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300B SET Design Project
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=2699
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Author:  rock4016 [ 04 Oct 2010, 10:44 ]
Post subject:  Re: 300B SET Design Project

When Pete Millett compared a resistive loaded 6SN7 to a CCS loaded 6SN7 his results showed lower distortion with the CCS load.
http://www.pmillett.com/current_source.htm

What were your 3rd, 5th, 7th and 9th order distortion numbers? What frequencies did you use when testing? What output signal levels?

Author:  mwhouston [ 04 Oct 2010, 16:46 ]
Post subject:  Re: 300B SET Design Project

As you may be aware I asked Matt to design a 300B amp for me as i have a customer who has asked me to build him one. I made few specifications; Basically a two stage SET amp based on a single 6SN7 and a pair of 300Bs with tubes rectification. The only other spec. was it had to produce around 8W.

I maybe old fashioned but currently I'm not mixing SS and tubes together. A diode based PS is acceptable where tube rec. cannot be managed. But I would not go for a CCS based tube amp. I know Bruce and others are building some dream machines using CCSs but for me (as the name suggests - retro-thermionic) I am staying strictly old school with my tube amps.

The tubes for the amp have been ordered and paid for. The 300Bs are TJ Full Music 300B/SE carbon plate and Shuguang 6SN7 Treasure. I would prefer Matt plays it safe with max voltages etc. as these tubes are expensive. I am quite pleased with Matts design philosophy. I am anxious for the final schematic and parts values so I can order them but it was kind of Matt to under-stake the task so I must be patient.

My client insisted on high-end Chinese tubes, being Chinese himself, and has selected Audio Note Silver foil caps as the inter-stage cap. All I need from Matt now is the value of these caps and they can be ordered.

Thanks so far for every-ones posts.

Author:  mwhouston [ 04 Oct 2010, 20:04 ]
Post subject:  Re: 300B SET Design Project

The tubes for the 300B amp arrived. These are TJ Full Music SE carbon plates. I have seen them listed for $US1200. The 6SN7 is a Shuguang 50 year Treasure. Both tubes are matched pairs. 100% matched according to the paper work.

I shook as I took them out of the boxes. The 300Bs are beautiful looking and now I can see why you can get 8 to 10W from a 300B is SE. The plates are massive. I'm still shaking.
Attachment:
300BSE2ss.jpg
Attachment:
300BSEss.jpg

Author:  Suncalc [ 04 Oct 2010, 20:25 ]
Post subject:  Re: 300B SET Design Project

WOW! :shock: Those are some Beautiful tubes!

I'll take extra care with the design for tubes like those.

Author:  Bennybuis [ 05 Oct 2010, 06:49 ]
Post subject:  Re: 300B SET Design Project

Those are beautiful Mark,

haven't had too mach chance to listen to B300, but I am very curious about how you gonna like it compared with your KT88 se.

I have to seize all activity for a while for medical reasons, so I 'll be watching.

All the best,

Author:  mwhouston [ 05 Oct 2010, 07:01 ]
Post subject:  Re: 300B SET Design Project

Get well mate!

The project is a way off yet. Matt is yet to finished the design. Once completed I can order parts. Edcor can take many weeks to deliver.

Funny part is I have to buy some cheap 300Bs to test the amp on (smoke test).

Author:  rock4016 [ 05 Oct 2010, 07:30 ]
Post subject:  Re: 300B SET Design Project

Once you are done with the amp, I'm curious as to how it will sound compared to your other amps.

Author:  mwhouston [ 05 Oct 2010, 16:21 ]
Post subject:  Re: 300B SET Design Project

rock4016 wrote:
Once you are done with the amp, I'm curious as to how it will sound compared to your other amps.

I'm busting to build it. I would never have thought SET amps could sound as good as they do. I'd built lots of SE pentode amps in the past and thought them great. My 6AS7 SET leaves my SE pentodes (even triode strapped) for dead by an order of magnitude.

The 300Bs along with 2A3s, 45s etc. are legendary tubes in SETs. After being shocked how good a SET can sound I'm guessing using a high-end 300B in a SET will take the experience to new heights.

Author:  mwhouston [ 08 Oct 2010, 06:15 ]
Post subject:  Re: 300B SET Design Project

Matt is not far off giving us a final schematic. I had this awfull thought of plugging in these expensive 300Bs, turning on the amp and waching them pop. I need some test 300Bs.

I have orderd some ElectroHarmonix Gold 300Bs. These are still very nice 300Bs and I will tube roll them againts the TJs. They will be the sacrificial lamb when the amp is first turned on. I have lots of 6SN7s so I don't need a sacrifice version of those but he TJs???? Yes.

Author:  Bennybuis [ 08 Oct 2010, 09:01 ]
Post subject:  Re: 300B SET Design Project

Very smart Mate,

I usually trust myself enough to fire up the amp with the good tubes, but those are more expensive than anything I have, behave maybe some 2A3's, but I never tried them. I am very curious about how it will sound.

For the final hum test, I use some vintage headphones with load resistors. The headphones are highly sensitive, 2000 ohm per earpiece, you can listen to AM radio, just with those headphones, a germanium diode and some wire, I am serious, what I wanna say is, they are unforgiving, you hear anything. If I don't heart no noise or hum using those, I consider the amp hum free.

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