Since you found the tubes on a chassis that has transformers, it means that you probably disassembled an amplifier. I'm pretty sure that you can at the very least build the power supply from the parts you found on that chassis (power transformer, tube rectifier, probably a choke). The 12ax7 can be your driver tube. Then you can either use one of the power tubes you found, or buy a couple (they're not that much) for a PP amp. Build a cabinet, buy a speaker or find one that comes out of an old tube organ.
The question about using the transformer in reverse, it depends. They sell something called industrial control transformer, sometimes for cheap, that can be used that way.
The question about using the transformer in reverse, it depends. They sell something called industrial control transformer, sometimes for cheap, that can be used that way.
I'm pretty sure that's what the OP has in his possession. I've used a 600V 1kva one that i scored for cheap in conjunction with a variac for a simple variable power supply (extremely heavy though), so I can say with a good deal of certainty that they'll work hooked up either way. The only real issue is the screw terminals they use, both from an aesthetic and a safety perspective, but if you're putting it inside a grounded box anyway it doesn't matter much.
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Yeah, see - I could wire this up with 24 volts on the secondary side and get a range of different voltages out of the primary. It's just too heavy.
You also get - I forget what it's called... hysteresis losses? - so instead of 480 vac it'll be something like 440-ish.
This one is particularly flexible about the primary voltages it'll take. Usually you get a simpler setup like maybe 240/120 on the primary and 24 on the secondary.
Yeah, see - I could wire this up with 24 volts on the secondary side and get a range of different voltages out of the primary. It's just too heavy.
You also get - I forget what it's called... hysteresis losses? - so instead of 480 vac it'll be something like 440-ish.
This one is particularly flexible about the primary voltages it'll take. Usually you get a simpler setup like maybe 240/120 on the primary and 24 on the secondary.
Latest adventure:
Found a gentleman who tested a few of the tubes - I have a very good 12ax7a and a good 6bg6. I can make a single ended champ with that.
Transformer situation - I found a step-down that will serve. It's a 480/120 rated for .075 kva. It's a little on the big side for my purpose but the weight difference between it and a suitable step-up power transformer is barely noticeable.
The output transformer is interesting. I am doing more math and thinking a lot harder than I expected. I have a sufficiently rated transformer that has a 19:1 turns ratio - which isn't quite right for a 6l6 if I'm not mistaken.
The 6l6 in single-ended operation appears to have an impedance of 4k (fixed bias w/ appropriate voltages) My output transformer would only have 3.2k reflected impedance if I assume an 8 ohm speaker.
Is that too far outside the operating range? Is it possible to bias the tube to lower the impedance value of the tube? If so - what would that do to the signal? Would it be detrimental to the tube?
I can see that I might have to just pony up for an output transformer. I'm trying to avoid that if I can.
I've tracked down a 10 watt Squier combo that's been listed for just 10 bucks. It's just about the worst-sounding amp that I've ever heard but the knobs and jacks will be useful and I will need a cabinet of some sort for testing my circuit.
Oh yeah I almost forgot:
I found out that the step-down transformers have extra windings on the primary-side. I guess it's supposed to help maintain a steady voltage on the secondary in the event of a voltage drop. The extra windings are responsible for lowering the primary-side voltage if you try to use it in reverse. The first one I tested was only putting out about 440 volts when reverse-wired, but the one that I'm planning to use is less heavy and it puts out about 465v.
There was some disagreement about how it affected the power rating of the transformer. The most-informed sounding arguments suggested a lowered power rating but not so low that I would have anything to worry about.
Found a gentleman who tested a few of the tubes - I have a very good 12ax7a and a good 6bg6. I can make a single ended champ with that.
Transformer situation - I found a step-down that will serve. It's a 480/120 rated for .075 kva. It's a little on the big side for my purpose but the weight difference between it and a suitable step-up power transformer is barely noticeable.
The output transformer is interesting. I am doing more math and thinking a lot harder than I expected. I have a sufficiently rated transformer that has a 19:1 turns ratio - which isn't quite right for a 6l6 if I'm not mistaken.
The 6l6 in single-ended operation appears to have an impedance of 4k (fixed bias w/ appropriate voltages) My output transformer would only have 3.2k reflected impedance if I assume an 8 ohm speaker.
Is that too far outside the operating range? Is it possible to bias the tube to lower the impedance value of the tube? If so - what would that do to the signal? Would it be detrimental to the tube?
I can see that I might have to just pony up for an output transformer. I'm trying to avoid that if I can.
I've tracked down a 10 watt Squier combo that's been listed for just 10 bucks. It's just about the worst-sounding amp that I've ever heard but the knobs and jacks will be useful and I will need a cabinet of some sort for testing my circuit.
Oh yeah I almost forgot:
I found out that the step-down transformers have extra windings on the primary-side. I guess it's supposed to help maintain a steady voltage on the secondary in the event of a voltage drop. The extra windings are responsible for lowering the primary-side voltage if you try to use it in reverse. The first one I tested was only putting out about 440 volts when reverse-wired, but the one that I'm planning to use is less heavy and it puts out about 465v.
There was some disagreement about how it affected the power rating of the transformer. The most-informed sounding arguments suggested a lowered power rating but not so low that I would have anything to worry about.
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