Do you have any way to determine (measure) if it is rolling off on the bass end, given the 124B specs?
I believe that much of what Andy listens to, such as opera, has very little bass so it may not be an issue for him.
And in many types of music the lowest instrument is the bass (upright or guitar). A 4 string bass only goes down to ~40Hz and a 5 string to ~31Hz. So while 20Hz to 20KHz is considered to be full range, in many cases 40Hz to whatever an individual's hearing allows is fine. I suspect many of us can't even hear 15KHz. So my concern would be mostly about the lower registers.
@sser2 With a low frequency spec of 150Hz (not 100Hz), how low would the impedance of the source need to be for the Hammond to play down to 20Hz? . . . . 40Hz? Is there a formula that applies?
And in many types of music the lowest instrument is the bass (upright or guitar). A 4 string bass only goes down to ~40Hz and a 5 string to ~31Hz. So while 20Hz to 20KHz is considered to be full range, in many cases 40Hz to whatever an individual's hearing allows is fine. I suspect many of us can't even hear 15KHz. So my concern would be mostly about the lower registers.
@sser2 With a low frequency spec of 150Hz (not 100Hz), how low would the impedance of the source need to be for the Hammond to play down to 20Hz? . . . . 40Hz? Is there a formula that applies?
FlaCharlie knows me well - this is all true and I listen to a lot of classical music and opera. But I do listen to a lot of jazz, since I was for many years a professional jazz bassist playing a 4 string bass, and around 40hz would be its lowest note. Following the old saying that the cobbler's children have no shoes, the bass is probably less important to me because my ears are tuned to listening to the rest of the band. Add in that my speakers are bookshelf 2-way without a subwoofer and what you get is that I don't feel the loss of extreme bass. I don't have the setup to measure the frequency response either, so regrettably I can't give any direct answer about what the 124B is producing in the lower frequencies. I am familiar with the datasheet FR, as has been pointed out. All I can say is that I like what I'm hearing higher up and the frequencies down to 40hz seem to be coming through, though that doesn't mean the response is flat or flattish. I too would be interested in finding out what the frequency response of the 124B is in this kind of setup. It's a good question, and this isn't a setup it was designed for. It's a cheap solution if in fact the bass response is acceptable, though it may indeed lack deep bass if that's a requirement. There are several alternatives including one or two at the same price point.
It is very simple. If a transformer has primary inductance of, say, 20 H, primary's inductive impedance at 20 Hz = 2pifL= 2×3.14×20×20 = 2.5 kOhms. With a source that has equal output impedance of 2.5 K, 1/2 of the signal voltage will be dropped in the source, and 1/2 will be dropped in transformer's primary. Signal will be reduced 2 times, or -3 dB. If the source impedance is lower, the -3 dB point will also move lower, like this:
At 1.25 K - 10 Hz
At 0.6 K - 5 Hz
At 0.3 K - 2.5 Hz
At 0.15 K - 1.25 Hz.
The Hammond transformer is rated -3 dB at 150 Hz with 10 K source. But as you can see, with standard line source of 600 Ohms, the -3 dB point is 5 Hz.
That has to include the copper resistance. Under your assumptions you won't get far below 10Hz, no matter if the source is zero.
Which is indeed good enough for jazz. In fact few recordings have any significance below 50Hz.
That's true. I explained the principle without going into much detail. Output impedance of a typical source, like CD player, may be very low (few Ohms), but making it lower than DCR of input transformer primary doesn't make sense.
For most audio transformers, primary DCR is in the ballpark of 10% of rated impedance. This means DCR does not considerably influence frequency response - if transformer is used as intended. However, if a 10 K transformer is used with 600 Ohm or lower source, the DCR should be factored into FR calculations.
Lundahl sometimes specifies things with a negative source resistance that compensates for most of the wire resistance.
Thanks for the calculations, guys - I'm unfamiliar with SUTs and transformers in general beyond the basic formulae, so this makes interesting reading. It's looking like my future path in all-DHT amps is going to include a SUT (or maybe a step-up interstage).
Still going through my schematics, here's what I have for 2A3:
And I know this next one is breaking the rules of this post because it has cathodes, and it's not even hi-fi but I thought it was cool and interesting and kind of historical in the sense that 2A3's were once abundant and cheap and a go-to tube. Included because it is transformer coupled and transformer phase inverted. It appears to be an old dobro instrument amplifier that uses 2A3's as the output. I would imagine this to be a good nightclub jazz guitar amplifier (maybe?), warm and clean a la Johnny Smith? Simple, just uses the guitar volume and tone controls, and a field coil speaker (field coil speakers.... another thing that was once cheap and plentiful but today requires a mortgage to buy) very cool. 57 is the same as 6C6 (the tube in the Radiotron application note) but the guitar plays right into the top cap which is the grid. 56 mu is 13.8.
Johnny Smith (famous Misty melody/chord number)
And I know this next one is breaking the rules of this post because it has cathodes, and it's not even hi-fi but I thought it was cool and interesting and kind of historical in the sense that 2A3's were once abundant and cheap and a go-to tube. Included because it is transformer coupled and transformer phase inverted. It appears to be an old dobro instrument amplifier that uses 2A3's as the output. I would imagine this to be a good nightclub jazz guitar amplifier (maybe?), warm and clean a la Johnny Smith? Simple, just uses the guitar volume and tone controls, and a field coil speaker (field coil speakers.... another thing that was once cheap and plentiful but today requires a mortgage to buy) very cool. 57 is the same as 6C6 (the tube in the Radiotron application note) but the guitar plays right into the top cap which is the grid. 56 mu is 13.8.
Johnny Smith (famous Misty melody/chord number)
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Talking of novel circuits when valves were aplenty, I read that the 47 can be wired as a diode, triode, and pentode, allowing one bulb type to build an entire amp and power supply.
No problem, even in a regulated supply. Just be careful in the rectifier mode!! Still needs a reference tho. A 991 from the same era wud do.👍
There is a question I wanted to ask since the start of this thread, but was afraid to ask. I'm not trying to be argumentative, I'm just curious.
What is the advantage of using directly heated valves?
I understand the disadvantages: as the cathode is the heater, you either need to connect all cathodes to each other or you need to make various heater supplies, and you have more hum issues with AC heater supplies than when you use indirectly heated valves.
I know there is one advantage, particularly for battery powered equipment: less heater power for a given type of cathode coating. That's why they were used in portable equipment until transistors took over.
What other advantages are there?
Of course anyone who builds anything with valves, including me, uses obsolete technology, but why restrict oneself to technology that became largely obsolete in the mid-1930's? Or is it just for the hell of it, or out of historical interest, or nostalgia if you are 90+?
What is the advantage of using directly heated valves?
I understand the disadvantages: as the cathode is the heater, you either need to connect all cathodes to each other or you need to make various heater supplies, and you have more hum issues with AC heater supplies than when you use indirectly heated valves.
I know there is one advantage, particularly for battery powered equipment: less heater power for a given type of cathode coating. That's why they were used in portable equipment until transistors took over.
What other advantages are there?
Of course anyone who builds anything with valves, including me, uses obsolete technology, but why restrict oneself to technology that became largely obsolete in the mid-1930's? Or is it just for the hell of it, or out of historical interest, or nostalgia if you are 90+?
What is the advantage of using directly heated valves? That's a fair question to which I can only answer "they sound better". By this I don't mean "they sound the same as indirectly heated valves but a bit more refined". I mean "they don't sound like indirectly heated valves". They have a particular family sound which is mainly in the areas of tone and clarity. Some DHTs are better than others but there is some kind of shared quality which isn't the same as the way indirectly heated valves sound.
As for all the rest of it, the circuits are more demanding since each DHT needs its own filament supply which has to be very clean, and usually needs chokes and/or filament regs like the Rod Coleman reg. Bias can be in conventional cathode bias or in filament bias where there is a small cathode resistor and no need for a bypass. Apart from the filament requirements you can treat them the same.
I don't know about other users but I doubt that the motivation would be "just for the hell of it, or out of historical interest, or nostalgia". I imagine that the motivation is the sound they can produce which isn't historical - it's current technology at its best. Very few of the original tubes are still being made but there are plenty of used ones available to the DIY builder so it's not a problem to build with them.
As for all the rest of it, the circuits are more demanding since each DHT needs its own filament supply which has to be very clean, and usually needs chokes and/or filament regs like the Rod Coleman reg. Bias can be in conventional cathode bias or in filament bias where there is a small cathode resistor and no need for a bypass. Apart from the filament requirements you can treat them the same.
I don't know about other users but I doubt that the motivation would be "just for the hell of it, or out of historical interest, or nostalgia". I imagine that the motivation is the sound they can produce which isn't historical - it's current technology at its best. Very few of the original tubes are still being made but there are plenty of used ones available to the DIY builder so it's not a problem to build with them.
I second Andy's opinion, but our opinions are just that - opinions. We need harder evidence for sonic advantage of direct heating. That would be comparison, in exactly same circuit, under same operating conditions, of closely related DH and IDH tubes, like, for example, 26-27, 47-6F6, 6A3-6A5, 2E24-2E26.
The amplifier that I am working now will allow swapping DH and IDH versions of the same output tube type.
The amplifier that I am working now will allow swapping DH and IDH versions of the same output tube type.
Hi Andy, have you come across the 1E7G - 2 DH pentodes on an octal base.
1E7G
Showing my ignorance a bit here, but looked like a possible driver with both halves in parallel.
Perhaps this will help. Curves from Smoking Amp. 👍
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I tried the 1E7G as an input tube when I had my most recent build breadboarded. Ran it in triode with halves in parallel. The amp is an iSET (inverted SET) using 6N6G output tubes. Details here:
https://www.audiokarma.org/forums/index.php?threads/the-nuance-my-inverted-set-diy-project.990205/
It sounded good overall and the bass was very distinctive and detailed. In the end I used 26s but I plan on trying it again in my currently breadboarded project, which is a directly coupled design. I didn't try it in pentode, I figured it might have too much drive for the 6N6G, which doesn't need much. Next time I'll try both pentode and triode.
I've just built a 10Y stage in filament bias, so I swapped that in to the first stage of my SE 2a3 amp in place of the 2P29L with SUT.
It's better in just about every way - tone, realism, presence. It's very good.
I still like the 2P29L though - it has most of the sound but kind of at 90% of the 10Y. In fact it's closer to the 46 preamp I made, which is very neutral. The 10Y is more towards a lush sound like the 26, but not as warm. I'd say it was a full sound. The 2P29L is leaner. Since I leave my system on 24/7 the 2P29L will stay as my daily amp with the 10Y in reserve, if I have any I haven't sold!
It's better in just about every way - tone, realism, presence. It's very good.
I still like the 2P29L though - it has most of the sound but kind of at 90% of the 10Y. In fact it's closer to the 46 preamp I made, which is very neutral. The 10Y is more towards a lush sound like the 26, but not as warm. I'd say it was a full sound. The 2P29L is leaner. Since I leave my system on 24/7 the 2P29L will stay as my daily amp with the 10Y in reserve, if I have any I haven't sold!