Greetings!  I tried a few searches but didn't find a clear answer - there's a good chance I'm not searching the boards correctly.  

I have several nice NOS rectifiers for the Taboo mkIII but am curious about the compatibility of some of my favorite new-production tubes that I've used in other amplifiers.  Can anyone give me a definitive answer on whether the following will work in the Taboo mkIII?

EML 5U4G-mesh
EML 274b-mesh
Sophia Princess 274b-mesh

I was about to email Steve, but saw that it was recommended to ask here on the boards first.  Thank you!

Greetings indydieselnut. All of these rectifiers will "work" in the Taboo (if the fatter 274b fits as Rivieraranch mentioned) and likely sound good. The larger issue is how long before they blow up (this event would not hurt the amp, since the fuse will blow with a rectifier failure).

Given the cost of these particular rectifiers, and based on the tube data information and warnings provided by Emission Labs, I'd recommend definitely not using these expensive 274b's; the EL 5U4G is OK but still somewhat questionable in terms of long life expectancy.

The reason for this is the value of the first capacitor in the power supply that the tube sees. If you go to the emissionlabs.com web site and look at the rectifier overview tube data comparison exhibit, you will see recommended maximum cap values of 4mF for the 274b and 33mF for the 5U4. The Sophia Electric site does not seem to provide tube data specifics, however there is a comment regarding suggested use of a cap less than 10uF with the 274b.

Steve's power supplies historically use first capacitor values equal to or in excess of 32mF. The specific 274b that Steve provides with his amps is, under the skin, actually electonically a modern 5U4 with a larger glass enclosure designed to optimally operate into a 40uF cap - which is why Steve also warns against using alternative 274'sin his amps. Check with Steve, I'm sure he will confirm this warning and the guidance provided by Emission Labs. Happy Listening!