CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

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AlexSauter
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CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

Post by AlexSauter » Mon Oct 03, 2011 5:27 pm

***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
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Re: Carverfest Tube Amp upgrades Please post ideas.

Post by AlexSauter » Mon Oct 03, 2011 5:41 pm

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

Post by angelod307 » Mon Oct 03, 2011 6:39 pm

since i have some jolida's, i will try it on them first, then the good stuff. thanks
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Re: CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

Post by Don » Mon Oct 03, 2011 8:10 pm

Excuse my lack of tube knowledge, but what is the advantage converting to the 12 over the 6? #-o Go easy on me.
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Post by treitz3 » 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.
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Re:

Post by AlexSauter » Tue Oct 04, 2011 1:51 am

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

Post by beemers417 » Tue Oct 04, 2011 11:37 pm

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.
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Post by treitz3 » 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....
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Re: CarverFest 20w Tube Amp 6AX7 - 12AX7 conversion

Post by tinpan » Thu Oct 06, 2011 4:36 am

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

Post by Chauss » Thu Oct 06, 2011 7:15 am

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

Post by Chauss » Thu Oct 06, 2011 2:48 pm

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? ... ng-sg-101b

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

Post by BrianT » Thu Oct 06, 2011 8:05 pm

Dan

Thanks I just ordered 2

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

Post by jerryj12 » Wed Jan 25, 2012 8:35 pm

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

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

Post by jerryj12 » Thu Jan 26, 2012 11:47 pm

Works like a champ. :D

Sounds damn good also.

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

Post by Zoot Horn » Fri Jan 27, 2012 6:47 am

attaboy Jerry =D>

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