112 RP lightly distorted at low levels

Hi,
the title just about says it, but it also sounds quite dark and distorted with a pre-amp pedal.
It still sounds great , but doesnt seem to have the headroom that these amps are legendary for.
Should i replace the valves?
Kind Regards
Brodie

Personally, I would check the driver section and "set" the bias. On that amp it has the SS driver so you're setting "kind of" the balance but let's just keep it simple. The bias adjust is set with the procedure described in the adjustments section here. MAYBE, the tubes are just worn out or it has something else going on. I would check the "bias" first and see what you get. If the cathode current is ridiculously low on BOTH tubes, you might have some crsossover distortion. Then you could replace both tubes bias and be done. Hav ethe tubes EVER been replaced? What kind are they? Mike.

Hi Mike Thanks for your reply,
The amp is new to me, but it looks the tubes have probably been replaced, they are
National Electronics 6CA7/EL34
and
Mazda EL34
The amp on the whole is in good condition , and looks like it has been well maintained.
Kind regards
Andy

Wat a minute-you have TWO different BRANDS of tubes? I'd be REALLY surprised if they were even CLOSE to being matched, unless somebody was sharp enough to check them under the same parameters. I'd start there and bias properly and see what it sounds like. Mike.

Thanks Mike,
I shall probably get some new ones! JJ El 34 seem to get good reports here, What do you think?
Andy

Further research suggests JJ EL34L ?

Either one should work fine. Winged C EL-34 is another great (but slightly more expensive) choice.
I should mention at this point, that a leaky coupling capacitor could introduce cross-over distortion because the bias circuit basically gets over-ruled. If you are unable to adjust the bias to satisfaction with new matched tubes, I would look at the coupling caps around the phase splitter stages.
Cheers,
Lars Verholt

Hi Lars,
Thanks for the advice, I was looking at the winged C EL-34 , and have now bought some !
Thanks for the advice re coupling caps.
Andy

Update.
The New wing C EL-34 and a proper biasing job did the trick.. Amp now sounds great .. mean and clean !