Tube DIY Asylum

Posted by Jim Doyle (A) on July 18, 2003 at 20:03:26

In Reply to: Re: Looking for a GOOD 211 / VT4-C Schematic posted by Super_BQ on July 18, 2003 at 13:54:30:

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

• Magnequest on the 845 at low volts..   (Open in New Window)