[quote]
**By the way, "5C3S" is an equivalent of 5u4, a "GZ34" is equivalent to a 5AR4. The voltages are different. It wouldn't be a good idea to put them in your Mesa if it a fixed bias amp. If you make the change to a "GZ34" in an amp designed for a 5U4, you need to check with an amp tech, or the Manufacturer as to whether it is safe. Otherwise you can do internal damage to your amp. I'm pretty sure you would have to re-bias your amp if you make that change, and a DR is a fixed bias amp.
Hope this helps. Cheers.
Shred
Hi.Thanx for useful info.
This wrote Bob from Eurotubes in his huge section about Mesa DR.
I quite often use the JJ GZ34's in place of the 5U4's to get a punchier and less mushy sound in the tube rec mode and the voltage drop is only about 10 volts down from the solid state diode mode. If the amp is played at high volumes with the GZ34's depending on your line voltage you may need to jump the fuse up from 4 amps to 5 amps which is what I do in my Dual Rec because no matter whether I'm running a combination of 6V6's and KT77's or KT66's and KT88's I'm always in the tube rec mode and usually in the Bold setting where the voltage is at it's highest.
Bold setting and in the tube rectifier mode utilizing the two GZ34's which gets the plate voltage to 450 volts and the current draw to 28mA per tube which is perfect! Using the solid state rectifier gets them a little too hot.
Using the GZ34's will get you that tube rectifier sound without the saggy feel that the stock 5U4 rectifier tubes give you so it's like playing in solid state bold but you get the rectifier tube dynamics.
http://eurotubes.com/euro-n.htm