Alternate tubes for SEX 3.0?

[audioengr]

The 6BL7GTA is a very similar tube.  Is it possible this tube could replace the 6DN7 in this design, particularly if headphones are efficient?

Both sides are the same versus the 6DN7.

[Natural Sound]

No, Its altogether different. The S.E.X. 3.0 uses a 6FJ7 which is electrically identical to a 6DN7. The only physical difference is that the 6FJ7 has a compactron base and the 6DN7 is octal. 

[Paul Joppa]

The 6BL7 draws 1.5 amps heater current per tube, much more than the 0.9A of the stock tube. It is similar to the power triode of the stock tube, but very different from the input triode.

The only drop-in alternate that I have calculated is a 6SN7-GTA or -GTB. (Only the GTA/GTB versions are rated for enough plate dissipation.) I have not actually tried it, so no promises! It would have a poor damping factor (less than 1) and produce less than 1 watt per channel, if it does in fact work. Neither should be a problem with most headphones.

[Paul Birkeland]

The 6BL7 draws 1.5 amps heater current per tube, much more than the 0.9A of the stock tube.

To expand on this a little, using the 6BL7 will blow the low voltage diodes in a SEX amp and potentially will destroy your power transformer as well.

[audioengr]

Thanks for your feedback.  Don't want to fry the transformer or the diodes.

[attmci]

Thanks for your feedback.  Don't want to fry the transformer or the diodes.

You can use a coupe of these as output tubes on Crack. No issues.

[Paul Birkeland]

I thought I'd expand on this thread a bit since there's some ambiguity. 

The SEX 2 had octal sockets, so the 6BL7 would at least plug into the sockets.  This tube would blow up the 1N5820 diodes due to thermal stress.  If they shorted, then they may take the power transformer with them.

The S3X has 12 pin sockets, so the 6BL7 won't plug in.  If you changed it to octal sockets, then plugged in 6BL7s, the diodes might take the thermal stress, but the heater winding on the power transformer would give up after a short time.

This, of course, doesn't cover the actual operational issues of attempting to make a 6BL7 work in a SEX amp of any kind.