i have also received my 2Sk82 , and the BIIIIG 300w 120 sylvania bulb , i don't know yet if i will use them or a big power resistor as my chassis is not very large. i will begin the build this week and i'll tell you if this DIY is really Idiot proof😀
Figure 11 is pretty straight forward.
With figure 10, the thing that could be tricky is remembering that the gate bias is negative. If you let it go too positive, Id goes up, and eventually it goes poof.
I tested all my power supplies out of circuit first. Then, I adjusted the bias supply for -12V, powered up the circuit, and adjusted the pot so I had around 13.4V from Drain to Source.
With figure 10, the thing that could be tricky is remembering that the gate bias is negative. If you let it go too positive, Id goes up, and eventually it goes poof.
I tested all my power supplies out of circuit first. Then, I adjusted the bias supply for -12V, powered up the circuit, and adjusted the pot so I had around 13.4V from Drain to Source.
I just verify that the pot is at the full -12V position and not the other way around before I turn it on for the first time.
You may want to look at your time constants in the PS filters, to make sure that the -12V supply doesn't come up significantly slower than the B+ as well....
Roscoe
Roscoe
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If one uses the schematic I provided in my first post, this is not an issue.
If you build something else or use significantly different capacitor values, then Roscoe's caveat applies
If you build something else or use significantly different capacitor values, then Roscoe's caveat applies
thanks michael ,i will stay with Fig11 with just the option 47000uf bypass cap on R1 i'm a tube man 🙂
Hi Choi,
Because it is two N-devices, the two drive voltages to the grid have to be referenced to the drain. What I once did was use a transformer coupling to both output devices (1/2+2, so two similar output windings), attached a proper bias, set the current, and presto, very nice sound, extremely high drivability too.
The traditional way is to use a bootstrap in the upper side (see e.g. the BA2).
albert
Please, I am looking for a source for this 300W/120V bulbs.
The only thing I find, are halogen bulbs.
Usable for this purpose? I dont think they have the needed resistance value.
Franz
The only thing I find, are halogen bulbs.
Usable for this purpose? I dont think they have the needed resistance value.
Franz
Franz,
You can determine the resistance of one of the halogen bulbs by hooking it up to a DC power supply and measuring the current. You can always use several in parallel to achieve the desired resistance. I've never tried other bulbs, so I don't know what to expect.
And, there's always the resistor route.
You can determine the resistance of one of the halogen bulbs by hooking it up to a DC power supply and measuring the current. You can always use several in parallel to achieve the desired resistance. I've never tried other bulbs, so I don't know what to expect.
And, there's always the resistor route.
franz you have a pm , i think i will not use mine... my chassis is too small
i will go with a 10ohm 300W ohmite resistor , hope it will sound as good?
i will go with a 10ohm 300W ohmite resistor , hope it will sound as good?
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franz you have a pm , i think i will not use mine... my chassis is too small
i will go with a 10ohm 300W ohmite resistor , hope it will sound as good?
I think so. Chatted with a guy who made the D-Lite with a bunch of 100R 25W ones, and he loved it with horns. Of course the sinking for such a beast was not trivial. He used most of Solid State chassis for resistors, and popped the transistor on it as well.
with this one you don't have heatsink but 72W watt of dissipation on a 300W resistor could be ok?
An externally hosted image should be here but it was not working when we last tested it.
