Has anyone auditioned the Balanced Audio Technology Rex II amplifier?
I think it is a Class A amp using 6C33C output tubes.
I think it is a Class A amp using 6C33C output tubes.
Balanced Audio Technology Rex II Amplifier
- Thread starter Ron Resnick
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- bat rex ii
Heard it several times...sounds good. Wonderful heat engine though. Can heat up a large room in no time at all! 6C33C's based tube amps sound very similar to my ears, and all are quite enjoyable. However, the heat they put out is just a complete loser...I would never consider an amp with multiple 6C33C tubes...totally impractical, IME.
Ron, why don't you place a very large space heater in your current room and see how long it takes before you want to vacate that space....close the space off and don't run the AC...and wear normal clothing. Remember, we live in S.Calif and it's warm almost all of the time.
This should give you a fair idea as to the operating conditions of most of the amps that you have inquired about. If no big deal, then great--most of them sound very nice.
I checked out the BAT site for details on their Rex II amp and don't see any indication of it operating in Class A, in fact there's no mention of its class of operation at all. If it was operating in Class A mode I'd think that they'd be promoting it as such, but it is reputed to be a fine sounding amp regardless.
Never had the later Rex, but did own the VK-75SE (and a ton of other BAT gear). Single chassis in my large listening room with 4 6c33s - didn't have heat issues. Only issue is it would trip a fuse once in a while (but I had power gremlins in that home)
Wonderful amp on Wilsons. BAT gear tends to be an entire system approach though.
Wonderful amp on Wilsons. BAT gear tends to be an entire system approach though.
It can't be class A at full power - the specifications show that power consumption is variable between 500 and 1000W.
So it is push-pull?
The "all triode" and unique design of parallel banks of the phases is just marketing speak for push-pull?
The "all triode" and unique design of parallel banks of the phases is just marketing speak for push-pull?
No, BAT is a circlotron, see their FAQ:
Amplifiers
Is the REX II Power amplifier a single-ended amplifier design?
"
No, the REX II Power amplifier is neither a traditional single-ended design nor a push-pull design. We refer to the REX II, VK-255SE and VK-655SE amplifiers as single-ended bridge designs. This fundamental circuit dates back to the early 1950's and was invented by Henry Wiggins while working for the ElectroVoice Company. The original name for this type of output topology was Circlotron. The single-ended bridge design relies upon two single-ended amplifiers arranged in a floating bridge formation. This differentiates it from other forms of bridge topologies, most of which effectively incorporate two push-pull sides. The output circuit is inherently balanced and is driven differentially from a preceding stage. The two DC bias currents that exist in each half of the output stage cancel each other in the load. It is a more expensive way of building an amplifier as it requires multiple floating power supplies, as opposed to the more traditional ground-referenced supplies. The benefits of this approach, however, include enhanced symmetry when compared to push-pull designs and lack of the DC saturation problem inherent to single-ended designs."
I have no experience with REX or recent BAT equipment, but a few friends owned the older designs in the late 90's. At that time the distributor had a lot of problems because of the 6C33 quality - in part because the factory sourced tube sets were very expensive and people used cheap russian tubes.
So we can think about it as an OTL style circuit design (two banks of parallel but out of phase tubes and then summed at the end) but with an output transformer?
I used to own a BAT VK75SE and later added a 2nd for a VK150SE. They are a very flexible design and you can strap more together. Pretty sure TAS did a review with 4 Rex amps. 2 per channel. I agree on the heat. Make sure your AC is up to it (when I moved to Austin was either new amps or new ac for me...I switched the amps) They are very well built. You will need a few spare output tubes...but they've added a protection circuit vs fuses so it's plug and play.
As for your question, their website seems to hit the points you are looking for "Think of REX II as two single-ended amplifiers per channel, with their waveforms summed at
the output transformer. "
http://balanced.com/sites/default/files/BAT_REX_II_Amplifier_Product_Sheet.pdf
The fact this amp has been in continual production, with upgrades, over what 20 years says something about its original design. I started off with a VK60...Had a VK51SE and VKP10SE and then added the 75SE/150SE...was a great system.
I had a whole VK system. P-10, 32 SE, Both Super Packed and VK150s. That was so long ago though I actually still have them all. I don't think I can imagine a comparison. The 150 se was a single generation jump and they were already much better than mine when they added the 6H30 input module. The REX module is a much more drastic change than that.
Thank you, gentlemen. I know what the BAT marketing literature says, but I do not understand it. It suggests to me a Class A, parallel push/pull design, using an output transformer. But I agree with Bill that if it were Class A the literature surely would make that clear.
I do not understand why the marketing literature describes the design as two SETs summed at the output with a transformer. Isn't that like an OTL Circlotron circuit but with an output transformer?
I do not understand why the marketing literature describes the design as two SETs summed at the output with a transformer. Isn't that like an OTL Circlotron circuit but with an output transformer?
As microstrip observed it simply can't be Class A at full rated power based on its power consumption. I'd respectfully suggest contacting BAT directly if you're looking for a more detailed explanation as they're known for providing excellent support.
Ron, I have a question?
Why do you care what the output type is...as long as it sounds great! Personally, I couldn't give a rats ass as to this issue...
If a Class D amp floats my boat and works with my system sound wise, that's all I need. Sure knowing the type of output is a talking point, but IMO, that's all.
Go and have a listen to the amps you are inquiring about, see if you can demo those in your room and your system and then make an 'informed' purchase.
Simple, No??
The real concerns for me prior to purchase...and sure i know YMMV, are a) price, b) compatibility with my speakers ( IOW, does it work and sound great in my room and with my particular speakers set up)
c) How much heat does it give off? d) Expected reliability e) Ease of use...do i have to change half of my system to utilize the amp in question...i.e if a balanced only design, change out my preamp to accommodate the connection...a no no to me, or is the biasing procedure a nightmare..these kinds of things.. f) Likelihood of the company existing in the future ( you would be surprised how important this one can be!)( Although we never really know this, but the guy working out of his garage/basement and producing just a few amps a year would concern me....even though my friend at CAT does something like this...and it concerns me ( although he does have a long track record
) and lastly, g) How easy is it to transport the amp(s) in the event that I need to move them across country, etc. ( Right now one of my beloved amps --which weighs 180+lbs shipped, costs a small fortune to transport across country--oh I know this is nothing to some people, but not all!). All IMHO.
BAT VK-150SE monoblocks x 4 --> DALI MegaLine III. Still have all of these amps. I initially matched the 6H30P-DR input tubes,
6SN7 drivers, and 6C33C output tubes using an Amplitrex AT1000. From the subset which passed the Amplitrex screen, I further
evaluated the tubes using a Tektronix 576 Curve Tracer. I maintained the same protocol for tubes which graced the BAT Rex, which
I have also kept.
Still have the Atma-Sphere MP-1 Mk. 3.2 preamp, though a Grace Design m905 splendidly serves the preamp function in my current rig.
Four A-S MA-1 Mk. 3.2 monoblocks drive the MegaLine, today.
BAT VK-150SE monoblocks x 4 --> DALI MegaLine III. Still have all of these amps. I initially matched the 6H30P-DR input tubes,
6SN7 drivers, and 6C33C output tubes using an Amplitrex AT1000. From the subset which passed the Amplitrex screen, I further
evaluated the tubes using a Tektronix 576 Curve Tracer. I maintained the same protocol for tubes which graced the BAT Rex, which
I have also kept.
Still have the Atma-Sphere MP-1 Mk. 3.2 preamp, though a Grace Design m905 splendidly serves the preamp function in my current rig.
Four A-S MA-1 Mk. 3.2 monoblocks drive the MegaLine, today.
Sam, when I last heard your system, you were using the Atmaspheres to drive your Dali’s. I thought these amps drove those speakers splendidly...and I did not notice that they gave off too much heat. ( at least not more than you would expect from tube amps of that size). Certainly not enough to over heat your room. OTOH, I did not hear the BAT’s. ( you were not using them). Do you think their heat output is a factor for you?
Hi Davey,
The Atma-Sphere amps are a wonderful companion for the Dali. A-S amps x 4 yield quite a bit of heat as will the BAT's.
Heat is not so much a factor for me, however, as central A/C is available. SDG&E says I'm #1 in the neighborhood
The Atma-Sphere amps are a wonderful companion for the Dali. A-S amps x 4 yield quite a bit of heat as will the BAT's.
Heat is not so much a factor for me, however, as central A/C is available. SDG&E says I'm #1 in the neighborhood
Hi Davey,
The Atma-Sphere amps are a wonderful companion for the Dali. A-S amps x 4 yield quite a bit of heat as will the BAT's.
Heat is not so much a factor for me, however, as central A/C is available. SDG&E says I'm #1 in the neighborhood
Sam, LOL...maybe you need Solar...would get you away from the clutches of the dreaded Stupid Dumb Grabbing money & Evil mongers. Worked for me...so far.
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