STF Electronics 5F1 Clone

[dporto]

Hi,
I built a STF electronics 5F1 clone a few years back and while the amp sounds really nice, it doesn't produce as much overdrive/distortion as I've experienced from other "champ" amps I've used. I did build it with a tone circuit, so I'm wondering if this is where some of the gain in the plain 5f1 circuit is being lost...Thx in advance for any ideas

[JHow]

What does your tone circuit look like? Is it a single-knob Princeton-style or something else?

[dporto]

Yes, single knob "princeton style"... Full left = Bassy sound... Full right = Trebley sound... Am I right to assume this is a simple HP filter? Thx

[dporto]

Anyone?...Anyone?...

[jmaf]

For added gain add a bypass cap across the 1k5 resistor on triode one. Don't do the same on triode two or you'll kill the negative feedback.

Edit: not tube one, triode one.

[dporto]

Thanks for the reply. Ok, this would be the cathode resistor correct? Grid bias is most often provided by a cathode resistor. If the cathode resistor is unbypassed, negative feedback is introduced and each half of a 12AX7 provides a typical voltage gain of about 30...The cathode resistor can be bypassed to reduce or eliminate AC negative feedback and thereby increase gain Now I'm a little confused because the little research I've done shows the cathode resistor on pin 3 (cathode - triode 2) while the cathode for triode 1 is pin 8...

[jmaf]

Thanks for the reply. Ok, this would be the cathode resistor correct? Grid bias is most often provided by a cathode resistor. If the cathode resistor is unbypassed, negative feedback is introduced and each half of a 12AX7 provides a typical voltage gain of about 30...The cathode resistor can be bypassed to reduce or eliminate AC negative feedback and thereby increase gain Now I'm a little confused because the little research I've done shows the cathode resistor on pin 3 (cathode - triode 2) while the cathode for triode 1 is pin 8...

That is common practice. Triode two in a 12ax7 is often quieter than triode 1, so often they use that for the input which is the most critical gain stage noise-wise and then come back to triode one for the 2nd gain stage. Follow the input lead, you'll get to either pin 2 or 7. If pin 2, you can bypass the resistor on pin 3. If input is on pin 7 you can bypass the resistor on pin 8. Just be careful to not bypass the other one, it's where negative feedback comes in.

[dporto]

Wow thatwas quick! Thanks very much. I'll dig in soon and give it a shot.