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Old 25th April 2006, 01:59 AM   #1
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Default 300b based monoblock plans

hey everyone,

i'm looking for complete plans (if there is such a thing) for 300b based monoblocks. i guess something classic, maybe based on a mullard design?

anything in that style would work as well. it would be even better if there would a PCB layout so i can make them my own as i hate to work with terminal stripes.

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Old 25th April 2006, 02:32 AM   #2
arnoldc is offline arnoldc  Philippines
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The "classic" is a WE91
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Old 25th April 2006, 02:38 AM   #3
kevinkr is offline kevinkr  United States
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Years ago I designed a PP 300B monoblock which was published in VTV, several people here are familiar with the design and the original article is available on my site. It's a fully differential design using one 6SL7 and one 6SN7 per channel.

Note that there is no commonly known mullard driver circuit that will adequately drive a pair of 300B due to the 180vpp swings (per tube) required, Mullard didn't make a 300B or equivalent and so did not design a circuit to drive them.

My design is not available in pcb form, but you could make your own using expresspcb.

Note that my design must be used with regulated supplies - its achilles heal.

It's a pretty simple design and if built according to the schematics will work the first time and is not fussy in set up either.

Something in excess of 30Wrms is possible depending on the output transformer chosen.

"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
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Old 25th April 2006, 03:06 PM   #4
vt_229 is offline vt_229  United States
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Default 300b

http://members.myactv.net/~je2a3/JELsc-300BDXPS.jpg power supply
http://members.myactv.net/~je2a3/JELsc-300BDX.jpg amp

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Old 25th April 2006, 05:46 PM   #5
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Old 25th April 2006, 08:29 PM   #6
sklimek is offline sklimek  United States
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Originally posted by space-cake
Hi space-cake,

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Old 25th April 2006, 08:39 PM   #7
phn is offline phn  Sweden
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The Western Electric 91A is perhaps THE classic design. But it is an old design. It lacks some bass. A Shindo owner told me the original design also lacks some detail (probably not the word he used; don't remember) in the highs compared to some of the newer imitators out there.

And you get a solid 10 pct distortion.

Should be loads of information on the 91A out there.
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Old 26th April 2006, 12:38 AM   #8
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thanks for the links everyone!

10% distortion
tube amp or not, that is way too much even if much of that is because of second order harmonics.

i thought that the old designs were kind of good but maybe i was wrong, i guess it was kind of naive of me. up to this point i only saw more modern amps like chip amps and some class D amps and i am kind of used to that kind of setup since they are very easy to put together after the spec. sheet wiring examples

a modern update a classic design might be the best idea... i saw a very nice design on that concept based around EL156 tubes. the design was by gerhard haas and i saw it in some magazine. the problem is that new production EL156 are only made in china and i'm not sure if they enjoy good quality or not and it would be a shame to build such a project and end up with crappy tubes and i don't want to start spending $400 - $1000 a year for NOS tubes. for this reason the 300B looks like a good choice since electro-harmonix makes it in the old reflektor factory in russia and the quality is very good from what i have heard.

so does anyone has some up to date design of 300b based monoblock or maybe i should look for something else? i guess only a directly heated triode for me... by the way how can i search in the archive? that will save me some questions.
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Old 26th April 2006, 12:59 AM   #9
phn is offline phn  Sweden
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Vintage stuff is like everything. You need to be selective.

As somebody mentioned on this forum, some of the shortcomings and sometimes weird stuff in the designs are the result of inadequate instruments. But the engineers working at places like WE and Telefunken knew what they were doing. They knew as much about tubes as Intel knows about microprocessors.

Try this link. Lots of useful info. Vacuum State
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Old 26th April 2006, 02:12 AM   #10
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Default Derek Walton's 300B monos

Hi Space-cake,

First, I would suggest that you save yourself a lot of trouble and inconvenience and look into some of the great kits for sale by companies like DiyHiFi Supply. Ordering all the different parts from several different locations, having the chassis made or making it, and the time that takes really can be a hassle(and more expensive) to get a good looking end result. But,.....

Derek Walton's 300B monoblocks has been one of the most widely known and built over the 5 years or so. He essentially took the ultra famous JE Labs 300B amp and made small improvements. Hundreds of people have successfully built this amp, some of which are fairly repsected amp designers themselves like Joseph Esmilla and James Yeung (see "World Builders" page).

His website provides all the information to make them - full parts list down to the smallest details, step-by-step-instructions, complete schematics for signal circuit and power supply, an exact component layout diagram for chassis cutouts, and pictures to go with each step.

You really can't get a more thorough guide to 300B amp building than this. No guessing, nothign to figure out and the supposedly sound amazing. It also provides an excellent platform.

In his mkII version, he uses higher quality Plitron transformers and power supply filtering.

Here's the original an famous JE Labs 300B schematic:

Click the image to open in full size.

Here's Derek's version:

Signal -

Click the image to open in full size.

Power Supply
Click the image to open in full size.

Top Plate, Parts layout and wiring:

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.
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