Subbing a 5751 with a 5755

[exurbia]

This is more of a "i did it and met with little success" post rather than a question.

A little while ago i decided to modify my phono amp (i get bored) by changing the valves. As the 5755 is quite similar to a 5751, (they both got nine pins ) I subbed them out, changed the anode dissipation and upped the HT.
Bigggggg mistake, the sound hardened up and went really brassy

is it possible that the 5755 is no good as an audio triode or am i just a **** for even trying.

 

[revintage]

The tubes are very far from each other elctrically so no wonder your try wasnt successfull .

 

[exurbia]

Lars, my point, exactly
next time i'm that bored, i'll use the 5755 and try it in an Aikido-ish setup.
It looks like it would do a sterling job as the second unit.
If it ever becomes more than an idea i'll post it.
TTFN,
Peter.

 

[revintage]

Sorry Peter,
The 5755 is an extremely low Gm ,low current tube. So it can only be be used at input, nowhere else!

 

[leadbelly]

It looks like it would do a sterling job as the second unit.

No it doesn't. It's a high mu, low gm dual triode, not what you want for the 2nd tube in an Aikido at all.

Your first idea, to sub a 5751, has much more chance of success. It sounds like you need to tweak the circuit, or check with another to make sure you don't have a bad tube.

 

[exurbia]

Oh dear,
I'm afraid you are both right, i just got the full pdf for it.
And, i've found someone who is using it as an input tube, for precisely the same reason as you have both given.
Back to the cupboard for this one.