Question about 12AX7Q and opinions needed

LMJS · Post by **LMJS** » 23 Jun 2008, 15:38

Behringer has released a line of tubes, which I suspect are coming from one of the relatively few suppliers in the world, and they are saying this about them.

"12AX7Q — Dual-triode preamp tube specially designed for “starved plate” applications that squeeze incredible tube tone into amps with solid-state power stages." From their newsletter.

I am particularly interested in the starved plate comment. Do you guys think there is any truth to this or am I just smelling some mojo? I don't know much about tubes but I also have never heard of a particular 12AX7 design just for starved plate applications. Thoughts?

soulsonic · Post by **soulsonic** » 24 Jun 2008, 08:55

I've never heard of a 12AX7 designed for starved plate designs. There are similar tubes that are designed for low plate voltages, but they are not 12AX7s and couldn't be considered to be. That being said, many people have found that certain brands of 12AX7 sound better in starved plate circuits than others - certain Sovtek ones come to mind - so, I'm assuming Behringer is selling one of those as a gimmick to compliment their various "tube" products which are all starved plate circuits.

bajaman · Post by **bajaman** » 24 Jun 2008, 09:25

What is this "starved plate" shit. Most of the designs I have seen are not starved of current - they are just run from a lower ht voltage to deliberately exploit the inherent non -linearity of the 12AX7 at these lower voltages. the heaters are of course run at the normal 6.3v ac or 12.6v ac voltages.
If you want linearity run the 12AX7 from 350v dc like Fender and Marshall do.
If you want a more bluesy (less linear) response then try 240v dc like Gibson or Vox do.
If you want extreme non-linearity like when a power tube section goes into saturation then try 50v dc and lower

All these use plate load resistors in the 47k - 220k range.
bajaman

gkaiomenos · Post by **gkaiomenos** » 24 Jun 2008, 18:31

got any link with pics?

LMJS · Post by **LMJS** » 24 Jun 2008, 18:44

Sorry, it was just the from the information in their latest E-newsletter and it can also be found on the Bugera website.
I have been searching for any legitimate info on a 12AX7Q tube (i.e. a data sheet) but haven't been able to come up with anything. I'll keep looking because I am interested in how they can say this tube is better than another 12AX7 for what is referred to as a "starved plate" application by them.

gkaiomenos · Post by **gkaiomenos** » 24 Jun 2008, 19:16

well i'm curious to see a pic of this "great" tube to see if it's a new design or just another rebrand...

JiM · Post by **JiM** » 25 Jun 2008, 00:01

Does it have an integrated yellow led for glowing-plate emulation ?

More seriously, Bajaman has modded a VT911, was there a special 12AX7 in it ?
I guess it's just standard chinese-made tubes, with additionnal sorting. Maybe some of them, not good enough to be used at high voltage (microphonics, etc.) still have enough grit in starved-plate designs ?

LMJS · Post by **LMJS** » 25 Jun 2008, 00:15

http://www.bugera-amps.com/_01/tubePage.cfm

That's a link but it just has a standard small photo shot.
Maybe someone who works in a music store can A/B one of the 12AX7Q's against a typical
12AX7 from say Tesla or another of the few tube producers?
I would be curious to see how it would sound in BajaMan's tube pedal design (the B K Butler re-do of his which uses a 12AX7A) vs. the one he uses.
I also noticed that fact that Bajaman has opened up a Behringer VT911 pedal and he mentioned on another thread that it was a Chinese type tube that wasn't all that bad.
Which leads me to wonder why Behringer themselves wouldn't use the 12AX7Q in the VT911 if it is supposed to be better for that sort of application (besides added cost)?
There are actually a lot of low voltage tube pedal designs that is could be A/B'd in.
Bajaman, have you seen Bugera stuff in your neck of the woods?
It smells like mojo to me but the A/B would be the acid test. My curiosity is piqued and poked.

bajaman · Post by **bajaman** » 25 Jun 2008, 04:07

Bajaman, have you seen Bugera stuff in your neck of the woods?

the only Bugera stuff i have seen was a couple of years ago - aluminium coned speakers in a 4x10 Behringer cabinet.
They had all perforated around the surrounds - metal fatigue - not impressed - sounds like Buggered here in english

Are they just a newer name for Behringer - because Behringer seems to be losing market share here daily

reached a peak in retail sales about 18 months ago - no one wants to sell or service it now - local agent has recently changed for the worse too.

Seriously, the Behringer VT911 (as well as being a blatant copy of the B K Butler US patent) was the most disappointing product I have ever heard - the tube heaters were run from 9v dc instead of 12.6v dc and the tube section was very poor in it's response - after modifying it to be more like the ACTUAL B K Butler Tube Driver, it started to sound quite nice - not an easy device to modify though

- which is why I have not provided any detail.
cheers
bajaman

LMJS · Post by **LMJS** » 25 Jun 2008, 12:14

I hear ya.
What I found odd was that I couldn't find a reference to any other model of 12AX7Q.
I might be searching incorrectly, but it was the first I heard of that designation for a tube.

selectortone · Post by **selectortone** » 25 Jun 2008, 12:53

bajaman wrote:- the tube heaters were run from 9v dc instead of 12.6v dc.....

Forgive me for asking:12.6v dc? Is this a new thing? Just about every old tube amp I've ever worked on has its heaters running at 6.3v ac or thereabouts.

JHS · Post by **JHS** » 25 Jun 2008, 14:43

Some Conrad Johnson Amps use 1 12AX7Q, but since now I couldn't clarify what's the difference between the Q and a normal 12AX7(A).The EH 12AX7LPS was designed for DC-heating and is more noisy and has a lot of hum when used in AC-heated circuits.

Someone told me "starved plate app" it's something like the Valvetronics stuff from VOX, but VOX uses the normal 12AX7 in those circuits.

Maybe the starved plate stuff is only marketing hype.
Never heard something about "starved plate app." in a preamp".

BTW: How is "starved plate app." defined or what's the difference to a "normal app."?

JHS

bajaman · Post by **bajaman** » 25 Jun 2008, 21:38

Forgive me for asking:12.6v dc? Is this a new thing? Just about every old tube amp I've ever worked on has its heaters running at 6.3v ac or thereabouts.

You are forgivven!!
Yes 6.3vac with the heaters in parallel was most common - also lower hum level in badly laid out circuits, but 12.6vac ( heaters in series) draws half the current from the power supply and is more useable with stompboxes - no hum if you follow sensible heater ground return practices.
cheers
bajaman

JiM · Post by **JiM** » 25 Jun 2008, 21:46

bajaman wrote: Seriously, the Behringer VT911 (as well as being a blatant copy of the B K Butler US patent) was the most disappointing product I have ever heard - the tube heaters were run from 9v dc instead of 12.6v dc and the tube section was very poor in it's response

I've built a Tube Driver almost-clone, based on Jack Orman schematic which is similar to the patent, with some mods (a Big Muff tone control and most important, a russian tube almost equivalent to a 2C51. Oh, and an univibed-Phase45 too

). I like it a lot, but since i have now a small class-A tube amp i realize that it is a bit on the buzzy/agressive/blocking-distortion side.
As i read some of your posts on this subject, it seems to be a characteristic of the Butler patent circuit, not to be heard in the original product and your upgraded design. Could you please explain what makes it so different ?

bajaman wrote: not an easy device to modify though - which is why I have not provided any detail.

I'm modding several Behringers, and i agree it's not easy with Pb-free SMD construction. Still, i was considering buying a VT911 for modding (read "a nice box already having a tube socket in it"). Do you think it's worth it ? If yes, could you please provide some details ? If no, just forget it, i'll build your RealTube

selectortone wrote: Forgive me for asking:12.6v dc? Is this a new thing? Just about every old tube amp I've ever worked on has its heaters running at 6.3v ac or thereabouts.

FYI, the first numbers in US and Russian tube numbering system is the (rounded) heater voltage.
http://www.duncanamps.com/technical/tubenumber.html
http://www.tubedata.info/tubnum.html
Hence the 12AX7 heaters runs on about 12V (12.6V exactly), and a 6BQ5/EL84 heater runs on 6.3V.
Most 12.6V preamp tubes happen to have a middle connection in the heater circuit, allowing a parallel wiring at half voltage. In the build i'm talking about above, i'm using a NOS Russian 6N3P in place of the 12AX7, and its heaters are always parallel connected, hence needing 6.3V. I run them on 5V (because i only had a 7805 to step down the 9V power supply and still deliver 350mA !) http://en.wikipedia.org/wiki/6N3P

bajaman · Post by **bajaman** » 26 Jun 2008, 00:22

Still, i was considering buying a VT911 for modding (read "a nice box already having a tube socket in it"). Do you think it's worth it ? If yes, could you please provide some details ? If no, just forget it, i'll build your RealTube

Modding involves lifting the cathode connections from a double sided board and connecting another -ve voltage supply - it can be done but it is not easy - far better solution is to sell the Behringer and build my Real Tube Overdrive - a lot less hassle and I know you will like it much better than the stock Behringer or Jack Orman buzzy fizzy boxes.
cheers
bajaman

selectortone · Post by **selectortone** » 26 Jun 2008, 08:48

bajaman wrote:
Forgive me for asking:12.6v dc? Is this a new thing? Just about every old tube amp I've ever worked on has its heaters running at 6.3v ac or thereabouts.
You are forgivven!!
Yes 6.3vac with the heaters in parallel was most common - also lower hum level in badly laid out circuits, but 12.6vac ( heaters in series) draws half the current from the power supply and is more useable with stompboxes - no hum if you follow sensible heater ground return practices.
cheers
bajaman

Ah... one valve, two heaters in series....gotcha. Thanks.

bajaman · Post by **bajaman** » 26 Jun 2008, 10:04

maybe the Q is for quality - something that has been distinctly lacking from those Russian preamp tubes - 12AX7A, 12AX7B, 12AX7C, 12AX7XT, 12AX7XT premium selected, 12AX7XT Plus, 12AX7LP, 12AX7LPS (did I miss any out - oh yeah the 12AX7CRAP

).
Maybe they finally got to Q in the alphabet - who knows - I have lost count of how many Russian 12AX7#$#@% tubes found in BRAND SPANKING NEW TUBE AMPLIFIERS

, that I have had to throw in the rubbish tin.
Avoid any tube with that yellow EHX writing on them - just some friendly advice, based on a lot of experience. Even when they test good on my tube tester (exception not the rule) they still sound like shit

bajaman

JHS · Post by **JHS** » 27 Jun 2008, 09:55

Bajaman is absolute right. Don't buy anything labeled EHS or Sovtek, it's a waste of money.

Nearly the same with JJ ECC83S. They sell a BTB version (low noise and hum with a small BTB sticker on the box), a very good tube, IMHO as good as the old Tesla, and the stock version (both for the same price).

The stock version sounds muddy, middy, dull and often has less gain than a ECC82 and often is microphonic too. If you buy a lot of 100 you can find both versions in it. IMHO a stupid way to mix the manufacturing crap in to sell it that way.

JHS

bajaman · Post by **bajaman** » 27 Jun 2008, 10:30

Nearly the same with JJ ECC83S. They sell a BTB version (low noise and hum with a small BTB sticker on the box), a very good tube, IMHO as good as the old Tesla, and the stock version (both for the same price).

i test EVERY tube before fitting in any amplifier i am servicing and I too have noticed some decline in the quality of the JJECC83S - I have been using the Silver Series Groove Tubes ECC83S and have noticed lower emission qualities AND uneven - one side 95% - the other 45% emission - these are brand new Groove Tubes JJ type.
The most consistant tubes currently on the market - and for the past 5 years or so have been the Chinese 12AX7A - rarely micro[phonic - always high emission qualities - they just lack a little detail at the top end and tend to have a boomy bottom end sometimes - they sound great in Marshall JCM 800 amps but make Fender Twin Reverbs sound very middly.
As for those Russian 12AX7 tubes - I have had many that do not make it past 5% emission - brand new

Strangely, I have encountered these tubes in brand new made in China Vox AC15 and AC30 amplifiers as well as Orange Rockerverbs. recently i have noticed that these amps are now coming fitted with either JJ or Chinese tubes and they do not have the same warranty problems as they had with the ruskis

bajaman

Tube2stomp · Post by **Tube2stomp** » 07 Jul 2008, 10:33

12AX7QRAP