Different power amps have different driver tubes, and I was wondering how an 845 is best driven, for optimal sonic performance.
For example, I have seen amps that use E88CC tubes and 5687 tubes to drive the 845, delivering 28Wpc. But I have also seen amps that use a 6NS7 and 12AU7 tubes.
So which combination would perform better sonically?
For example, I have seen amps that use E88CC tubes and 5687 tubes to drive the 845, delivering 28Wpc. But I have also seen amps that use a 6NS7 and 12AU7 tubes.
So which combination would perform better sonically?
Hi!
here is my opinion:
The 845 needs close to 400Vpp drive voltage for this kind of output power. This is quite a challenge. I prefer to have a lot of headroom in the driver, which makes it even more challenging.
The best driver I have used for the 845 was a 211. You could use a second 845 like Sakuma does, but a 211 has more voltage gain. Coupling was with interstage transformer.
If you want to stick to a more 'sane' approach, I'd recommend the 6AH4 transformer coupled. This is a strong indirectly heated triode which can provide large voltage swing.
I'm about to finish a 211 amp whih uses a 6HS5 as driver. I will introduce this project with schematics on my blog in a few days, just need some more time to finish the article.
Best regards ... Thomas
here is my opinion:
The 845 needs close to 400Vpp drive voltage for this kind of output power. This is quite a challenge. I prefer to have a lot of headroom in the driver, which makes it even more challenging.
The best driver I have used for the 845 was a 211. You could use a second 845 like Sakuma does, but a 211 has more voltage gain. Coupling was with interstage transformer.
If you want to stick to a more 'sane' approach, I'd recommend the 6AH4 transformer coupled. This is a strong indirectly heated triode which can provide large voltage swing.
I'm about to finish a 211 amp whih uses a 6HS5 as driver. I will introduce this project with schematics on my blog in a few days, just need some more time to finish the article.
Best regards ... Thomas
Russian tube 6E5P /6Е5П/ or similar octal 6P9/6П9/ with current 30-40 ma and You will have two stages ampl. with minimum passive elements for very good sounding. It gain is enough to drive 845. If You will use it in triod mode, You will need interstage transf. 1:3
with power about 5 watts. /I prefer 2 stages ampl./.
with power about 5 watts. /I prefer 2 stages ampl./.
I have built 845 single ended using all types of driver tubes; they are very hard to drive and you end up with a dull sound.
i run mine at 800 volts with 3.4k sowter Output transformer about 15 watts; i use horns so no need for more watts. I got the best results using a High Gm pentode and screen driven 5881. all the other circuits sounded very dull no Dynamics. The sound is excellent with powerful bass and fast and dynamic sound. Mush cheaper than using interstage transformers. An advantage of this circiut is that the 5881 runs with 800 volts supply; 400 volts on the plate.
Phil
i run mine at 800 volts with 3.4k sowter Output transformer about 15 watts; i use horns so no need for more watts. I got the best results using a High Gm pentode and screen driven 5881. all the other circuits sounded very dull no Dynamics. The sound is excellent with powerful bass and fast and dynamic sound. Mush cheaper than using interstage transformers. An advantage of this circiut is that the 5881 runs with 800 volts supply; 400 volts on the plate.
Phil
I haven't built a 845 amp, but I've fidgeted around with some designs on screen (for a ESL direct drive amp). When I someday build it, my first choise for driver tube is a 45, with an input stage of maybe the 27.
6E5P is a very good tube, especially at good currents (35mA+). However I find it a bit cold and uninvolving as a spud. Very detailed and clean however. Definitely worth a try.
6E5P is a very good tube, especially at good currents (35mA+). However I find it a bit cold and uninvolving as a spud. Very detailed and clean however. Definitely worth a try.
This is a common problem with power triodes of all sorts. The disappointing sonics of 300Bs seems to trace back to inadequate grid drive. I have a 845 SET project in the works (attached). The headroom/output swing problem is solved with active plate loading on a vertical deflection type that can stand up to higher voltages.
The small signal section is quite linear with a 100K plate load, and there is ample DC available to make this possible.
For grid drive, you just can not beat the power MOSFET source follower. The MOSFET has a higher Gm, and much lower rds(on) than any hollow state solution. It also doesn't mess up the open loop phase characteristic, making the application of gNFB possible.
Going with higher Vpp and lower Ipq here. Already have the 9000R : 8R OPT.
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I have tried the El34 circuit. I am very happy with the driver circuit I am using; Peter millets High Gm pentode 12HG7 {as he used to drive the 813} and Rickard Berglund’s Screen driven power pentode {Glass audio 6/96}. I used the 5881 as I have lots of them and they don’t require a top cap. I am sure a driver transformer would give good results, but I don’t have the funds and the circuit I am using sounds great. Using 750 volts the 845 requires 90 volts peak A-F grid voltage { RCA DATA Sheet} and 3.4k Load resistance.
I have a tube regulator to supply the 400 volt for the 12HG7 and a transistor regulator for the 150 volts g2 voltage.
I have a tube regulator to supply the 400 volt for the 12HG7 and a transistor regulator for the 150 volts g2 voltage.
I designed my Tamura Permalloy 845 amp to use a triode connected sweep tube as a driver. Designed around the 6AV5 and the EL500 (with a dedicated - and cool looking - adapter), but I can also drop in a 6AU5, or 6DB5 and it sounds great - if not different. Anyone who says that triode connected sweep tubes do not make good sounding drivers (because they are not true triodes) has probably never heard a well designed example - let alone built one. Of course power triodes like the 250, 300B, 45 and 10 types can sound very good - as can the very best of the 6L6 (EL37, We 350B, etc...) and 6550 family, triode connected.
Of course (speaking from personal experience) high quality interstage transformers like tha original Tango NC-20 with the right driver tube makes a darn good driver.
Whatever you do, I suggest using a driver that has 20 to 35ma of current running through it.
For smaller twin triodes, I like the 6BL7 or 6BX7. The truth is, there are a ton of tubes that with proper design, can be set up to drive an 845. I for one, would use any of the tubes above, before I would use a 9-pin minature.
Of course (speaking from personal experience) high quality interstage transformers like tha original Tango NC-20 with the right driver tube makes a darn good driver.
Whatever you do, I suggest using a driver that has 20 to 35ma of current running through it.
For smaller twin triodes, I like the 6BL7 or 6BX7. The truth is, there are a ton of tubes that with proper design, can be set up to drive an 845. I for one, would use any of the tubes above, before I would use a 9-pin minature.
Multi, the screen-drive 5881 sounds like an interesting implementation. Could you tell us about the idle-current, idle screen-voltage, Vg1 and Load for the 5881?
I have been looking at my Sowtwer SA08 (may be same as yours?) and found that these are tested at 2500V - raising the temptation to try the 845 or GM70 with them.
using tube cadaver, and a 5k ohm load, 1250 volts B+, 88ma gives a power disipation of 96%, and 1650 ohm cathode resistor, 26 watts RMS power out, 8% 2nd harmonic distortion, 1.8% 3rd harmonic, it needs a voltage drive of 147 volts, so that's +/- 147 volts from your driver, and a slew rate of 18.5 volts/ U second.
these are close to max conditions, do design your driver for that.
6sn7 tube will do it, perhaps 6922 also, dunno about "strange" tubes tho'.
suggest a 2a3 or 300b driver, interstage coupled, or choke loaded, also, el34/5881, perhaps el84, not looking at specs. tho so some may not be upto task.,
5687, 300b interstage, 845 output, probably a safe combo. I can design with a 6sn7 driver, too someday...
these are close to max conditions, do design your driver for that.
6sn7 tube will do it, perhaps 6922 also, dunno about "strange" tubes tho'.
suggest a 2a3 or 300b driver, interstage coupled, or choke loaded, also, el34/5881, perhaps el84, not looking at specs. tho so some may not be upto task.,
5687, 300b interstage, 845 output, probably a safe combo. I can design with a 6sn7 driver, too someday...
Well, I drive currently a 845c@860V/65mA into 7k4 primary...with 801A @ 400V/25mA...Vinp is 230Vpp from the 801A at digital 0db from my DAC...Interstage Transformer is from 50AE, Nano with OcC wire...
I have to say I am really impressed by the unbelieveable clarity and brutal micro and macro dynamics...the tube is anything but dull or boring...the whole 300B family sounds like toys in comparison...except maybe the Kron 842...
...I guess that is what Thomas is preaching the whole time about TT filament effect...I will test the 814,813,gm70 and 4242 next...all with metal plates of course.
Nevertheless I would like to see what happens when change the small 801A to another pair of 845 or 4242 (I dont like carbon plates)....Can these tube be run as a driver at something lower like 600V/25mA or do they sound than nasty ?
I have to say I am really impressed by the unbelieveable clarity and brutal micro and macro dynamics...the tube is anything but dull or boring...the whole 300B family sounds like toys in comparison...except maybe the Kron 842...
...I guess that is what Thomas is preaching the whole time about TT filament effect...I will test the 814,813,gm70 and 4242 next...all with metal plates of course.
Nevertheless I would like to see what happens when change the small 801A to another pair of 845 or 4242 (I dont like carbon plates)....Can these tube be run as a driver at something lower like 600V/25mA or do they sound than nasty ?
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I have curve traced today my 4242a...
16129682115323491372520753005037 — ImgBB
This looks quiet cool... 25mA seems to be fine...
An externally hosted image should be here but it was not working when we last tested it.
16129682115323491372520753005037 — ImgBB
This looks quiet cool... 25mA seems to be fine...
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