Don't expect to necessarily "lose bass" with a tube phonoamp. Compared to solid-state tubes might show a little less bass control (if the rest of your system can reveal it), however weak bass would be the result of an impedance mismatch with the preamp or interconnects in relation to the output impedance of the phonostage, not of using tubes per se. In fact if you're comparing relatively inexpensive SS and tube phonostages, you might find that on average the SS ones could be leaner sounding overall. A possible disincentive to using a tube phonostage can be tube noise -- finding tubes with minimal "rush", microphonics, spurious little farts, squeaks or tones and resonant colorations in general, which can be laid bare in the high-gain environment of the phonostage. (The lower the gain, meaning a higher outupt cartridge is required, the less these problems are likely to intrude.) All in all you should try to choose based on sound quality in general and compatibility with your cart.