Crucial TUBE question

@carlsbad2

I know! But everything checks out: the PL is in the signal path alright, volume control for all sources, turn off the PL = no sound and vice-versa. The KT 150s lit up as well (mostly at their tops, because KT105s don’t glow much because of how they are constructed). I’ll say this, not as an excuse, because i should still have checked further: but Upscale promoted the KT 150 as being compatible with “all” of their Prima Lunas. There is no where on there tube info dictating to NEVER place a KT150 into a PL preamp. But, in fairness to them, they probably assume no one’s that stupid. What made me stop to ask them when everything was going great as far as I knew? I couldn’t find any posts, reviews, reports, ANYWHERE about using the KTs the way I did, only with integrateds and amps. It spooked me, so I wrote Upscale about it. Glad I did,and glad I posted about here too. All of you are being super helpful. But, still don’t know how come it worked.

Are you sure you aren't using the Home Theater bypass inputs?

But looking at the underside photo on the web site, it actually *is* possible that the KT150 worked.  There's a zener or diode wired from pin 8 to pin 7 on the rectifier sockets, and that's where the B+ is taken from. Maybe the the KT150 was acting as a half-wave rectifier, with the screen as the plate?  It wouldn't be elegant but it might work.

I will say, I have to hand it to PrimaLuna for designing a preamp that's fool-proof enough that dropping a totally inappropriate tube into the rectifier slot doesn't result in a catastrophy. ;-)  No knock on you, audiodidact.  It happens.  Much worse damage can occur when an octal tube's key is broken and the tube gets inserted in ways that can cause some serious damage.  It's possible the KT150s could have continued to operate that way, but it wouldn't be wise.  Sorry you lost the magic, but best to stick with a true rectifier tube.

But speaking of magic, you might want to try a pair of Mullard GZ32's.  Should not cause any problems, and that's a really magical rectifier, IMO.

One more thing…

What got me started down this dark path was the simple quest to  acquire the best (rectifier?)sounding  tube I could get for the PL.  My PL feeds 2 amplification outputs (Luxman switches between them): 1. Parasound Halo A1+ 2. Two Quicksilver M60s monos (with Zeros, into GR Research outboard crossover) into 1.7i Maggies.  (I use the QS for quieter jazz/acoustic, or just for a different flavor, if not great power).  So, really I wanted to have the PL kick a bit more juice to the monos.  Maybe I should’ve just started here with asking you all what tubes you’d use to get something like  that accomplished, if any tube other than the standard PL 5r4gy might do it.  

@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.