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The best tube pre from Vietnam - 818 Pre

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kevinkr

kevinkr

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Joined 2004
kta-hifi.net
Paid Member
quanghao said:
Hi kevinkr!

Well thank you!
Well yes, the LM317 can not be the best, I used Jfet replace it! I recently tested the following schematic, and I enjoyed it! 6h30pi particular tube,
Thank you and hope you add comments to this pre!

With tube 6h30 i like:
Anode = 90V, 40mA/ Tube
6h6 I like:
Anode = 170V, 40ma/Tube
This is other circuit, Please see it!
Thanks
Quanghao
Click to expand...

Simple balanced pre-amp. I did something similar long ago and also experimented with cross-connected cascodes, excellent balance, but too much noise with the Amperex E82CC I was using at the time. Consider using a cascode CCS with a small negative supply (-12V or so), CMRR will be greatly improved. (Ability to reject hum, and other common mode noise)
I'd think you might want to increase the plate load resistor values slightly? _ I haven't checked rp for this type, but bear in mind that with differential connection it will be much higher than you think. (twice or more is possible)
 
quanghao

quanghao

Member
Joined 2009
quanghao.com/
kevinkr said:
Simple balanced pre-amp. I did something similar long ago and also experimented with cross-connected cascodes, excellent balance, but too much noise with the Amperex E82CC I was using at the time. Consider using a cascode CCS with a small negative supply (-12V or so), CMRR will be greatly improved. (Ability to reject hum, and other common mode noise)
I'd think you might want to increase the plate load resistor values slightly? _ I haven't checked rp for this type, but bear in mind that with differential connection it will be much higher than you think. (twice or more is possible)
Click to expand...

yes! it is very nice idea . the circuit follow the basic with CCS + bias!
 

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