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Old 10th April 2011, 12:42 AM   #11
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by slav View Post
Hi
What about 300B in parallel , it should give reasonable power to source any speakers ?
Only for speakers that are happy with 15W or less and a still fairly high source impedance.

Possibly you might also want to consider PP 300B amps, they bring most of the virtue of SE 300B to the table with 30W being quite easily obtained on a B+ of 400V with fixed bias.

Tube wise the JJ300B has proven to be a good choice in both SE and PP designs I've done.
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Old 10th April 2011, 02:18 AM   #12
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Originally Posted by kevinkr View Post
Possibly you might also want to consider PP 300B amps, they bring most of the virtue of SE 300B to the table with 30W being quite easily obtained on a B+ of 400V with fixed bias.
You are not equating SET sound with P-P sound, are you?
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Old 10th April 2011, 03:59 AM   #13
Bigun is online now Bigun  Canada
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If you are getting new speakers you may not need to limit yourself to 8W and can still consider a SE amp based on the 2A3. By all accounts the 2A3 looks like a very nice tube. I have a box of 10 of the Russian 6V heater equivalent (6C4C) and plan to build a nice SET with these some day.

Have a look at:

Finally built my 6SL7, 2A3/6A3 amp

New 2A3
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Last edited by Bigun; 10th April 2011 at 04:01 AM.
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Old 10th April 2011, 09:43 AM   #14
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Hi
14-15W would give me more options while choosing speakers, I belive I could play it with 90-92dB as well as with high effieciency speakers .On the top of it I could still run amp. on my Proacs(hardly but still) and patiently look for new set.
I ask differently what brands(models) are worth considering if I built :
1. SE 2A3 (3-4W)
2. SE 300B (7-8W)
3. PSE 300B (14-15W)
PP is out of equation , I want to try pure SE.
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Old 10th April 2011, 03:02 PM   #15
Bigun is online now Bigun  Canada
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I know all the conventional wisdom suggests you need ultra-sensitive speakers if you only have a flea powered tube amp but I haven't found that to be the case when I'm using my single full range driver based speakers. Heck, my current listening set up is a pair of my DIY Martello speakers which are around 85dB sensitivity and my tube amp puts out 1W. OK, I'm not using it for rock music and I do plan to upgrade the speakers to something over 90dB but my point is that it's easy to overestimate how much power you need. Your pro-acs may sound quite fine with 2-3W so long as you don't want to use it for parties.


I measured the voltage swing going into my speakers with an oscilloscope once and was quite shocked how little power normal listening levels require. I read somewhere that to get 'twice as loud' you need a huge increase in power, meaning the difference between 4W and 8W is probably insignificant.

Anyhow, there are people here with far more experience than me, I'm just trying to say that it was my thought that if you have a strong interest in the 2A3 I wouldn't give up that dream for a few watts of power that may just end up heating your room. You'll enjoy the project more if you build what you really want to build not what looks right on paper.

p.s. if cost of tubes is a concern, the Russian 6B4G is an equivalent to the 2A3 except that it's an Octal base and runs off 6V heater (which you'd want to run with dc not ac).

I would google for some further opinions too. e.g.

http://forums.klipsch.com/forums/p/62564/611244.aspx

http://www.6moons.com/audioreviews/fi/mono_2.html
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Last edited by Bigun; 10th April 2011 at 03:24 PM.
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Old 10th April 2011, 03:17 PM   #16
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by Evenharmonics View Post
You are not equating SET sound with P-P sound, are you?
No, but 0fdbk class A 300B PP operation is surprisingly close in some key areas that attract people to SE in the first place. (Mids and highs) The additional power is always welcome and in general the performance is better below 100Hz than is usually the case with bogey 300B SE designs. No question that even loop the linearity is substantially better. My last designs achieved 1% thd @ 25W with no global feedback over a fairly wide (and now forgotten) range of frequencies.

Note that my personal preference is definitely towards fixed bias SE, however I designed a number of PP amps to cater to people who wanted to use speakers of normal efficiency with 300B amplifiers... It's a viable choice in many instances. I'm much less sure about PSE as IMLE they seem not to perform sonically as well in some ways as a single tube SE. (Entirely subjective on my part, nothing I could easily measure, and in the particular case other features of this design might have been responsible. It just seemed not to resolve the way I expected, and at the time I had no bias one way or the other.)
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Last edited by kevinkr; 10th April 2011 at 03:20 PM.
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Old 10th April 2011, 03:44 PM   #17
Bigun is online now Bigun  Canada
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and check out... New 2A3 SET / Simple, but gentle sounding amplifier
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Old 10th April 2011, 04:55 PM   #18
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Ok
Thanks for your input , stupid qestion but very important to me :
which tube 2A3 or 300B for univeral listening ( as I mentioned I listen to almost everything)?
Secondly ,what's your oppinion about interstage transformers in SE design?
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Old 10th April 2011, 06:52 PM   #19
Bigun is online now Bigun  Canada
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From what I have read of the opinions and experiences of others I think both tubes can be used to listen to all types of music. From my own experience I suspect that your speaker choice will probably be more important than the choice between these two tubes.

In fact, I would go another step and say that I believe the circuit topology and choice of components around the tube will also be more important that your choice of which output tube.

I've only ever used RC coupling, not interstage. For reasons of cost. I believe interstage has some advantages over RC coupling providing you use a good quality transformer.
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Last edited by Bigun; 10th April 2011 at 06:59 PM.
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Old 10th April 2011, 08:24 PM   #20
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Thanks
What about PSU tube or solid sate?
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