Never heard either of these tubes, but the price looks attractive for the output power I want to achieve. Besides I like the looks of big tubes in the dark 🙂 What are the thoughts of each sonically. If I am not mistaken these tubes should have a similar sound to 6L6's. Looks interesting. Any experience with these in a SE parallel setup?
Tubes...
The 811A and its 'relation' the 572B isnt an easy tube to drive for audio....
The 807 is very basically a 6L6 with anode-top-cap connection intended for RF service, so you can follow a good/popular 6L6 scheme for that tube...
Ive built an 811A P-P amp running at 420V anodes/plates, but you need to run them in Class A2, meaning the Grid is always Positive with respect to Cathode. This means a driver stage capable of supplying many 10's of mA to achieve any real power in the Anode cct. A good strong tube like a KT66/88/etc will supply that if it ALL must be tube...
I found in SE they are rather 'flat' to my taste so I re-designed into P-P....
I used MOSFETS to drive them. Works well, and sounds pretty good. Use a transformer of around 4-5K P-P, and around 60mA Bias, for which you'll need around 20V Positive on the Grid at 400V Plate/Anode Expect around 30-50W, in P-P depending on how you drive them
811A are very good asthetically...The Thoriated Directly heated cathodes will light up the room, and form a great talking-point, unlike the 807, although the 807/6L6 is a better choice to make a an amp with!
The 811A and its 'relation' the 572B isnt an easy tube to drive for audio....
The 807 is very basically a 6L6 with anode-top-cap connection intended for RF service, so you can follow a good/popular 6L6 scheme for that tube...
Ive built an 811A P-P amp running at 420V anodes/plates, but you need to run them in Class A2, meaning the Grid is always Positive with respect to Cathode. This means a driver stage capable of supplying many 10's of mA to achieve any real power in the Anode cct. A good strong tube like a KT66/88/etc will supply that if it ALL must be tube...
I found in SE they are rather 'flat' to my taste so I re-designed into P-P....
I used MOSFETS to drive them. Works well, and sounds pretty good. Use a transformer of around 4-5K P-P, and around 60mA Bias, for which you'll need around 20V Positive on the Grid at 400V Plate/Anode Expect around 30-50W, in P-P depending on how you drive them
811A are very good asthetically...The Thoriated Directly heated cathodes will light up the room, and form a great talking-point, unlike the 807, although the 807/6L6 is a better choice to make a an amp with!
Curly Woods said:
Here, you are asking for a comparison that really won't mean very much. The 807 is a beam tetrode, whereas the 811A is a high u, "zero bias" RF power triode. Vastly different VTs which will require vastly different circuit topologies. About the only point in common is that both types have a rather highish r(p).
I have experience with 807s, and I can tell you that, given the right Q-Point, ~7.0db(v) of local NFB, and a bit of gNFB that they sound fantastic. And, yes, it's just like a 6L6GB with a plate connect button so that it can operate at higher Vpp's than can a 6L6GB where all connections are made at the base. As far as "glowey bottle kewelness", 807s really aren't all that impressive, as they have rather thin cathodes, and the heater requirement is but 6.3V @ 0.9A. Not like the Th/W filaments of the RF power triodes at all.
As for 811As, were I going that route, I'd opt for 812A instead. Same Pd, both will still require grid-positive (i.e. enhancement mode bias) to work right, but the 812A is a bit more linear, and has a lower r(p) dur to its lower u factor. Lower r(p) means better bass performance.
As for these, Class A2 triodes won't sound the same. They seem to perform their best when working at high volumes, and are very dependent on the quality of the driver stage. The latter isn't a prob with the 807, since it's a very easy load even in Class A2, or more likely, AB2.
811A
Forgot to add, another dis-advantage of the 811A type is hum can be a problem from the directly heated cathode, unless DC is used or some cunning design is done...The Heater of one 811A needs 6.3V at 4A so if you decide to regulate this supply, you may need a BIG heatsink!
I have AC heating on my 811A P-P, but hum is audible if you listen closely at the speakers. At normal distance, it is just barely audible between tracks if you listen hard......I really should do something about it, but never seem to get the time! One thing in its favour, It has been very reliable, Bias good and stable, It just 'works'.......
As Myles pointed out, These two valves are totally different animals really. For ease of design and ongoing reliability/performance the 807 would be recommended over the 811A, but dont look half as 'cool'!
Forgot to add, another dis-advantage of the 811A type is hum can be a problem from the directly heated cathode, unless DC is used or some cunning design is done...The Heater of one 811A needs 6.3V at 4A so if you decide to regulate this supply, you may need a BIG heatsink!
I have AC heating on my 811A P-P, but hum is audible if you listen closely at the speakers. At normal distance, it is just barely audible between tracks if you listen hard......I really should do something about it, but never seem to get the time! One thing in its favour, It has been very reliable, Bias good and stable, It just 'works'.......
As Myles pointed out, These two valves are totally different animals really. For ease of design and ongoing reliability/performance the 807 would be recommended over the 811A, but dont look half as 'cool'!
I have built SE amps with both 807 and 811A.
Let me put it this way:
Unless yoy have great experience in designing and building tube stuff or are on a limited budget, stay away from 811A.
These babies differs a lot from the regular triodes we use in hifi amps, they require massive DC PSU´s for the filaments and very low-impedant driver stages.
I gave them a try just for the challenge and there was some degree of success but I never got it quite right (PSU problems).
Will give A2 another chance soon, this time I´ll use 808´s instead just because they look cool.
807 on the other hand is an easy tube to work with, capable of producing great sonics too if you don´t need a lot of power.
Let me put it this way:
Unless yoy have great experience in designing and building tube stuff or are on a limited budget, stay away from 811A.
These babies differs a lot from the regular triodes we use in hifi amps, they require massive DC PSU´s for the filaments and very low-impedant driver stages.
I gave them a try just for the challenge and there was some degree of success but I never got it quite right (PSU problems).
Will give A2 another chance soon, this time I´ll use 808´s instead just because they look cool.
807 on the other hand is an easy tube to work with, capable of producing great sonics too if you don´t need a lot of power.
I've done SE 811A, SE 845 and have listened to SE KT66. If no
more than 9W works with you, then any of these projects are attainable. The 811A sounds different than the 6L6 by a long leap.
811A: crystal clear, detailed. KT66: warm, lush, rounded out. The
difference in sonics is the distortion profile. The 811A is extremely linear. I liked driving my 811A with a 6Y6GT as a cathode follower.
You can drive it a 6V6 or EL84 just as well.
I'd not attempt parallel 811A. You need to add another 25W of
filament power to do the second 811A. This is just not worth the
cost of additional hum injection, finding a driver that can power
a 500 ohm load at 40mA idle. That is just madness.
You are far better off doing a 800V amp using 211/845 than PSE 811A.
Dont be scared of considering the 211 or 845. They are $40 ea.
The socket is another $13. They last forever (dont drop 'em).
And, they look incredible. I think a nice project for not alot of
money would be a Cathode biased 211 (permits ultrapath bypass
of Output Transformer), 6600 ohm SE OPT. Use the mu-follower
driver from the old Svetlana App Notes (EL84 + 6N1P).
-- Jim
-- Jim
more than 9W works with you, then any of these projects are attainable. The 811A sounds different than the 6L6 by a long leap.
811A: crystal clear, detailed. KT66: warm, lush, rounded out. The
difference in sonics is the distortion profile. The 811A is extremely linear. I liked driving my 811A with a 6Y6GT as a cathode follower.
You can drive it a 6V6 or EL84 just as well.
I'd not attempt parallel 811A. You need to add another 25W of
filament power to do the second 811A. This is just not worth the
cost of additional hum injection, finding a driver that can power
a 500 ohm load at 40mA idle. That is just madness.
You are far better off doing a 800V amp using 211/845 than PSE 811A.
Dont be scared of considering the 211 or 845. They are $40 ea.
The socket is another $13. They last forever (dont drop 'em).
And, they look incredible. I think a nice project for not alot of
money would be a Cathode biased 211 (permits ultrapath bypass
of Output Transformer), 6600 ohm SE OPT. Use the mu-follower
driver from the old Svetlana App Notes (EL84 + 6N1P).
-- Jim
-- Jim
811A P-P scheme...
Its already here somewhere....
Have a search on all my Posts, It will be under a thread about the 811A Cant quite remember where, Ill try and find it or if not Ill re-post it for you.
In the scheme as I recall, I made a small silly error on the 'Mu-Stage' but its glaringly obvious! The driver/O/P etc is fine however...
Here you go....http://www.diyaudio.com/forums/showthread.php?s=&threadid=54935&perpage=10&pagenumber=5
About halfway down the page....
Its already here somewhere....
Have a search on all my Posts, It will be under a thread about the 811A Cant quite remember where, Ill try and find it or if not Ill re-post it for you.
In the scheme as I recall, I made a small silly error on the 'Mu-Stage' but its glaringly obvious! The driver/O/P etc is fine however...
Here you go....http://www.diyaudio.com/forums/showthread.php?s=&threadid=54935&perpage=10&pagenumber=5
About halfway down the page....
I once built a 811A SE amp,was a while back,I think I used a 6SN7 drivertube,so it was NOT A2.😀 I had DC filiament and there was no hum..Sounded fine,think it would have sounded better in A2,later changed to SV572-10,they sounded better.😉
I'm running DC heaters on my SV811 SE's...I get a little bit of hum next to the speakers, but they are Klipsch Forte II's with horns, so anything gets picked up 😀 I'm sure if I ran less-efficient towers, I wouldn't hear it as much.
And yeah, those cathodes get *bright*. Quite romantic, I've been told 😉
And yeah, those cathodes get *bright*. Quite romantic, I've been told 😉
Well that´s easy,I just hocked them up and out came the sound.😎
No.I´ll try to find those OLD schema and see,maybee I´m wrong..🙄
No.I´ll try to find those OLD schema and see,maybee I´m wrong..🙄
If you have not built amps before, then start with an easier tube to deal with than the 811a or a variant thereof. It's a Class B "zero bias" transmitting tube designed to run in P-P class B for ~150 to 200watts of output in audio service.
The plate impedance is high, so the iron is both big, expensive and hard to find... of course dropping the B+ and then biasing the tube into class A you do get a lower plate Z, so it might "fit" into a transformer that you could find somewhere... two in parallel means bigger iron even in Class A SE operation since the quiescent current will be fairly high compared to say a pair of 300B...
So, 807s being beam tetrodes, not my first choice, but they are cheap and plentiful. No prob if you blow a few up.
They are like 6L6s, but differ in one very important way. They will take a ****load more B+ than any 6L6 will!
I'd strap 'em for triode if you want to try to use them.
They're ok for a "getting started" project amp.
Of course once you run the B+ up, you might as well skip the 807 and go directly to another tube... FYI 4 x 807 in P-P AB2 will do ~200 watts, iirc.
So, I'd recommend doing 2A3s/6A3s or 300Bs - they're not too pricey from Russia or China, sound very very good, and there are scads of xfmrs designed for SE operation out there already. Want to do it a little better? Go for class A2.
_-_-bear
The plate impedance is high, so the iron is both big, expensive and hard to find... of course dropping the B+ and then biasing the tube into class A you do get a lower plate Z, so it might "fit" into a transformer that you could find somewhere... two in parallel means bigger iron even in Class A SE operation since the quiescent current will be fairly high compared to say a pair of 300B...
So, 807s being beam tetrodes, not my first choice, but they are cheap and plentiful. No prob if you blow a few up.
They are like 6L6s, but differ in one very important way. They will take a ****load more B+ than any 6L6 will!
I'd strap 'em for triode if you want to try to use them.
They're ok for a "getting started" project amp.
Of course once you run the B+ up, you might as well skip the 807 and go directly to another tube... FYI 4 x 807 in P-P AB2 will do ~200 watts, iirc.
So, I'd recommend doing 2A3s/6A3s or 300Bs - they're not too pricey from Russia or China, sound very very good, and there are scads of xfmrs designed for SE operation out there already. Want to do it a little better? Go for class A2.
_-_-bear
I realy cant tell you,I can´t fin the schema,was about 15ears ago I built this one,and at that time I "just" built after a schema,then it workt!Locking at the plate characteristics,you have to apply a possitive
suppy to the grid to even get a few milliamperes out.I later switched to SV-572-10 and they had about 1000-1100v at the anodes,biased to get about 20w out,to high if you ask me now,as they do get warm and wear out fast.In the future verision I am not going to bias for more than 8-10w.Going of toppic... 😉
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