Did anyone find a suitable OPT of rather high impedance to match the high rp of the 6SN7.
Are the Antek AN-0105’s still ok to use for the current 6SN7 build?
Thanks
I'm thinking that a pair of Edcor GXPP 12K:4 may be a good choice for an 8 ohm build, as they should yield a ~24k load if running 8 ohms on the 4 ohm secondary. Massive overkill, but would be worth trying out. I just don't have the spare cash to try any spurge types of experiments at this time. ~$62 before shipping.
I'm trying to find alternative transformer types for something a little more fancy than the toroid option, and I'm not finding much other than old radio replacement types (such as the Hammond 125H, which doesn't look too good, really) or stuff that needs to go with higher impedance speakers. The toroids work well, but part of the magic in using them is in regards to the performance versus cost, and the fact that 90% of my listening keeps them in Class A pretty well, reducing the distortion one otherwise gets from an otherwise too-low of load impedance.
Since this amplifier isn't really meant to go very deep for bass response, something like the XPP series in 10K may work, but it would limit you to 16 ohm or higher speakers. This wouldn't be a problem if you build your own speakers (of which the Faital-Pro 3FE25, or Dayton PA130-16 are a great driver to base it on!) but it is only available in 8 ohm, so to load it properly on a single tube would require a 16 ohm speaker on the 8 ohm tap, for ~20K load. I've reached out to Edcor regarding options, and they stated very clearly, that they will not have alternative output impedance options available for these, what's listed is all they will do. Either way, rated frequency response will go down to ~70hz with the XPP series, which is not too bad anyways. If anybody has some comments regarding other possible transformers let me know. Most everyone I talk to runs 8 ohm speakers, but 16 ohm would be a lovely match for anyone wanting to take on a easy project. I heartily recommend building a .4x scaled Karlsonator using the 3FE25-16, or a .53X scaled version using a single PA130-16 per side.
Of course, if not married to the idea of a PCB, simply running a parallel pair of output tubes per transformer would be a great solution, and will not require you to do any creative impedance mismatching. I have to say, the idea of a parallel build with the fancy blue Edcor iron does sound intriguing
Another good option, and some general comments while I'm at it-
Use an active crossover (or DSP like the MiniDSP or similar) and cross the signal to the flea amplifier at ~80hz, and run a class D TPA3116D2 mono module with a cheap subwoofer, and enjoy the bass response. This can be a very affordable option, especially if you pick up a cheap home-theater type sub from a thrift store, and a TPA3116D2 board on Amazon or similar place. I just grabbed a mono "100 watt" amplifier for $11 shipped, and it works stupid good at running the cheap sub that's been taking up space in my storage the last few years. To run it, I put together a nice little 12db/octave Linkwitz-Riley using the circuit here at Elliot Sound Products that works nicely, and although a little complex, is very nice in performance using OPA2132P opamps. You could cross the sub over even higher if you used two of them, but as set I'm somewhere round ~75hz or so. Just enough to get the bottom filled in I'm working up a 24db/octave version using tube buffers here pretty soon too, since I've become interested in some multi-way designs lately.
Couldn't play with high voltage yesterday (I have a two year old running around, so as a rule I try not to much when he's running around, since he really likes to be involved) so I was doing low voltage stuff primarily, and running errands. Next up on the list is finishing the noval board casing and testing, which I really can't wait to finish, as I really like the "big amp" look it gives, with the smaller tubes up front, with the bigger octals out back.
Has anybody got any sweet spot areas they like to run their 12AT7's at? I have a set that I can't find, but a couple users expressed interest in using them in the design. Last I played with them (at around ~290 volts after filtering) I think 47K plate, with 820R cathode was what I liked, and assuming some decent GNFB a 1K cathode resistor with something like 12~15k or so for feedback may be a good starting point. 22k loads top and bottom on the concertina would be a good fit here, in my opinion.
I'm trying to find alternative transformer types for something a little more fancy than the toroid option, and I'm not finding much other than old radio replacement types (such as the Hammond 125H, which doesn't look too good, really) or stuff that needs to go with higher impedance speakers. The toroids work well, but part of the magic in using them is in regards to the performance versus cost, and the fact that 90% of my listening keeps them in Class A pretty well, reducing the distortion one otherwise gets from an otherwise too-low of load impedance.
Since this amplifier isn't really meant to go very deep for bass response, something like the XPP series in 10K may work, but it would limit you to 16 ohm or higher speakers. This wouldn't be a problem if you build your own speakers (of which the Faital-Pro 3FE25, or Dayton PA130-16 are a great driver to base it on!) but it is only available in 8 ohm, so to load it properly on a single tube would require a 16 ohm speaker on the 8 ohm tap, for ~20K load. I've reached out to Edcor regarding options, and they stated very clearly, that they will not have alternative output impedance options available for these, what's listed is all they will do. Either way, rated frequency response will go down to ~70hz with the XPP series, which is not too bad anyways. If anybody has some comments regarding other possible transformers let me know. Most everyone I talk to runs 8 ohm speakers, but 16 ohm would be a lovely match for anyone wanting to take on a easy project. I heartily recommend building a .4x scaled Karlsonator using the 3FE25-16, or a .53X scaled version using a single PA130-16 per side.
Of course, if not married to the idea of a PCB, simply running a parallel pair of output tubes per transformer would be a great solution, and will not require you to do any creative impedance mismatching. I have to say, the idea of a parallel build with the fancy blue Edcor iron does sound intriguing
Another good option, and some general comments while I'm at it-
Use an active crossover (or DSP like the MiniDSP or similar) and cross the signal to the flea amplifier at ~80hz, and run a class D TPA3116D2 mono module with a cheap subwoofer, and enjoy the bass response. This can be a very affordable option, especially if you pick up a cheap home-theater type sub from a thrift store, and a TPA3116D2 board on Amazon or similar place. I just grabbed a mono "100 watt" amplifier for $11 shipped, and it works stupid good at running the cheap sub that's been taking up space in my storage the last few years. To run it, I put together a nice little 12db/octave Linkwitz-Riley using the circuit here at Elliot Sound Products that works nicely, and although a little complex, is very nice in performance using OPA2132P opamps. You could cross the sub over even higher if you used two of them, but as set I'm somewhere round ~75hz or so. Just enough to get the bottom filled in
I'm working up a 24db/octave version using tube buffers here pretty soon too, since I've become interested in some multi-way designs lately.Couldn't play with high voltage yesterday (I have a two year old running around, so as a rule I try not to much when he's running around, since he really likes to be involved) so I was doing low voltage stuff primarily, and running errands. Next up on the list is finishing the noval board casing and testing, which I really can't wait to finish, as I really like the "big amp" look it gives, with the smaller tubes up front, with the bigger octals out back.
Has anybody got any sweet spot areas they like to run their 12AT7's at? I have a set that I can't find, but a couple users expressed interest in using them in the design. Last I played with them (at around ~290 volts after filtering) I think 47K plate, with 820R cathode was what I liked, and assuming some decent GNFB a 1K cathode resistor with something like 12~15k or so for feedback may be a good starting point. 22k loads top and bottom on the concertina would be a good fit here, in my opinion.
Back in 2012 I was fiddling around with a couple circuits. one was push pull 12au7 and the other was a 6MD8 pse.
Unfortunately I do not have a schematic as they were bread boarded off the top of my head.
Links to them playing: 12au7pp mono YouTube
6MD8pse in stereo: YouTube
It is fun DIYing!
Have fun with the 6sn7 build it will sound great, I built one using some old stock Hewlett Packard pp transformers bought in Tokyo's Akihabara district.
Unfortunately I do not have a schematic as they were bread boarded off the top of my head.
Links to them playing: 12au7pp mono YouTube
6MD8pse in stereo: YouTube
It is fun DIYing!
Have fun with the 6sn7 build it will sound great, I built one using some old stock Hewlett Packard pp transformers bought in Tokyo's Akihabara district.
Not yet, haven't dug the pair I've got out for testing, and as usual I'm a far busier man than I'd like. I'm thinking I'll have time this weekend, but no promises.
Last night I tore apart the fuse console in the family SUV to fix a contact and broken solder joint. Tonight I'm replacing a seatbelt latch in my car.
I've been messing with PCB design on my off time at work, too bad I can't bring a tub of parts to play with and get away with it! I updated my 6N2P/6CW5 thread with some pics of the board design for that one.
Last night I tore apart the fuse console in the family SUV to fix a contact and broken solder joint. Tonight I'm replacing a seatbelt latch in my car.
I've been messing with PCB design on my off time at work, too bad I can't bring a tub of parts to play with and get away with it! I updated my 6N2P/6CW5 thread with some pics of the board design for that one.
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Slower than Mollasses, and busier than ever, I finally found a little time to try out the noval input board, and it works very well. Those little 6N2P sure are a handy little tube, and I can happily report that they work great with the same values used on the 6SL7/6N9S for plate and cathode resistors
I need to clean up the holes in the chassis for the input tubes (the bit wandered, so i need to oblong the holes a bit, they are visibly skewed) and throw some paint on it. I still can't find my 12AT7 tubes to try out, unfortunately. This noval board build will use a small SMPS module set for 315 volts at the output tube plates, for 2.6W idle dissipation per 6SN7 triode. I have it all running off of a 4A,12 volt DC power supply, with series-connected heaters for the tubes. Dead silent without signal
Since work is slow enough to give me some design time to play around, I'm working up a cleaner version of the schematic, and even a build guide to accompany the boards. I've been strapped for cash and have very little spare time, so I haven't sent any boards out yet, and I am sorry. The engine on my beloved 73 Super Beetle (daily driver of 160-odd miles a day, 6 days a week!) decided to seize on the highway on Christmas of all days, and this was just after the family SUV developed a misfire on cylinders 3 and 4. Luck has been my enemy as of late
I need to clean up the holes in the chassis for the input tubes (the bit wandered, so i need to oblong the holes a bit, they are visibly skewed) and throw some paint on it. I still can't find my 12AT7 tubes to try out, unfortunately. This noval board build will use a small SMPS module set for 315 volts at the output tube plates, for 2.6W idle dissipation per 6SN7 triode. I have it all running off of a 4A,12 volt DC power supply, with series-connected heaters for the tubes. Dead silent without signal
Since work is slow enough to give me some design time to play around, I'm working up a cleaner version of the schematic, and even a build guide to accompany the boards. I've been strapped for cash and have very little spare time, so I haven't sent any boards out yet, and I am sorry. The engine on my beloved 73 Super Beetle (daily driver of 160-odd miles a day, 6 days a week!) decided to seize on the highway on Christmas of all days, and this was just after the family SUV developed a misfire on cylinders 3 and 4. Luck has been my enemy as of late
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Ling,
Thanks for the report, and sorry to hear about your bad luck. No apologies needed for your progress on this. I too have a lot on my plate these days and haven't finished my breadboard of the 6AS7 using a similar approach. Hope to be able to finish that and compare your approach.
BTW, I used to have a 73 super beetle with sunroof. I put some bad gas in one day and the valves seized up on me on the highway. Thankfully I was able to get off the highway and then get it to a local bug guru for a valve job. Although I'd rebuilt VW engines at the time, grad school was getting in my way and I didn't have the heart to do the job myself.
Good luck with the cars, cheers and happy new year!
Thanks for the report, and sorry to hear about your bad luck. No apologies needed for your progress on this. I too have a lot on my plate these days and haven't finished my breadboard of the 6AS7 using a similar approach. Hope to be able to finish that and compare your approach.
BTW, I used to have a 73 super beetle with sunroof. I put some bad gas in one day and the valves seized up on me on the highway. Thankfully I was able to get off the highway and then get it to a local bug guru for a valve job. Although I'd rebuilt VW engines at the time, grad school was getting in my way and I didn't have the heart to do the job myself.
Good luck with the cars, cheers and happy new year!
Generally speaking, I like 12AT7 with about 200V at the plate, 3mA plate current, which is usually about -2.8V grid bias (or Rk = 910 or 1k ohms). Like 12AX7, they like a 'tall' B+ of 350V or higher. 12AT7s tend to draw grid current with bias voltages of -1.5V or more positive, so I like to try to keep the grid bias to more negative than -2V.
Well, for a ~350 volt supply that sounds pretty close to good for a 47K load, and should probably be good for the 6N1P as well based on my experiments. Easy to find parts values and a pretty "classic" operating point it seems.
Maybe I'll have to break down and order a pair to play with, I'm not able to find the ones I had set aside. I'd like to try them out for an eventual 6AS7G build anyway. I'll keep my eyes peeled on eBay for some old ones
Maybe I'll have to break down and order a pair to play with, I'm not able to find the ones I had set aside. I'd like to try them out for an eventual 6AS7G build anyway. I'll keep my eyes peeled on eBay for some old ones
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You never know - you might well be able to trade PCBs for tubes!Maybe I'll have to break down and order a pair to play with, I'm not able to find the ones I had set aside. I'd like to try them out for an eventual 6AS7G build anyway. I'll keep my eyes peeled on eBay for some old ones
Lots of never-to-be-used tubes sitting in 'stash boxes' out there.
Some folks would like to see a bigger barter economy....
I would be more than happy to do that, actually! If anyone is interested let me know
I have several PCB designs nearing completion currently, so in the next month or so I'll have the mosfet PSU board(done), SE noval board, PP noval board, and both flea PP variations (done) ready for testing, and I'm currently working on a universal gain/splitter board that is meant to be air-wired to the socket for semi point-to-point builds, suggested/commisioned by a member here
Since I am very literally a kitchen table effort (I literally eat dinner in the same place setting where I do my electronics work) bartering fits the theme very well IMHO for what is meant to be a community project.
I have several PCB designs nearing completion currently, so in the next month or so I'll have the mosfet PSU board(done), SE noval board, PP noval board, and both flea PP variations (done) ready for testing, and I'm currently working on a universal gain/splitter board that is meant to be air-wired to the socket for semi point-to-point builds, suggested/commisioned by a member here
Since I am very literally a kitchen table effort (I literally eat dinner in the same place setting where I do my electronics work) bartering fits the theme very well IMHO for what is meant to be a community project.
Yeah, there's not really an "off the shelf" transformer to use here without some creative miswiring/load mismatching, or being creative with running alternative types like the toroids that I'm using. There are inherent issues when using any transformer at such high reflected load impedance, so they aren't very common at all for higher bandwidth applications, as there is often a rolloff at high frequency due to parasitic losses due to capacitance and other wonderful nonideal issues.
This design does not claim to be the lowest distortion and flattest frequency response, but due to the design goals of low average output/listening levels, a slightly lower than ideal load impedance, and the use of overall negative feedback it is drawn into a very useful and lovely sounding amplifier, that works out very well in spite of the nonideal issues. The amplifier is in class A up to about 1/2W depending on your chosen operating point, and this keeps distortion acceptable by keeping the reflected load higher than the overall ratio dictates.
I sort of agree with the idea the statement regarding the worth of those nicer 6SN7 tubes in your stash, I would sell a handful and if building something like my project some standard types will do well, as the design doesn't really make tubes stand out all that strongly due to the use of feedback to keep things all "homogeneous" for lack of better term.
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Small update on things, It was pouring and storming outside yesterday, keeping me from doing car stuff, so I was able to do a little bit of chassis work on the build using the noval board. Cut out the IEC inlet, and cleaned up the holes for the input tubes. Gave it a scrub with some sandpaper to take the edges off, and hit it with some hammered paint. I'll give it a few days to set (it's been pretty cold lately) and start on final assembly.
Next build that I do will likely get a smaller chassis, and maybe some black wrinkle paint, with externally mounted EI type transformers, in either dark grey hammertone paint, or semigloss black.
Next build that I do will likely get a smaller chassis, and maybe some black wrinkle paint, with externally mounted EI type transformers, in either dark grey hammertone paint, or semigloss black.
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Hi, thanks for the explanations. No way to get the 2 small Antek to Switzerland, 34US$ shipping for 20$ OPTs... not a sane approach. I might once order a bunch more PTs and OPTs from Antek to spray the shipping costs to multiple articles. I intend to sell a part of my tube stock, but I need to test them first. I have the uTracer but I lack the time. If someone is in Switzerland and wish to group an order to Antek USA, let me know. Not sure I can advertise tube sale in this thread, when that happens I will post something in the swap/meet, I think this is more appropriate. Lingwendil is eligible for a super deal on them to thank him for his development work but I need to check the shipping to USA first.
No worries.
My recommendation- find some 10K or so PP iron meant for 6V6 or EL84 use, and run double the recommended load impedance on the secondary. For example, an 8 ohm load on a 4 ohm secondary, or a 16 ohm load on a 8 ohm secondary. If building point-to-point, one could also run two 6SN7s per transformer, rather than one, with individual cathode networks, and individual coupling capacitors so that they bias up independently. This would be a nice use for some older iron that is undersized and can't do big power, and would likely work as well or better than load matching to get a nice result, and could even be used in tandem with it. This would also work with some domestically available iron a bit more easily.
Worse case drop some coin on some similar iron from Toroidy or similar EU source.
My recommendation- find some 10K or so PP iron meant for 6V6 or EL84 use, and run double the recommended load impedance on the secondary. For example, an 8 ohm load on a 4 ohm secondary, or a 16 ohm load on a 8 ohm secondary. If building point-to-point, one could also run two 6SN7s per transformer, rather than one, with individual cathode networks, and individual coupling capacitors so that they bias up independently. This would be a nice use for some older iron that is undersized and can't do big power, and would likely work as well or better than load matching to get a nice result, and could even be used in tandem with it. This would also work with some domestically available iron a bit more easily.
Worse case drop some coin on some similar iron from Toroidy or similar EU source.
Worse case drop some coin on some similar iron from Toroidy or similar EU source.
This UK product look like the perfect article, €35/pièce : VTP15671-1100 - Firefly Push Pull Output Transformer 22.5k to 8 ohms 1.5 watts
Or this one : Fender Vintage Style Reverb Driver, 125A20B, 022921 & 037099
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