Well, in theory, but as I said previously "Given that my drive is a function of the load/bias circuit the 6.3v is fixed hence my question about using the 6.3v or the 150ma rating of the heater. I have tried various mfg and found >10% variability in current drawn. " So I assume the mfg provides the appropriate temp/emission for the materials they use and 150ma is nominal current draw for purposes of filament supply design. I'm using a voltage of 6.37 atm. Source is actually 13.55v and voltage across anode resistor of 3.980k is 12.06v within the accuracy of my meter (Fluke 27).
I don't know how much a class a mosfet instead of an output tube/xfmr affects the 'sound' but it is working fine in my room, doesn't draw the power or heat the space my monoblocks do and is small/safe as headphone amp design it was derived from. I can take this using the 12au7 camping and hardly drain a solar powered battery.
I don't know how much a class a mosfet instead of an output tube/xfmr affects the 'sound' but it is working fine in my room, doesn't draw the power or heat the space my monoblocks do and is small/safe as headphone amp design it was derived from. I can take this using the 12au7 camping and hardly drain a solar powered battery.
I actually got interested in this as small project after fighting with recapping the monoblocks with dual-series caps to replace original that was operating near max voltage. Part of my research at improving the input led me to this little headphone amp.
In the monoblock the original sprague was rated for 525v and was operating at 512v with spikes to 545v due to nominal line voltage of 126v. Now I have dual series connected 400v caps for all of the sections of the original. I also added a 30s delay to the rectifier so all the filaments would be lit before voltage was applied. Along with a change to a 5U4GB I now have 479v nom with no spikes on startup. The outputs are running with 65ma in P-P/UL and sound great.
Well, these kinds of projects can be fun. Sometimes I make a small amp with a strange tube just for fun.
The question here is are you interested in improving the design, going further down the DIY path?
The question here is are you interested in improving the design, going further down the DIY path?
Yes, is why I posted. I am not familiar enough with tubes. I should have listened more to my G'dad. 😱
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