. The pentode plates are the same, the pentode cathodes are at 36Vdc, and the triode cathodes ar at 2v, evenon the tube with the low plate voltage! Wondering if it is a bad tube or just mis-matched. Second: power transformer isgetting very warm, like uncomfortable to handle for more than a few seconds. Anyione selse have this going on? Wondering if the

I am in the middle of the 6LU8 build, and found something I didn't before. re-re-rewatching videos, I see a resistor not6 shown in any of the schematics. I think it is the 470k resistor to drain the elrctrolytics in the power supply. is this correct? I will need to order one. so far everything is proceeding well. roger

I have completed the 6BM8 build, and I am impressed with the sound. However, with the transformer wired up for 125vac, my pentode plate voltage is only 203-206vdc (tubes in). If I wire the transformer for 115vac, the pentode plate now sees about 240vdc. I would like to get the voltage right at 220vdc. First, is it necessary? I know it is not because it works, but I would like just a bit more power. Second, is it possible? I would think that voltage drop resistor might help, but I am not sure which one I should change. Any advice on the approach would be helpfull. I DO have psuds2. Roger

Quick question. On the 6BM8 power supply, the B+ is specified as 225v. I have my Hammond 269EX wired to my 120v mains using the white, or 115v tap. I am getting 238v for B+ and 3.5v*2 for heater voltage. I would guess that I need to rewire my input ac to the 125 tap on the transformer to bring these back in line. Or is this 'clode enough"? Roger

I rewatched the 6LU8 build looking for a round 2 project. I forgot that it was built as a power amp requiring a preamp. In addition, I also have seen/heard of these compactrons being used in stand alone or integrated amps. I looked up the specs for 6LU8 and the triode at 155v and biased at 2 volts is really no where near the sections max plate dissapation of 2.5 watts. I suspect that one could use a different resistor froom teh plate of the pentode to the plate of the triode to drop the plate voltage to 250v instead of 155v. Any suggestions for values? I will attempt to calculate them, but a hint or two, or even do not do this!!! would be helpful. I would like to build it this way, looking for a little more power than the 6BM8. Roger

Again continuing to build my 6BM8 amp. Right now I am, wiring up the tubes, and I am a little confused. I do not think I ever saw how you hooked up the Zener Diode to pin 8 of the tube and through the 270ohm resistor. The zener has two relatively large legs, and a heat sink. Should the heat sink be mounted to the chassis? I suspect it is not going to conduct much, but thought I would ask. One more thing, what kind of shielded cable do you use for your input signals? There are zillions and soome are perversely expensive. In addition, what size teflon tubing are you using? I see many sources but most seem to have too large an ID. Thanks in advancce of any guidance you or others can provide. Roger Ayotte

Well, I have begun construction of my 6MB8 amp. I purchased some Svetlana 6F3P tubes as they were noted as replacements for 6MB8 and ECL82. Well, the Svetlana data sheet for 6MB8 is somewhat different than several other sheets for the 6MB8 and ECL82, and even old Soviet 6F3P tubes. For example in the sheets that are similar, the triode anode current at grid at -1.5v is about 2.75mA in several sheets. In the Svetlana sheet, the same conditions indicate the tube drawing about 3.5mA. I am a little confused and contacted the seller, but I do not know if they would even know. I am going to proceed with the build as specified by Steph, but want to reach out for some guidance. Thanks in advance, Roger Ayotte

Well, seems I am in good company! I first got into the 'maker' thing when I was about 14 years old, that is 56 years ago! A lot of record players were found in the trash walking home from school. I took them apart, recombined them in various ways, used the motors for strobe lights etc. Traveled from there throughout my life learning and being self taught in many endeavors. Retired in 2015 and moved from Pensacola Fla to upstate NY, built a beautiful home on the Battenkill (river). Now that that is done, I have begun new hobbies, I am self taught in Arduino and python programming of microcontrollers, built a packet radio linked weather station. Now I am continuing to explore what started me on my life long journey of learning. I am building the 6MB8 amp, and nearly have all of my equipment and parts on hand (including an isolation transformer and variac). I cam across this site while just poking around the internet, and was planning on finding an example of a well documented build of a simple tube amp. I intend to use it on my desk for music. I posted a request for an example on Audio Karma, and someone sent me here! While I am happy to be doing this build, why oh why Skunkie did you choose the ECL82 instead of the very similar ELC86? You even mentioned that the 6MB8 was close kin to PCL86, which is the 12 volt version of the ECL86, which has about twic ethe power of the ECL82/6MB8. Oh well, once my 6MB8 isbuilt, I will likely build the SPUD and then go back and re-do the 6MB8 as an ECL86. Best to all. Roger