2x12AX7 EL84 amp ideas requested

[TacosSupreme]

Hi! First time poster here, I've found a lot of great info on this forum but I'm now looking for something quite specific.

I'm looking for my first diy amp project. I already did a bunch of pedals, guitar wiring, even mods to existing amps but never a full amp from scratch. I'm fairly handy and soldering isn't an issue for me. I'm fairly confident I can work in an amp without killing myself (seems doable with proper precautions).

I have a 2x12AX7 and 1xEL84 tubes I'd like to use for this project (can buy more if necessary).
I also have a 10" 16Ohm speaker (a nice WGS G10C).

What I don't have is the technical knowledge to design or modify a circuit so I need clear instructions, schematics and good wiring diagrams (that's the hard part).

So far it seems I could go with the following:
- Blues JR (need more tubes but it's fine)
- Vox AC10 (can't find instructions for that though)
- Something bassbreaker or bluebreaker based

The instructions I find so far are often for 8Ohm speakers but it seems I can just swap the output transformer to make it work with a 16ohm (no other modifications needed?)

Any ideas?

[Latole]

    "  The instructions I find so far are often for 8Ohm speakers but it seems I can just swap the output transformer to make it work with a 16ohm (no other modifications needed?). "

Yes, no other mod .
______________

You want to build a single end amplifier . One EL84 = single end

I'll go for the 5F1 Champ .https://robrobinette.com/How_To_Build_a_Tube_Amp.htm

Sketch show a 6V6 , you can use a EL84 with different connections on socket.

More if you need.

[TacosSupreme]

Wow thanks for that answer. I love the simplicity of that Champ. Looks like I'll need a rectifier tube as well though.
Is it true that a 6V6 would sound more "Fendery" while the El84 would be on the "Voxy" side (especially for overdriven tone)? I just read that on the Seymour Duncan blog ( and elsewhere) but I'm a bit sceptical. I wouldn't have imagined that the power tube would matter that much.

That Rob Robinette website is amazing by the way.

[AlNewman]

Do you already have a power and/or output transformer you plan on using?

[Jalmeida]

Hi! First time poster here, I've found a lot of great info on this forum but I'm now looking for something quite specific.

I'm looking for my first diy amp project. I already did a bunch of pedals, guitar wiring, even mods to existing amps but never a full amp from scratch. I'm fairly handy and soldering isn't an issue for me. I'm fairly confident I can work in an amp without killing myself (seems doable with proper precautions).

I have a 2x12AX7 and 1xEL84 tubes I'd like to use for this project (can buy more if necessary).
I also have a 10" 16Ohm speaker (a nice WGS G10C).

What I don't have is the technical knowledge to design or modify a circuit so I need clear instructions, schematics and good wiring diagrams (that's the hard part).

So far it seems I could go with the following:
- Blues JR (need more tubes but it's fine)
- Vox AC10 (can't find instructions for that though)
- Something bassbreaker or bluebreaker based

The instructions I find so far are often for 8Ohm speakers but it seems I can just swap the output transformer to make it work with a 16ohm (no other modifications needed?)

Any ideas?

You can build a modern iteration of an AC4C1 clone with that. They use 2 12AX7 as basically a top boost channel fed into a single 12AX7.

[TacosSupreme]

Do you already have a power and/or output transformer you plan on using?

I don't, there's a local supplier that has pretty much any Hammond models though.

[Latole]

TacoSupreme you can use solid state rectifier instead of the 5Y3, here's the circuit from the Jalmeida schematic.

[Latole]

Fender Champ 5F1 schematic. Same as robobinette layout

[Latole]

Vox AC4 with one EL84 ; schematic and layout from the member Kagliostro


https://el34world.com/Forum/index.php?topic=29359.0

[Jalmeida]

Vox AC4 with one EL84 ; schematic and layout from the member Kagliostro


https://el34world.com/Forum/index.php?topic=29359.0

This one is pretty close to the AC4TV amps which did not use a topboost circuit. They sound more like the normal channels on a Vox.

You could take this approach and then use the extra 12AX7 for a tremolo oscillator like the EF86 variant uses. Although I am not sure how that would work on triode V1 versus a pentode. Maybe you can make it work by oscillating the power tube bias?

[Lectroid]

Greetings,

Yeah, either the Champ or the AC4 are good starter amps.  Have a look at the Champ AA764 version, it's a cleaner schematic. 

Have you built any tube-based circuits before?  This can be a gravely dangerous hobby if you don't know how to stay safe.

Do you have basic soldering skills?

Do you have patience?   

Have you ready any tube amp books?

[Latole]

Greetings,

Yeah, either the Champ or the AC4 are good starter amps.  Have a look at the Champ AA764 version, it's a cleaner schematic. 

Have you built any tube-based circuits before?  This can be a gravely dangerous hobby if you don't know how to stay safe.

Do you have basic soldering skills?

Do you have patience?   

Have you ready any tube amp books?

He wrote :

 "I'm looking for my first diy amp project. I already did a bunch of pedals, guitar wiring, even mods to existing amps but never a full amp from scratch. I'm fairly handy and soldering isn't an issue for me. I'm fairly confident I can work in an amp without killing myself (seems doable with proper precautions). "

[TacosSupreme]

Greetings,

Yeah, either the Champ or the AC4 are good starter amps.  Have a look at the Champ AA764 version, it's a cleaner schematic. 

Have you built any tube-based circuits before?  This can be a gravely dangerous hobby if you don't know how to stay safe.

Do you have basic soldering skills?

Do you have patience?   

Have you ready any tube amp books?

What? Nobody said I would have to read books! I'm out!
Isn't danger the main appeal of amp building? I might as well die doing something cool like that, can you imagine the epitaph on my tombstone?

More seriously though, I appreciate your concern but I'm a 40 y.o. dude with functional asperger. I can assure you that patience (or lack thereof) is not a problem.
My uncle (electronic engineer) gave me my first soldering iron when I was 9 and taught me how to properly solder, I should manage.
I also already read a bunch of articles on how to safely work in a tube amp, which is why I'm 90% confident I'm not going to kill myself.
I'm fairly handy and I don't suck at cabinetry too (I'm really into dowel joints those days). I don't know how this amp is going to sound but it's going to look superb!

[dwinstonwood]

Here are my AC4 schematic and layout drawings. I added an Intensity control and a small choke (which, along with a two-point grounding scheme, made a huge difference in killing hum). I built it in an old Fender Frontman 15 cabinet.

[Latole]

Here are my AC4 schematic and layout drawings. I added an Intensity control and a small choke (which, along with a two-point grounding scheme, made a huge difference in killing hum). I built it in an old Fender Frontman 15 cabinet.

Very nice job !

That is what TacoSupreme need ;

[AlNewman]

Here are my AC4 schematic and layout drawings. I added an Intensity control and a small choke (which, along with a two-point grounding scheme, made a huge difference in killing hum). I built it in an old Fender Frontman 15 cabinet.

The transformers you used would be key to this type of build, imo.

[dwinstonwood]

The transformers you used would be key to this type of build, imo.

Yes, I used the Hammond 270CAX PT and their 125CSE OPT.

[Latole]

The transformers you used would be key to this type of build, imo.

Yes, I used the Hammond 270CAX PT and their 125CSE OPT.

IMO, 125 CSE is very ( too ) low in power.


270CAX   65   117   50/60   500V C.T. @ 81ma.   5V @ 2A   6.3V @ 2.5A

125CSE   8watts   60ma   1.3   

[TacosSupreme]

Here are my AC4 schematic and layout drawings. I added an Intensity control and a small choke (which, along with a two-point grounding scheme, made a huge difference in killing hum). I built it in an old Fender Frontman 15 cabinet.

Very nice job !

That is what TacoSupreme need ;

Beautiful! This AC4 circuit looks surprisingly simple (ant there's beauty in simplicity)

[TacosSupreme]

TacoSupreme you can use solid state rectifier instead of the 5Y3, here's the circuit from the Jalmeida schematic.

I also saw that Rob Robinette suggests a solid state rectifier with 4 x 1N4007 diodes. Pretty cool (and cheap)

[TacosSupreme]

The transformers you used would be key to this type of build, imo.

Yes, I used the Hammond 270CAX PT and their 125CSE OPT.

IMO, 125 CSE is very ( too ) low in power.


270CAX   65   117   50/60   500V C.T. @ 81ma.   5V @ 2A   6.3V @ 2.5A

125CSE   8watts   60ma   1.3

Related question regarding output transformers: If I see on a schematic that a Hammond 125B is used for an 8 Ohm speaker, can I use the same model for a 16 Ohm speaker?
I read somewhere that the speaker impedence rating is supposed to be the minimum load of the speaker, which means (I assume) that the output transformer should be at least 16 Ohm, but the datasheet for the 125B mentions a max speaker load of 15 Ohm only. Is the difference negligible enough or should I look for a different OT?

[Latole]

Hammond 125B can use any speaker impedance from 1.5 ohm to 15 ohms
So a 16 ohms speaker will work

It is for a Push Pull tube output, not single ended, your project


https://www.hammfg.com/files/parts/pdf/125B.pdf

[TacosSupreme]

Hammond 125B can use any speaker impedance from 1.5 ohm to 15 ohms
So a 16 ohms speaker will work

It is for a Push Pull tube output, not single ended, your project


https://www.hammfg.com/files/parts/pdf/125B.pdf

Ah right, I was looking at the bassman micro from Rob Robinette which does have a push pull power tube. Interesting design.
Thanks for your answer. The logic of that statement though... 
"from 1.5 ohm to 15 ohms. So a 16 ohms speaker will work"

[acheld]

The logic of that statement though... 
"from 1.5 ohm to 15 ohms. So a 16 ohms speaker will work"

  Tube amp logic!  And it works.

Seriously, a 16 ohm speaker will be within tolerance.

When selecting an output transformer, the logic path is:
1) Is it single ended, or push pull.   (The transformers are very different).
2) What are your expected impedances?
    a)  Primary impedance?  This is related to your output tube.
    b)  Secondary impedance?  Your speaker.
3) How much power will you be producing?

For the most part, that's all you need to know.  For reference purposes, here is a link to the most common Hammond OTs, with their specs:   https://www.hammfg.com/electronics/transformers/classic/1750.   But, it's dealer's choice!

[Latole]

Hammond 125B can use any speaker impedance from 1.5 ohm to 15 ohms
So a 16 ohms speaker will work

It is for a Push Pull tube output, not single ended, your project


https://www.hammfg.com/files/parts/pdf/125B.pdf

Ah right, I was looking at the bassman micro from Rob Robinette which does have a push pull power tube. Interesting design.
Thanks for your answer. The logic of that statement though... 
"from 1.5 ohm to 15 ohms. So a 16 ohms speaker will work"

Hammond 125B is a 5 watts transformer. How many watts the Bassman Micro ?

[TacosSupreme]

Hammond 125B can use any speaker impedance from 1.5 ohm to 15 ohms
So a 16 ohms speaker will work

It is for a Push Pull tube output, not single ended, your project


https://www.hammfg.com/files/parts/pdf/125B.pdf

Ah right, I was looking at the bassman micro from Rob Robinette which does have a push pull power tube. Interesting design.
Thanks for your answer. The logic of that statement though... 
"from 1.5 ohm to 15 ohms. So a 16 ohms speaker will work"

Hammond 125B is a 5 watts transformer. How many watts the Bassman Micro ?

2 to 4 watts https://robrobinette.com/Bassman_Micro.htm

[Latole]

Thank's