Can changing output tube type give more headroom ???

riffpowers

i just wondered if swapping out the el34's in my jcm800 for something like kt88's  might give me more headroom for a solo boost .

anyone tried it ? Anyone know ?!

olafgarten

You usually can't just swap output tubes without changing the circuit. The kt88 would give more headroom but an easier solution is to get a more efficient speaker or just add more of them.

ecc83

The power output of an amplifier is V x I so unless you change one or the other you will get no more power. IF you have 550V available AND you can bias the valves at 50mA each AND the PI can drive them hard enough, sure you could get 100 watts per pair! But can you?

Then, different output valve types need to "see" the optimum load impedance to deliver maximum power. It MIGHT be that a pair of KT88s will be loaded so as to deliver a few more watts but things could just as easily go the other way.

Err? Jusfort? IF you feel you need a solo boost with a 100W amp either IT is well down on power or you are deaf mate. Where are you playing? Hyde park?

Dave.

ICBM

You won't get more headroom or volume unless you're already overdriving the EL34s, and even then only marginally. It may sound like you do because the KT88s will need more input signal to reach the same power output so you'll have to turn the master volume up further, but it's not really going to give more headroom.

You probably will also get a chunkier, clearer tone but that may actually make solos cut through less well.

ESchap

I'd leave the output valves and try a 12AT7 (ECC81) swap for the 12AX7 in the phase inverter.  Might give you what you are looking for without having to mess with bias and output impedances..

ICBM

ESchap said:

I'd leave the output valves and try a 12AT7 (ECC81) swap for the 12AX7 in the phase inverter.  Might give you what you are looking for without having to mess with bias and output impedances..

An ECC82/12AU7 also works well for this and gives a cleaner, thicker sound than the 81/AT.