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In Reply to: Looking for a GOOD 211 / VT4-C Schematic posted by Super_BQ on July 17, 2003 at 23:47:58:
Given your 104dB/1W/SPL speakers, I see no reason why you need to get
into the proposed kiloVolt range of operation with a 211. I run an 845 at
450V into 91dB efficient speakers and get a very satisfying listening
experience, you could do the same with the 211.Lower voltage operation all around lowers the cost of building this amplifier
because lower voltage parts are more easy to find.I might be wrong making this statement but here goes: I'd conjecture the
reason why you see higher-voltage, higher-powered 845/211 commercial
amps is so that they can be mated easily to far less efficient but more
popular high end speakers such as the B&W Nautilii, the 801s, Martin Logans
et cetera et cetera. So unless you have such savage drive needs, maybe you
should shy away from the high-voltage design point that these products run at...The design I've roughed up sounds pretty darn good... You can certainly
upgrade the output transformer, and you can use different drivers - the
6C45, 5842WA are all options. It's going to be harder to get more than
4-5W out of my design because getting more power means swinging the grid
of the 845 over 100V. Tough to do with two stage amp *and* 2V sensitivity.
Pretty much have to go to three stages to get more - and you add more circuit
complexity...-- Jim
Follow Ups:
Thanks for your input Jim, is that 845 schematic much different than for a 211?
To be quite honest, I'd forget about the 211 and just go with the 845.
I'm not saying anything is wrong with the 211, its just for your application
you're in the money for this tube and so many people just have such good
things to say about the 845 at this operating point, as well as people saying
great things about the cheap $40 current production Chinese tubes.You have massively efficient speakers. ;) 4W is gonna be just fine and you
will be able to build this safely and cheaply. A guy here built a similar amp using
SRPP and 845's on LaScala's and just says great things about the music.
Check out the link below with Magnequests comment on this operating point.At 104dB, you're biggest concern is going to be hum. You will probably have to
go to DC filaments. groverg has done this with his 845 and can recommend a
topology that includes common mode chokes. I havent heard DC filaments, but
I like AC because its so simple.I'd say the only reason you might want to go for a 211 is:
- Need for serious crazy SET power (i.e. 20W and more)
- You have a stash of NOS RCA or Marconi 211 valves already. Serious Money.Another reason to choose the 845, its easier to get 5K transformers than the
10K you will need for the 811... Far easier. If you dont want to go the
Hammond route as I did, you could get the affordable but very good One Electron
UBT-2, or the Lundahl 1620/60mA or you might get an Electra-Print.I can assure you, for 4W, it's really magical. Most people that come over my
house immediately comment on the sound... And these are the kinds of people
that would say that they cant hear any different between "receivers" or speakers
when they listen at Tweeter or other such places... ;)I pulled out the stops on my design.... No capacitors in the signal path, just
glowing glass envelopes and magnetics... Ultrapath capacitor now. CLCLC
power supply - all oil caps everywhere - mercury rectifiers. Cheap to do -
at 500V. The coolest thing about my amp is the utterly massive powersupply.
It's totally over-engineered. It's heavy. It needs it own chassis. I think the
psycho power-supply is alot to do with why it sounds so good.You'll get what you want... Which is warm, transparent, charming sound... And
a big tall 1930's tube with bright filaments aglow. The look is definitely cool
too. Sure beats a 300B or 2A3 with their barely orange filaments.-- Jim
Hi Jim,Actually, i'm think of the 845 as next year's project. There will be many years for me to build. In my lifetime - could mean dozens of amps to fill a living room full.
I also plan to build speakers which I know will never be as efficient as the Klipschorns. Realistically, 90db/1w/1m speakers is probably all i'm gonna get so in times - I will need some tubes amps to drive them.
Also i'm use to listening to my Klipsch Chorus with a 400 watt SS amp - just enough to get me to rock concert level SPL. I would be short changing myself if I couldn't at least feel the music with some decents amount of watts.
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