What is the B+ average on a HDRX20 head?

[88prs]

What is the B+ average on a HDRX20 head? I guess I could tear apart and measure but since the bias is easy to do externally, I would like to calculate based off the B+ and decide the best tube.

 

[László]

That head is gonna need better than a B+ average to get into a good grad school.

[cymbal crash]

 

[88prs]

From PRS (Matt) and Thank YOU!.....

" We recommend a bias of 30mV because that allows for optimum operation of the tubes through a range of 333 - 400 VDC on the plates. So I would say that the average B+ is ~370V. "

Let's me know what variety of 5881 I can slam in there, or 6L6.... but I knew that already since a 6L6's can take about anything, but more output and glassier sounding.

Cool!!!!

 

[Em7]

If I had designed that amp, it would have a B+ that is closer to 300VDC than 400VDC.

 

[DreamTheaterRules]

If I had designed that amp, it would have a B+ that is closer to 300VDC than 400VDC.

Why?

 

[Bogner]

Why?

Who Knows? I Would Have Guessed He Would Design A Solid State Amp.

 

[DreamTheaterRules]

Who Knows? I Would Have Guessed He Would Design A Solid State Amp.

LOL, but no, I’m serious.

 

[Bogner]

LOL, but no, I’m serious.

Me Too!

 

[Simon Says]

Why?

Lower V+ is more preamp compression. Modern amps often have lower plate voltage.

 

[Simon Says]

Further to that, some builders like Fortin, Friedman, Larry and others are using PT with higher voltage taps and splitting V+ on V1 via two resistors. First, V1 via 100k plate resistors feeds a clean channel for big headroom, and the drive channel is fed by a second resistor in series (100-220k) for more compression.

It is probably what PRS do as well

 

[Bogner]

Further to that, some builders like Fortin, Friedman, Larry and others are using PT with higher voltage taps and splitting V+ on V1 via two resistors. First, V1 via 100k plate resistors feeds a clean channel for big headroom, and the drive channel is fed by a second resistor in series (100-220k) for more compression.

It is probably what PRS do as well

"Builders" And "Fortin" In The Same Sentence?

 

[DreamTheaterRules]

Lower V+ is more preamp compression. Modern amps often have lower plate voltage.

I’m familiar with what various changes do, I was curious as to why he’d prefer it that way.

 

[DreamTheaterRules]

Lower V+ is more preamp compression. Modern amps often have lower plate voltage.

P.s. I’m guessing his preference would be more for the effects on the power stage… softer, more “vintage” sounding and less odd order harmonics.

 

[Simon Says]

P.s. I’m guessing his preference would be more for the effects on the power stage… softer, more “vintage” sounding and less odd order harmonics.

It's a preference on a paper. My Fillmore 50H has 440v on the plates, yet it's full of harmonics and quick enough to be mistaken for a modern amp when gently boosted.

"Builders" And "Fortin" In The Same Sentence?

Not a fan of Mike?

 

[Simon Says]

For the OP. Get this meter. That's the only one I know of giving the plate voltage info without risk of shock. https://www.eurotubes.com/store/pc/Eurotubes-Pro-One-Bias-Probe-for-octal-power-tubes-6p144.htm

 

[Bogner]

It's a preference on a paper. My Fillmore 50H has 440v on the plates, yet it's full of harmonics and quick enough to be mistaken for a modern amp when gently boosted.



Not a fan of Mike?

There Are A Few "Mike's" I Don't Hold In High Regard...

 

[DreamTheaterRules]

It's a preference on a paper. My Fillmore 50H has 440v on the plates, yet it's full of harmonics and quick enough to be mistaken for a modern amp when gently boosted.

Yes, but he said his preference would be to reduce B+ from 400v to 300v. All other things being equal, wouldn’t we expect a bit softer “more vintage” sounding power stage, with some reduction in odd order harmonics, with that change? Admittedly, I haven’t looked at a schematic, but have seen one for other “versions” of this circuit. And, I’m now a solid 10 years past any reading or study of that stuff….

 

[Simon Says]

Yes, but he said his preference would be to reduce B+ from 400v to 300v. All other things being equal, wouldn’t we expect a bit softer “more vintage” sounding power stage, with some reduction in odd order harmonics, with that change? Admittedly, I haven’t looked at a schematic, but have seen one for other “versions” of this circuit. And, I’m now a solid 10 years past any reading or study of that stuff….

No, it would be just the opposite. That's kind of what EVH was doing with starving his Marshall to 90vdc, effectively reducing the plate voltage for a more compressed tone.

JTM45/100, to me, is a definition of vintage tone. B+ on the plates could be as high as 550v, and more in these amps. The 200w Major had close to 720v on the plates - these amps have been dedicated to bass players and hardly expected to clip

 

[DreamTheaterRules]

reducing the plate voltage for a more compressed tone.

I think we’re saying almost the same thing but you’re disagreeing…. Let’s forget “vintage” then as that must be what’s throwing you off. I meant, reduring the voltage would soften the power stage. Reduce punch and impact… you said “more compressed.” That’s what I’m talking about. Less punch, softer/more compressed…. I know every vintage amps isn’t that way, but was referring to the ones that are. If I wasn’t clear I guess that’s on me, but I think we’re saying the same thing.

 

[Simon Says]

I think we’re saying almost the same thing but you’re disagreeing…. Let’s forget “vintage” then as that must be what’s throwing you off. I meant, reduring the voltage would soften the power stage. Reduce punch and impact… you said “more compressed.” That’s what I’m talking about. Less punch, softer/more compressed…. I know every vintage amps isn’t that way, but was referring to the ones that are. If I wasn’t clear I guess that’s on me, but I think we’re saying the same thing.

Probably I'm four hours past my bedtime.