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300B Amplifier Schematic


Brumjam
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My next project is going to be a valve power amplifier and I'm interested in building a circuit that uses 300B valves.  The attached circuit is one that I found over on DIYaudioprojects.  I'll probably use a similar filament supply to the one in my 01A preamp, with Coleman regulators, rather than the one shown here.  The circuit doesn't look overly complex.  Has anyone heard this design or care to comment on it?  Part of me wants to order the Bottlehead 300B Kaiju kit, but I can go DIY, order high quality output transformers and still save a lot of cash instead.

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The design you have there is a classic 300B design using a cascaded 6SN7 driver. It's been around for donkeys years in various guises a-la JE Labs, Walton Audio, Sun Audio etc.

I built a pair of mono blocks using the same driver stage 18 years ago. It's a nice sounding amplifier, but the 6SN7 is nowhere near the ideal driver for a 300B.

I would suggest doing a lot more reading before building anything. If you still decide to build it 'as is' I'd suggest you replace the 5U4G in the power supply with a 5Z3 which is electrically the same rectifier, but much cheaper to buy NOS versions of. If you use the Coleman regulators for the 300b filaments be sure to strictly follow his design rules for the raw power supply.

Edited by Disarmamant
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4 hours ago, Disarmamant said:

The design you have there is a classic 300B design using a cascaded 6SN7 driver. It's been around for donkeys years in various guises a-la JE Labs, Walton Audio, Sun Audio etc.

I built a pair of mono blocks using the same driver stage 18 years ago. It's a nice sounding amplifier, but the 6SN7 is nowhere near the ideal driver for a 300B.

I would suggest doing a lot more reading before building anything. If you still decide to build it 'as is' I'd suggest you replace the 5U4G in the power supply with a 5Z3 which is electrically the same rectifier, but much cheaper to buy NOS versions of. If you use the Coleman regulators for the 300b filaments be sure to strictly follow his design rules for the raw power supply.

Thanks Martin. 

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10 minutes ago, edd9000 said:

I was looking/dribbling over those earlier.

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I would like one of his kits at some point. After the giant horns.

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Cost wise of the Thomas mayer ........ kits ..any idea , spoke to him at munich 2016 very likeable fella indeed.

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1 minute ago, deggie said:

Cost wise of the Thomas mayer ........ kits ..any idea , spoke to him at munich 2016 very likeable fella indeed.

Not sure about his kits, but I think that ultimate 300B of his is in the region of £32k O.o.

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Yep I know his built up amps aren't cheap, ....... kit wise are u able just to purchase the plans.

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1 hour ago, deggie said:

Yep I know his built up amps aren't cheap, ....... kit wise are u able just to purchase the plans.

There are a few schematics on his website.  

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If you already have a 01A preamp you just need a driver and the 300b outputs otherwise you'll have too much amplification. Since you have built the 01A, it should be simple to build a 4P1L stage using the same gyrator. Use Ale's latest design using the BSSH111BK, which will give you enough current, i.e. 25-30mA. 

This will be by far the best sounding option, and also a pretty cheap option. Get the soldering iron out and start licking your lips in anticipation. It will be special.

Frankly, forget 6SN7 and all those indirectly heated tubes. Don't go back to the dark ages.  

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1 hour ago, pmcuk said:

If you already have a 01A preamp you just need a driver and the 300b outputs otherwise you'll have too much amplification. Since you have built the 01A, it should be simple to build a 4P1L stage using the same gyrator. Use Ale's latest design using the BSSH111BK, which will give you enough current, i.e. 25-30mA. 

This will be by far the best sounding option, and also a pretty cheap option. Get the soldering iron out and start licking your lips in anticipation. It will be special.

Frankly, forget 6SN7 and all those indirectly heated tubes. Don't go back to the dark ages.  

Thanks Andy.  I'll have a look on Ale's website.  

4 minutes ago, awkwardbydesign said:

The 01A is pretty dark, actually.  I've had to shine LEDs onto mine to show they are on!

Even my mesh rectifier hardly glows - rubbish!

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