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Old 28th December 2014, 12:15 PM   #1
Vidre is offline Vidre  Spain
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Default 2A3 input sensitivity

Hi everybody.
Does anyone know the input sensitivity of an amplifier type Loftin-White 2A3 Single-Ended Triode (with 6SL7)?
Thanks
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Old 28th December 2014, 08:14 PM   #2
THD+N is offline THD+N  United States
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If you use the "original" circuit as a reference and the cathode resistor is bypassed with a cap, then the input sensitivity of the amp will be approximately 1VRMS for 3.5 Watts out at 5% THD+N.

Many factors come into play here, but that is a good estimate based on a few 2A3 amps I have built using a 6SL7 tube as a driver.
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Old 28th December 2014, 11:55 PM   #3
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It is difficult to address your question without a schematic, and I am not attempting to disagree with TDH+N; but, in my estimation, it is difficult to obtain much more than 3 Watts out of a 2A3 into a reasonable OPT impedance...especially in your typical Loftin-White circuit.

Assuming a plate load equal to 200% of the 6SL7's R(p), and a fully bypassed R(k), I'm guesstimating that 1.3 vac input will give you approx 3 Watts into a 3k5 load.

Last edited by dowdylama; 29th December 2014 at 12:13 AM. Reason: corrected spelling
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Old 29th December 2014, 12:05 AM   #4
THD+N is offline THD+N  United States
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Power output will also depend on the output tube used. I am using Sovtek 2A3's and there appear to be very robust (And sound fairly good to me) and you can drive them harder than NOS 2A3's.

Check out the 2A3 schematic I just posted.
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Old 29th December 2014, 11:13 AM   #5
Vidre is offline Vidre  Spain
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I will seek the schematic. Thanks for the replies.
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