12 AX7 or 12 AX7? (LSC Content)

[Sadhaka]

Hi folks,

I use a LSC amp (original version) and recently had some valves changed in in both pre and power sections of the amp. Since then I have been experiencing volume drops and complete cutouts similar to others' experiences in this forum. I have a few questions regarding this:

Firstly, there has been mention that there has to be a Chinese 12 AX7 in V1 and V3. Can someone explain why this is the case? You can be as technical as you like because I will show this to my amp tech as he thinks that it is strange that this should be the case.

What is the difference between a Chinese 12 AX7 and one from somewhere else?

Who makes these 'Chinese' 12 AX7's (I don't know which brands are Chinese eg Sovtek, EH etc...)

Thanks. I appreciate any help or advice,
Sadhaka.

 

[trem]

Nah, you can use whatever 12AX7 that you like, as long as the tube position in your amp calls for it (some amps use a mixture of 12AX7 and other types, like 12AT7). I believe LSC uses only 12AX7 though. If you're in doubt of which brand you should use, simply use the Mesa's one (although their Russian-2 tubes are simply relabelled 12AX7EH). If you can, experiment with different brands in V1 (where different tubes make the most impact in sound), they all sound different and see which one you like.

 

[Sadhaka]

Thanks for the feedback Trem. It's just that I called Mesa from Australia today and spoke with Rich. I think he was a little annoyed by my questions and for that I am sorry.

He did say that I would need a Chinese tube in V3. He wouldn't go into details though...

 

[trem]

That's new to me. This thread seems to confirm what you're saying:
http://forum.grailtone.com/viewtopic.php?t=27467&highlight=lsc+chinese+tube%2A

The one condition that I know that puts a lot of stress on a pre-amp tube is when it's put in a cathode follower position, usually before the tone stack. Some brand can withstand higher voltages better than others. I don't have the schematics for LSC so I don't know whether LSC employs cathode follower circuitry for the tone stack though.

 

[Sadhaka]

Thanks again Trem,

I must have searched through tens of threads in here for some reasoning but somehow I missed that one!

Do you know if the JJ tubes are made in China?

 

[trem]

These are some of the most common current production pre-amp tube brands.
Shuguang - Chinese
Ruby - Chinese
Pentalab - Chinese
JJ - Slovak
Sovtek - Russia
SED - Russia
Tung-Sol "reissue" - Russia
Mullard "reissue" - Russia
Electro-Harmonix - Russia

 

[Sadhaka]

Cheers mate.

 

[stokes]

Sounds like more Mesa "tube voodoo" nonsense.If you look at the schem,V3a has 315v's on it,but that tube is only used if the effects loop is used.V4b has 405v's on it and is the reverb driver.So if V3 has to be Chinese to take the extra volts,what is going on with V4?I have to doubt thes "over-voltages" would affect a Russian tube more than a Chinese tube.Sounds more like Mesa just has too many Chinese tubes in stock.

 

[ShamefulAddiction]

ah, no wonder every Ruby I've ever used was a piece of crap.