Checking pre amplifier sound quality

I want to check the sound quality on my Radford SC22 pre amplifier going in to the Radford STQA 25 amplifier.
I think that the sound has dropped off but it is hard to tell. Could anyone suggest the type of music to best test the range of sound (I have classical and jazz files). There are 4 ECC83 valves in the pre amp and I thought of changing them individually to see if it affects the sound or is there a better way to do it? Any suggestions appreciated.

 

There are only two ways I know of:-
The best way by far is to put the preamp on a test bench and measure what it's doing, and compare that to the original spec. An hour on the bench, and you can see exactly what any faults are.

Alternatively, you need another identical system and run blind, carefully level matched, listening comparisons, which is unrealistic.
Sadly, what you're suggesting won't help much, as changing valves takes time, and as our audio memories are very short, a matter or seconds at most, by the time you've made the change, the earlier sound will have been forgotten. Any conclusions then will be wishful thinking or just plain guessing.

Depending on where you are located, find a friendly tech that will help you do this. If you are anywhere near East Anglia, I would be happy to put your amp on my bench, as I think would others if you're elsewhere.

Best of luck, as your amps are great. Arthur Radford was a master of audio design, especially transformers.

S

 

I presume that's a typo in the name of the power amp....take the "Q" out and STA25 yes?

As with pretty much all pre-power combinations of that era the power amps are better than the pre amps by modern standards. Unless using the SC22 for historical reasons I recommend replacing it with a more modern alternative. This could be as simple and cheap as a basic passive "pre" or there are of course numerous active preamps available.

 

Thank you.
I shall check with a tech friend.

 

How old are the valves? No harm in replacing all 4 if they are several years old. JJ and Sovtek are reasonably priced.

I think Sovtek do short and long plate. The long plates can be more microphonic so I'd go with short.