2a3 Se Amp With 5k Opt? - diyAudio
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Old 27th August 2003, 03:01 AM   #1
zxx123 is offline zxx123  United States
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Default 2a3 Se Amp With 5k Opt?

I heard that with over 300V B+ voltage, 5K OPT give better sound.
However, I cannot find its plate curve graph in any data sheet.
What do you think?
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Old 27th August 2003, 04:45 AM   #2
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http://www.mif.pg.gda.pl/homepages/frank/ has one.

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Old 27th August 2003, 08:15 AM   #3
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Default ...works for me...

I run my 6B4G PP amp with 11K Ra-a giving 5.5K per leg. It has 275V Va. It my best sounding amp to date.

I have a WAD 2A3 PSE with 1.5k primary giving 3K per valve and 275V Va and it isn't close to the 6B4G PP. (this is not comparing apples with apples. The PSE is a kit design and needs re-working to get it close to the PP. It's not a bad performer for its price)

By going to 5K load you are sacrificing power for more linear performance - so it depends on your speakers and their sensitivity and reactance. It might sound better - might sound worse...

Unfortunately all these changes are system dependent - not just amplifier dependent.

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Old 27th August 2003, 08:48 AM   #4
TG is offline TG  Ukraine
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My 6S4S (Soviet 6B4G) PP amp has Ra-a = 12kOhm at Ua = 350V.
Gives 9.5 W in A1, 15 W in A2.

By increasing both Ra and Ua you get more output power and better speaker damping, but also you change output spectrum - generally decrease low order and increase high order harmonics.

Good luck!
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Old 1st September 2003, 12:01 PM   #5
GAK is offline GAK
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I have made a 2A3 amp with Ra=5K.
It's sounds great and I have test it with 2K5 too.
The frequency responce with 5K was bigger.From 30Hz(2K5) to 20hz(5K) -3db.And from 18KHz to 30Khz!
I'd like to wind an other transformer too with Za=7K!
I'm sure that it'll be better.
All these to get about 2,5Watts with handwinded OPTs (by my own) with 12 primary windings and 12 secondary windings in parallel.Of course with only one tap at 8Ohm.

The tube doesn't look exactly the OPT's primary impedance.According to the speaker character and the OPT and of course the amps' design the tube looks 1/2 or smaller primary impedance.
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