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Old 25th June 2009, 12:42 AM   #1
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Default First Project: 300B SET Monoblocks

Here I am pondering my first electronics project… I know I want to build a stereo amplifier and have investigated T-amps, Gainclones, and tube amps. (I know those first two are probably dirty words in this neck of the diyAudio forums.) Anyway, I have settled upon the idea of building a pair of 300B SET monoblocks. I have read the entire tube safety thread and am aware of the lethal voltages employed and will take the proper precautions. I hold a Comp Sci / EE double major but have spent my career on software although I do dabble in building PCs from components.

I am seeking some of the more experienced builders’ advice on a schematic. I have found various takes on the JE Labs 300B amplifier and it seems to be a simple design that I have read many good things about. Then I searched the diyAudio forums and found several threads that start out with folks stating they want to build this amp that quickly deteriorate into “that schematics no good”, “those parts are lousy”, “change this”, “change that” types of discussions that seem never ending.

Is the JE Labs schematic a good place to start? If not, is there a simple 300B SET amplifier / power supply plan / schematic / kit you would recommend? Are there updates to the JE Labs 300B? Any help, hints, sage advice and schematics would be greatly appreciated.

Thanks,
Martin
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Old 25th June 2009, 01:04 AM   #2
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Default Re: First Project: 300B SET Monoblocks

Quote:
Originally posted by mhconley
Is the JE Labs schematic a good place to start?
This one?

Click the image to open in full size.

Not really.

Quote:
Originally posted by mhconley
If not, is there a simple 300B SET amplifier / power supply plan / schematic / kit you would recommend? Are there updates to the JE Labs 300B? Any help, hints, sage advice and schematics would be greatly appreciated.
There are a lot of things that can be done better. A good place to start that addresses many of these things is http://tubelab.com/TubelabSE.htm
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Old 25th June 2009, 01:16 AM   #3
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That's the schematic...

I've been looking at the 300B DX:

Click the image to open in full size.

Click the image to open in full size.

and this variant:

Click the image to open in full size.

Click the image to open in full size.

Great start...

Martin
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Old 25th June 2009, 02:02 AM   #4
athos56 is offline athos56  United States
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I think the JE labs ones are pretty standard except the 2 stages, I think there are schematics that only use one gain stage, like the WE 91a, or the Angela model 91.

I think there is some discussion about the operating points on the JE lab though, buy multiple cathode resistors to try different operating points.
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Old 25th June 2009, 02:14 AM   #5
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Quote:
Anyway, I have settled upon the idea of building a pair of 300B SET monoblocks.

With all respect, I think this is an unwise decision. You are going spend LOTS of money on a 300B project. IMO, the unfortunate likelyhood of a very costly mistake suggests the thinking be revised.

What sort of speakers are available in your collection, now? Proper mating of speakers and amps goes a long way towards obtaining satisfactory results. SE 300Bs yield approx. 8 W. Speakers whose efficiency is upwards of 94 dB. and whose impedance curve is "flat" are needed.
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Old 25th June 2009, 03:33 AM   #6
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Quote:
Originally posted by Eli Duttman


What sort of speakers are available in your collection, now? Proper mating of speakers and amps goes a long way towards obtaining satisfactory results. SE 300Bs yield approx. 8 W. Speakers whose efficiency is upwards of 94 dB. and whose impedance curve is "flat" are needed.
I understand the costs involved and the low power output. I am looking at building a high efficiency full-range single-driver TL speaker in conjunction with the amps. I have never seen a driver with a "flat" impedance curve, they all have peaks and valleys. Is there some maximum impedance I should stay under?

Martin
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Old 25th June 2009, 04:10 AM   #7
rtsang is offline rtsang  Hong Kong
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Don't discourage anyone buliding a 300B amp.

It seems that it is a ritual to DIY adulthood to build a 300B amp. (Just joking).

As long as the guy understood the cost and the speaker requirement, I think the money is still worth spent.

Build it like a universal SET, esp. with filament and output transformers with multiple taps, than one can later change to a 2A3, 45, 50, PX4 or what ever SET he would like to try.

Quite a bit of fun to try out different output tubes.

He can always sell the tubes that he does not like in eBay to recover part of the cost.
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Old 25th June 2009, 05:21 AM   #8
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Quote:
Originally posted by mhconley
I have never seen a driver with a "flat" impedance curve, they all have peaks and valleys.
Only ones I know if

Click the image to open in full size.
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Old 25th June 2009, 06:20 AM   #9
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Quote:
Originally posted by dsavitsk

Only ones I know if

Click the image to open in full size.
Wow How much do these headphones go for?
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Old 25th June 2009, 06:59 AM   #10
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http://www.headphone.com/guide/by-ma...rado-rs-1i.php
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