Carvin BX500: Pt. 3

[Vic]

Hey folks...

I ran across a Carvin BX500 here locally and I had some questions about it.

The owner says he bought it a couple months ago new off ebay without a tube. I checked there and carvin has a listing for them that way so I'm figuring that's legit.

I could be wrong, but I couldn't find anything on Carvin about ordering one without a tube. Sounds like bullcrap to me. Regardless, putting a 12AX7 in the amp is trivial to do, and it's switchable in/out from a button on the back, so it should just be in there.

IMHO, the tube doesn't make a night/day difference, so I would just go for any quality 12AX7, and if I would select on anything, it' be to look for one that tested low in "microphonic" levels.

 

[Vic]

I bought mine from ebay without a tube.

Ok, my interest is piqued. Got a link?

 

[optikhog]

Carvin sells 'em that way on the 'bay:

CARVIN BX500NT 500W BASS AMP AMPLIFIER HEAD w/ NO TUBE | eBay

 

[Vic]

Carvin sells 'em that way on the 'bay:

CARVIN BX500NT 500W BASS AMP AMPLIFIER HEAD w/ NO TUBE | eBay

Ahhh, ok. It's an ebay-only thing, but from Carvin, ok, that's cool. Strange (to me), but cool... has it's own part number "BX500NT", clearly NT means no tube.

Thanks.

 

[Robear22]

I was going to get one but decided to get one with a tube. Like you all say the tube warms the sound up but I have been preferring it bypassed.

 

[optikhog]

Ahhh, ok. It's an ebay-only thing, but from Carvin, ok, that's cool. Strange (to me), but cool... has it's own part number "BX500NT", clearly NT means no tube.

Thanks.

Yah, they've been listing them out on eBay for some time now, one listing at a time. I dunno if it's to get it sold for a lower price (given that it's eBay) or what.

 

[fhm555]

Thanks for info.

 

[Chef]

After you buy a decent 12ax7, you've saved about "no money."
Might as well order one with a tube if that's what you want.

 

[masonsjax]

Unless you already have tubes laying around, like I did, or you have a preference for a certain make of tube. But yeah, the difference in sound between brands of tubes (in this amp) is negligible (to my ears anyway).

 

[fhm555]

After you buy a decent 12ax7, you've saved about "no money."
Might as well order one with a tube if that's what you want.

If what I'm reading here is correct, that one 12ax7 is about as good as another, I've got one.

I have to wonder though, why can you buy a tube for around $10 or spend as much as $80~$100 on the same type of tube if they are all pretty much the same. Is it a case of the emperor's new clothes where our single tube pre stage is concerned, or is there some other application where gold pins, wide widgets, coiled other thingys, etc, make that much difference?

The tube carvin sells as a replacement is less than $15.00 so I'm assuming that's the same thing they put in the amp. I've seen some hobby electronics where all the user replaceable parts are ultra cheap and should be replaced with better before it can be used properly, but I just don't see carvin doing that kind of thing.

 

[JimTMich]

Noobie question, buying my first amp.
I understand this amp can be really clean sounding.
Does the tube offer some interesting sound?
Can we crank up the gain and down the master to get some interesting overdirve like on a rumble 75 or a markbass lmIII?

Thanks

 

[::::BASSIST::::]

First I've never heard any overdrive coming from an LMII/III.

For the record, I dont think the tube does much or anything. On my bx1500, the bx500's bigger brother, I just disengage the tube and it sounds great. I'm not into overdrive or anything so...

For my personal taste if I were to buy a bx500 I would not care if it didnt have the tube.

 

[JimTMich]

First I've never heard any overdrive coming from an LMII/III.

I guess I'm thinking of the "Vintage Loudspeaker Emulator"......

 

[Vic]

First I've never heard any overdrive coming from an LMII/III.

I guess I'm thinking of the "Vintage Loudspeaker Emulator"......

Nope, that doesn't introduce overdrive. That just raises and lowers the "ceiling" on higher frequencies that are passed through. And before you (might) ask, the VPF also does not introduce overdrive.

 

[craig.p]

I just took a real quick look at the [Invalid or Expired Link Removed]. The tube (both halves apparently parallelled) seems to show up late in the signal chain, and I believe it's being used in a common-plate configuration, where the output to the following stage is taken off the tube's cathode resistor. But it's been three decades since tech school so maybe someone else can verify these statements. If they're true, though, then I'd expect the tube would contribute little or nothing to the sound of the amp.

 

[Vic]

...I'd expect the tube would contribute little or nothing to the sound of the amp.

At least in my subjective testing, it does contribute, but it is subtle.

 

[craig.p]

I think I discussed this before, but in case my memory has failed, I'll just say that putting the tube earlier in the signal chain and making it a gain stage would have made its presence much more noticeable because its nonlinearities (along with the BG's signal itself) would've been amplified down the line. But there's good and bad to that. The good is that you do get those nonlinearities, i.e. the nice tube-ness. The bad is that to maintain unit-to-unit consistency sound wise, you have to use the same brand tube from the beginning of the production run to the end, AND you have to make sure all those tubes fall into a very narrow range of characteristic curves. That would necessitate curve-tracing each and every one before it was installed into an amp, or trusting the supplier to do it at his shop and not drop the ball. (That's assuming you could even get enough tubes from one manufacturer that ran similarly. And what about second-sourcing?) Far cheaper, therefore, simply to stick "a" tube downstream and run it as a cathode follower: no gain, and low distortion. (Well, that's if it IS being run that way. Still need one of the tube guys here to verify w/ the schematic, 'cause if I'm wrong, you can throw out everything I've said except the part about the tube showing up late in the signal path.) Anyway . . . Must've been some interesting engineering discussions when they were coming up with this deal. Purists vs the Manufacturing Engineers, hurled items, and so on..

 

[masonsjax]

Yeah, it's not that preamp tubes never make a difference, just the design of this particular amp doesn't reveal the differences very much. After experimenting, I recommend adding a tube, but I think an el cheapo will do just fine.

 

[fenderhutz]

If what I'm reading here is correct, that one 12ax7 is about as good as another, I've got one.

I have to wonder though, why can you buy a tube for around $10 or spend as much as $80~$100 on the same type of tube if they are all pretty much the same. Is it a case of the emperor's new clothes where our single tube pre stage is concerned, or is there some other application where gold pins, wide widgets, coiled other thingys, etc, make that much difference?

The tube carvin sells as a replacement is less than $15.00 so I'm assuming that's the same thing they put in the amp. I've seen some hobby electronics where all the user replaceable parts are ultra cheap and should be replaced with better before it can be used properly, but I just don't see carvin doing that kind of thing.

If you have an amp with say 3-4 preamp tubes having a good set of tubes with low microphonics is going to make a big difference. Having a single preamp tube it's just a minor change. I can hear the difference between say a JJ/Tesla tube and a Groove Tubes or EHX tube. The JJ sounds warmer to my ears, but just a little. I just got Mullard at 25 bucks to compare to the JJ and see what the difference is. A JJ is only 12ish bucks online.

 

[Lo-E]

Craig.P, you're absolutely right. It's a cathode follower placed fairly far downstream in the signal chain. No gain, low impedance. This indicates that the tube is in there acting as a "flavor enhancer", for the most part. Different tubes will probably have some slight effect on the tone, but not much. Most of the tonal differences between tubes will be most noticeable in the first or second gain stage, where the differences are then amplified by each further stage. Not so in this case.

All that said, I do prefer the tone of mine with the tube engaged. It's a subtle difference, as others have stated, but it's there. I doubt I would notice if I changed it out for another 12AX7, however.