Audio circuits archive

This is an archive for audio stuff that I find interesting - amplifiers and speakers only for now. In many cases they are a little hard to find on other web sites. None of these designs are my own, this is merely an archive making access to these designs convenient.
Please feel free to email me on my email adress mats at digitalakuten dot com (replace at and dot with @ and .) if you want to publish a unique design but lack access to web space for it.

Ralph Power's PP6B4G - Ralph Power's interstage push-pull amp.
This is one of the early web examples of the rebirth of the IT transformer push-pull amp. Sadly, the page that hosted it, Meta-Gizmo, is gone as of January 2008. I have reconstructed it to keep this information available for the DIY community.

Stiglas´ Ralph PP6B4G - Ralph Power's 6B4G interstage push-pull amp redesigned and built by Stig Larsen.
ECC99 input stage, Lundahl interstage and redesigned power supply with higher HT. It may be a little hard to read, but it has
297V/60mA on the 6B4G's, 206V/20mA on the plate of the ECC99, 200mA off the choke in the PS (but measured to 160-170mV), and 20mA going to the VR tubes.
See corresponding thread on, which has the info but lacks the schematic. Component list for stigla 6B4G PP (in swedish)

Stig Larsens tube regulator alt. 1
Stig Larsens tube regulator alt. 2

The Foz line stage (no longer available at

The Duelund collection - A collection of PDF:s, some of them in Danish, others in English, written by Steen Duelund, a Danish audio designer.
These circuits are no longer gone from the internet. They have been made available again from the people that continue mr. Duelunds work, on
Maybe they will disappear again, but until then, please download them at the Duelund web site.
Mr Duelund regrettably passed away some time ago, a legend in my part of the world- this is a very interesting read.

Last archive update:20080204