Info & opinions on the Vaccum Tube Hybrid

[psycho72 1]

I was going through the site and happened upon these Vaccum Tube Hybrid amps that USAmps sells and got curious. I have been thinking about a tube amp, only because I have heard how warm they are (whatever the hell that means). And I have been looking for a different sound so I have been considering a tube amp. First off has anyone heard one of these first hand? What do you think? To any of you harware gurus, what do you see as the pluses and minuses on this concept?

As far a tubes themselves go, what are the pluses and minuses? Can they hack the automotive environment, especially one that has alot of bass? What do they do to the electrical system? I am looking at the AXTU-4360. What do you guys think? And if tubes are so nice, why does'nt everyone run them?

[brad 0]

I have been considering the 4360 also, I don't really know of any downsides to these amps other than the price and the fact that they have no internal crossover(but this considered a plus for many that run external processing).

As far as the current load of these tube amps, it isn't really a problem because the tubes run off a 12 volt plate voltage; therefore the draw is about the same as a solid state amp.

I think the reason that they havent really caught on is because so little people know about them, and therefore maket for them is relatively small.

[flakko 1]

let me start with the upsides and the downsides (all you audiophile tube pple correct me if im wrong)

Upside: Close to the purest sound quality you can attain from and amplifier. The VTCSD "follows" the high voltage tube signal straight into the speakers meaning nothing is blocking the signals way to the speaker.

Downside: Does tend to get hot compared to a D or an A/B and a lot less efficient.

the reason why very few people are running these amps are because as brad has stated barely anybody knows about tube/Class A amps. THe majority of the market is class A/B or D.

as for the price of these amps, well all i have to say is that they are no more expensive than thier class A/B counterparts.

pm me for the prices if you want.

edit: I am going to run an AX TU 300 or 600 for my rainbows. Ill write a review when i get it installed.

[DBfan187 0]

Tube amps are more of a Class A.(current hogs)

High THD. 2%+(warmth you hear), some people enjoy this.

Tubes are fragile & expen$ive.

[DBfan187 0]

now that I reread the thread. This is a HYBRID Tube amp.

Looks like a Class A/B w/ an tube input. Not a TRUE tube amp.

[flakko 1]

now that I reread the thread. This is a HYBRID Tube amp.

Looks like a Class A/B w/ an tube input. Not a TRUE tube amp.

<{POST_SNAPBACK}>

No this is a different type of "hybrid"

its usamps VTCSD (Vaccum Tube Current Sync Drive).

"has a direct input signal fed Directly into the tube, There are no solid state gain stages or processors in the signal path, and the original high voltage tube signal is joined by a null gain current following circuit that is pulled in to the voltage rails by an opposing pair of current syncs providing a sort of amplifier power steeringto deliver speaker driving power without taxing the character of the original tube voltage output"

whereas the plain old hybrid tube has

"a solid state input with negative feedback trhough a solidstate amplifier and transistor switching noise creating uneven clipping odd-order harmonics."

in other words, usamps has created a new type of tube amp using no solid state processors.

[DBfan187 0]

I said it has tube input, so?

Also, if it doesn't have tube output, then wtf does it have?

[flakko 1]

oh oops my bad, i misread your post :

im just quoting this stuff from a little handout i have.

"The VTCSD divides audio signal amplification into two separate areas, voltage and current. By starting with the vaccume tube as a source of hgh voltage VTCSD adds a second "amperage amplifier" the amperage amplifier is a null-gain cirucuit driven by current syncs that mirror the voltage signal and provide torque to the speakers in perfect syncronization with the voltage content that neither distorts nor colors the original tube sounds."

i dunno im still new to this kinda stuff (esp. tubes)

edit: so yea youre right DBfan, its not a TRUE class A

[JimJ 11]

Have a schematic? That would really help in deciphering how exactly it works. Unless it's a trade secret, which I'm expecting it is...

Alright, it uses a tube input followed by a MOSFET PA stage. Nothing new there

Would you happen to know what kind of input tube we're talking about here? I assume it's a 12VDC dual triode, but whether or not it's a 12AX7, 12AT7, or 12AU7 might depend on the mu and the amount of gain required to drive the transistors. Also, you might be able to change the tone of the amplifier by swapping the input tubes - I'm sure USAmps doesn't supply them from the factory with new-old-stock triodes, so some experimenting there could gain some SQ

[flakko 1]

Have a schematic? That would really help in deciphering how exactly it works. Unless it's a trade secret, which I'm expecting it is...

Alright, it uses a tube input followed by a MOSFET PA stage. Nothing new there

Would you happen to know what kind of input tube we're talking about here? I assume it's a 12VDC dual triode, but whether or not it's a 12AX7, 12AT7, or 12AU7 might depend on the mu and the amount of gain required to drive the transistors. Also, you might be able to change the tone of the amplifier by swapping the input tubes - I'm sure USAmps doesn't supply them from the factory with new-old-stock triodes, so some experimenting there could gain some SQ 

<{POST_SNAPBACK}>

dang jack maybe i SHOULD send you a schematic lol but i think they are a secret

but umm the amps from 2001 use the 12AX7 compared to the others youve stated how does it compare?

[chinny 0]

jacks a god

[JimJ 11]

jacks a god

<{POST_SNAPBACK}>

...in bed.

[psycho72 1]

Hey frosty can you share some more of your tube knowledge? I have been thinking about maybe getting an tube amp, like an old butler tube drive 1500 or maybe even a blue if I can find one for a decent price.

[JimJ 11]

Like...umm...what do you want to know?

Butler functions much the same...tube preamp stage with a MOSFET PA. So you get some of the tone/flexibility of a tube amp without the weird output impedance and low power, not to mention the high current draw of a "full" tube amp.

[psycho72 1]

Well recently I read somone bishing about tubes and basically saying that tube amps for the car were not real tubes and that they suck. So basically, what are the pluses and minuses? How do car tubes compare to home tubes? What should I be looking for? I am a poor man with rich guy tastes so I will be checking egay and the recycler and I want to know what to check for. No rush because I will be searching for months. I still have to reinstall my car, put deadener...get the speaks re aimed, etc.

[JimJ 11]

They're the same tubes...there's no such thing as "car tubes" or "home tubes".

The difference is exactly what I've been saying...the 12VDC vehicle amps only use vacuum tubes for the preamp/input stages, while home amplifiers use them for everything.

[psycho72 1]

They're the same tubes...there's no such thing as "car tubes" or "home tubes".

The difference is exactly what I've been saying...the 12VDC vehicle amps only use vacuum tubes for the preamp/input stages, while home amplifiers use them for everything.

<{POST_SNAPBACK}>

That actually what I meant, I just said it differently....nevermind...

[95stroked1500 0]

the amp is sweet. very good sounding. it's not quite designed like the tru technology pure tube amps, but is an awesome amp. it does a a cleaner crisper sound to tweeters and warmer vocals and instruments.

once you use the amp, you will understand "warmer".

[flakko 1]

the amp is sweet. very good sounding. it's not quite designed like the tru technology pure tube amps, but is an awesome amp. it does a a cleaner crisper sound to tweeters and warmer vocals and instruments.

once you use the amp, you will understand "warmer".

<{POST_SNAPBACK}>

hey man! great to see you here. i cant wait to try one for my rainbows...

[95stroked1500 0]

when i put one on my dynaudio's, i ended up listening to all of my old music over again. great amp, great speakers will really appreciate it.

[thch 0]

notes on thread:

1.) shunt components are still in the signal path. (#3)

2.) amp class is based upon biasing. there are class AB tube amps. such would be inappropriate for a hybrid amp though. (#4)

3.) sounds like a class-A output stage. and without feedback i'd hope so! (#6)

4.) audio amps are typically a voltage gain stage followed by a current gain stage. (#8)

5.) classA only means the output devices never change states from the active region to a fully on or off region. (#8, #5)

6.) not necessarily MOSFET, but likely given the MOSFET's high input impedance. (#9)

7.) do not run 12AU7, 12AX7, or 12AT7 from 12 volts. (#9)

8.) car tubes might be concidered things like (IIRC) the ECC88 dual triode which unlike the 12AU7 was designed to work at low plate voltages like 12-36 volts. further, something can be done to reduce mechanical noise in the tube. (#15)

9.) some car audio tube amps have placed orange LED's near the tubes to give excessive tube glow. because this is deceptive, it caused controversy. (#15)

10.) home tube amps are allowed to have the large output transformers and the high impedance, high efficinecy speakers that allows tube amps to drive the the speakers. car audio is not known for high efficiency or high impedance speakers. (#16)

11.) nice subjective reviews. (#18, #20)

[95stroked1500 0]

i can look and see what tubes are in the tu 600, but they run @ 50v off the top of my head. tru tech tube amps run @ around 250v on their tubes. and tru tech amps are a true full tube amplifier.

[thanosdbfan 0]

I use one TU 600 to run a couple of veritas horns...Never heard a greater sounding amp...And it does not get too hot at all (well compared to the 2000X and the 600X which i also own driven at 2 ohms)

[troublemaker 0]

i can look and see what tubes are in the tu 600, but they run @ 50v off the top of my head. tru tech tube amps run @ around 250v on their tubes. and tru tech amps are a true full tube amplifier.

<{POST_SNAPBACK}>

Whoever told you that is chatting poo.

The 12AX7's in the TU series are being run from a 300v supply, not 50 as Tru like to claim.

The TU300 from my listening sounds nicer than the TU600. a bit sweeter.

I am not over enamoured by the TU4360 as we have had issues with them cooking the 4th tube in the row as they receive their gate voltage in series.

other than that excellent amps.

The reason they are called "class a" is a bit weird.

They use a class A/B biased mosfet output stage, however by using a pair of "null gain" current following fets to drive it, it completely eliminates crossover notch distortion, which is the main difference between class A and class A/B from and audible point of view, therefore you end up with a close approximation of a class A waveform at the speaker outputs.

Hope this helps.

[95stroked1500 0]

i can look and see what tubes are in the tu 600, but they run @ 50v off the top of my head. tru tech tube amps run @ around 250v on their tubes. and tru tech amps are a true full tube amplifier.

<{POST_SNAPBACK}>

Whoever told you that is chatting poo.

The 12AX7's in the TU series are being run from a 300v supply, not 50 as Tru like to claim.

<{POST_SNAPBACK}>

no, that 50V is from what i remember, but i could be wrong. it's been over a year since i looked into that portion of the amp. i'll look it up the next time i remember. i've got the paperwork from us amps where i thought i read it. better yet,.... when ever i get caught up, i can go in the amp and test for myself as to how much V is there.

Edited November 3, 2005 by 95stroked1500