Hi All,
Over the years, JE Labs (via Angela Instrument) has published several versions of his simple 2A3, 2A3/45 schematic.
I didn't take my decision at this moment, that's why i'd like to know wich of all those versions is/are your favorite.
Thanks in advance for your useful inputs !
Over the years, JE Labs (via Angela Instrument) has published several versions of his simple 2A3, 2A3/45 schematic.
I didn't take my decision at this moment, that's why i'd like to know wich of all those versions is/are your favorite.
Thanks in advance for your useful inputs !
My schematic of SE2A3 RCA:
https://picasaweb.google.com/109570777566485968551/KVM#5413313827582447474
Now plate res. 33 kom is 15 kom and 12 kohm is 3 kom.
Regards!
https://picasaweb.google.com/109570777566485968551/KVM#5413313827582447474
Now plate res. 33 kom is 15 kom and 12 kohm is 3 kom.
Regards!
There is a mistake in that schematic: the 20 ohm resistors that are in series with the hum pot are incorrectly drawn. Each 20 ohm resistor should be in parallel with half the pot. In other words one end goes to the 2A3 filament as drawn but the other end goes to the wiper of the pot, e.g. to the cathode resistor. The way the schematic is drawn all of the current for the 2A3 goes through the wiper of the pot. This will, over time, degrade the pot, but more important will add noise and distortion to the amp.
The noise is abs. zero in 96 dB speakers, now 20 ohm /I tried both variants 2 years ago/ are disconnected. With them or without - never mind. My poti is not from carbon, but from wire - /I don't know how is in English, sorry/ - I hope - eternal. Cathode resistors are Mills - 12 W. All cathode shunts are Black Gate. The sound is amazing, with great bass, band is wider than 20-30000 Hz with amplitude +- 0 Db, measuring with generator and scope. 125FSE with current 55 ma works great.
And E180F in triode is my favorite!
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I really don't care how you wire up your amp.
I am just noting for general reference and for others that see the schematic: the schematic is drawn incorrectly. Those two resistors are there for a reason and best engineering practice would be to use them correctly.
I am just noting for general reference and for others that see the schematic: the schematic is drawn incorrectly. Those two resistors are there for a reason and best engineering practice would be to use them correctly.
There is nothing incorrect to connect serial and increase poti with 40 ohms. I haven't problem with hizzzz, hmmm and I don't need to use some schematic to wiring added R-R to stop problem that I haven't. 2A3RCA is not hummming tube. /You think acc. Your problems with DHT and how to decrease them. You see R-R for another reason and You are right/. This is my schematic and I decide my problems. If some is not good acc. my criteria, I will ask Google or skill of word guru.
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Why the strange input arrangement with 2.2 Kohm pot ? Also B+ looks little on low side at 270V which would give 225V on anode .And before you jump on me I'm just asking to learn not to play a smart **** :0)
Regards, L
Regards, L
The first single-ended amplifier I ever built - 1995? - was based on the original Radiotron schematic
http://2.bp.blogspot.com/-P0IGwEGoYMA/UB4TAxzuVUI/AAAAAAAACe4/1XlkyCH3Dfg/s1600/RadiotronSE2A3.jpg
I would recalc the capacitor values, both bypass and coupling. I would also replace the 1M pot with something like a 50K. 6J7 and company can be used instead of the 6C6.
http://2.bp.blogspot.com/-P0IGwEGoYMA/UB4TAxzuVUI/AAAAAAAACe4/1XlkyCH3Dfg/s1600/RadiotronSE2A3.jpg
I would recalc the capacitor values, both bypass and coupling. I would also replace the 1M pot with something like a 50K. 6J7 and company can be used instead of the 6C6.
2.2 kom is correct for using CD player with low output resistance, like new kinds.
If poti is 50 -100 kohm and if middle point of poti is in low position, the upper part will be big resistance for input signal in some moments with low level and dynamic and You will sense it decreasing. I use poti about 2-10 kohm, no more.
+U 225-230 v will provide plate dissipation about 13 wt, instead max. 15. I can increase I plate, but sound is very good in this area of data sheet about I, U and P. More I gave me little bit tense sound from my 96 dB Fostex. I used Russian 2A3 and they need really more I and +U for good sound.
This mode of RCA 2A3 is very suitable for amazing sounding. If You will try different tubes, You will notice the different of modes. Really proof is direct listening, bot no explaining.
If poti is 50 -100 kohm and if middle point of poti is in low position, the upper part will be big resistance for input signal in some moments with low level and dynamic and You will sense it decreasing. I use poti about 2-10 kohm, no more.
+U 225-230 v will provide plate dissipation about 13 wt, instead max. 15. I can increase I plate, but sound is very good in this area of data sheet about I, U and P. More I gave me little bit tense sound from my 96 dB Fostex. I used Russian 2A3 and they need really more I and +U for good sound.
This mode of RCA 2A3 is very suitable for amazing sounding. If You will try different tubes, You will notice the different of modes. Really proof is direct listening, bot no explaining.
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Oh , OK . I just got RCA 2A3 and 5K output transformers but will have to live with ~320 B+
I assume I can drop D3A in without issues ? Also , expensive BG caps for bypasses so why cheap Wima 0.47 for coupling ?
Regards, L
PS Never liked any fostex (except expensive 500 MkII tweeters 😉 -go Lowther if you must have yellow drivers
I assume I can drop D3A in without issues ? Also , expensive BG caps for bypasses so why cheap Wima 0.47 for coupling ?
Regards, L
PS Never liked any fostex (except expensive 500 MkII tweeters 😉 -go Lowther if you must have yellow drivers
I use my Fostex in horne /about 100 pounds each🙂/...I tried in boxes, but sound was insufficient for me.🙂
If You will use on tube rectifier 320vAC, You will have +U about 350 v /with switched on ampl./ After OT - 340 - 345 v, IMO. If tube will be with auto bias and I plate about 55-60 ma, U cathode = 45 - 49 v on resistor 820 ohm /If You use res. about 700 ohm with 55 ma, Your +U on the tube will increase/. On the tube You will have about 290 - 300 v. The plate dissipation will be 16-18 W, that is very high.
Or You can decrease I plate less 50 ma, that lead to dry and blurred sound. Using buffering power resistor in PS is not very good idea....
But You will decide....🙂
Good luck!
If You will use on tube rectifier 320vAC, You will have +U about 350 v /with switched on ampl./ After OT - 340 - 345 v, IMO. If tube will be with auto bias and I plate about 55-60 ma, U cathode = 45 - 49 v on resistor 820 ohm /If You use res. about 700 ohm with 55 ma, Your +U on the tube will increase/. On the tube You will have about 290 - 300 v. The plate dissipation will be 16-18 W, that is very high.
Or You can decrease I plate less 50 ma, that lead to dry and blurred sound. Using buffering power resistor in PS is not very good idea....
But You will decide....🙂
Good luck!
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For what it's worth, I really like the sound of the JJ 2A3-40 and they should have no issue with 16-18w Pd. Of course, they are a bit more expensive than other new 2A3's, but not terribly.
Maybe I have some inaccuracy in my calculation? LIMONO can check, when hi build his amplifier😎....2A3-40 is another beer....
Limono....today I checked plate graphics and plate U of my 2A3....Sorry, mistake in drawing ....270v is on the tube, but not +U, that is 316v. Maybe 2 years ago I measured and incorrect notice in the schematic. Now all modes, incl. E180F, are in their places.😱
Not all 2A3's are the same. I have tried many types over the years and although measurements for identical operating condition might be similar and in some cases exactly the same the sound is different!
The closest types to the original RCA (double plate) are the Chinese Golden Dragon and Billington Gold. These both have gold plated grid. They bias and sound remarkably the same if well selected.
The Russian 6C4C does not appear to have gold plated grid and this could be the reason why in "classic" simple amplifiers, where the driver is RC coupled, it performs best at 300-320V with 55-60 mA 3-3.5K impedance instead of the typical 2.5K. No problem with 18W plate dissipation.
The Electro Harmonix, other silmilar Chinese designs and the JJ are not precisely 2A3's.
The Electro Harmonix has a gold plated grid but it doesn't bias exactly as a true 2A3 double plate. Typically it needs a bit more anode voltage for 43.5V bias (with DC filament supply) at 60 mA current otherwise for 250V/60 mA the average bias voltage is 42V (with DC filament supply). A similar thing happens for the JJ 2A3-40 which I would think more like a 300B with 2.5V filament.
The closest types to the original RCA (double plate) are the Chinese Golden Dragon and Billington Gold. These both have gold plated grid. They bias and sound remarkably the same if well selected.
The Russian 6C4C does not appear to have gold plated grid and this could be the reason why in "classic" simple amplifiers, where the driver is RC coupled, it performs best at 300-320V with 55-60 mA 3-3.5K impedance instead of the typical 2.5K. No problem with 18W plate dissipation.
The Electro Harmonix, other silmilar Chinese designs and the JJ are not precisely 2A3's.
The Electro Harmonix has a gold plated grid but it doesn't bias exactly as a true 2A3 double plate. Typically it needs a bit more anode voltage for 43.5V bias (with DC filament supply) at 60 mA current otherwise for 250V/60 mA the average bias voltage is 42V (with DC filament supply). A similar thing happens for the JJ 2A3-40 which I would think more like a 300B with 2.5V filament.
Aren't the new single plate (such as the affordable JJ 2A3-40) an improvement (More like a 45) sonically over the double plate (even NOS)? NOS single plate are too rare and so $.
They are more like a 300B. Sonic improvement? The result always depends on the design of the amplifier. A device alone doesn't sound. Nothing in common with a 45, anyway.
The KR 2A3 is a replica of the original single plate. The Emission Lab is as well but with increased headroom. They are expensive but I think they are a much better investment in comparison to very old single plate 2A3's....
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