I recently acquired a pair of nice SE Lundahl LL2765 (60 ma version) and have been trying to find a good headphone amp schematic to use with them. They are 5K primary and 32/300/600 ohm taps. I will be using these with 300 and 600 ohm headphones. I was originally thinking of 45 tubes or maybe even 112a.
I’m planning to build a 6c45p spud headphone amp soon - slowly acquiring the parts. I like the idea of Brian Clark’s El Spuddo described here: Any good flea-watt SET designs?
The input transformer and cathode pot looks like a nice way of handling variations in tubes.
The input transformer and cathode pot looks like a nice way of handling variations in tubes.
45 or 2a3
with those irons it will blow your socks off 
(let´s hope no low quality h-p will be hooked on)
5k with 2a3 will be well damped, i´d try even a no global fb
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https://frank.pocnet.net/sheets/021/1/112A.pdf
https://frank.pocnet.net/sheets/021/7/71A.pdf
12a has ideally gain 8.5, when resistor loaded it will be less.
total ideal gain could be 25.5x; opt ratio like 3:1
best case gain will be 8.5x including opt.
line out is about 0.3vrms, output will be 2.55vrms
https://frank.pocnet.net/sheets/021/7/71A.pdf
12a has ideally gain 8.5, when resistor loaded it will be less.
total ideal gain could be 25.5x; opt ratio like 3:1
best case gain will be 8.5x including opt.
line out is about 0.3vrms, output will be 2.55vrms
So, I decided to go ahead with the 71a for the outputs, I just cant decide on the driver. So far I have 300v choke loaded into a salas shunt reg (K&K audio version, one for each channel), which will be adjusted for 220v at the plate of the 71a, then a dropper resistor for the voltage to my driver tube, which will be choke loaded with two Hammond 156c chokes. For filament I am using separate DC filament supplies for each 71a and the driver tube will also be DC, but will share one board (series connected). I am leaning toward the 112a due to the low filament current and I have a bunch of them. I also have 26,01a, and 27/56 globes. I will probably run my headphones off the 300 ohm tap (currently use HD650 and DT990 600 ohm version) since Lundahl only gives the option to use one tap at a time.
Also, I have the power supply in a separate chassis and all of the regulation is in the signal chassis.
Also, I have the power supply in a separate chassis and all of the regulation is in the signal chassis.
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if you search the ebay, you can see some µ30 dht; but not all cheap.
here you go, you can thank me later.
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did you consider firmer, better supply? like gas rectifiers...?
humpots are missing, i think you will need fight hum.
i use chines switching suplies, it goes good.
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i am using these no prob, but the 2a3 ones needs some fan on it.
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I would strongly recommend selecting a driver tube that is quiet and has a decent amount of gain. I do not believe this is the 112.
If you select a quiet, high-ish gain driver tube (think a mu of 30 or more), then you will have the flexibility to use taps other than the 300 Ohm tap on your headphone output transformers. My experience with DHT headphone amps tells me that you are not going to be happy with the noise performance on the 300 Ohm setting.
If you select a quiet, high-ish gain driver tube (think a mu of 30 or more), then you will have the flexibility to use taps other than the 300 Ohm tap on your headphone output transformers. My experience with DHT headphone amps tells me that you are not going to be happy with the noise performance on the 300 Ohm setting.
No, I did not measure the noise and I did not attempt driving headphones with it. I understand that this will be a difficult venture, but...challenge accepted!
Maybe I can add a third supply for the driver filaments? I have a dual secondary 18v toroid and two large chokes that I can feed into a Coleman regulator? I really want a DHT headphone amp as I love the DHT sound, I just cant listen to my 45 stereo amp much due to a new baby girl (sleeping) and the rest of my family HATES jazz LOL.
Maybe I can add a third supply for the driver filaments? I have a dual secondary 18v toroid and two large chokes that I can feed into a Coleman regulator? I really want a DHT headphone amp as I love the DHT sound, I just cant listen to my 45 stereo amp much due to a new baby girl (sleeping) and the rest of my family HATES jazz LOL.
I guess if I am using the coleman regulators then I mind as well go with the #26
If there is too much (any) hum, I am not above going with an IDHT as I love the sound of the mesh plate #27.
Would there be any benefit to using a 1:1 interstage (replacing the 2uf coupling cap)? I have a pair of Electra Print on the shelf just dying to be installed
Looking at the schematic I posted, I am not too sure about the 2uf coupling cap, that seems a lot higher than what I normally see and use.
If there is too much (any) hum, I am not above going with an IDHT as I love the sound of the mesh plate #27.
Would there be any benefit to using a 1:1 interstage (replacing the 2uf coupling cap)? I have a pair of Electra Print on the shelf just dying to be installed
Looking at the schematic I posted, I am not too sure about the 2uf coupling cap, that seems a lot higher than what I normally see and use.
Okay, I got most of the drilling done for the two chassis and looking at the tube datasheets, I am thinking that the 56 tube would be best for my applications as it has a gain of 13 and the filament current is almost half of what a 27 is.
Also for volume control, I was wondering if I could use a Langevin 600/600 dual stepped attenuator? I have never used one of these, so any inputs on that are welcome.
Also for volume control, I was wondering if I could use a Langevin 600/600 dual stepped attenuator? I have never used one of these, so any inputs on that are welcome.