Modwright PH 9.0X Tube Rolling Question

Correction: Kristen did list the GZ34 (5AR4). My error.

Maybe because changing from a 5R4 or the like to a 5AR4 will increase the DCV delivered to the tubes by 50V. That’s a big difference.

It’s interesting to me that Kristen at Modwright did not list the 5AR4 as an option (see above). Whereas Dan mentions the GZ34, which is a 5AR4 by another name. 

Travis, I can only tell you that if you look up what tube rectifiers are cross-compatible with the 274B, the only tube that comes up is 5U4G.  I leave it to you to do further research. One other found fact: the 274B does not like to be followed by a filter capacitor of greater than 10uF value.  Many rectifier tubes come with a specification for the max value of the first capacitor following the rectifier.

This reference might help:http://www.fourwater.com/files/fullrect.txt

Keep in mind, 5AR4 and 5R4 are very different electrically.  5AR4 drops 17V, whereas 5R4 drops 67V.  This means that the resulting B+ voltage available to run the audio circuit is 50V higher when using the 5AR4, compared to 5R4.  There are other differences in requirements as well.  Thus any difference in ultimate SQ could simply be due to the differences in these other parameters.  In some cases, the 5AR4 might stress downstream tubes served by the PS due to increases in plate voltage and/or possible changes in bias voltage.

Just a pedantic note, 7DJ8 is not equivalent to all those other tubes.  7DJ8 requires a 7V filament supply.  You probably could get away with an actual 6.3V, since most tubes allow a 10% error, but no less than 6.3V for best results.

I agree that tube rectification adds a certain je ne c’est quoi, but I have never understood why.  Among solid state rectifiers, only Schottkly diodes equal or surpass tube rectifiers in my personal experience. (Others may legitimately differ.) Does Wright use a choke load on the rectifier tube?

Blisshifi, My bad. The prior post led me to believe that the unit uses only 6922.

6C45 is a single section triode. How did you manage to use them as a sub for 6922, a dual triode? Not to mention that the two types are electronically quite different even if you could mount two 6C45s to replace one 6922.