Sorry for my crude hand drawing - I am posting from my cell phone.
The input is 10-step autotransformer attenuator, followed by transformer phase splitter. The 3D6s are independently biased by Li-ion cells whose voltage can be finely adjusted from 3.2 to 4.0 V. 3D6 filaments (connected parallel) are powered by a NiMH cell, which is automatically recharged when the amplifier is off (charger and it's connection are not shown). Filament battery switch is ganged with power switch. The choke between primary CT and B+ serves as CCS, ensuring strict Class A differential operation. The choke is sectionally wound (to reduce winding capacitance) on 2-bobbin nanocrystalline C-core; it is a custom job. Solid state CCS can be used instead, but choke sounds better. Depending on the source signal level, the output power is 50-100 mW. The amplifier is intended for the Sennheiser HD650 phones.
The input is 10-step autotransformer attenuator, followed by transformer phase splitter. The 3D6s are independently biased by Li-ion cells whose voltage can be finely adjusted from 3.2 to 4.0 V. 3D6 filaments (connected parallel) are powered by a NiMH cell, which is automatically recharged when the amplifier is off (charger and it's connection are not shown). Filament battery switch is ganged with power switch. The choke between primary CT and B+ serves as CCS, ensuring strict Class A differential operation. The choke is sectionally wound (to reduce winding capacitance) on 2-bobbin nanocrystalline C-core; it is a custom job. Solid state CCS can be used instead, but choke sounds better. Depending on the source signal level, the output power is 50-100 mW. The amplifier is intended for the Sennheiser HD650 phones.
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Because they are directly heated, dirt cheap, and sound really good. You've been asking about good-sounding low power tubes, didn't you?
Yes, I have built it, as well as the 1P24B version of the same circuit. No noise or microphonics.
Not sure but I think the 3D6/1299 was designed for Radiosondes. So needs low microphonics, helps with audio quality.🙂
I'd not heard of the tube until now, but it looks some what between the capabilities of the russian rod pentodes, 1J29B and 1P24B.
The former, I have used single ended and got more than 50mW out of a single triode wired tube. (I also use HD650 😉 )
I reckon 100mW is easily possible with the same tube in push pull.
This from something with filament current of only 60mA or so per tube.
Gain is quite low in my case, about 7 V/V, when triode wired.
I
definitely needed another gain stage, you may not (I used Local FB, if I recall correctly gain was about 10 V/V open loop)
With a tube with more dissipation, like the 3D6, then I think it could work, but you may need some feedback to get a good bass response, at a guess.
The former, I have used single ended and got more than 50mW out of a single triode wired tube. (I also use HD650 😉 )
I reckon 100mW is easily possible with the same tube in push pull.
This from something with filament current of only 60mA or so per tube.
Gain is quite low in my case, about 7 V/V, when triode wired.
I
definitely needed another gain stage, you may not (I used Local FB, if I recall correctly gain was about 10 V/V open loop)
With a tube with more dissipation, like the 3D6, then I think it could work, but you may need some feedback to get a good bass response, at a guess.
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Yes, I am interested in such semiconductors, and 3D6 at this time still did not fall into my vision. But as I understand it, this field is not plowed, there are thousands of models not known to the wide world, spoiled by many watts of power.
Yes, 1J29B is on my list too as low power output tube. There is also 1J24B - not good for power, but excellent medium mu gain stage tube. Two in parallel have Rp of 7.5 k at only 2 mA Ik, and mu of 20! Quite linear too as triode. A unique medium mu tube well suitable for interstage transformer coupling, with such low Rp at such low current. Something to consider if you want extra gain stage.
I am trying to avoid feedback. In my circuit, no feedback is necessary for good bass: transformers have enough inductance so that there is no roll-off at lowest frequencies, and I mostly listen to music that does not need bass boost. Open loop distortion is lower than in equivalent SE. The amplifier sounds like SE, but in a way better because it does not have the high level of 2nd harmonic. The keys to good PP sound are high quality phase-splitting transformer and truly differential Class A operation, in addition to the merits of 3D6 tubes.
Hi,
My small headphone stage uses 1J24B gain stage, and 1J29B output stage.
Triode wired, CCS anode loaded and gain is a little more than 12 V/V open loop (1J24B), and 10 V/V (1J29B).
Getting output impedance low is a challenge, where the 3D6 might do better. The output stage is run at about 6mA, gain stage at <1mA
Yes as triodes both the 1J24 and 1J29 are really quite linear, especially if you bump up the HT and run with about 150V on the plate
My small headphone stage uses 1J24B gain stage, and 1J29B output stage.
Triode wired, CCS anode loaded and gain is a little more than 12 V/V open loop (1J24B), and 10 V/V (1J29B).
Getting output impedance low is a challenge, where the 3D6 might do better. The output stage is run at about 6mA, gain stage at <1mA
Yes as triodes both the 1J24 and 1J29 are really quite linear, especially if you bump up the HT and run with about 150V on the plate
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60 H at 40 mA DC, as measured at 60 Hz. Regular iron choke will not work alone because its inductance will collapse above 400 - 500 Hz. A series 3 - 5 H ferrite core choke should solve this problem.
Hi sser2 and everyone,
Could 3D6 be used in a two-stage amp with another DH tube (let’s say 1J24 or maybe 3A5) in the first stage?
Thank you very much!
Could 3D6 be used in a two-stage amp with another DH tube (let’s say 1J24 or maybe 3A5) in the first stage?
Thank you very much!
For the really adventurous how about PP 3D6s in Class AB2 Triode or UL, IT driven by another 3D6 in triode.
Still need a front end loctal with some gain, I'll have a look. Run the 3D6s with filament heaters in parallel.
I did something similar about 20 yrs ago with PP 33s in Class AB2. The first watt is Class A.
About 4.5 Watts all out, its got some head room & sounds good.👍
Any of these concoctions will sound as good as your best speaker system.
If your amp is running properly, that will be the limiting factor. And no boutique parts required. 😀
Still need a front end loctal with some gain, I'll have a look. Run the 3D6s with filament heaters in parallel.
I did something similar about 20 yrs ago with PP 33s in Class AB2. The first watt is Class A.
About 4.5 Watts all out, its got some head room & sounds good.👍
Any of these concoctions will sound as good as your best speaker system.
If your amp is running properly, that will be the limiting factor. And no boutique parts required. 😀
In my original schematic, there is no need for voltage amplifying/driver stage - if the source is CD player. But it may be needed with a low output source, like some phono preamps.
1J24B is not suitable as driver for triode-connected 3D6. 1J24B has maximum DC cathode current of only 1.6 mA. 3A5 would be Ok.