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Zenpeace69
 Post subject: 18 Watt TMB tube layout?
PostPosted: Wed Feb 13, 2019 7:57 pm 
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I just picked up a Trinity 18 watt TMB, and I was curious about the preamp tube layout. If you are looking into the back of the amp, from left to right, there are three consecutive 12ax7 tubes. What are each of these for?

I have a guess that the first one is for the Tone/Volume channel, and the second is for the TMB channel? Perhaps the third is for both?

thanks in advance
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mitch m
PostPosted: Thu Feb 14, 2019 1:50 am 
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Each 12AX7 has two triodes.

The first tube is designated V1 on the layout and schematic. One of its triodes is the preamp for the normal channel. The other triode is the first stage of the preamp for the TMB channel.

The second tube is designated V2. Both triodes are used for the second stage of the TMB preamp.

The third tube is designated V3. Both triodes are used for the phase inverter for the power amp, so you could say it's common to both channels.
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Zenpeace69
PostPosted: Thu Feb 14, 2019 8:08 pm 
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mitch m wrote:
Each 12AX7 has two triodes.

The first tube is designated V1 on the layout and schematic. One of its triodes is the preamp for the normal channel. The other triode is the first stage of the preamp for the TMB channel.

The second tube is designated V2. Both triodes are used for the second stage of the TMB preamp.

The third tube is designated V3. Both triodes are used for the phase inverter for the power amp, so you could say it's common to both channels.


thanks
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coco
PostPosted: Sat Feb 16, 2019 4:04 pm 
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Zenpeace69 wrote:
I just picked up a Trinity 18 watt TMB, and I was curious about the preamp tube layout. If you are looking into the back of the amp, from left to right, there are three consecutive 12ax7 tubes. What are each of these for?

I have a guess that the first one is for the Tone/Volume channel, and the second is for the TMB channel? Perhaps the third is for both?

thanks in advance


That's actually a Plexi model you got, bit the tube description is correct.

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etzeppy
PostPosted: Mon Mar 04, 2019 4:01 pm 
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I mostly use the TMB Plexi channel. I have a nice NOS 12AX7 that I want to try out. In theory, which position has the biggest impact on tone for the TMB channel, V1 or V2?
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coco
PostPosted: Wed Mar 06, 2019 8:53 am 
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v2 is exclusive to the TMB channel it drives the tonestack and a second gain stage. v1 is the first preamp for both channels. Try it in positionbut not v3 . V3 would be a waste of a good tube.

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etzeppy
PostPosted: Wed Mar 06, 2019 9:28 am 
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coco wrote:
v2 is exclusive to the TMB channel it drives the tonestack and a second gain stage. v1 is the first preamp for both channels. Try it in positionbut not v3 . V3 would be a waste of a good tube.

I think something got lost there. I think you were recommending to try in both V1 & V2 but don't mess with V3. I'm running a new JJ balanced 12AX7 in V3. Does a "balanced" PI tube make any difference in this design? I know some people claim it makes a difference in many Fender designs.
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coco
PostPosted: Wed Mar 06, 2019 11:05 am 
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Either V1 or V2. Try them both and decide.
A balanced PI tube is questionable. Some of the tone of an amp comes from the imbalance and in fact, some designers do it on purpose or trim it to suit!

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