I've split this into a seperate group as the supplies alone deserve to be called a project by itself. I have been working on supplying my amps totally on batteries. As they tend to be very bulky and take up some space I split them into two chassis, one for each channel.

The supplies will make up three chassis: one for the filament supplies, one for the B+ of the left and one for the B+ of the right channel. This will allow me to switch to a replacement rectified supply without luggin along 100kg of unused batteries. Each B+ section will house 24 batteries (12V/3.3Ah) and all the necessary chargers and other circuitery. The filament supply will hold batteries etc for 6 tubes (3 per channel). It carries four 12V/17Ah and two 12V/24Ah batteries.

This project is not a cheap one as a new SLA battery would cost about $25 (12V/3.3Ah) each. It will weigh a ton and pose some serious safety issues. A battery has a very low internal resistance, this means a short circuit will cause an immence current to flow. Depending on the capacity of the battery, this can go ashigh as 1500 amperes (12V/24Ah). This is a lot of power being released in a short period of time, so shorts will have to be prevented in order to guarantee safety. See my Warning on the projects page to see why this precaution has to be taken.

Why batteries?

That being said, why did I even start on such a project ? Am I crazy?! No, actually it all started with my problems on the 26 preamp. I could not remove the hum by any means other than using a battery to feed the filament. This solution was absolute, no more hum, dead quiet. I have not looked back since and will not switch to anything but batteries on my 26. This idea got to me and I wondered what it could do for the other tubes. The KC3 in my Arhus amp was soon converted, also the 1H4 preamp used batteries for the filaments. If they helped so much on the filaments, what would happen if I were to use them as B+ ? Whoah... 180V on the anode means a lot of batteries, couldn't I use the 26 on a lower B+? 90V would only require seven 12V batteries (13.5V each), this could be done without spending a fortune.

Luck would have it that I found someone who was selling 32 batteries for only $3 each, great!!!! 32 batteries, now I could build a stereo supply with 208V, perfect for my 26 (180V + 13V bias + 5V loss in the choke). The batteries were used in a UPS for a few years and had to be replaced during maintenance. They should have a few years of life left in them. The batteries for the filament were obtained at ham fairs etc, I scored some nice surplus Yuasa 12V/17Ah batteries for $12 each (never used) and a pair of 12V/24Ah for the same price (used though). I was on my way!!!!

After breadboarding the B+ supply with a lot of clip-leads, I hooked it up to my preamp. A little spark from flash-charing the capacitors of the old rectified supply. The B+ was there immediatly, no slow rising voltage, SLAP!!! there is your B+. This results in a kind of thud through the speakers as the B+ goes from 0 to 208V in a millisecond. I now had a completely isolated preamp, no 220V rubbish or hum. Wow!!! really quiet.

Playing some music I quickly realized how much more detail and openness I had gained. It all sounded so easy and fluid. The quiet passages were really pitch-black, I don't know how to describe it in another way. The attaques were very fast, dynamics seemed to have doubled from what I had before with the rectified supply. My path is now set...

Connecting all the batteries from series (B+ mode) to parallel (charging mode) can be a pain in the butt if you have to do this all by hand. For this reason I used some small relays to switch the poles of the batteries from the series mode to disconnected. In the disconnected mode the battery will be hooked up to it's own charger. This means using a double-pole relay for each battery, but I find it to be the nicest way. If you take a good relay, you really will not notice they are there.