Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders.

---

[ Follow Ups ] Thread: [ Display  All  Email ] [ Tube DIY Asylum ]

---

[ Alert Moderator ]

---

EL34, triode connected....

Posted by Thomas Martens on April 3, 2007 at 17:28:49

In Reply to: What PP amp to build? posted by speleo on April 2, 2007 at 06:47:34:

fixed bias ( because of your 5000ohm OPT impedance).
Then use the Van der Veen direct coupled 12AU7 driver: 1/2 direct-
coupled voltage amp to 1/2 split-load inverter.

IMPORTANT: feed the above mentioned Menno Van der Veen drive
circuit (both halves of each channel's 12AU7) from a regulated
300v supply comprised of a stack of two 150V VR tubes which are
fed through a single power dropping resistor from the same +400
volt poer supply supply point as the EL34 output tubes. This dropping
resistor feeding the driver stages should be calculated so that
the VR tube stack draws about a static 10-15mA current to ground
after the currebt draw to the driver stages is factored in.
each of the four 12AU7 sections (remember, both channels here)
should have it's own INDIVIDUAL 22uf filter cap (450V rating)
charged to +280 volts through INDIVIDUAL dropping resistors which
tie together directly at the regulated +300V supply. DO NOT apply
ANY capacitance DIRECTLY to the +300 VR tube supply rail --this
will case instability and oscillation. The four little droppping
resistors which reduce the voltage from +300 to +285 to each one
of the drive stages 22uf filter caps will provide such isolation.

This will give you a drive circuit with AWESOME filtration and
isolation form the output stage transients -even at less than 1Hz!.
This will result in truly excellent bass and transient performance
--FAST dynamics.

Try it --you will thank me.

Again, you can use Menno Van der Veens exact fixed bias P-P EL34
amp design schematics and just change the b+ supply line
feeding the driver stages to +300V VR tube regulation --that's it.

Oh yeah, and I strongly suggest you do use TRIODE connection config
(this nets around 12-15 watts out) and do NOT use ANY loop inverse
feedback.

See: 'Tubes and Transformers in Power Amplifiers' by Menno van der
Veen or his newer 'Modern Valve Amplifiers' book for the schematics.

Good luck.

-T.M.

This post is made possible by the generous support of people like you and our sponsors:

Herbie's Audio Lab

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---