The Logic Off Topic list

--- In logic-ot@yahoogroups.com, "Gert van Santen" <g.vansanten@c...>
wrote:
> So what happens if you exchange the valves? Will the machine get 
> better?

Maybe. I've never done so on low-voltage 12AX7 stuff. But probably not
much better without also beefing up the plate voltage, which will
likely mean exchanging the power supply and modifying the supply
circuit, if it can be done at all. Then you'll want to look at the
quality of any capacitors & op-amps in the circuit, resistor/capacitor
values, decent grounding, and on it goes. Good parts don't come cheap.
By the time you've finished, it would likely have been better to just
work a bit harder, save a bit longer, and buy a better preamp in the
first place. And for X dollars, you'll always be able to buy a better
solid state pre than a valve pre.

Guitar amps, on the other hand, run the valves at the voltages they
were designed for (often 100V and up) and in my experience are often a
fine candidate for a bit of simple valve exchanging, especially after
a few years use - if you have a friendly valve-amp tech guy and a
supply of assorted matched valve pairs, an afternoon's swapping and
testing can be very rewarding.

John Pitcairn