Crucial TUBE question


I  placed a KT 150 power tube into a Prima Luna Evo 300 preamp rectifier slot. I know. But what happened was surprising. The sound was, well, magnificent glorious. Nothing burned out. No smoke. No arc lights. I asked Upscale Audio to advise me as to what damage I may have done or could have done to the PL. They only said they would not advise placing anything but the original tubes in the slot. They would not commit to whether or not that power tube could be used in place of a rectifier to tube. So, is it an absolute or not? If so, why?  I’d appreciate feedback (please, no slams) from anyone having any experience with this. Thanks!

128x128audiodidact

@dogearedaudio,

Just saw your post after my last upload.  That’s sounds promising.  I’ll definitely look into it. Thanks.  

If you want the best possible rectifier for your PrimaLuna, then spring for a pair of vintage NOS Mullard GZ34s. The price may seem off-putting, but they will literally last a lifetime in that preamp, and offer the best possible sound, IMO. For maybe $500 you will get a $2K upgrade in the sound of the preamp. No modern GZ34, and I mean NONE, even remotely compares to the quality of a NOS Mullard.

@dogearedaudio,

Just checked-out what’s available for NOS GZs. You’re right, they fetch a hefty price. I’l l just put it out there that since I can’t use them, I’m willing to do a straight swap of the essentially brand new Tung-Sol KT-150s (cryo/matched), for a pair of used good matched and balanced pair of the NOS GZ34s.

I don't know what it is that makes power tubes in the rectifier position have such a big bold sound. I have a unit that can use power tubes in the rectifier position, it just plugs into a 5ar4 rectifier socket.

Sounds like @dogearedaudio found the connection between pins 7 and 8 that allowed it to work.

I also agree with his recommendation of the  Mullard GZ34.

Jerry