Cut-Throat Posted January 1, 2007 Share Posted January 1, 2007 When I turn on my AE-25 Push-Pull amp, I get a Pop in the left speaker. You can actualy see the woofer jump a bit. After about 5 minutes of warm up the popping will happen intermitently, sometimes in rapid succession. After about 10 minutes of warm-up the popping goes away. Moved the tubes to the other channel, but remained with the left. Someone suggested changing out the 2 coupling caps in that channel to see if the popping was gone. So I did that, but the popping remained. I built this amp from a kit about 6 years ago, and it has been running with no problems since about last month. The Popping is seeming to get worse as times goes on. This is in my upstairs system, which we just use for backround music for parties. No serious listening. Should I just leave the thing, until it gets worse so that it will be easier to troubleshoot? - Anyone have any other ideas that I should try? Quote Link to comment Share on other sites More sharing options...
mike stehr Posted January 1, 2007 Share Posted January 1, 2007 I'm just guessin'.......obiviously you are getting DC blasting through your speaker at turn-on. Possibly a PS problem? Maybe a main filtering cap going bad, or maybe a de-coupling cap on one side? I wouldn't think a coupling cap would cause that problem, but like I mention, I'm guessing....you can check the coupling caps in circuit powered up for leakage. I searched for AE-25. Isn't this a 6550 push-pull with solid state rectification? Gotta love online troubleshooting...... Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted January 1, 2007 Share Posted January 1, 2007 Kevin: Is this a 'put-put' motorboating sort of sound? Quote Link to comment Share on other sites More sharing options...
Cut-Throat Posted January 1, 2007 Author Share Posted January 1, 2007 I'm just guessin'.......obiviously you are getting DC blasting through your speaker at turn-on. Possibly a PS problem? Maybe a main filtering cap going bad, or maybe a de-coupling cap on one side? I wouldn't think a coupling cap would cause that problem, but like I mention, I'm guessing....you can check the coupling caps in circuit powered up for leakage. I searched for AE-25. Isn't this a 6550 push-pull with solid state rectification? Gotta love online troubleshooting...... The AE-25 can use 6550's, EL34's, KT66's, etc. - I currently am running KT-88 Valve Arts. Maybe this schematic will help the challenge of on-line troubleshooting! Quote Link to comment Share on other sites More sharing options...
Cut-Throat Posted January 1, 2007 Author Share Posted January 1, 2007 Kevin: Is this a 'put-put' motorboating sort of sound? Yes Erik, I think you nailed it! - That is how I would describe it. Especially when it happens in rapid succession/ Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 1, 2007 Share Posted January 1, 2007 I've seen this type of thing just be a tube but you have ruled that out. I would first try cleaning (deoxit) and tensioning all the tube sockets first myself. If it persists after than I'd say you have some caps going in the PS. Always take one step and a time and try the easiest and obdvious first. The voltages on that schematic show plenty of headroom so PS cans should live a very long life in that amp. It's ppssible its a cold solder joint in the channel also. I hate to mention the worst thing I have seen cause this since it may jinx you. Craig Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted January 1, 2007 Share Posted January 1, 2007 Kevin: Motorboating can be caused by some things already mentioned. I've had open grid circuits cause the problem, and Mark also mentioned the bias circuit. I agree that PSU issues would mostly cause problems in both channels, unless maybe there are some problematic heater supply connections on that one side. In addition to what's been suggested, look closely at all the connections on the tube socket pins and the cathode and grid connections, resistors, and cathode bypass capacitors. Good luck! Erik Quote Link to comment Share on other sites More sharing options...
Cut-Throat Posted January 7, 2007 Author Share Posted January 7, 2007 All good suggestions which I will try in the next week or so! One other piece of information is that evertime on time powerup after the amp has warmed to the point where you could hear sound from the speaker. Immediately before the sound is one pop! And this behavior is very consistent. It does it every time I power up the amp. This may hint at something? Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted January 7, 2007 Share Posted January 7, 2007 Does your amp have a standby switch, Kevin? And do you notice this noise when you take the amp OUT of standby in order to play music? Okay -- I remember the schematic, and it shows the standby installed on the power transformer center tap. The sound you are hearing may be the result of B+ being applied. The heaters on the tubes will begin to warm as soon as you turn the amp onto the first position, but high voltage isn't applied until the center tap switch is thrown. Since this amp uses solid state diodes, that turn on surge is going to be instantaneous. Erik Quote Link to comment Share on other sites More sharing options...
Cut-Throat Posted January 7, 2007 Author Share Posted January 7, 2007 Does your amp have a standby switch, Kevin? And do you notice this noise when you take the amp OUT of standby in order to play music? Okay -- I remember the schematic, and it shows the standby installed on the power transformer center tap. The sound you are hearing may be the result of B+ being applied. The heaters on the tubes will begin to warm as soon as you turn the amp onto the first position, but high voltage isn't applied until the center tap switch is thrown. Since this amp uses solid state diodes, that turn on surge is going to be instantaneous. Erik OK, Erik I tried this. I powered up the amp in standby mode and let it sit there a minute or so. Then I flipped the standby switch to operate and immediately saw the left woofer jump (the pop). Does this tell you anything? Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted January 7, 2007 Share Posted January 7, 2007 Kevin: "Then I flipped the standby switch to operate and immediately saw the left woofer jump (the pop)." What you're seeing is the woofer respond to the LF 'thump' caused by the instantaneous high voltage in-rush. What left woofer!? Oh yeah, I remember now this is a secondary system. Some turn-on thumps (which is different from a higher-frequency 'pop' or snap.) can be pretty severe, but it's probably not something to be worried about. I want to go check something on that schematic you posted. Erik Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted January 7, 2007 Share Posted January 7, 2007 Kevin: Is this a 'pop' or a deeper, less sharp-sounding 'thump'? Quote Link to comment Share on other sites More sharing options...
Cut-Throat Posted January 7, 2007 Author Share Posted January 7, 2007 Yeah, I powered it up again and noticed that the woofers in both channels jump when I flip the switch to operate. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted January 7, 2007 Share Posted January 7, 2007 Right: I was going to say this would probably be common to both channels. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 7, 2007 Share Posted January 7, 2007 Kevin, Out of curiousity what is the tube compliment of this amp? Did you happen to try cleaning and re-tensioning tube sockets yet? Especially the output tubes sockets. I'd be surprised if any of the caps are bad. I bet it's either the contacts to the tubes or a cold solder joint. I have no clue what made me write the PS caps that was a real brain xxxx on my part. Mark suggestion of the cathode bypass caps would be a good one but at 100V rating it would surpise me after just 8 years to have a failure at that point. The stand by switch like Erik mentioned could be the culprit also if the switch is become oxidized! Good call Erik! Craig Quote Link to comment Share on other sites More sharing options...
Cut-Throat Posted January 7, 2007 Author Share Posted January 7, 2007 Craig, The amps tubes are outlined in the document below. I have not cleaned the pins or touched up the solder joints yet, but I am planning to in the next week or two. An interesting thing has happened though. When Erik mentioned the standby switch, and I flipped it on and off to see if I would get the pop, I noticed that the next time I turned the amp on, it did not pop! - After your post, I worked the switch back and forth about 20 times and powered up the amp after it had sat for 4 hours or so. To my amazement, it did not pop. I don't understand this, but maybe you guys do. I never use this switch, as I just fire up the amp and play the music. It probably was corroded and not making good contact and causing this popping noise? I won't know for sure for a couple of days, but it looks like this could have been my problem. If so, I'll put my Paper-in-oil Coupling Caps back in and clean the switches really good! Right now I'm glad Erik got me to fiddle with this switch! Quote Link to comment Share on other sites More sharing options...
ben. Posted January 7, 2007 Share Posted January 7, 2007 Stand by switches are wonderful. I wish all tube gear had them. All my instrument amps have them, but of all the hifi gear I've played with only my Blueberry has one. Really, you should turn the amps on with them in stand-by then switch out of stand by after 30sec - 1min. Power down without using stand-by. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 7, 2007 Share Posted January 7, 2007 Kevin, Yup you most likely found the problem. The switch just simply has become oxidized over time. If the problem resurfaces just replace it. Ben, Yea stand-by is cool in a way but in some cases kind of complicated to implement and has very little benefit with amps that have slow start rectifiers. If using a 5AR4 or similar rectifiers you would also have to lift its heaters or I suspect the slow start rectifier would give up the ghost pretty fast. In a SS rectified or fast start tube rectified circuit the benefits are pretty substantial but in a slow start rectified situation the only benefit would be the tubes are always warm. You also have to factor in that tube heaters if left on 24/7 are not without detriment they die like the rest of the tube from hours use but at a longer span. I'd say with the hundereds of vintage amps that show up at my door and a good number of them still have original tubes that test pretty good it has little benefit when a tube rectifiers is used. Guitar amps I believe are mostly all SS rectified. Not really sure I have done little work on guitar amps. Craig Quote Link to comment Share on other sites More sharing options...
ben. Posted January 7, 2007 Share Posted January 7, 2007 I can understand that. I never really gave any thought to what it would take to implement. With MI amps they're useful as a mute switch if nothing else. With those, part of the reason is to make sure that if something get knocked over or goes haywire, the power amp is not going to let much of anything get to the speakers. Plus, real world conditions are less controlled and that bit of noise that can't be detected during the set can get obnoxious between sets. I've always been told that it prolonged component life as well. It made sense, so I just kind of accepted it years ago and thought it was a good idea for home use as well. My Ampeg B15 is a 6L6GC with 6SL7 and 5AR4 (straight out of the RCA tube manual, supposedly) that has standby. I have a schematic if you're curious as to how they did it. Quote Link to comment Share on other sites More sharing options...
EL34 Posted January 8, 2007 Share Posted January 8, 2007 Hi, Do as Ben suggested and use the standby switch. That's what it is there for. Most hi-fi amps have relays that automatically allow the timed heater warm-up before the B+ high voltage kicks in. More simple amps will have a standby switch or just "bang on" if the voltage is not radical. -Bill Quote Link to comment Share on other sites More sharing options...
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