Question for a AX84 Single Ended Lead Tube Guitar Amplifier project?

[Rod]

HI everyone !

If later i want to add or upgrade this project with more 2 or 3 gain stages , what will be the parts that will change?

The power transformer will have to be other model? wich one?

Thanks.

[Rod]

BumP, anyone can help here?

[tubeswell]

Can you post a schematic of the revised amp incorporating the sort of stages you want to add?

(That way you'll save people stabbing around in the dark with their pointy opinions.)

[Rod]

No, i dont have any schematic, i just want to have amp parts that are prepared for 2 more stages, and a fx loop in the future.


I think that i will have to have a bigger power transformer, the power transformer will have to handle with 4 more b+ voltages, other resister values, what else?

Can you post a schematic of the revised amp incorporating the sort of stages you want to add?

(That way you'll save people stabbing around in the dark with their pointy opinions.)

[Amp Kat]

No, i dont have any schematic, i just want to have amp parts that are prepared for 2 more stages, and a fx loop in the future.


I think that i will have to have a bigger power transformer, the power transformer will have to handle with 4 more b+ voltages, other resister values, what else?

I doubt you will need a bigger transformer unless the heater amp draw is maxed out which it shouldn't be. What you will need is available space to add 2 more sockets, some caps and resistors and a place to put them like maybe a terminal strip board. If you just add two gain stages all you will need is a tube socket and you can always go SS on the loop unless you want it all tube and then you will need a return buffer stage which means another tube and socket and resistors and caps.

[Rod]

Hi thanks Kat!


Ok i have other amp schematic that uses a tube amp loop effects that i will use to make my preamp tube loop effect stage based on this ax84 project.

But i'm curous on how do you select a power tansformer and output transformer for a given preamp?what guidelines and calculations show i make to select the right transformers?

I doubt you will need a bigger transformer unless the heater amp draw is maxed out which it shouldn't be. What you will need is available space to add 2 more sockets, some caps and resistors and a place to put them like maybe a terminal strip board. If you just add two gain stages all you will need is a tube socket and you can always go SS on the loop unless you want it all tube and then you will need a return buffer stage which means another tube and socket and resistors and caps.

[Amp Kat]

Hi thanks Kat!


Ok i have other amp schematic that uses a tube amp loop effects that i will use to make my preamp tube loop effect stage based on this ax84 project.

But i'm curous on how do you select a power tansformer and output transformer for a given preamp?what guidelines and calculations show i make to select the right transformers?

The only preamp calculations you really need to be concerned with are the heaters because preamp signal currents are very low in the 10's of milli-amps. So the heaters depend on how many and which way you wire them because they draw more current wired in parallel than they do in series. If you are using 12AX7's than they use 300 ma's in parallel and 150 ma's in series. This added on to the power tube heater currents which can get up to 2 amps depending on the tube used should be added and give yourself another amp in case you want to add additional tubes which is likely or hopefully what the designer of this one did. The other portions of design is the high voltage supply and the bias tap if one exist which most these days do. Tube amps don't generally use lots of current since they are voltage devices so 300 ma's is usually tops for a tube power transformer so the rest is just calculating how much voltage you want on the plates and which rectification you are going to use whether it's tube or solid state. The preamp voltage is derived from the power tube voltage through dropping resistors in series with the power supply so they can be set to the desired voltage set by the resistance to get that voltage. Since the bias supply carries so little current this can be a very small amperage at about 75 to 100 volts max. Other transformers like Toroidals are calculated in VA (Volt/Amps) . You'll also notice the size of the wire for the heaters are much larger than the others because the amperage is so much higher for them than the plates and bias supplies. If you do use a tube rectifier you will need an additional 5 volt winding or whatever heater voltage requirement for that rectifier plus it's amperage rating.


The output transformer should be selected by how much power output you want to use and which tubes you plan on using. The primary impedance can have different ratio calculations for the tube type you want to use and the secondary speaker ohm load you plan to use can have an effect on tone and bandwidth among other very complex calculations. There are very many things going on inside output transformers and many designers only give out very limited specs as the final parameters but it is a very diverse and an extreme complex subject that is far beyond the scope of this discussion.