Big Dog tube project ideas?

[djunk]

I'm looking for a DIY tube project to tackle. I want to have one ultimate tube amp. Maybe a 300b or something.
I want to hook up some hi-end speakers in my office to a one-and-only, big-daddy, tubeist-maximus! :o
Any project ideas?
JE-Labs has some good ones and Tom McNally has a 300b I really like.
What do you think?
Thanks, Derek

[TomMcNally]

As you know, you can spend a boatload of money on a 300B, and although they sound really nice, you still only have 9 watts max, so the speakers are important. I took my 2A3 amp to the office, with a small pair of Klipsch bookshelf speakers on the wall, and it's got plenty of volume for the office environment. It's hard to play Nine Inch Nails real loud when the room next door is the studio for a Country radio station anyway !

I would have to weigh the coolness factor of what the amp looks like against the target budget ... I think I'd do it again. The look of a pair of 300Bs beats a Quad of 6BQ5's anytime.

[erichayes]

Hi All,

I think Tom's nailed it. As my thrust is toward reference systems for studios and reenforcement systems for acoustic musicians, my goal is almost purely sonic. The main bitch I get is the amps aren't portable enough. I don't design for visual impact, and when someone shows me a really sexy amp for evaluation, my first comment is "Put it in the closet, and then I'll listen to it". If you want a pretty good amp with a high eye-candy quotient, the 300Bs are definitely on the short list. If you want even higher quality on both fronts (and can afford it) go with WE's original intention for the tube's use and build push pull amps. Just bear in mind that, even in push pull, you're only going to get about 25 watts of sound that's worth a damn, so efficient speakers are a must.

[EWBrown]

300Bs are kool! Start out with the Sovtek or Electro-HArmonix 300Bs (basically the same thing, other than the markings). SET will deliver 8 or 9 watts, maybe 10 with a good stiff tailwind and a smooth downhill slope Yellow_Light_Colorz_PDT_01 Valve Farts, maybe, if the budget's a tad tight.

If you want more power, then PP 300Bs would be a good way to go, and a NFB loop might not be necessary. A 6SL7 VA, a 6SN7 PI and the pair of sexy 300B firebottles for each channel. 9 pin minis work just fine, but they lack the visual coolness factor... Extra points for ST or globe-type tubes all around. Yellow_Light_Colorz_PDT_11

If you're into loud head-banging rock, PP amps are the only way to go, whether 300Bs, PPP EL84s, EL34s or KT88s or killer-watt transmitter tubes. SET just wont do Jimi, NIN, Ozzie or Deep Purple real "justice"... Yellow_Light_Colorz_PDT_06

The next step beyond the Russkie 300Bs would be the JJ 300Bs, or some of the Chinese TJ "meshplate" 300B variants, and if you hit the Power Ball Gigabucks lottery, then WE or Westrex 300Bs.

/ed B in NH

[lndm]

If you're into loud head-banging rock, PP amps are the only way to go, whether 300Bs, PPP EL84s, EL34s or KT88s or killer-watt transmitter tubes. SET just wont do Jimi, NIN, Ozzie or Deep Purple real "justice"...

I'm curious as to whether you feel this is power related or sound quality related, or maybe even overload characteristic related. I ask this as I am considering class A push pull, could this be a good option?

[EWBrown]

300Bs should be quite happy in class A PP. Just keep in mind that the B+ PSU current requirements can be fairly high, we're talking a minimum of 300 mA continuous, with a safety margin, go at least 400 mA capacity.

I would imagine that the basic ST70 design can be used with 300Bs, just change the output sockets, tape off the UL taps, and mind the B+ voltages. Typically, 300Bs are happy with a 800 to 1000 Ohms, 20Watt (I like to use a power rating about 3X the actual dissipation, for safety margin) "cathode" resistor for each tube, and at 70 to 80 mA plate current, the filaments will "float" at around 70-80VDC above ground. For PP, the resistor can be half the value, shared between the two tubes, this requires well matched pairs. Since these are DHTs (directly heated triodes) they will need their own 5VCT filament transformers, and four will be required for separately "cathode" biased tubes, and two if each pair of tubes shares a common 400-500 Ohm "cathode" resistor. Fixed bias could also be used, or a combination of fixed and cathode (using lower value resistors). One thing about DHTs, is they can tend to be hummy at times, with AC filament voltage, unlike a power tube with an indirectly heated cathode.

This is mostly a power consideration, your mileage may vary. It all depends on personal preferences / taste, the speakers being used, and the desired sound pressure levels. With a pair of homemade "Karlson" speakers, running about 96-98 dB SPM/w/m efficiency, SET 300Bs can cause "pain level" loudness, and on an ST70, they're almost lethal... The Karlsons are a 50-something year old design, and goldurn, they really work. My application, I use a Pyle Pro / Eminence Kappa 12 inch woofer and old Altec 800 Hz horns, drivers and crossovers, mounted on top. This eliminates the infamous "Karlson Honk"

Backloaded horns are efficient, but they have their own unique characteristics, some love 'em some hate 'em, once again personal preferences, etc. I like them for acoustic, jazz classical, but they're not as great for rock, metal, hiphop (gasp!) or other bass-heavy material. BLHs can sound "congested" (or nasally) to some.

/ed B in NH (I've rambled enough for now) Yellow_Light_Colorz_PDT_02

[djunk]

Ed,
Thanks for the great ideas. I really like the 300b push-pull. Im not much of an engineer, but I know how to read schematics and have a good understanding of the basics. Have you found any good 300B PP amps on the web that layout the project in detail?
Thanks again.

[EWBrown]

Start here: http://www.bonavolta.ch/hobby/en/audio/300b.htm

this has both SET and PP 300B circuits, and also look around on the "triode" website, and goodle "300B PP" or 300B pushpull" and see what appears. Somewhere inbetween all the references to Chrysler 300 series cars, maybe some amplifier info will appear Yellow_Light_Colorz_PDT_01

Triode has one (the WE86A) http://www.triodeel.com/we86a.jpg

/ed B in NH

[EWBrown]

This is indeed and interesting, and very unconventional approach:

http://boozhoundlabs.com/keto/

http://boozhoundlabs.com/keto/images/keto-2.jpg




/ed B in NH

[EWBrown]

The PGP8.1 trannie is 350-0-250 @ 75 mA, 6V @ 2A and 2X 2.5V @ 1.2A
these are special trannies made for Bottlehead by Magnequest. These are used with some of the earlier 2A3 / 300B monoblock amps.

The other p/ns are probably Magnequest part numbers for chokes, and input and output trannies.

For GP use any Hammond 350-0-350 @ 150 mA, 6.3V @ 2A (or more) and 5V @ 3A can be used with a external 2.5VCT @ 3A (or more) filament trannie. Replace the 6BY5 with a 5U4, 5R4, or similar tube rectifier.

From the marked voltages, it looks like the CCs (C4S) are set for 4.2 mA each. The 2A3 pair is running around 125 mA (52.5 mA each, if matched).
The net effect is that the 2A3 grids are -45VDC relative to the cathodes.

/ed B in NH

[TomMcNally]

google/eBay tip .... when searching either eBay or the Web for 300B stuff ... put a -chrysler in the search line !

[TerrySmith]

Is it possible to tweak the 6B4G Eiclone circuit to use 300B's? I like using ST or baloon shaped tubes whenever possible! Yellow_Light_Colorz_PDT_06

[erichayes]

Hi All,

A 300B is basically a 2A3 that's been eating its Wheaties--and has a 5 volt filament. Since a 6B4G is a 2A3 with a 6 volt filament and an octal socket, there shouldn't be any problem. You might have to alter the gain structure a bit to optimize the 300Bs' slightly lower µ, but it should operate right off the rack.

[ashok]

Hi,

Here is something that might be of interest. A single board can be used to build a 45, 2A3 or 300B amplifier (with appropriate jumpering).

http://www.tubelab.com/TubelabSE.htm

Ashok

[EWBrown]

The main consideration to convert a 6B4G Ike to 300B is the 4 pin tube sockets, finding PC mount 4 pinners is like trying to find chicken lips or turtle fur. Unobtainium... So some mechanical work, and chassis mounting the 4 pin sockets will be needed.

Also, the cathode( filament) biasing resistors are too big and too much power dissipation to be board-mounted. Typical resistor values range from 800 to 1000 Ohms, and 20 watts is a good safe power handling capacity (remember the 3X rule).

The Ike inout and PI circuit should be just fine, the 300Bs and cathode resistors off the board, and the NFB loop (if used) will have to be re-tweeked to play well with the triodes. Each 300B (if cathode biased) will require its own 5VAC filament trannie.

/ed B in NH