ETI Valve Distortion Unit

DrNomis · Post by **DrNomis** » 12 May 2015, 07:06

Hi Everyone,

Here's something I'm going to try building this fortnight, it's the ETI Valve Distortion Unit from the Electronics Today International magazine that used to be available about thirty years ago before ETI went bust, I had been trawling the internet for some time looking for a copy of the original circuit without any luck, but, I managed to find a hand-drawn schematic while I was looking for something else amongst my stuff, I made a new drawing and added some notes and then scanned the new drawing into my PC, then converted the image to a PDF file using CutePDF, anyway, this is for all those FSB members interested in building one of these......

Note: I've breadboarded a basic version of the circuit without the tone control, it's not a high-gain distortion, more like a light crunch, but you could use it as a dirty boost as the output is pretty high....

Here's the PDF:

uncleboko · Post by **uncleboko** » 12 May 2015, 07:10

Don't expect too much from that rag!!!

mictester · Post by **mictester** » 12 May 2015, 13:26

It tried something a bit like this (a long time ago) using a 12AX7. The supply rail was 45V. It was very fuzzy, but didn't make any better sound than I could get from two or three transistors at 9V. It was a bit of a waste of components. In the end, I stripped it for parts and made a nice little 1 valve radio receiver for medium wave. I still have the thing in a cupboard somewhere.....

tonyharker · Post by **tonyharker** » 12 May 2015, 14:11

A bit like a higher voltage ValveCaster without gain control.

DrNomis · Post by **DrNomis** » 12 May 2015, 14:45

While I was trying out the breadboarded version of the circuit, I tried using my Rangemaster stompbox to overdrive it a bit more, I found that I got some interesting results with it, the overdrive was a bit squishy and I found that the tone changed the harder I picked, I used my Gibson Les Paul Studio guitar....

I have a feeling that the original designer of the circuit intended the circuit to be used for overdriving an already distorting amp harder....

DrNomis · Post by **DrNomis** » 14 May 2015, 06:42

Out of curiosity, I tried one of my spare Russian 6N17B miniature valves in my breadboarded version of the circuit, just to see if it would work and it does....

hgamal · Post by **hgamal** » 16 May 2015, 13:32

I've made some enhancements to the image in order to be more readable.

DrNomis · Post by **DrNomis** » 16 May 2015, 15:03

@ hgamal.....Thanks for that, in hindsight I really should have gone over all the pencil lines with a thin black marker pen before I scanned the circuit into my PC.....my bad.....