
dgatwood
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I'm considering building a tube preamp (non-starved plate). Here's the schematic I'm basing it on:
http://www.tubecad.com/october99/page15.html
The design is kind of nice in that I can use a common 110/220V transformer with center taps ($12) and a full wave bridge to get a close approximation of the correct voltage (about 156VDC, by my math).
It's also nice because for under $30, I can get all the parts I need except for the tubes, the tube sockets, a chassis, and connectors, so the entire preamp should come in under $50 (and with enough of the small parts left over to build several more, transformer/rectifier/jacks/chassis/tubes notwithstanding).
I'm running into one really nasty snag, though. It specifies a 0.1uF polarized capacitor. I can't find any evidence that such a thing exists in nature, much less at the 100V level or higher.
Does anyone on this board understand tube circuit design enough to tell me what the effect on the overall circuit will be if I substitute a .47uF electrolytic? Is this thing just being used as a DC block?
That's not the only substitution, but it's the only one that's far enough that I'm worried about it. All the others fall well within the tolerances you'd get for an ideally-rated part if I could easily get them. That said, the complete substitution list follows:
.1 uF electrolytic -> 4.7 uF electrolytic
500 ohm resistor -> 510 ohm
12.5k resistor -> 12.51k (12k + 510 ohm)
2.5k resistor -> 2.51k (2k + 510 ohm)
Thoughts?
http://www.tubecad.com/october99/page15.html
The design is kind of nice in that I can use a common 110/220V transformer with center taps ($12) and a full wave bridge to get a close approximation of the correct voltage (about 156VDC, by my math).
It's also nice because for under $30, I can get all the parts I need except for the tubes, the tube sockets, a chassis, and connectors, so the entire preamp should come in under $50 (and with enough of the small parts left over to build several more, transformer/rectifier/jacks/chassis/tubes notwithstanding).
I'm running into one really nasty snag, though. It specifies a 0.1uF polarized capacitor. I can't find any evidence that such a thing exists in nature, much less at the 100V level or higher.
Does anyone on this board understand tube circuit design enough to tell me what the effect on the overall circuit will be if I substitute a .47uF electrolytic? Is this thing just being used as a DC block?
That's not the only substitution, but it's the only one that's far enough that I'm worried about it. All the others fall well within the tolerances you'd get for an ideally-rated part if I could easily get them. That said, the complete substitution list follows:
.1 uF electrolytic -> 4.7 uF electrolytic
500 ohm resistor -> 510 ohm
12.5k resistor -> 12.51k (12k + 510 ohm)
2.5k resistor -> 2.51k (2k + 510 ohm)
Thoughts?