Martian Headphone Amplifier

Page 1: January 4, 2007

Not from this world?

This is the first project that I work on in the new year 2007. During one auction on eBay I bought 4 triodes (6AS7) from an American buyer. Of-course I looked in his other auctions as well since he mentioned combined shipping. And as shipping is expensive from the USA I decided to have a look at his other offerings.

Amongst the other items offered by that seller were two lots of 832A Tetrode tubes. These tubes are rare and do look unusual as well. It is family of the 829 tube with similar shape and behaviour.

Just before making my offer of $4 for 7 tubes which are University surplus according to the seller and most likely NOS, I looked on internet for circuits and datasheets of the 832. I found little, but on the other hand I did not expect a mainstream design also ;-)

As far as I could find on internet, the 832A tube was used in telecom applications. Other than that there was little background information available on this tube. Only that the tubes most likely were used inside some sort of swappable modules. I found somewhere a picture of the 832A embedded in a larger module, which of course made replacing these tubes a lot easier and safer.

Remco Stoutjesdijk (Ultranalog) did use these tubes before and built a nice power amp with these tubes. I might decide differently, the output power of these Tetrodes do not provide enough power for most of my speakers. I therefore might go a different route and build a headphone amp with these tubes. OTL must be possible, still to decide whether to build a PP amp with a tube each or put them in parallel.

Heaters: 12.6V, 0.8A,
Plate voltage 300-500V, about 40mA.

Links

• The 832 amplifier of a Malaysian DIY audiohobbyist
• Ultranalog probably built the first version of a 832 amp, the Coldware
• Remco also made a datasheet for the 832
• My only commercial reference amp: The Little Dot 2++ (LD2++)

© Maarten&Annemarie, January 2007

last modified 1 January, 2010