Ok guys.... its a bit hard to start on a cold morning
but .this toobe amp that uses an ignition coil certainly is an odditie in itself.... I wonder how it sounds? BTW: The guy that wrote up this little gem seems to dislike buying NOS toobes from now defunct American manufacturers.... Go figure....
Mark
but .this toobe amp that uses an ignition coil certainly is an odditie in itself.... I wonder how it sounds? BTW: The guy that wrote up this little gem seems to dislike buying NOS toobes from now defunct American manufacturers.... Go figure....Mark
qq said:
Maybe he didn't want the vast throngs of people trying his project to use up the remaining stock of NOS 12ax7s?
This appears to be a part of an electronics course- there would be no point in spending £££ on a NOS 12ax7 when a current production one will work for the demonstration.
Parafeeding the 'OPT' would appear to be a good, if expensive, idea- no high voltage DC on the speaker terminals.
James
I've seen this idea somewhere before, but never tried it. I'm sure I have an ignition coil around here somewhere. If I were more motivated I'd measure the inductance and stepdown ratio...
Anyway, it seems to me that the coil is not really hooked up right. As drawn, the speaker voice coil (along with any interconnecting wire) is riding up and down with the plate of the tube. That's a huge common mode signal that serves no purpose and loads the tube with all of the capacitance to earth.
It makes a lot more sense (to me) to put the small section of the winding (the part that the speaker is connected across) at B+ rather than at the plate of the tube. To make the change just swap the plate and B+ connections in the drawing: connect B+ to the '+' terminal on the ignition coil and connect the plate to the center plug.
-- Dave
Anyway, it seems to me that the coil is not really hooked up right. As drawn, the speaker voice coil (along with any interconnecting wire) is riding up and down with the plate of the tube. That's a huge common mode signal that serves no purpose and loads the tube with all of the capacitance to earth.
It makes a lot more sense (to me) to put the small section of the winding (the part that the speaker is connected across) at B+ rather than at the plate of the tube. To make the change just swap the plate and B+ connections in the drawing: connect B+ to the '+' terminal on the ignition coil and connect the plate to the center plug.
-- Dave
Glenn_G said:
I assume you'll have two 240/12VAC xfmrs or similar? The output should behave in theory just like the mains supplying current to the load. The 12V windings would be handling 20 times that current. The combination is limited by the capability of the xfmrs to deal with this load.
In theory, current won't flow unless you load the second secondary (or primary just for confusion's sake
) but the inefficiency of the xfmrs will make that less than ideal.I feel that toroids may be better for this duty, and a smaller turns ratio would also be desirable.
Glenn_G said:
Assuming you have two identical transformers, it would be the secondary current rating divided by the voltage ratio, for instance if you had two 120V to 12V transformers and the 12V secondaries were rated at 10A it would be 10A / (120V / 12V) = 10A / 10 = 1A.
Since there are losses in the transformers you'd get a little less than that, so leave a little safety margin.
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