Hi All,
I am planning to build a small guitar amp for use at home and I thought of building a Real McTube II distortion unit into the amplifier. I would like to use a 6SL7 instead of a 12AX7 since I will have the extra room and since I like octals better. I looked at the curves of the two tubes and they look almost identical. Does anyone have any opinions on whether this would be an acceptable substitution? The circuit can be found here:
http://www.dogstar.dantimax.dk/tubestuf/mctube.htm
I am planning to build a small guitar amp for use at home and I thought of building a Real McTube II distortion unit into the amplifier. I would like to use a 6SL7 instead of a 12AX7 since I will have the extra room and since I like octals better. I looked at the curves of the two tubes and they look almost identical. Does anyone have any opinions on whether this would be an acceptable substitution? The circuit can be found here:
http://www.dogstar.dantimax.dk/tubestuf/mctube.htm
> like to use a 6SL7 instead of a 12AX7
Very different tubes.
> I looked at the curves of the two tubes and they look almost identical.
??? Well, they are both triodes, High-Mu, with 1 watt heaters. How different could they be? In fact the zero-bias lines lay on top of each other. But the 12AX7 has 40% more Mu than the 6SL7. And at the low currents typically run on 12AX7, the plate impedance is significantly higher.
Note that the -2V line on 12AX7 lies close to the -2.8V line on 6SL7.
> Real McTube II distortion unit
Fuzzboxes are all about "too much gain", so the loss of gain may be significant. Also Fred's plan "mis-biases" the tubes to get them off their most linear swing; a different tube will need re-mis-biasing to get the same/similar effect.
There is no octal quite like the 12AX7.
The octal with Mu=100 like 12AX7 is the rare (but only $6-$7) 6F5 (double-ended) and 6SF5 (single-ended) single-triode. Because it is an old design, and uses more heater (per cathode) than 12AX7, it may be more linear. Like the difference between Tri-X film in 120 and 35mm sizes: big difference in the knee of the curve.
Very different tubes.
> I looked at the curves of the two tubes and they look almost identical.
??? Well, they are both triodes, High-Mu, with 1 watt heaters. How different could they be? In fact the zero-bias lines lay on top of each other. But the 12AX7 has 40% more Mu than the 6SL7. And at the low currents typically run on 12AX7, the plate impedance is significantly higher.
An externally hosted image should be here but it was not working when we last tested it.
Note that the -2V line on 12AX7 lies close to the -2.8V line on 6SL7.
> Real McTube II distortion unit
Fuzzboxes are all about "too much gain", so the loss of gain may be significant. Also Fred's plan "mis-biases" the tubes to get them off their most linear swing; a different tube will need re-mis-biasing to get the same/similar effect.
There is no octal quite like the 12AX7.
The octal with Mu=100 like 12AX7 is the rare (but only $6-$7) 6F5 (double-ended) and 6SF5 (single-ended) single-triode. Because it is an old design, and uses more heater (per cathode) than 12AX7, it may be more linear. Like the difference between Tri-X film in 120 and 35mm sizes: big difference in the knee of the curve.
He can just try that tube... and see (hear?) the results. Usually lower gains in Real McTubes (and other starved plate pedals) are the best solution to get a better overall sound... In fact Fred himself(RIP) suggested to use lower gains tubes for better sound... For me nothing beats the creamy overdrive of an ECC82 when compared to the noisy fuzzyness of the ECC83...
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.