12AX7 versus 12AT7 or equivalent

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12AX7 versus 12AT7 or equivalent

Postby The_Crossroads » Sat Apr 11, 2009 6:12 am

Please help - Hello there,

I saw that here are some people that know what they are talking about.

I have a situation... I own a guitar amp from 1978 - Roland Bolt 30 with tubes

the V1= 12AT7 - on the original schematics.. but..
when i got the amp many years ago i had a Tesla tube i don't know what kind ... than a "friend" told me that the tube was not good anymore and had changed it...

b4 the switch i had a nice edge and drive on the amp it was a little nervous and i could use... controlled feedback with my guitar and pedals...
know i have the original 12AT7 like the schematics sais...

after the switch that is possible only if i raise the volume more than i used to...

can you please tell me what should i do. can i get the original tone back?

what tube should i put on without ruining the amp in order to get that kick i used to have?


thank you for your time guys...
in advance,
Mike
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Postby dhuebert » Sat Apr 11, 2009 7:19 am

Give a 12AX7 a try. You can't hurt the amp this way.

Don
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Postby EWBrown » Wed Apr 15, 2009 6:41 am

The 12AX7 has more gain than 12AT7, in the circuit. As Don sez, just use a 12AX7, and there should be no problems.

/ed B
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Postby Geek » Wed Apr 15, 2009 1:04 pm

12AX7, 12AT7 and 5751 used interchangeably in that position can give you three tones. Even amongst different manufacturers of the same tube [:)

WARNING: Tube rolling is addicting (lol)

Cheers!
-= Gregg =-
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Postby The_Crossroads » Thu Apr 16, 2009 2:33 am

thanks a lot guys,...

i will try it..

peace...
i will post the results of teh experiment.. ;o)
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Postby The_Crossroads » Sat Apr 25, 2009 7:28 am

hhhhheeeyyyy

My guitar amp is back to life...

it is nervous again... ;o)

hugs to you all... i have a bunch of ECC83 which in some sites tell me it is equivalent with 12AX7...

is there a tube with more punch than this.. just to try it out.. ;o)

cheers..
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Postby EWBrown » Sat Apr 25, 2009 1:04 pm

12AX7, 12AX7A, ECC83 and 7025 are all directly interchangeable.

IIRC, ECC807 has a higher mu, around 140-150, but these are not low cost nor easily available as compared t the 12AX7 family.

/ed B
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