From what I understood CD player output (rated 2V at 0dB recording level) is less than 750mV because maximum levels were recorded up to -5dB. From this source level, the least amplification to drive a 55V biassed 2A3 into clipping is 55V*/0.75V = 73.3 times. Right? If OP were using a pre amp or a DAC with 2V output he would need 47V*/2V = 23.5 times amplification. Right? (* noticed differences between schematics shown).
OP describes impressions with several builds which might arrive from differences in harmonic distortion structure or in driver slew rate. Even a resonating PS might colorize music.
If one was to develop an amplifier it would be wise to first choose the topology. I'd go for minimal distortion in the voltage amplification stage, with or without using semi conductors, arriving from either pentode stage or cascaded triodes or a three stage setup. Shown amplifiers are lacking GNF. The use of GNF complicates needed amplification and succes would be dependent of OT quality but should -in theory- result in the least distortion possible. Am I wrong?
Wondering if something like this (see link below .....optimized for 2a3 instead of the 300B) would capture the interest of the OP. Will using a c3g to drive a 2a3 have enough drive? I suppose the c3g has the option of being triode or pentode connected to suit. I don't claim to have any expertise in developing circuits but have always been curious about c3g>2a3
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I see two different ways of looking at the need for swing.
1) 2A3 is a limited output power tube so you want to squeeze all you can from it
2) 2A3 sounds best under certain conditions, where the driver was chosen for optimal subjective sound and you've chosen very sensitive speakers
1) 2A3 is a limited output power tube so you want to squeeze all you can from it
2) 2A3 sounds best under certain conditions, where the driver was chosen for optimal subjective sound and you've chosen very sensitive speakers
I've seen CDs fully clipped at 0 dBfs. Easy enough to confirm, just rip a few of your target selections to wave files and view them in a sound editor.
Well, the OP hasn't posted in this thread for over 2 weeks . . . so . . . ??
FWIW, I've been breadboarding that basic circuit after reading the comments in the link you posted. Somewhere on here, Palustris posted a schematic of a 2A3 version he built using an E180F input tube.
I prefer to use less expensive tubes that are easier to drive, so no 2A3s or 300Bs for me. I've been trying a few different input tubes and plan on trying a few different outputs too. This is the first time I've put together anything that's directly coupled and I'm liking it a lot.
In another thread, the OP mentioned that he's working on a directly coupled circuit too.
DC-coupled is appealing. However, compared to transformer coupling, for the same level of driver distortion, one needs double the B+ voltage, 500 V instead of 250 V. High transconductance driver providing DC bias to 2A3 (run at maximum plate dissipation) is not safe and will require close monitoring of current. The circuit avoids coupling capacitor at the tradeoff of adding driver bypass capacitor.
Actually, he uses diode bias with no electrolytic bypass cap in his 2A3 version. So, again, not an either / or situation. I have no idea about the requirements / limitations of the E180F and the 2A3. I'm using the same basic circuit, which he's been helping me with, but not the same tubes or power supply. I believe he's on vacation and I have no idea if he's monitoring this forum. Here's his schematic:
I'm still putzing around with various input tubes but, while I've been using cathode bias with and without bypass caps on the breadboard, I'm sure that I'll ultimately be using battery grid bias, which also eliminates the need for a bypass cap. Although I may try diode bias too since I've never tried them. Either way, no bypass cap on the driver tube and no electrolytics in the amp.
That looks like a do-able, build-able design, lotsa iron, lotsa fun! And it would be nice to know what the builder thought of the sound it delivered.
The bias point of the E180F looks to have a fairly big influence the operating point of the 2A3 output - and I'm wondering about the indicated operating point of the triode-strapped E180F/6688. With approx 144V anode-to-cathode, the Mullard data (attached) would indicate current of 20mA through the E180F (twice that shown in the schematic?) - which would knock-on to significantly change the bias of the 2A3.
- For the operating conditions shown, the Mullard data indicates cathode bias closer to 1.5V at 144V and 10mA, which could be why the designer chose a series pair of UF5408s to bias the E180F.
- Put another way, stable bias of the E180F is likely to be quite important for this design (diode bias could help) with some juggling and tweaking of resistances in the 2A3 cathode leg to look forward to!!
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Back when these were used for their long-line high bandwidth original gig, they specified them for use with a really big cathode resistor and +9VDC on G1. Easy to assume that they wanted a defined cathode current, so maybe a more controllable transconductance over life. Maybe we should take note.
It does raise the issue for tweaky audio use of connecting things to signal "ground". Such is life.
All good fortune,
Chris
It does raise the issue for tweaky audio use of connecting things to signal "ground". Such is life.
All good fortune,
Chris
If you use "hybrid" biasing (cathode bias with larger resistor + elevated grid voltage), and driver tube anode voltage mostly stable (for example "gyrator" loading), the grid voltage drifting has little effect on power tube anode current.
In this sample +/- 5V drift causes only -about- +/- 1mA current change.
We should be very careful here to define exactly which currents we are talking about. The transconductance of the driving valve is sensitive to its cathode current, but if its current is well controlled, gain is also well controlled, and output DC voltage (significant in DC coupled designs) is also well controlled - in an ideal case a constant current into a simple resistor gives a simple voltage.
So maybe here especially we must divorce the issues of DC voltages to the output valves from the DC voltage requirements of the driving valves. Step 1: choose a driving valve and its configuration. Step 2: add an output valve of mu=3.5 (or whatever). Step 3: make the DC voltages add up. Step 4: find a younger friend, not on the wagon, and buy him or her a beer. Done deal.
The amazingly great thing about 2A3 amplifiers is that nobody, in the history of the World, has ever been disappointed building one. Live large.
All good fortune,
Chris
So maybe here especially we must divorce the issues of DC voltages to the output valves from the DC voltage requirements of the driving valves. Step 1: choose a driving valve and its configuration. Step 2: add an output valve of mu=3.5 (or whatever). Step 3: make the DC voltages add up. Step 4: find a younger friend, not on the wagon, and buy him or her a beer. Done deal.
The amazingly great thing about 2A3 amplifiers is that nobody, in the history of the World, has ever been disappointed building one. Live large.
All good fortune,
Chris
We were talking previously about a 3 stage SE 2a3 amp using 10Y as driver tube, and I've now hooked this up and am listening to it. Just to explain, my daily 2a3 amp is just a 2 stage with various 6J5 varieties as input tube, my personal choice being CV6 which is my reference.
So in search of a good 3 stage design I used the 2P29L as input tube and played around with some driver tubes, 4 in all. I listened to my usual selection of demo tracks on all four. Each stage had a resistor load, FT-2 teflon output caps and cathode bias with a DC Link bypass cap. The only exception was the 2P29L which was in filament bias with resistor load and FT-2 cap.
2P29L > 1626 > 2a3. This was the least successful. The 1626 sounded rather flat and I was not getting the presence and holographic quality I am used to. Tone and timbre was nothing special. Not a bad tube, but this 3 stage was not as good as plain CV6 into 2a3.
2P29L > 6AH4 > 2a3. This was quite good. The 6AH4 had better mids and treble than the 1626 and had more presence. However, the total 3 stage sound was not better than the plain CV6 into 2a3, which was cleaner. Not a huge difference but I would stay with the CV6.
2P29L > 10Y > 2a3. Now this was in most ways better than the 2 stage CV6 version. Tone and timbre were definitely improved and a level up from the previous indirectly heated driver tubes. The only way in which the CV6 version was better was just in being slightly cleaner, but the improvement in tone and overall presence would swing the choice to this all-DHT version. The downside is that it's a lot more complex and expensive. All my DHT builds have robust filament supplies with chokes and Rod Coleman regs, and this represents a lot of real estate. Is it worth building a 3 stage version? Yes if the last ounce of quality means everything. Frankly I'll go back to the CV6 for my daily amp. I did also try 2P29L directly into 2a3, and while it didn't have the gain required it was a very nice sound.
I'm fond of the CV6 and I also tried 2P29L into CV6 as a 3 stage amp. This is better with a voltage divider in front of the CV6 to reduce the gain as a driver tube. And in this configuration it was a little better than using the 6AH4. The CV6 is only one of many versions of the 6J5, and of course a good 6SN7 can be used instead. The CV6 has 2 top caps so it's a bit of a pain to use, but it is what it is. There are a few nice versions of the 6J5 without top caps.
So I've finally tried the versions of 2a3 I wanted to try. I don't have a 46 stage to try - it's out on loan - but that could replace either the 2P29L or the 10Y. I will listen some more to the 2P29L > 10Y > 2a3 today just for the pleasure of the tone it has. But after that I'll put the CV6 back. The 10Y stage is already sold so I'll be packing it up and saying goodbye to it. All in all, an interesting day's listening.
So in search of a good 3 stage design I used the 2P29L as input tube and played around with some driver tubes, 4 in all. I listened to my usual selection of demo tracks on all four. Each stage had a resistor load, FT-2 teflon output caps and cathode bias with a DC Link bypass cap. The only exception was the 2P29L which was in filament bias with resistor load and FT-2 cap.
2P29L > 1626 > 2a3. This was the least successful. The 1626 sounded rather flat and I was not getting the presence and holographic quality I am used to. Tone and timbre was nothing special. Not a bad tube, but this 3 stage was not as good as plain CV6 into 2a3.
2P29L > 6AH4 > 2a3. This was quite good. The 6AH4 had better mids and treble than the 1626 and had more presence. However, the total 3 stage sound was not better than the plain CV6 into 2a3, which was cleaner. Not a huge difference but I would stay with the CV6.
2P29L > 10Y > 2a3. Now this was in most ways better than the 2 stage CV6 version. Tone and timbre were definitely improved and a level up from the previous indirectly heated driver tubes. The only way in which the CV6 version was better was just in being slightly cleaner, but the improvement in tone and overall presence would swing the choice to this all-DHT version. The downside is that it's a lot more complex and expensive. All my DHT builds have robust filament supplies with chokes and Rod Coleman regs, and this represents a lot of real estate. Is it worth building a 3 stage version? Yes if the last ounce of quality means everything. Frankly I'll go back to the CV6 for my daily amp. I did also try 2P29L directly into 2a3, and while it didn't have the gain required it was a very nice sound.
I'm fond of the CV6 and I also tried 2P29L into CV6 as a 3 stage amp. This is better with a voltage divider in front of the CV6 to reduce the gain as a driver tube. And in this configuration it was a little better than using the 6AH4. The CV6 is only one of many versions of the 6J5, and of course a good 6SN7 can be used instead. The CV6 has 2 top caps so it's a bit of a pain to use, but it is what it is. There are a few nice versions of the 6J5 without top caps.
So I've finally tried the versions of 2a3 I wanted to try. I don't have a 46 stage to try - it's out on loan - but that could replace either the 2P29L or the 10Y. I will listen some more to the 2P29L > 10Y > 2a3 today just for the pleasure of the tone it has. But after that I'll put the CV6 back. The 10Y stage is already sold so I'll be packing it up and saying goodbye to it. All in all, an interesting day's listening.
Update to the above - the 2P29L > 10Y > 2a3 is sounding really good the more I listen to it. There's no doubt that an all-DHT amp is something special. Vocals and piano in particular are totally seductive, but it's all good.
A simpler version from the point of view of building it would be 2P29L > 2P29L > 2a3. The filament supplies are much smaller and simpler, even in filament bias. I'm tempted by that, I must say. Don't know how it would sound. I'll have to build another 2P29L stage and find out! I could even use an 01A in the first stage - that would be nice.
A simpler version from the point of view of building it would be 2P29L > 2P29L > 2a3. The filament supplies are much smaller and simpler, even in filament bias. I'm tempted by that, I must say. Don't know how it would sound. I'll have to build another 2P29L stage and find out! I could even use an 01A in the first stage - that would be nice.
Bias stability of high transconductance tubes isn't a problem in a capacitor- or transformer-coupled stage. But if 2A3 bias depends on stable plate voltage of DC-coupled driver tube, it IS a problem.
Andy - what is your operation point for 6J5 or CV6? There are many different versions of these tubes, and other tubes with mu of about 20, that are worth trying.
6SN7 or 6CG7 have higher plate dissipation than 6J5, so they can be run hotter, which may result in improvement. Have to use only one section.
Andy
You mentioned the 46 as driver in a 3 stage SE amp - have you looked at using the type 59, an idh valve of similar periid and design. And, as you like dh triodes as 1st stage, might I suggest the MOV HD24......a dh triode...
You mentioned the 46 as driver in a 3 stage SE amp - have you looked at using the type 59, an idh valve of similar periid and design. And, as you like dh triodes as 1st stage, might I suggest the MOV HD24......a dh triode...
Here is another suggestion for all-DHT 3-stage. 1J29B triode-connected input. 150 V, 8 mA, mu=10, Rp=4K. Heater is only 30 mA 2.4 V, so can be run from a pair of D-size rechargeable NiCd batteries, which also provide bias. Driver is 45, choke loaded, running off full B+. This way need only 2 filament regulators per channel.
To answer the questions. Operating point for the CV6 is 34K anode resistor, 330R cathode resistor bypassed with a 40uF DC Link cap. 102V, 6.3mA, -2.1V. B+ is 320V.
I wouldn't use a 59 - don't have any. I don't have any HD24 either, but I love European radio valves and have quite a collection of REN904 types, AC2 types, TDD4 and many others. So good call there. Radio valves of that era were really good and very little talked about here. Lots of triodes with a mu of 30-ish. TDD4 is a favourite. The 1J29B is intriguing, but I already have a big stock of 2P29L and it's quite easy to use.
I took the 10Y stage out and put the 6AH4 stage back. It's a good tube and allows me to use the 2P29L on the input so I'll try that out for a while. The 6J5 as a driver tube after the 2P29L would have to have a plate choke, but I have a nice amorphous pair so I'll try that as well.
I wouldn't use a 59 - don't have any. I don't have any HD24 either, but I love European radio valves and have quite a collection of REN904 types, AC2 types, TDD4 and many others. So good call there. Radio valves of that era were really good and very little talked about here. Lots of triodes with a mu of 30-ish. TDD4 is a favourite. The 1J29B is intriguing, but I already have a big stock of 2P29L and it's quite easy to use.
I took the 10Y stage out and put the 6AH4 stage back. It's a good tube and allows me to use the 2P29L on the input so I'll try that out for a while. The 6J5 as a driver tube after the 2P29L would have to have a plate choke, but I have a nice amorphous pair so I'll try that as well.