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Friday, 05 January 2007

In keeping with the Sopht idea of making low wattage tube amps, I wanted to make something very simple that sounded good. I wanted to play with a design that only used 1 tube for an amp that could produce distortion with less than 1 watt. Just like an iceberg (ijsberg in dutch), I wanted something that looked deceptively simple yet produce cranked tube distortion at low wattage. This is why the ijsberg was created. It produces lush cleans and cranked power tube distortion all of that at about 1/2 of a watt! There is also a line out in the design so that you can either record the amp directly or plug it into another amp as a distortion pedal.

This is the fourth version, it might move, so keep an eye on this page:

This is the voltage chart:

wall voltage: 123VAC
b+: 300V
b+1: 300V
b+2: 295V
pentode plate: 148V
pentode grid2: 83V
pentode cathode: ~2.5V
triode plate: 296V
triode cathode: 12.5V

Transformers used:

- 269EX for the power transformer
- 125C wired as single ended (brown b+, blue plate of triode, red not connected) and wired to reflect a 17.6k load with an 8 ohm speaker (pins 3 and 5 are used on the secondary for the speaker connection).

A few pictures of my build:

Sound Clip

Click here for a sound clip. I am still fine tuning the amp to reduce the flabbiness in the distortion.

Clips of version 1.3:

This is the clean sound clip

This is the cranked sound clip

Clips of version 1.4:

This is a cranked sound clip.  No reverb was added, that is the room accoustic. 


Version 1.1: initial version
Version 1.2: modified the cathode resistor for the triode from 1k to 1.5k. It was overdissipating with 1k.
Version 1.3: changed plate of pentode to 470k and grid 2 to 2.2Meg. Changed cathode bypass cap on the pentode to 0.47uF and upped the cathode bypass on the triode back to 47uF. Now, it is in clear AC/DC territory!
Version 1.4: changed the pentode operating point and a few tone shaping caps all thanks to Iain.


Last Updated ( Saturday, 09 June 2007 )