Tube buffered phase inverter

P

paulyc

Well-known member
Anyone ever heard of this ? What would be the advantage ? I saw it on a Hermanson build thread on FB. I’ve reached out to Henrik, waiting for his answer but figured I’d ask here too.
 
That doesn't make sense to me :dunno:

Without searching the internet I would just say it is more of tube vs solid state? Differences that is. But because you saw it on a Hermansson build FB post it now has me curious as well. I don't suppose you can copy paste the sentence or whatever in here for context? So unless Hermansson is adding a 'clean' tube (aka 12AU7 or similar) before the phase inverter tube for some sort of capability or enhancement - I'd have no idea. Even that wouldn't make sense as the PI is part of the power section. But then again, I'm not an EE nor amp tech etc.
 
The amp in question is that 6 6550 output tube Marshall 2000 series amp from 1981 I think that was rebuilt for the guy from Messhuga (or whatever), the list of features included a tube buffered PI and a tube buffered efx loop. The amp has 6 12-x7 tubes in it and 6 6550s. No separate clean. It’s his 5 gain stages design.
 
That helps. Again, I think because the PI is part of the power section, I think the writer (of that description) is just saying the phase inverter is tube vs solid state. Which to most of us, would be pretty obvious as Hermansson wouldn't put a solid state phase inverter in one of his amps (in this case, his modded Marshall). That would take some serious reverse engineering to do that me thinks. Again, I'm not an EE nor amp builder. So my guess is that this Meshuggah amp has 2 or 3- normal preamp tubes, a 12a_7 tube for buffered FX, and a 12a_7 in the power section as the Phase Inverter. Keep in mind, a preamp 'stage' does not equate to the number of preamp tubes. Each preamp tubes has 2 sides, A and B. Each can act as a 'stage'. A picture might speak a thousand words. I'm jumping on google now :LOL:

Do any of the smart people here want to confirm or correct that?
 
I’ve never heard the phrase “tube buffered phase inverter” so I’m not totally sure what he may mean by it.

I’ve read about “post phase inverter driver” tubes, which is basically another tube between the phase inverter and the power tubes. I’m not super well versed on it, but they seem to have been used on some larger amps that run 3 tubes in parallel (like maybe a 6 X 6550 amp)
 
Ive never seen a tube amp with a solid state phase inverter, and I don’t think he’s referring to a regular tube phase inverter. I know VHT/Fryette used 12AU7 tubes as the phase inverter tube to drive their power sections, the way it was explained to me was the AU7 has less gain but more current and lower output impedance, so it actually drove the power sections harder but cleaner. BUT, AU7 tubes are getting hard to find, so I was wondering if using a tube buffered phase inverter accomplishes something similar (more current/lower impedance) but still uses commonly available AX7 tubes.
 
311splawndude said:
That helps. Again, I think because the PI is part of the power section, I think the writer (of that description) is just saying the phase inverter is tube vs solid state. Which to most of us, would be pretty obvious as Hermansson wouldn't put a solid state phase inverter in one of his amps (in this case, his modded Marshall). That would take some serious reverse engineering to do that me thinks. Again, I'm not an EE nor amp builder. So my guess is that this Meshuggah amp has 2 or 3- normal preamp tubes, a 12a_7 tube for buffered FX, and a 12a_7 in the power section as the Phase Inverter. Keep in mind, a preamp 'stage' does not equate to the number of preamp tubes. Each preamp tubes has 2 sides, A and B. Each can act as a 'stage'. A picture might speak a thousand words. I'm jumping on google now :LOL:

Do any of the smart people here want to confirm or correct that?
Click to expand...
Heinrik wrote the description.
 
Aynirar27 said:
I’ve never heard the phrase “tube buffered phase inverter” so I’m not totally sure what he may mean by it.

I’ve read about “post phase inverter driver” tubes, which is basically another tube between the phase inverter and the power tubes. I’m not super well versed on it, but they seem to have been used on some larger amps that run 3 tubes in parallel (like maybe a 6 X 6550 amp)
Click to expand...
Bruce Egnater agrees with you… still waiting on Henrik.
 
Marshall ALSO made an 8 6550 sister amp to this, for bass, the 2001. Imagine THAT with these mods…
 
paulyc said:
Ive never seen a tube amp with a solid state phase inverter, and I don’t think he’s referring to a regular tube phase inverter. I know VHT/Fryette used 12AU7 tubes as the phase inverter tube to drive their power sections, the way it was explained to me was the AU7 has less gain but more current and lower output impedance, so it actually drove the power sections harder but cleaner. BUT, AU7 tubes are getting hard to find, so I was wondering if using a tube buffered phase inverter accomplishes something similar (more current/lower impedance) but still uses commonly available AX7 tubes.
Click to expand...
As @Aynirar27 mentioned already, when driving lot of high power tubes, you have an option to:
- Insert driver tubes with higher anode current (i.e. 12AU7/ECC82, which are pretty available) after the PI (which then can be based on 12AX7/ECC83). This approach is used i.e. in a Marshall VBA400, where 12AU7's are used as cathode followers IIRC.
- You can use "stronger" tubes in a PI, I believe Ampeg has that at least in some bass amps.
 
Maybe they say things differently across the pond but I think it’s gotta be a long tail PI given everybody’s used one for the past 70 years of amp building. There’s not a lot of room to reinvent the wheel in terms of phase inverters.
 
Chubbs said:
Maybe they say things differently across the pond but I think it’s gotta be a long tail PI given everybody’s used one for the past 70 years of amp building. There’s not a lot of room to reinvent the wheel in terms of phase inverters.
Click to expand...

Maybe he meant to say tube buffered loop. Otherwise, I'm gonna advertise all my amps like this:

Tube buffered input stage for increased raunchiness!
Tube buffered tone stack for the most brutal brown-sound tightness with a bouncy squish!
Tube buffered phase inverter for more phase! Get 3x the inversion!
Tube buffered POWER! TUBES!

*solid state loop
 
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