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In Reply to: RE: 274B Rectifier posted by nhparrot on March 07, 2015 at 08:27:24
Only Western Electic made a true 274B. The current crop of 274Bs are essentially 5U4Gs with a 274B label on them. Notice the filament current is fudged a little at 2.5A while the 274B is 2A and the 5U4G is 3A.
Follow Ups:
The Valve Art 274B looks just like a 5U4, but the EML 274B mesh plate is another animal altogether. Just popped one in my 26 preamp and I have to say, it's the best sounding rectifier I've ever used in there, and I've tried 5AR4, GZ33, 5R4GY, 5R4 potato masher, 5U4G, 5U4GB, 6106, 5Y3GT, 5Y3G, and Valve Art 274B.
The sound is at once more detailed and cleaner while also being more 3D and warmer than the Sylvania 5Y3G I had in there - neat trick! Ya pay the price, though.
G
Perhaps you'd like to expound on your ideas, rather than hit and run?Rather than looking at the power supply as a source of power for the amplifier circuit, maybe we should look at the amplifier circuit as merely a means to modulate the power supply. After all, the original signal never makes it out of the amp, only a copy impressed upon the PS does. Does that perspective change things?
Edits: 03/07/15
Try the two different rectifiers that give different sound. Measure B+. If its different you've changed all the operating points. I have done this and picked the one that gave higher B+, variac -ed the voltage down till it was the same and then it sounded pretty much the same. Yes we are "painting with DC" really, really, really fast, when it comes to tube amps.
The preamp has a CCS-fed VR tube regulator holding the B+ at 225V, followed by a plate plate CCS that fixes plate current at 7mA. Voltage changes upstream shouldn't change the 26 operating point in that setup.
I'm leaning toward some kind of noise/resonance reduction being the cause. Or maybe I'm just nuts...
The higher the voltage across the depletion mode MosFet, the lower the self capacitance of the MosFet.
Assuming the circuit maintains enough voltage across your CCSs no matter which rectifier tube you try to keep this from being an audible factor........I'm gonna go with "just nuts". :-)
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Well in all cases the voltage difference is 225-165=60V, since it's regulated, plenty to keep the capacitance of the plate CCS low.
What about the CCS feeding the VR tube(s)?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Lowest voltage I've seen is from the 5Y3G, about 270V. 270-225=45V, still quite a bit of headroom.
Edits: 03/08/15
I've played with enough rectifiers in enough different circuits to be convinced that some just sound better than others. This despite all the CCS's, Chokes, regulated PSUs different caps etc etc.
Yes, I have a technical background but I'm not afraid to say I hear the difference and no, I can't explain it either. And it's not imagined because all of my audio buddies pick the same as I do in blind testing, they have always been my nuts barometer:)
So I'm with you ... same as on Schottkies for bias.
Cheers,
Naz
Good to know I'm not alone in my dementia.
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