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CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

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AlexSauter

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Location: Fort Myers FL

Post Mon Oct 03, 2011 5:27 pm

CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

***Do this modification at your own risk, I have not tried this yet and cannot confirm that it will work***

After talking to Tubular Joe for a few minutes, he explained how to rewire the input tubes to use 12AX7's rather than 6AX7's.

He explained that pins 4 and 5 on the 12AX7's are two 6.3v paths and pin 9 is the other end of said path. If you want to wire the tubes in this perticular way, you must run the tubes in parallel instead of the configuration that Bob has us running the heater wires for the 6AX7's.

Here is a photo of two different paths for the two different tubes:

6AX7_&_12AX7_wiring.jpg
RIP BillD
BillD wrote:Well, some people are glass half empty people and some are glass half full. Being an engineer, I just think the glass is the wrong size.


My system (sitting in the garage):

(Stereo System)
Modified Carver AL III+'s (Pushed into the corners to make room for the ALS speakers)
Modified CarverFest 2011 20w tube amplifier
Carver Pro PT-1800
Sunfire Prototype TGA-2375
Carver TX-2 Tuner (not used)
Logitech Squeezebox (replaced Tuner & dad's CD player)
CARVERaudio Directional RCA interconnects
RCA-Headphone jack for iPod & iPhone
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AlexSauter

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Posts: 609

Joined: Sun Apr 13, 2008 5:41 pm

Location: Fort Myers FL

Post Mon Oct 03, 2011 5:41 pm

Re: Carverfest Tube Amp upgrades Please post ideas.

engtaz wrote:What would be the output of the amp when switching to 12AX7's?



These are the input tubes, there should be no wattage change when switching to the 12AX7's
RIP BillD
BillD wrote:Well, some people are glass half empty people and some are glass half full. Being an engineer, I just think the glass is the wrong size.


My system (sitting in the garage):

(Stereo System)
Modified Carver AL III+'s (Pushed into the corners to make room for the ALS speakers)
Modified CarverFest 2011 20w tube amplifier
Carver Pro PT-1800
Sunfire Prototype TGA-2375
Carver TX-2 Tuner (not used)
Logitech Squeezebox (replaced Tuner & dad's CD player)
CARVERaudio Directional RCA interconnects
RCA-Headphone jack for iPod & iPhone
<<

angelod307

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Post Mon Oct 03, 2011 6:39 pm

Re: CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

since i have some jolida's, i will try it on them first, then the good stuff. thanks
CarverFest: I just go for the arts and crafts
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Don

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Post Mon Oct 03, 2011 8:10 pm

Re: CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

Excuse my lack of tube knowledge, but what is the advantage converting to the 12 over the 6? #-o Go easy on me.
Remember, this is from a guy who just now has his first tube amp, courtesy of Carverfest.
To argue with a person who has renounced the use of reason is like administering medicine to the dead.
— Thomas Paine


"Try not to become a man of success, but rather a man of value" Albert Einstein

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RIP Bill D.
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treitz3

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"Julian"
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Post Mon Oct 03, 2011 8:12 pm

Sure. According to Bob? More distortion.

Straight from the horses mouth.

[To Alex]....Also, Bob said...

Bob Carver wrote:Short pins 4 and 5 together [green/black wire] and then connect the green wire to pin 9


.....which is exactly what Tubular Joe said to do and exactly what your CAD drawing displays.
In search of accurate reproduction of music. Real sound is my reference and while perfection may not be attainable? If I chase it, I might just catch excellence.

The best way to enjoy digital music reproduction is to never listen to a good analogue reproduction.

Robert R. - "Did you see my North Korea analogy? I should have named it Carversite.kim"
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AlexSauter

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Location: Fort Myers FL

Post Tue Oct 04, 2011 1:51 am

Re:

We spoke to Joe again and we asked him about the pros and cons of going to the 12AX7 and he said you would get less noise out of ANY 12AX7 than the 6AX7. Joe said that the Russian 6AX7 were cheaper to get than the 12AX7s and that was the reason Bob went with them... He also said that 12AX7's are a much more flexible in the brand names and qualities.

Joe's favorite 12AX7 tubes :

Telefunken (unobtainable)
Tall plate 13 or 17mm red text GE tubes
Amperex
Late 50's Mullards
Testla tubes
Military 7025 tubes (a very good substitution tube)


Joe's favorite 6BQ5 tubes:

Amperex (very good tubes)
Mullards (2nd best)
Sevtlana tubes (really good Russian tubes)
Black plate RCA's (not the best, but good)


---------------------------------------------
Sylvania tubes (inaduiqate)
GE tubes are inconsistent.. (lucky to get 2/5 that work as a matched pairs)

All Russian tubes are not a good choice of tubes, they are remarketed tubes, they are CLOSE to what they are called, but not 100% the right tube... Joe says that Russian tubes are noisey...


** Interesting fact ** Samsung tubes was originated in Japan and eventually became Schuguang tubes.
RIP BillD
BillD wrote:Well, some people are glass half empty people and some are glass half full. Being an engineer, I just think the glass is the wrong size.


My system (sitting in the garage):

(Stereo System)
Modified Carver AL III+'s (Pushed into the corners to make room for the ALS speakers)
Modified CarverFest 2011 20w tube amplifier
Carver Pro PT-1800
Sunfire Prototype TGA-2375
Carver TX-2 Tuner (not used)
Logitech Squeezebox (replaced Tuner & dad's CD player)
CARVERaudio Directional RCA interconnects
RCA-Headphone jack for iPod & iPhone
<<

beemers417

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Location: Pittsburgh, PA

Post Tue Oct 04, 2011 11:37 pm

Re: CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

I picked up some shuguang 6AX7 tubes and they are stellar. However, for simplicity, 12ax7 is the way to go. The Commie output tubes are still working fine. I have been running the amp every day on Snell model B speakers without a hitch.
Gunter the wonder dog is watching you...
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treitz3

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"Julian"
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Post Wed Oct 05, 2011 9:55 pm

I would LOVE to hear the conversation between Joe and Bob on this subject. It would be like the Miller Lite commercial.....

Lower noise. [Tastes great!]

More distortion. [Less filling!]

Lower noise. [Tastes great!]

More distortion. [Less filling!]

Lower noise. [Tastes great!]

More distortion. [Less filling!]

For one second in time, I would love to be in the shirt pocket that Bob is wearing and listen to the answers to this very conversation (live) between him and tubular Joe....one day maybe....
In search of accurate reproduction of music. Real sound is my reference and while perfection may not be attainable? If I chase it, I might just catch excellence.

The best way to enjoy digital music reproduction is to never listen to a good analogue reproduction.

Robert R. - "Did you see my North Korea analogy? I should have named it Carversite.kim"
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tinpan

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Post Thu Oct 06, 2011 4:36 am

Re: CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

I think Alex hit the nail on the head. There are many more choices for 12AX7's.

Hey Beemers, where did you find the Shuguang's? All I can find are the russians
Tinpan

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Chauss

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Post Thu Oct 06, 2011 7:15 am

Re: CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

Image
Good sound—like good music, good wine and good fellowship—is meant to be shared.
"The difference between genius and stupidity is that genius has its limits" Albert Einstein
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Chauss

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Post Thu Oct 06, 2011 2:48 pm

Re: CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

Chinese version of Bob's amp??? 4 x EL84 and 2 x 12AX7 - I will bet it sounds NOWHERE NEAR BOB"S!!! :D

http://www.audiogon.com/cgi-bin/cls.pl?ampstube&1322217140&/changsha-shuguang-sg-101b

Image Image
Image
Good sound—like good music, good wine and good fellowship—is meant to be shared.
"The difference between genius and stupidity is that genius has its limits" Albert Einstein
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BrianT

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Post Thu Oct 06, 2011 8:05 pm

Re: CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

VPI Classic Turntable (blk)
Transfiguration Phoenix Cartridge
Sunfire Vacuum Tube Control Centre. C/W Mod'ed Phono Stage
Carver Silver 7's Tube Amps
Raysonic CD-168 CDP (silver)
Carver TX11.
B&W 802D's Rosenut
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jerryj12

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Location: Atlanta, Area

Post Wed Jan 25, 2012 8:35 pm

Re: CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

Has anyone tried this Mod yet?
Thought I may try it ...
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jerryj12

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Post Thu Jan 26, 2012 11:47 pm

Re: CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

Works like a champ. :D

Sounds damn good also.
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Zoot Horn

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Post Fri Jan 27, 2012 6:47 am

Re: CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

attaboy Jerry =D>

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