#27 tube preamp schematic

[Biwado]

Hi,

I have a pair of used #27 tube tested in good condition. I'd like to build a preamp with the tubes but I haven't schematic yet. Can anyone here help me to find #27 tube preamp schematic?

Thank's

 

[analog addict]

Try this one. You may not want to duplicate the power supply, but realize that this pre amp was designed with the help of Dennis Had, and is very similar to his LP-27 line of preamps. He uses a cathode follower, and I use a VR tube to stabilize the power supply.

27 pre amp by Analog Addict, on Flickr

 

[analog addict]

27 pre amp-2 by Analog Addict, on Flickr

27 pre amp-3 by Analog Addict, on Flickr

 

[PakProtector]

Try a 140V/5mA idle point, give or take a bit. The -9V of grid bias can be done with a string of 4-5 red LED's. For the plate load, I'd suggest a cascode MOSFET CCS, and output from the lower source, or mu output. Cap couple with a 5 uF motor run cap, like an ASC or GE. Use 440VAC ones; the dielectric is thicker...though a 220VAC one would be no where near its limits. B+ in the low 200's; 220-240 or so.
cheers,
Douglas

 

[nerdorama]

I used this one but with a 37 instead of 85. Mine will also work fine with a 76. These are the same as 27/56 except for 6.3V filaments.
http://web.archive.org/web/20050223104456/http://www.pacifier.com:80/~gpimm/85ls_3.gif

 

[Biwado]

Thank you for all advices. I'm gonna start my learning project on 27 tube soon and whatever the result I'll post here.