Metropoulos Forum

Posted: **Mon Oct 06, 2014 3:49 pm**

Hi guys. Just wondering what 3 12au7s will sound like in a jtm45 with el34 power tubes, and a gz34 rectifier tube? Will it sound like crap? I won 2 sets of these tubes(12au7) on ebay which are supposed to be vintage.....one set from 59 and the other from 60......sorry for the dumb question, I'm just new to amp building and want my amp to sound good. Thanks to any replies.

Posted: **Mon Oct 06, 2014 4:09 pm**

Pretty low gain

12AX7 = gain factor 100
5751 = gain factor 70
12AT7 = gain factor 60
!2AU7 = gain factor 19

Look here:http://www.thetubestore.com/Gain-Factor

So it will be quiet and stable but I doubt a rock monster!

I often like a CV4004 or 5751 in the PI or in a cascaded preamp if it is a bit fizzy otherwise 12AX7/7025 or ECC83 work best for me.

Posted: **Mon Oct 06, 2014 4:19 pm**

neikeel wrote:Pretty low gain

12AX7 = gain factor 100
5751 = gain factor 70
12AT7 = gain factor 60
!2AU7 = gain factor 19

Look here:http://www.thetubestore.com/Gain-Factor

So it will be quiet and stable but I doubt a rock monster!

I often like a CV4004 or 5751 in the PI or in a cascaded preamp if it is a bit fizzy otherwise 12AX7/7025 or ECC83 work best for me.

Thanks.....but what if I put a tube screamer in front of it until I can afford good valves.....will it do?

Posted: **Mon Oct 06, 2014 4:27 pm**

12au7 draw a lot more current than 12ax7, I'm not sure it's totally safe for the amp...

Posted: **Mon Oct 06, 2014 4:37 pm**

bill bokey wrote:12au7 draw a lot more current than 12ax7, I'm not sure it's totally safe for the amp...

According to the build instructions. ....I can use 12ax7, 12at7, 12au7, 12at7, 12az7, 12dw7, or 5751 in the preamp section

Posted: **Mon Oct 06, 2014 4:45 pm**

danwelsh wrote:
bill bokey wrote:12au7 draw a lot more current than 12ax7, I'm not sure it's totally safe for the amp...
According to the build instructions. ....I can use 12ax7, 12at7, 12au7, 12at7, 12az7, 12dw7, or 5751 in the preamp section

Give it a go and report back, I would drop some in one of m amps but I do not have any ECC82 or 12AU7s

A set of Sino 12AX7s can be incredibly cheap

Posted: **Mon Oct 06, 2014 4:50 pm**

neikeel wrote:
danwelsh wrote:
bill bokey wrote:12au7 draw a lot more current than 12ax7, I'm not sure it's totally safe for the amp...
According to the build instructions. ....I can use 12ax7, 12at7, 12au7, 12at7, 12az7, 12dw7, or 5751 in the preamp section
Give it a go and report back, I would drop some in one of m amps but I do not have any ECC82 or 12AU7s

A set of Sino 12AX7s can be incredibly cheap

Okay.....will do

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What will 3 12au7s sound like?

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