I have a quad of 2A3 and 6B4G that have the same structure, an "H"
like this:
No type 6B4G Philco NOS amplifier audio radio vacuum tube valve ST shape 6B4 | eBay
I have some US 6B4G: Smoke glass Ken-rad, Smoke glass Tung-sol,
RCA clear glass bi-plate (twin #45 plates); and Sovtek 6B4G.
They all sound different to me.
Sovtek sounds leaner, better top end, some what metallic.
Ken-rad sounds "thick" ... good with vocal, smoke glass Tung-sol sounds grainy, RCA bi-plate is the more balance of all.
fossa,
Thanks for that!
I have posted in more than one thread about how parallel tubes do work very good.
2 plates, 2 grids, 2 filaments in a single envelope . . .
They are in Parallel.
See, I tried to tell others that parallel tubes work very well.
And, they can even be in separate envelopes and work very well too, if the design, circuits, and parts are implemented carefully and properly.
IRMC
Thanks for that!
I have posted in more than one thread about how parallel tubes do work very good.
2 plates, 2 grids, 2 filaments in a single envelope . . .
They are in Parallel.
See, I tried to tell others that parallel tubes work very well.
And, they can even be in separate envelopes and work very well too, if the design, circuits, and parts are implemented carefully and properly.
IRMC
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6a3sUMMER, shouldn't the 2A3 and 300B use different impedance transformers and bias points to more closely optimize each and more closely match the ratio to the ra of the tubes to the load impedance of the speakers?
I am thinking of converting the second board I built from it's current cascode driver to two cascaded common cathode stages like the first board. Then I plan to build a second system using it driving 2A3 tubes with One Electron 4.8K OPT (UBT-3) instead of the One Electron 3K (UBT-2) which are driving the 300B system. The 2A3 would run off lower voltage (250Vak, Ia 60mA) than the 300B.
I have an old Radio Shack speaker select switch which I could wire up backwards to select the amp that is driving the speakers. I plan to place 100R resistors on each amp output to prevent open circuit when not driving the speakers.
Adjust one amp to a nominal listening level, then drive a test tone through it and measure the rms voltage. Switch to the second system and adjust it to match the first.
This of course is not a double blind test, however with a partner one of us could be out of sight performing the switching operation.
The Gimp,
Matching the gain of two different amplifiers, or identical except the output tube, or identical except for the output transformer is quite difficult.
But I had to do that for a seminar I gave at VSAC 2008.
Take just the Left channel out from a CD player. Connect a hard wire splitter adapter, and connect to both amplifiers, and use an identical pair of speakers, one for each amplifier.
Purposely connect one speaker out of phase (reverse the speaker cable connections at the speaker).
Face the speakers to each other, 1 inch away (front to front).
Adjust the gain of the amplifiers until the sound is cancelled (it will null out when the gains are identical). That means the amplifier gains are precisely matched.
Now, properly connect the speaker cable that was out of phase, to get it in phase again.
Face both speakers forward to the listeners.
Then switch the CD signal between one amp and speaker, and the other amp and speaker.
For an even more correct test, use switches to change both the input signal and the speaker to one amp, and then change the input signal and to connect the same speaker to the other amp.
That means the sound does not change position (it is not first going to one speaker, and then to the other speaker).
This is one the factor that I did not think of when I did the seminar at VSAC 2008.
One post in this thread mentioned using the same driver for all 2 output tubes.
That may, or may not, be optimum for each tube type, but it does level the playing field.
1. A 2A3 and 300B in a single ended amplifier that can switch filament supplies, and uses the same plate voltage and plate current, and most importantly that uses one and only one output transformer.
Admittedly, the primary impedance is not optimum for all 2 tube types (Unless you consider the more than 20 combinations of operating plate current, plate voltage, and output transformer primary impedance that are listed in the Western Electric 300B data sheet).
Consider the question:
What is optimum?
2. A 2A3 and 300B in a single ended amplifier that can switch filament supplies, B+ supplies, and uses the 'optimum' plate voltage, plate current, and output transformer primary impedance according to the tube type.
Use different output transformers that have the same set of lamination material, same manufacturer, just different primary impedances.
Anything other than 1, or 2 above is not only comparing the tubes, it is comparing what are totally different output transformers, not just the primary impedance.
Hint:
The 2A3 and 300B should both be able to nicely drive a UBT-3.
And the 2A3 and 300B should both be able to nicely drive a UBT-2.
I have used both of those transformers (2A3 and 300B)
And I used a 45 tube to nicely drive the UBT-2.
Do not worry about exactly 'matching' the ratio of tube plate impedance, ra, to the output transformer primary impedance.
2A3 ra = 800 Ohms
300B ra = 700 Ohms
Pretty close, versus a 3.5k or 4.8k primary.
Happy experimenting, and happy listening.
Matching the gain of two different amplifiers, or identical except the output tube, or identical except for the output transformer is quite difficult.
But I had to do that for a seminar I gave at VSAC 2008.
Take just the Left channel out from a CD player. Connect a hard wire splitter adapter, and connect to both amplifiers, and use an identical pair of speakers, one for each amplifier.
Purposely connect one speaker out of phase (reverse the speaker cable connections at the speaker).
Face the speakers to each other, 1 inch away (front to front).
Adjust the gain of the amplifiers until the sound is cancelled (it will null out when the gains are identical). That means the amplifier gains are precisely matched.
Now, properly connect the speaker cable that was out of phase, to get it in phase again.
Face both speakers forward to the listeners.
Then switch the CD signal between one amp and speaker, and the other amp and speaker.
For an even more correct test, use switches to change both the input signal and the speaker to one amp, and then change the input signal and to connect the same speaker to the other amp.
That means the sound does not change position (it is not first going to one speaker, and then to the other speaker).
This is one the factor that I did not think of when I did the seminar at VSAC 2008.
One post in this thread mentioned using the same driver for all 2 output tubes.
That may, or may not, be optimum for each tube type, but it does level the playing field.
1. A 2A3 and 300B in a single ended amplifier that can switch filament supplies, and uses the same plate voltage and plate current, and most importantly that uses one and only one output transformer.
Admittedly, the primary impedance is not optimum for all 2 tube types (Unless you consider the more than 20 combinations of operating plate current, plate voltage, and output transformer primary impedance that are listed in the Western Electric 300B data sheet).
Consider the question:
What is optimum?
2. A 2A3 and 300B in a single ended amplifier that can switch filament supplies, B+ supplies, and uses the 'optimum' plate voltage, plate current, and output transformer primary impedance according to the tube type.
Use different output transformers that have the same set of lamination material, same manufacturer, just different primary impedances.
Anything other than 1, or 2 above is not only comparing the tubes, it is comparing what are totally different output transformers, not just the primary impedance.
Hint:
The 2A3 and 300B should both be able to nicely drive a UBT-3.
And the 2A3 and 300B should both be able to nicely drive a UBT-2.
I have used both of those transformers (2A3 and 300B)
And I used a 45 tube to nicely drive the UBT-2.
Do not worry about exactly 'matching' the ratio of tube plate impedance, ra, to the output transformer primary impedance.
2A3 ra = 800 Ohms
300B ra = 700 Ohms
Pretty close, versus a 3.5k or 4.8k primary.
Happy experimenting, and happy listening.
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Just a bit of an aside here. I've been trying out different rectifiers in my 6B4G/6C4C PSU and after trying GZ34 Sovtek, 6BY5 and 5U4 the choice is 5U4. No surprise I'm sure. Fuller sound, more body. The GZ34 was a little thinner though clear. The 6BY5 was rather trebly, lighter in the lower mids and bass.
Within the 5U4 range there's a huge choice obviously. Presently I have a Philips in there, sounding nice.
Within the 5U4 range there's a huge choice obviously. Presently I have a Philips in there, sounding nice.
Was this a simple plug and play experiment or did you adjust the PS so that the B+ was the same for each rectifier?
The 5AR4 drops very little voltage, the 6BY5 a bit more and the 5U4 drops quite a bit more. If no adjustments are made, what you're hearing might be related to the different operating points and not necessarily the type of rectifier.
Yes, I adjusted the B+ by sizing the first capacitor. I shoot for 315v using the book 250v, -45v, 60mA. The OPT drops around 20v.
Thanks for the clarification. What size caps were you using with the various rectifiers?
I would not have thought that simply changing the value of the first cap could result in that much change in B+. The data I've seen says the nominal voltage drop of a 5AR4 is 17v while the 5U4G and GA drop 44v and the heavier duty GB version drops 50v. So that's a difference of between 27v and 33v less than a 5AR4.
I have some PSUs that were made for my 300b amps, so there's B+ to spare. They are all CLCRC. If you vary the first cap between 0.1uF and 15uF you get a big change in voltage.
Is there a general and so approximate slope of harmonics for a well designed 2A3 and 300B at 1 Wrms? I would like to understand what is the "too much 2nd harmonic" of the 300B compared to the 2A3.
Thanks
Roberto
Thanks
Roberto
Wrong method applied.
You can taste a great wine in its full bloom with your tongue only. No measurements will help you to understand the differences for tube audio sound as well.
I tasted both and would like to make the statement, that its very hard in a double blindfold test to tell which tube (2A2 or 300B) actually plays music with unknown amps behind a curtain. Both are excellent performers and both have that same tube magic (speaking of old originals and not of replica tubes).
You can taste a great wine in its full bloom with your tongue only. No measurements will help you to understand the differences for tube audio sound as well.
I tasted both and would like to make the statement, that its very hard in a double blindfold test to tell which tube (2A2 or 300B) actually plays music with unknown amps behind a curtain. Both are excellent performers and both have that same tube magic (speaking of old originals and not of replica tubes).
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In general, if you "put" a ruler on harmonics and they are evenly decreasing (from base signal) -at least the first three-, the gain stage probably OK.
Increasing of third harmonic worse to the ear, than second prominence, but both of them shows error (distortion).
Increasing of third harmonic worse to the ear, than second prominence, but both of them shows error (distortion).
Thank you Bernie88 and euro21,
the reason why I'm asking is that I haven't heard any of them yet, and I would like to understand what to chase in setting Tubelab's UNSET (with KT88 and 10% a-g1 plus 40% a-g2 feedback, by now on simulation and then in reality).
On simulations at 1Wrms I get on driver 0.04% 2nd, and others dropping 20dB each; on output 1% 2nd, 0.04% 3rd, 0.003% 4th, etc...
at 10Wrms I get on driver 0.14% 2nd, and others dropping 20dB each; on output 3.5% 2nd, 0.5% 3rd, 0.09% 4th, etc...
So, based on euro21 suggestions, it seems a good starting point to then refine the parameters hearing music and making some measurements.
the reason why I'm asking is that I haven't heard any of them yet, and I would like to understand what to chase in setting Tubelab's UNSET (with KT88 and 10% a-g1 plus 40% a-g2 feedback, by now on simulation and then in reality).
On simulations at 1Wrms I get on driver 0.04% 2nd, and others dropping 20dB each; on output 1% 2nd, 0.04% 3rd, 0.003% 4th, etc...
at 10Wrms I get on driver 0.14% 2nd, and others dropping 20dB each; on output 3.5% 2nd, 0.5% 3rd, 0.09% 4th, etc...
So, based on euro21 suggestions, it seems a good starting point to then refine the parameters hearing music and making some measurements.
In terms of 2a3 versus 300b preference, I've always been a 2a3 person. This is true in the output stage, but what is interesting for me is to hear them both in a DIY preamp. I hear the same difference - the 2a3 is focussed and more dynamic and detailed. The 300b is euphonic and very smooth, very like a bigger version of a 26 tube. However smooth and pleasant it is, it just doesn't excite me. In my preamps I haven't used the 2a3, I've used the Svetlana 6C4C which was modelled on the RCA 2a3 as far as I know. This is an excellent tube, less microphonic in a preamp as well. The 300bs I've tried - an EH and an older 4300 Chinese one - were both microphonic if moved. The 6C4C, or 6B4G which I don't have, are easier to use in terms of a DC filament supply using Rod Coleman regs. I can understand why there are a handful of commercial 300b preamps and no 2a3 ones I know of besides the Line Magnetic AS-133 and some with 2a3 just as output with other input tubes, like the Blazebird Dual Mono and Ming-Da/Meixing. But while it's understandable to use the 300b in a commercial product, it's not the best choice sonically for me.
