I was bored so i started building an inverter, originally designed to power battery valves or somethgin. However, two days into the project, and now i have a prototype for a whole amp!
It's built into the wooden case from a ''suitecase'' type pye radio. I have a scrap one of these, so i pulled the shassis out and used it.
This amp is a total hybrid, and probably the wierdest thign i'v built yet.
The solid state circuitry is kept on two stripbords. One has the oscillator and power transisor, and one has the high voltage stuff (rectifier and smoothign caps/resistor). The actual valve circuitry is built in nails nailed into the wood.
Hers the schematic.
http://img.photobucket.com/albums/v4...brook/6at6.gif
The inverter actually works quiet well. What really got me is that the bdx53a is amazingly cool. It's cool to the touch and although riginally i was going to include a heatsink, now i dont think i'll bother. It never even gets higher than human body temp!
The transformer is run at 55.7Hz if i remember rightly. The 150ohm resistor was chosen pretty much on the spot, as it seemed to work the best. Lower values gave no improvement but overheated the 555.
I'm sure peopel woudl want to know what the output is. Well...the short answer is i dont have a clue! It's over 150v, sicne it fires a neon lamp, and it cant be over 400v since non of the caps blew up yet. I think maybe about 200 ish?
The preamp is a 6at6 because i accidently killed my only ef91, but dropping an o/p transformer on it! I ususally use a ef91 for jobs like this, but i just appened to have a 6at6 handy so i just used it.
Hers a coupel of photos of the amp.
http://img.photobucket.com/albums/v4...brook/amp1.jpg
http://img.photobucket.com/albums/v4...brook/amp2.jpg
It works quiet well, but distorts abit. I'm not sure if it's because the 6v6 is being starved of voltage/current, or because of the preamp. The cathode resistor looks abit high. I got it from some french hifi amp design or somethign. Maybe it's too high and it doesnt have much headroom.
Also, i think the amp would be better off with somethign like an el85. It would use less heater power and i think would work better under these low voltage conditions. A 6v6 is abit overkill.
Interastign project tho. And it works. I think if i take it further i'll put in alot more filtering and decoupling. maybe tying HT earth to battery earth would be a good idea too?