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Post subject: 12AX7 info needed
Posted: Thu Aug 19, 2010 7:46 pm
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Hi Everyone-
I need to replace the 12AX7's in my HotRod Deluxe. The Owner's manual
says they are color-coded (1=Red 2=white 3=blue numbers). It has Groove Tubes in it now, but I want to try the 12ax7LPS's. I don't know if the LPS's come in different color codes or not. I don't wanna hafta have the bias adjusted.
Can anybody enlighten me on this?

Thanks!


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Post subject: Color code tubes
Posted: Thu Aug 19, 2010 8:27 pm
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Hi phiftybuick,

The color codes only apply to the output tubes (the big ones). The Blue tubes are for early breakup, the white are mid range and the red are for clean headroom. You can use just about any 12AX7 type preamp tube that you want (small ones), with no bias adjustment required. :)

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Posted: Thu Aug 19, 2010 11:50 pm
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V1 and V2 by standard 12ax7 (or at7 for less gain) but for V3 it is better to choose a twin matched one. V3 is a phase inverter that performs better when it is well balanced.
for instance: https://ssl.eurotubes.com/cart/index.ph ... gory_id=32
ECC83=12ax7

Personnally, I tested several valves on V3 without hearing problems, prehaps its a pure chance, on top of that I'm not sure that 7ender makes a sorting for V3.

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Posted: Fri Aug 20, 2010 12:27 am
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Tissan wrote:
V3 is a phase inverter that performs better when it is well balanced.


A quality phase inverter (whether 12AX7 or 12AT7) is vital since an out-of-balance dual triode creates undesireable second-order harmonics between the uncoupled outputs which sound metallic and artificial when those signals are re-summed at the output tranny's primary as the amp is overdriven.

HTH

Arjay

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Posted: Fri Aug 20, 2010 3:12 am
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+1 Retroverbial 8)

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Posted: Fri Aug 20, 2010 3:17 pm
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Ok, so the 12AX7's don't have to be matched. I can just order three tubes & install...right?


Thanks in advance!


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Posted: Fri Aug 20, 2010 3:31 pm
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To be fully clear V3 has to:

In one 12ax7 there are 2 noval Triodes. For V3 the 2 triodes shall be matched.

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Posted: Fri Aug 20, 2010 3:49 pm
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Tissan wrote:
To be fully clear V3 has to:

In one 12ax7 there are 2 noval Triodes. For V3 the 2 triodes shall be matched.


Actually, all three of the subminiature tubes in a HRDlx are dual triodes. But it's critical to amp performance that the phase inverter should be as balanced between the halves as possible. Less so with V1 and V2 whose stages are cascaded as in a daisy-chain.

HTH

Arjay

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Posted: Fri Aug 20, 2010 4:09 pm
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May be my american is not clear as I'm french. :)

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Posted: Fri Aug 20, 2010 4:30 pm
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Tissan wrote:
May be my american is not clear as I'm french. :)


Je m'excuse, mon ami

It was not my intent to "steal your thunder", Tissan.

Arjay

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Posted: Sun Aug 22, 2010 2:21 am
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I work often in Detroit MI for Automotive electronics, and believe me, a lot of misunderstanding with my "standard french-american" and the american of america !

I was not upset at all, but gosh: Do I made myself understandable? !

:wink: :wink:

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Post subject: Preamp tubes
Posted: Sun Aug 22, 2010 6:05 am
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Tissan wrote:
In one 12ax7 there are 2 noval Triodes. For V3 the 2 triodes shall be matched.

I was not upset at all, but gosh: Do I made myself understandable? !

:wink: :wink:


Your English is great! Much better than many American HS students. :lol: I understood that you were pointing out that each preamp tube has 2 Triodes, and that V3 is the only one that needs to be balanced. :)

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Posted: Sun Aug 22, 2010 6:14 am
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I kinda like the Sovtek 12AX7LPS. Neutral tone. Clean highs and strong bass. Mates well with classic 6L6GC sound, IMHO.

Like other said, matching across the duo-tiode sections may only be noticeable in the phase inverter section. For other positions, try to get the strongest testing & most quiet of the buyer's batch.


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