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Thinking of one of those little triode preamps from eBay?

Got to a point where I might benefit from having a buffer amp in one rig I'm fooling with, so I was looking at those little tube preamps from eBay that run on a wall-wart power supply. Their main attraction is that are certainly cheaper than anything I can build myself. Then my old tube-design synapses started tingling...

They *can* work but there are critical design considerations. I think the performance potential of a miniature twin triode with 12-25V on the plate is pretty limited. Ultimately I was dissuaded by not wanting electrolytics in the signal chain, which this kind of rig would likely introduce. Unless maybe if it's a cathode follower... A cathode follower is very sensitive to input and output impedances (and power supply) so again, low probability of getting high performance potential.

Whatever the case, if you get one of these and the bias isn't adjustable, you can't "roll" tubes.

This article about the design of these is intelligible and points to the limitations of putting a very low voltage on the plate of a tube designed for at least 100V B+.


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Topic - Thinking of one of those little triode preamps from eBay? - mr.bear 12:48:25 12/03/16 (10)

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