Hello all,
I just put out a site with a schematic for a 2A3 stereo amp and its power supply. It is simple and cheap, inasmuch as it only uses one transformer for all power needs.
It can be found here:
http://gabevee.tripod.com/2a3diy.html
Try it out!
Have fun!!
Gabe
I just put out a site with a schematic for a 2A3 stereo amp and its power supply. It is simple and cheap, inasmuch as it only uses one transformer for all power needs.
It can be found here:
http://gabevee.tripod.com/2a3diy.html
Try it out!
Have fun!!
Gabe
The Stereo SE...
Hi Gabevee!
The only sugestion that i can make...is that the shared catode resistor comum to the 2 chanels will introduce same crosstalk and consequent intermodulation in the low frequences...
In my opinion a resistor and the capacitor in each catode will be a improvement for such a small cost as a resistor and a capacitor!
Of corse in this last case the resistor must be doubled in value!
In a push pul amp it could be allright as a shared catode resistor in each chanel
Thanks for sharing!
Jorge
PS..IMHO of course!
Another drawback is if one tube fail or is geting weak the other will be overbiased!
Hi Gabevee!
The only sugestion that i can make...is that the shared catode resistor comum to the 2 chanels will introduce same crosstalk and consequent intermodulation in the low frequences...
In my opinion a resistor and the capacitor in each catode will be a improvement for such a small cost as a resistor and a capacitor!
Of corse in this last case the resistor must be doubled in value!
In a push pul amp it could be allright as a shared catode resistor in each chanel
Thanks for sharing!
Jorge
PS..IMHO of course!
Another drawback is if one tube fail or is geting weak the other will be overbiased!
Tube_Dude,
You would be surprised about the cross talk. I thought so too, but I have built several different types of single ended amps with a common cathode for both channels. There is no cross talk because the bypass capacitor takes care of that.
If there is cross talk, the actual effect will be that of a sort of imaging enhancement, since any audio that gets past the bypass capacitor will be inverted from the other channel. So if anything, a wider soundstage will be the result.
The thing I do not think you are aware of also is that I need to have a common cathode resistor in order to use only one power supply for both 2A3s. To separate the cathode resistors means using two separate 2.5 volt power supplies for the filament of the 2A3s. More cost. No budget.
Thanks for the input!
Gabe
You would be surprised about the cross talk. I thought so too, but I have built several different types of single ended amps with a common cathode for both channels. There is no cross talk because the bypass capacitor takes care of that.
If there is cross talk, the actual effect will be that of a sort of imaging enhancement, since any audio that gets past the bypass capacitor will be inverted from the other channel. So if anything, a wider soundstage will be the result.
The thing I do not think you are aware of also is that I need to have a common cathode resistor in order to use only one power supply for both 2A3s. To separate the cathode resistors means using two separate 2.5 volt power supplies for the filament of the 2A3s. More cost. No budget.
Thanks for the input!
Gabe
The 2A3 Circuit
Since it uses a series filament scheme, I think it would be a good idea to use a non-polarized capacitor for the cathode bypass.
Another issue is the filiment supply. Depending on the filiment filter capacitor, the filiment voltage could rise to 7 volts. (3.5 volts per tube) At 3.5 volts, the 2A3 won't last.
Since it uses a series filament scheme, I think it would be a good idea to use a non-polarized capacitor for the cathode bypass.
Another issue is the filiment supply. Depending on the filiment filter capacitor, the filiment voltage could rise to 7 volts. (3.5 volts per tube) At 3.5 volts, the 2A3 won't last.
Wow cool circuit- simple, logical and looks easy to construct. I will definitely give it a go at some stage, I am just in the process of building a 2a3 amp at the moment, if I am not happy with it I will try your circuit. BTW What is the technical name when the ouput stage is driven from the cathode of the previous stage?
I am curious as to your reason for using DC on the 2A3 filaments- some people say there is a huge difference in sound and AC is better? Is there any difference?
I am curious as to your reason for using DC on the 2A3 filaments- some people say there is a huge difference in sound and AC is better? Is there any difference?
It's an interesting circuit and one I'll be trying out in the future, although in my case I'd use 6B4s and a power supply with multiple 6.3v heater windings, simply because I have these available.
Otherwise, one option for using 6A3s or 6B4s might be to cannibalise old CB power supplies to provide the LT. These supplies, at least in the UK, are often cheap second-hand from the classifieds, junk shops and even eBay, going for as little as £5 ($7.50) and these could provide the innards for stabilised heater supplies for series connected 6B4 tubes (a little fiddling to reduce 13.8v out to 12.6v). This would certainly help keep the amp on a budget, even if it means an extra tranny on the chassis.
Otherwise, one option for using 6A3s or 6B4s might be to cannibalise old CB power supplies to provide the LT. These supplies, at least in the UK, are often cheap second-hand from the classifieds, junk shops and even eBay, going for as little as £5 ($7.50) and these could provide the innards for stabilised heater supplies for series connected 6B4 tubes (a little fiddling to reduce 13.8v out to 12.6v). This would certainly help keep the amp on a budget, even if it means an extra tranny on the chassis.
The famous cathode resistor....
I was talking about shared cathode resistors...but in two diferent chanels...
Two diferent chanels runs diferent signal programs...
If it is used elsewhere....my only coment is:
-like in politics a lie doesn't become true by being repeated to many times.
The only reason for using it is if you can't afford one more resistor and a capacitor....
Jorge
I was talking about shared cathode resistors...but in two diferent chanels...
Two diferent chanels runs diferent signal programs...
If it is used elsewhere....my only coment is:
-like in politics a lie doesn't become true by being repeated to many times.
The only reason for using it is if you can't afford one more resistor and a capacitor....
Jorge
Tube_dude,
There are many circuits, including stereo push pull (and I have a few) that use one cathode resistor for all output tubes, designed by much more qualified engineers than I.
Decware's famous Zen amp uses one cathode for both output channels, AAMOF.
The reason for the use of the common cathode resistor is for fixed bias. For one channel, the tubes of the other channel and the cathode resistor act as a fixed bias. This tends to tighten up bass. Yes, it is cheaper to use the tubes that are already in the circuit that already dissipate the 5-10 watts rather than getting a 20 watt 2K resistor to do the same job. Pure simple techology, not lies.
BTW, I have already run tests and crosstalk is lower than the power supply noise....
As for the other questions from others:
I have listened to my 300B amp with AC, and then changed to DC. No noticable difference, except no hum whatever. Beautiful silence when no music is played. I suspect that the 60 Hz and harmonics are somewhat enhancing some of the music to make it seem to sound better.
I use Hammonds 273JX for power, and One Electron's output transformers.
Valveluver,
I did not see such a transient with my 300B amp. In fact, since cold starting causes the filaments to seem like zero ohms, there should also be almost zero volts. I again suspect the same to be true for the 2A3's.
As for cathode bypass... why non-polar? The cathode bias is in relation to B+.
Gabe
There are many circuits, including stereo push pull (and I have a few) that use one cathode resistor for all output tubes, designed by much more qualified engineers than I.
Decware's famous Zen amp uses one cathode for both output channels, AAMOF.
The reason for the use of the common cathode resistor is for fixed bias. For one channel, the tubes of the other channel and the cathode resistor act as a fixed bias. This tends to tighten up bass. Yes, it is cheaper to use the tubes that are already in the circuit that already dissipate the 5-10 watts rather than getting a 20 watt 2K resistor to do the same job. Pure simple techology, not lies.
BTW, I have already run tests and crosstalk is lower than the power supply noise....
As for the other questions from others:
I have listened to my 300B amp with AC, and then changed to DC. No noticable difference, except no hum whatever. Beautiful silence when no music is played. I suspect that the 60 Hz and harmonics are somewhat enhancing some of the music to make it seem to sound better.
I use Hammonds 273JX for power, and One Electron's output transformers.
Valveluver,
I did not see such a transient with my 300B amp. In fact, since cold starting causes the filaments to seem like zero ohms, there should also be almost zero volts. I again suspect the same to be true for the 2A3's.
As for cathode bypass... why non-polar? The cathode bias is in relation to B+.
Gabe
resistor choice...
Using a resistor in the cathod is for cathod bias...be it one chanel...two or three........
If you say it!...
In one of yours first post you say that the decision of the shared cathod resistor is for reasons of economy not sound quality!
At what frequency??...50 Hz ???
So you like the sound and the project...you are in your right...
But anybody need to agree???
Jorge
Using a resistor in the cathod is for cathod bias...be it one chanel...two or three........
If you say it!...
In one of yours first post you say that the decision of the shared cathod resistor is for reasons of economy not sound quality!
At what frequency??...50 Hz ???
So you like the sound and the project...you are in your right...
But anybody need to agree???
Jorge
The use of a shared supply for both output tubes is for economy. This necessitates the use of one cathode resistor for both tubes. Cathode resistor is for cathode bias, but one can also make it a fixed bias by putting a resistor from B+ to the cathode such that it and the cathode resistor can form a divider. Hence fixed bias.
As for sound quality, you brought that up, so I replied with my experience.
As for crosstalk being in relation to the power supply noise, I was referring to amplitude not frequency.
As for agreeing... I am merely pointing out facts of electronic science. I didn't think that that could be argued or disagreed with. My mistake. I should know better.
Now if I said it sounded spectacular compared with... whatever... then that would be an opinion that no one needs to agree with.
Fdegrove,
No it isn't. I have already done it. I have made the measurements. Again, how can one argue with measured results???
Again, my mistake. So I will let it go here until someone else actually does it and can put in an opinion based on experience.
Gabe
2A3 AMPS.
Hi,
The fact remains that the two channels are only separated by the heater/cathode resisitance.
The same effect can be achieved by connecting two separate channels through some resistance, it may give a pleasing effect but has nothing to do with Hi-Fi.
Sorry to downtalk but facts are facts,
Hi,
The fact remains that the two channels are only separated by the heater/cathode resisitance.
The same effect can be achieved by connecting two separate channels through some resistance, it may give a pleasing effect but has nothing to do with Hi-Fi.
Sorry to downtalk but facts are facts,
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