scott opt's for a st35 project?

[bsmif]

I have a chance to pick up (cheap!) some Scott transformers that were pulled from a 299 or 222( I think) that used 7189 tubes. Would those work with the diytube board? I assume I'd build it for el84's if thats possible.

[paart]

The Scott amplifiers that you reference were built for pentode operation, rather than ultra-linear mode. This means that the taps for the output tube screen grids are missing on these transformers. You can verify this yourself, simply by counting the number of leads on the primary side. Pentode=3 leads, UL=5 leads. Do check them though, as the transformers could have been changed by a prior owner. (stranger things have happened!) While it would be possible to to reconfigure the amp for pentode operation, I personally don't feel that it would be worth all the effort for a potential reduction in sound quality from the UL design. I'd continue to look for other transformers.

[TomMcNally]

Isn't a 7189 an "industrial" 6BQ5/EL-84 ?
My opinion is you'd have nothing to lose by trying it, since you already have the transformers. If you don't like the results, throw some money at it !

[paart]

Yes, the designation 7189 is/was the "industrial' version of the 6BQ5, while EL84 is the European designation for the 6BQ5. However, from both personal experience, and from reading opinions of others, choice of numbering for the tubes was apparently at the discretion of the manufacturers. While RCA, at one time made both a 6BQ5 and an 7189, I don't think that Mullard ever made anything but an EL84 (with some specifications higher than any 7189), and Siemens apparently called their "industrial" version an "84L" or something close to that. It appears that there were far more variations in performance and quality from brand to brand than there ever were between the "numbers". With the tube situation today, all bets are off! Pick a number, any number ...................................

[TerrySmith]

Go ahead and get the Scott outputs and try them with the ST35.

I triode connected one of my ST35's, and it sounds excellent!

[bsmif]

I may pick them up and try a triode st35 for the time being. Its for an office amp so big watts arent needed. I can always get ultralinear transformers later and update it if need be. Is it like the st70 you just need an extra pair of resistors to connect it in triode mode?

[mesherm]

To run the EL84s in triode, connect a 250 ohm 1 watt resistor between pin 7 (plate) and pin 9 (screen grid) of each EL84. Pin 7 should also have one of the output transformer leads connected to it.