A couple of weeks ago I posted some schematics about a 6B4G project. Thanks to all who helped me with that design. Unfortunately, last night I started the parts layout and realized that I do not have a matched pair of the tubes. Having done some calculations, I have determined that 1 watt is the outside audio power that I ever use per channel. So, the question is what to build instead. I have dozens of 6L6 variants, which I have never used in an amp. Does anyone have experience with these tubes as triode strapped outputs? I have some really cool looking Navy 6l6ga, some original 6l6 in the metal cans, some clear globe types, and 6l6gcs. Many matched pairs in the bunch. I also have a kazillion 6v6 variants, but I have played with this family before, although I have more varieties of these than when I did 6v6 experiments.
In case it matters, my musical tastes leans toward classic country, jazz, bluegrass, 40s pop, and classical. I like a thick midrange with and an airish top that is slightly recessed relative to the midrange and bass. Bass is controlled by subwoofers so I can usually get it to match the amp du jour.
Thanks in advance.
In case it matters, my musical tastes leans toward classic country, jazz, bluegrass, 40s pop, and classical. I like a thick midrange with and an airish top that is slightly recessed relative to the midrange and bass. Bass is controlled by subwoofers so I can usually get it to match the amp du jour.
Thanks in advance.
If 1W is enough for you then 6V6 might be a better choice than 6L6. I think 6V6 is more linear in triode mode.
Here is one with 6L6GC, maybe not "flea", but anyway
http://www.pmillett.com/push-pull_kt88_class_a_amp_with_universal_driver_pcb.htm
UPS, not SE
http://www.pmillett.com/push-pull_kt88_class_a_amp_with_universal_driver_pcb.htm
UPS, not SE
I have made several amps using triode strapped 6L6 and 6V6 type tubes. The details and schematics can be found here:
http://www.tubelab.com/SimpleSE.htm
I have a ton of new material that will be posted to these pages when I am actually home long enough to upload it. It won't be this weekend, maybe the following weekend.
The 6L6 types come in two basic flavors:
All of the variants made before the 6L6GC ( 6L6 metal, 6L6G, 6L6GA, 6L6GB, 807, 1625, 6BG6 etc) have 19 watt plates and don't really like to operate over 400 volts. They seem to work best at about 350 to 370 volts, with a 3000 to 5000 ohm load. All will make at least 2 watts in triode, usually close to 3.
The 6L6GC and newer clones (Sovtek etc) have 25 watt (or higher) plates and can usually handle 450 volts or more in triode. The recommended load is 3600 to 5000 ohms. I like to use a higher load for cleaner sound at reduced power. I am running 6000 ohms in one of my amps. 5 watts is possible in triode mode with A Sovtek 6L6WXT tube on 465 volts.
The 6V6 type tubes are very linear in triode, and will out perform many 6B4 amps. Many (especially older) 6V6 types don't want to be operated over the 315 volt limit. Some of the 50's vintage RCA's and GE's will take 350 volts or more, but if you don't need the power, don't push them. I have a SimpleSE amp running with 6V6G's in it at 300 volts (about 275 volts across the tube) using the $19 5K ohm Edcor transformers. It makes just under 2 watts and sounds almost as good as my 45 based DHT amp which costs 5 times as much to make.
http://www.tubelab.com/SimpleSE.htm
I have a ton of new material that will be posted to these pages when I am actually home long enough to upload it. It won't be this weekend, maybe the following weekend.
The 6L6 types come in two basic flavors:
All of the variants made before the 6L6GC ( 6L6 metal, 6L6G, 6L6GA, 6L6GB, 807, 1625, 6BG6 etc) have 19 watt plates and don't really like to operate over 400 volts. They seem to work best at about 350 to 370 volts, with a 3000 to 5000 ohm load. All will make at least 2 watts in triode, usually close to 3.
The 6L6GC and newer clones (Sovtek etc) have 25 watt (or higher) plates and can usually handle 450 volts or more in triode. The recommended load is 3600 to 5000 ohms. I like to use a higher load for cleaner sound at reduced power. I am running 6000 ohms in one of my amps. 5 watts is possible in triode mode with A Sovtek 6L6WXT tube on 465 volts.
The 6V6 type tubes are very linear in triode, and will out perform many 6B4 amps. Many (especially older) 6V6 types don't want to be operated over the 315 volt limit. Some of the 50's vintage RCA's and GE's will take 350 volts or more, but if you don't need the power, don't push them. I have a SimpleSE amp running with 6V6G's in it at 300 volts (about 275 volts across the tube) using the $19 5K ohm Edcor transformers. It makes just under 2 watts and sounds almost as good as my 45 based DHT amp which costs 5 times as much to make.
Very nice indeed - you are my new favorite
Its just what I have been looking fore - rest assured I WILL build one of the SE you show 🙂
Its just what I have been looking fore - rest assured I WILL build one of the SE you show 🙂
Cool responses. I always see 6v6 types as drivers for bigger output tubes and have always wondered why people don't just save a stage. If you don't need the power, you don't need the power.
Tubelab, you're stuff is interesting. I played around with 6v6, 6f6, 6av5, 6cdg6as, and 6w6s a few years ago. I never could find a decent operating point for the av5s and gave up on them. If I remember correctly, no one had published curves of them triode strapped. At that time I did not have any 6l6 variants, so I still have never heard one. Of those listed, the 6v6 (RCA smoked glass) sounded the best. In fact, to date I believe a 6sn7/6v6 combo is the best amp I've heard, although my experience is limited (In addition to the triode strapped pentodes I have built 1626 Darling, and 6em7 based amps). Current amp is a tube buffered pot driving a tripath chip. It sounds very nice but could be a little more organic. As I return to this hobby, I have more knowledge and more experience with picking good Ops, so I really look forward to building my next pure tube amp. I also have the advantage of having amassed gobs of tubes that I always meant to Ebay, so I can experiment like hell.
In your experience how do 6l6s sound in comparison to 6v6s?
Tubelab, you're stuff is interesting. I played around with 6v6, 6f6, 6av5, 6cdg6as, and 6w6s a few years ago. I never could find a decent operating point for the av5s and gave up on them. If I remember correctly, no one had published curves of them triode strapped. At that time I did not have any 6l6 variants, so I still have never heard one. Of those listed, the 6v6 (RCA smoked glass) sounded the best. In fact, to date I believe a 6sn7/6v6 combo is the best amp I've heard, although my experience is limited (In addition to the triode strapped pentodes I have built 1626 Darling, and 6em7 based amps). Current amp is a tube buffered pot driving a tripath chip. It sounds very nice but could be a little more organic. As I return to this hobby, I have more knowledge and more experience with picking good Ops, so I really look forward to building my next pure tube amp. I also have the advantage of having amassed gobs of tubes that I always meant to Ebay, so I can experiment like hell.
In your experience how do 6l6s sound in comparison to 6v6s?
The 6V6 in triode sounds more like a DHT amp. You can hear more details in the sound, but the "big amp" slam isn't there. The 6L6 in triode will sound more like a bigger amp with better bass and dynamics but some of the details are lost. The KT88 in triode takes that concept further. I currently have one each of the three amps mentioned. All share the exact same passive circuitry, but direct comparisons can not be made because each amp has different output transformers.
The same thing can be said for the output transformers, the physically small ones often resolve details better than monster transformers, but the bigger ones have far better bass and can handle more power before saturating and distorting the signal. My theory is that it takes some energy to dynamically change the magnetic field in the transformer iron. The bigger the iron, the bigger the energy requirement. Too much iron for the job just seems to suck up a lot of the small details in the music. If you are using a subwoofer, don't use 12 pound OPT's in a 1 watt amp.
The 6V6 amp has small (maybe 1.5 pounds in weight) transformers and runs at 300 volts of B+. It resolves musical details almost as good as my 45 based DHT amp which uses custom Electra Print transformers. The bass and transient response is not quite as good, but close on my big speakers. Popping 6L6's or KT88's into this amp with no other changes takes away some of the "you are there" quality that this amp has but improves the bass. This amp does very well on music that doesn't tax its power capabilities (my speakers really need more power) like Norah Jones or Diana Krall. It doesn't do rock very well, but this is because I have inneficient speakers. My big ones are 96db and the small ones are 86db.
The "6L6 amp" uses 7 pound Transcendar transformers that present a 6K ohm load to the tubes (3K transformers with the 8 ohm speakers on the 4 ohm taps). This amp gives up a little detail but has far better bass and transient response. It runs at 450 volts so 6V6 tubes can't be tried. I have used 6L6GC's, EL34's and KT88's in this amp. The 6L6GC's have the best overall balance. The KT88's have the best bass and transient response, while the EL34's make the most power. I haven't decided which tubes that I would keep in the amp yet. My preference changes daily.
I have a bigger amp that is electrically identical to the "6L6 amp" mentioned above. It uses Hammond 1628SEA transformers that weigh about 12 pounds each. Awesome bass (I can shake my neighbors walls) and transients. No problem playing Pink Floyd at any volume setting. I have decided that the best tubes for this amp are Electro Harmonix KT88's. These tubes complement the characteristics of the amp. This amp can be operated in UL mode for about 14 watts of power with the KT88's at the flick of a switch.
What would I do in your case? Build an amp that runs on 280 to 320 volts of B+. Try any of the 6L6, 6V6, 6W6, type tubes that you have and choose the ones that you like to listen to. Since you only need 1 watt, you have a lot of choices!
I have experimented with the 6AV5's in P-P, SE mode, triode and UL. There is a wide variation amond these tubes, and there are at least 7 different constructions all claiming to be a 6AV5GA. Each one seemed to work a little different. I was experimenting in the higher power extremes since 1 watt won't even wake up my lab speakers. It might be worth trying some of them at the same 280 to 320 volts. They sounded great at the 5 watt level (far more punch than a 6L6GC). I quit playing with them in SE because they were too inconsistent at the higher dissipation levels required to make 4 or 5 watts of output power. I have discovered that these tubes just beg to run in screen driven push pull where any of them can make over 80 watts!
The same thing can be said for the output transformers, the physically small ones often resolve details better than monster transformers, but the bigger ones have far better bass and can handle more power before saturating and distorting the signal. My theory is that it takes some energy to dynamically change the magnetic field in the transformer iron. The bigger the iron, the bigger the energy requirement. Too much iron for the job just seems to suck up a lot of the small details in the music. If you are using a subwoofer, don't use 12 pound OPT's in a 1 watt amp.
The 6V6 amp has small (maybe 1.5 pounds in weight) transformers and runs at 300 volts of B+. It resolves musical details almost as good as my 45 based DHT amp which uses custom Electra Print transformers. The bass and transient response is not quite as good, but close on my big speakers. Popping 6L6's or KT88's into this amp with no other changes takes away some of the "you are there" quality that this amp has but improves the bass. This amp does very well on music that doesn't tax its power capabilities (my speakers really need more power) like Norah Jones or Diana Krall. It doesn't do rock very well, but this is because I have inneficient speakers. My big ones are 96db and the small ones are 86db.
The "6L6 amp" uses 7 pound Transcendar transformers that present a 6K ohm load to the tubes (3K transformers with the 8 ohm speakers on the 4 ohm taps). This amp gives up a little detail but has far better bass and transient response. It runs at 450 volts so 6V6 tubes can't be tried. I have used 6L6GC's, EL34's and KT88's in this amp. The 6L6GC's have the best overall balance. The KT88's have the best bass and transient response, while the EL34's make the most power. I haven't decided which tubes that I would keep in the amp yet. My preference changes daily.
I have a bigger amp that is electrically identical to the "6L6 amp" mentioned above. It uses Hammond 1628SEA transformers that weigh about 12 pounds each. Awesome bass (I can shake my neighbors walls) and transients. No problem playing Pink Floyd at any volume setting. I have decided that the best tubes for this amp are Electro Harmonix KT88's. These tubes complement the characteristics of the amp. This amp can be operated in UL mode for about 14 watts of power with the KT88's at the flick of a switch.
What would I do in your case? Build an amp that runs on 280 to 320 volts of B+. Try any of the 6L6, 6V6, 6W6, type tubes that you have and choose the ones that you like to listen to. Since you only need 1 watt, you have a lot of choices!
I have experimented with the 6AV5's in P-P, SE mode, triode and UL. There is a wide variation amond these tubes, and there are at least 7 different constructions all claiming to be a 6AV5GA. Each one seemed to work a little different. I was experimenting in the higher power extremes since 1 watt won't even wake up my lab speakers. It might be worth trying some of them at the same 280 to 320 volts. They sounded great at the 5 watt level (far more punch than a 6L6GC). I quit playing with them in SE because they were too inconsistent at the higher dissipation levels required to make 4 or 5 watts of output power. I have discovered that these tubes just beg to run in screen driven push pull where any of them can make over 80 watts!
That's good info. The recommended bias varies a few volts between 6v6 and 6l6, so I may add a bias switch to the amp rather than aim for a compromise bias point. I've noticed in the past that tubes preserve sonic characteristics over a wider range of OPs than the curves would indicate, so it may not matter. Naturally, I'll probably do what you said and just try everything. In past experiments I found that many of the 6v6s were too detailed with digital sources except for the RCA smoked glass, which I remember standing out from the crowd with a thicker, creamier sound. I don't listen to much vinyl as a source, and I do not at present have an audiophile grade CD player (I used to but it died). I spend most of my time listening to XM from my cable box. Audio snobs wouldn't approve, but I like music. The purpose of this amp is to present the signals that I am actually using as best they can be heard rather than wowing myself with one or two perfectly presented vinyl cuts. I also have a bunch of cap tubes, I think beam pentodes, some of them are huge *** tubes. Unfortunately I have kids, so I would have to build a cage to mess around with them.
I have read your page on using the FETs to drive power tubes. In this case, biasing a 6sn7 to 15 mA with a CCS should easily drive the capacitance of triode-strapped pentodes. And they should be able to drive them to full power since the bias is going to be so low. Am I correct here? I notice people never run n7s anywhere near their limit.
Which leads me to a question that I ought to know the answer to. If I use the 10m45 IC CCS, and set the current, where do I set the tube's bias? That is, which becomes the limiting factor, the IC or the cathode resistor?
I have read your page on using the FETs to drive power tubes. In this case, biasing a 6sn7 to 15 mA with a CCS should easily drive the capacitance of triode-strapped pentodes. And they should be able to drive them to full power since the bias is going to be so low. Am I correct here? I notice people never run n7s anywhere near their limit.
Which leads me to a question that I ought to know the answer to. If I use the 10m45 IC CCS, and set the current, where do I set the tube's bias? That is, which becomes the limiting factor, the IC or the cathode resistor?
I usually set the CCS for the desired current. I remove the driver tube, and wire a current meter in its place. Then adjust the CCS for the desired current. Then remove the current meter, install the driver tube, and use the cathode resistor to set the plate voltage to the desired value. Yes, most people tend to under bias most driver tubes.
If you use cathode bias in your output stage, make up some resistors with aligator clips on the ends. Then you can clip them across the existing cathode resistor when you want to increase the current. If you are using fixed bias, make it adjustable.
Don't tell them! I have friends that use $200 speaker wire and interconnects, mine came from the automotive dept at WalMart. They think that my system sounds great.
I don't know, I haven't tried either of them yet. I got a large box of "pre auditioned" Russian tubes for $10 each from a tube dealer friend. I would have never tried some of those tubes if it wasn't for this deal. The EH KT88's absolutely rock and will run at 100 mA in my amp without complaining. The power transformer doesn't like it though. I even got a pair of those new "Tung Sol" reissue KT88's and a pair of Sovtek KT88's. They look and sound like the same tube to me.
I have used JJ EL34's with good success but I haven't tried any of their other tubes yet. I will try the KT77's and KT66's sooner or later, but I have a limited tube budget.
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