Yes, all of the input has helped my understanding. I am glad that I did not screw anything up! Now to build the other monoblock!
weeelllll... recently finished winding the power transformer for my AB2 6P3S/6L6 amp... spent hours winding, a couple of days waiting for the varnish to dry before finally excitedly plugging it in... only to realize i'd somehow wound an extra layer on the primary so all my voltages are about 16% too low... i could cry... 🙁
haha true... now i just need a way of running 6.3v heaters off 5.4v.
urgh.. i'm going to have to re-wind it, which makes me want to beat myself over the head with it for making such a dumb mistake.
urgh.. i'm going to have to re-wind it, which makes me want to beat myself over the head with it for making such a dumb mistake.
if you don't make mistakes, you learn nothing....
i try out my traffos with lams not fully tight, just to see if voltages are right, and then i finalise the core and varnish...
i try out my traffos with lams not fully tight, just to see if voltages are right, and then i finalise the core and varnish...
agreed; still, i'm annoyed that i did it. the math tells me that if i hadn't added that extra layer of turns the secondary voltages would have been pretty much exactly where i wanted them, which is good for a first attempt i suppose. Unfortunately i varnished as i wound.
Lesson learned i guess. This time round i'll check the filament voltages before i wind over the top of them.
Lesson learned i guess. This time round i'll check the filament voltages before i wind over the top of them.
one thing i learned from making traffos is that there is no "exact" voltages, you either get a bit high or a bit low...
that is why in my calculations, i use 6.9 instead of 6.3, a little more voltage won't hurt..
that is why in my calculations, i use 6.9 instead of 6.3, a little more voltage won't hurt..
How about running your power transformer off of say 260 volts. Calculate what primary voltage you need to make your transformer work, subtract your actual line voltage and find a small transformer that will provide a voltage nearest this voltage. Wire its primary across the line and the secondary between your transformer and the line (series). This is called bucking or boosting the primary voltage depending on the phasing. Often a small toroid can be hidden under the deck to accomplish this.
Success!
Well, after nearly two years(!) I have two monoblock 6L6 (well 6P3S-E at the moment) amps in my system!
There was a bit of troubleshooting with the first monoblock. A ground loop issue that took some time to diagnose. I used the back to back diodes in parallel with a 100R resistor and a ceramic cap to lift the ground. Still had the problem. After much searching, I discovered there was a bad diode in the setup. I had to remove the power supply a few times, and every time I placed it back in the chassis it blew. I think the LM317 was shorting to the chassis by arcing across the spacer between the bolt and the metal tab of the package. Replacing with a nylon bolt appears to have fixed the issue.
Second amp went together this week with no problems, other than a slight measurement error on amp layout, which resulted in no construction problems, just that the amps are not completely identical (the rear tubes are 70mm back from the front tubes in the second amp, 80mm in the first). I was pretty pissed off about that! Nothing to do about other than remember next time to measure twice, cut once. It is only noticeable if the amps are right next to each other and you look closely...
With two CCS and a DC balance pot and fixed bias adjustment for each output tube, there is a bit of fiddling to do to set it up right. Setting the CCSs on the first diff amp for about 120 volts on the screens of the second and setting the second CCS for about 295 volts on the plates of the second looked the best on the scope.
Listening now, they sound great! Zero hum, and just the gentlest hint of some hiss from the tweeters audible only with ear just about touching it.
Photos to follow in a few days. I am off to work in the morning, away for a couple of days.
Thanks to everyone for the help developing this project! Thanks to Eli, Sy, Miles and Johan for the ongoing helpful discussion. Thanks Spreadspectrum for the power supply help. A huge thank you to Tubelab for his assistance with providing the design of the driver section and the help integrating it and for answering all of the stupid questions I had!
😀😀😀😀😀
Chris
Well, after nearly two years(!) I have two monoblock 6L6 (well 6P3S-E at the moment) amps in my system!
There was a bit of troubleshooting with the first monoblock. A ground loop issue that took some time to diagnose. I used the back to back diodes in parallel with a 100R resistor and a ceramic cap to lift the ground. Still had the problem. After much searching, I discovered there was a bad diode in the setup. I had to remove the power supply a few times, and every time I placed it back in the chassis it blew. I think the LM317 was shorting to the chassis by arcing across the spacer between the bolt and the metal tab of the package. Replacing with a nylon bolt appears to have fixed the issue.
Second amp went together this week with no problems, other than a slight measurement error on amp layout, which resulted in no construction problems, just that the amps are not completely identical (the rear tubes are 70mm back from the front tubes in the second amp, 80mm in the first). I was pretty pissed off about that! Nothing to do about other than remember next time to measure twice, cut once. It is only noticeable if the amps are right next to each other and you look closely...
With two CCS and a DC balance pot and fixed bias adjustment for each output tube, there is a bit of fiddling to do to set it up right. Setting the CCSs on the first diff amp for about 120 volts on the screens of the second and setting the second CCS for about 295 volts on the plates of the second looked the best on the scope.
Listening now, they sound great! Zero hum, and just the gentlest hint of some hiss from the tweeters audible only with ear just about touching it.
Photos to follow in a few days. I am off to work in the morning, away for a couple of days.
Thanks to everyone for the help developing this project! Thanks to Eli, Sy, Miles and Johan for the ongoing helpful discussion. Thanks Spreadspectrum for the power supply help. A huge thank you to Tubelab for his assistance with providing the design of the driver section and the help integrating it and for answering all of the stupid questions I had!
😀😀😀😀😀
Chris
Congratulations!
I'm sure its got to feel good to finally have things together! I've been following your progress for quite some time and can't wait to see some pictures of how it all finally came together.
Enjoy the fruits of your labors!
I'm sure its got to feel good to finally have things together! I've been following your progress for quite some time and can't wait to see some pictures of how it all finally came together.
Enjoy the fruits of your labors!
Managed to take some shots.
Sorry for the large size, could not get the image shack thumbnails working.
Still have the Russian tester tubes in them, when I am sure all is OK I will put in 6L6 or 6BG6GA in adaptors and 6SN7s
Cheers,
Chris
Sorry for the large size, could not get the image shack thumbnails working.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Still have the Russian tester tubes in them, when I am sure all is OK I will put in 6L6 or 6BG6GA in adaptors and 6SN7s
Cheers,
Chris
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Chris,
Very nice job. I am sure you will enjoy them.
I have followed this thread as well and learned alot from your endevours. Thanks for keeping us informed and being part of this forum.
Very nice job. I am sure you will enjoy them.
I have followed this thread as well and learned alot from your endevours. Thanks for keeping us informed and being part of this forum.
Thank you! Following your similar project helped me along too! Been meaning to ask you, do you fly that Bonanza in your avatar?
Cheers,
Chris
Cheers,
Chris
Looks great chrish; chassis is awesome, is that DIY? I want to do something similar. Where do you get your aluminium? I find it ironic that Australia is the worlds biggest exporter of aluminium but i've found it so hard to find anyone who'll supply DIY quantites for a reasonable price.
Thanks for the suggestion George, I could have boosted the mains voltage enough for the correct output voltages, but I've already unwound and started to re-wind it. I hadn't heard of boosting like that until you suggested it!
Thanks for the suggestion George, I could have boosted the mains voltage enough for the correct output voltages, but I've already unwound and started to re-wind it. I hadn't heard of boosting like that until you suggested it!
Thanks for the comments. I wish I could claim credit for scratch building the chassis, but I picked them up from a shop in Singapore that sells tube gear and parts, the same place I got my Tamura transformers. The top plate is quite thick, which allowed me to blind tap holes for the valve sockets and other hardware from underneath leaving a clean top with no screw heads. CCS and MOSFETs are attached to top plate from underneath for heat sinking. Drilling the holes was interesting though, too thick for standard punches. Used hole saws in a drill press at slow speed and plenty of lube.
Away with work for a few days now. Time to think about next project? Probably nothing as ambitious, have a EL84 amp that is ringing. What I have learned on this journey may help improve that previous project.
Cheers,
Chris
Away with work for a few days now. Time to think about next project? Probably nothing as ambitious, have a EL84 amp that is ringing. What I have learned on this journey may help improve that previous project.
Cheers,
Chris
Yep when I get a chance. Most of the time is spent in Piper's/Cessna's to keep current. Maybe once my kids are done with college I can fly it more often. That is a few years down the road however.
Have been listening for a while now, they sound great! I modded my speakers back to passive crossovers so that I now have one of these amps per channel - no need for a second stereo amp for tweeters. I did some mods to the passive crossovers including zobel network for woofers and tweeking the capacitor values for the tweeter crossover. The system sounds really good now.
One problem I had with the amps was the 105 volt regulator tubes would stop working after about half an hour. I was getting about -130 volts from the power supply and with the current limiting resistor this was dropping the voltage too low. I had two unused 5 volt windings on the power transformer, so added them to the 110 from the neg supply transformer and this was enough for stable operation.
Cheers,
Chris
One problem I had with the amps was the 105 volt regulator tubes would stop working after about half an hour. I was getting about -130 volts from the power supply and with the current limiting resistor this was dropping the voltage too low. I had two unused 5 volt windings on the power transformer, so added them to the 110 from the neg supply transformer and this was enough for stable operation.
Cheers,
Chris
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