tube amps/low capacitance cables?

That's strange. I would expect high capacitance cables to affect high frequency, not low. A tube amp, with relatively high output impedance at high frequency would be affected more than a low impedance ss amp.

Ask the amp manufacturer.

Tube amps have output transformers and their secondaries (the portion that connects to your speakers) can be electrically represented by a series inductance. If you then connect high capacitance cables to this inductance, you effectively produce a low-pass filter. This would mean that your highs would be a little rolled off but it shouldn't affect the bass. Technically speaking.

However, many of us have witnessed that the impact of cables is much more complicated than that. Our ears can hear more than we can measure. As a result, the only good way to find the right cables is to try several and pick the ones you liked best. The explanation for why they are the best will not be clear - everyone will have opinions but no one will have proof. Lucky for us, the outcome of experimentation will be sufficient for great sound. Good luck!

Arthur

I don't think there is a rule of thumb. In general, if the speaker cables have a major impact on the sound then I would be more concerned about the amplifier design, how the speaker load varies with frequency and the way the two match...just my two cents.

Strange indeed -- unless the older cables were higher gauge (i.e. thinner) than the new ones -- and generally too thin for the new application?

It's not so strange. Tube amps have relatively low output current and low damping factors which make it more difficult to control woofers at low frequencies. The impedance of the speakers plus the cables affect the damping factor. If high capacitance cables are used, the impedance is higher at low frequencies, increasing the output impedance the speaker "sees" which makes things worse for low end performance.

Whatever the deal is causing the lack of bass with that cable, its not capacitance. Length, cross sectional area and the characteristic impedance are more likely variables.

By decreasing the 'damping factor' the bass would actually increase, although there may be less definition.