JAN6418 Tube Headphone Amplifier
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- Опубліковано 15 жов 2024
- This is a tube headphone amplifier based around a pair of sub-miniature JAN6418 beam tetrodes designed for low voltage operation. They are directly heated and only draw 10mA of filament current. The warm up time is almost instant. The anode current is only a few hundred microamps so an audio grade op-amp is necessary to drive the headphones. I tried to make an improvement to the Oatley Electronics version by biasing the tubes differently and adding a balance control with a stereo volume control instead of two separate trimpots on the board.
The Oatley Electronics Kit: oatleyelectroni...
Hi, what voltage good in Plate and Grid ? In my version, I am using 22V, then 180k ohm resistor for Plate and Grid, so I get only 8V in these position. In addtion, I am using cathode bypass resistor for Cathode with 140ohm for auto bias. Can I remove 180k resistor to upgrade voltage to 22V for Plate and Grid ? Because in 6418 tube datasheet I found that class A mode should be 15-22.5V for grid and plate
since these stereo pots are meant for stereo use I think you just got the connections the wrong way for one channel, i.e. swap pin 6 and 4 and it should be ok... Actually from your pcb layout I don't quite get how you connected any of the channels and your balance trimmer...
Hello. Do you happen to have a corrected schematic I could use to build this?! I bought ten of these tubes looking to build a headphone amp with, but the schematic I found doesn't have all values listed😢 thank you so much if you happen to be able to help!
The original one that inspired this build came from the oatley electronics kit. The link is in the description. The schematic is listed there as a pdf download which you can look at for reference. Or you can just use the schematic I provided and change the front-end volume control to your liking.
Hi, why you not using Aluminium Case ? or Using Plastic Case will reduce noise ?
An aluminum case would help noise. However, PCB has power planes on both sides that shield the traces to some degree. Also, the gain of the circuit is rather low, which helps. The shot noise of the tube and the thermal noise of the resistors are nearly as loud as the mains hum anyway.
What's the input impedance of this preamp? Thanks.
With the volume control all the way up, about 500K ohms with the balance pot centered. With the volume turned all the way up and the balance pot all the way to one side, it would be close to 0 ohms for the nulled out channel and 1M ohm for the other. This design is actually not good for an input stage because it really needs to be buffered. If you take out the balance pot, the input impedance simply becomes 1M ohm for each channel as usual.
You have Pin #3 as Cathode, and Pin #3 as Filament!!
Yeah, I know it looks a little confusing in this schematic. Pin 3 is the cathode and part of the filament because the tube is directly heated. There is no separate cathode as with most tubes which are indirectly heated.
@@thetuberoaster8321 - Enjoy your video', BUT MOST TUBES HAVE THEM SEPARATE.