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Re: Want to built a 300B PP amp, Kevin please advise

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Louis Sit

(A)

In Reply to: Re: Want to built a 300B PP amp, Kevin please advise posted by KevinC on April 4, 2005 at 13:57:33:

Hi Kelvin,
Thanks for your advices and support.
It would be nice if you can email me your schematic for three variants for my reference. Email: louissit@hotmail.com
Here is my idea:
1. Output - I think 25W should be enough for me
2. Output tube - Use normal but not super 300B like 32B so I can test different tubes easily
3. Size - Monoblock would be nice
4. Driver stage - no idea.....I heard that 2A3 is great, but which sounds better?
5. Transformer - I would use all amorphous core transformers if possible
6. Pre-amp - S&B TX102 or K&K line stage. Will the gain is high enough for S&B TX102?
Sorry for many questions. Look forward to hearing from you soon.
Best regards,
Louis

Follow Ups:

PP 300B monoblock questions - KevinC 10:23:39 04/06/05 (1)
Louis,
The choice of driver tube is a matter of preference and some convenience. I find the 6BX7GT to be nearly the sonic equal in this application to the 2A3. However, the 2A3 is a bit of a pain to use to get that little bit extra. You need a separate filament supply, of course. If it's AC, then the amplifier output noise will suffer to some degree, even if you use "hum pots" to null 60Hz noise. A DC supply will make it quiet, but at a substantial extra parts count.
How much gain you need in the line stage is dependent on your system specifics. From memory, the fully differential/push-pull amplifier has about 23dB of gain with the 6SN7GT/6BX7GT/300B and 1:1 input and interstage transformers. Connecting the input transformer for 1:2 step-up has minimal impact on the sound, but gives an additional 6dB of gain if it's needed. Unless you possess speakers with less than 88dB sensitivity, this should be adequate with any reasonable source to allow you to use either a TX-102 or Raleigh Audio line stage circuit.

Kevin Carter
K&K Audio
www.kandkaudio.com
- Re: PP 300B monoblock questions - Louis Sit 21:11:22 04/06/05 (0)
  Hi Kevin,
  Thanks for your schematic and advice.
  Could you send other two schematics for 2A3-32B and 300B parallel PP amp to me as well? I just want to compare them and decide which one I should make.
  Will LL1671 sounds better than LL1660S/PP in this application? I saw some post said so.
  Are the transformers for 300B filaments from Lundhal? If not, could you provide them for me?
  Best regards,
  Louis

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