Tube Amp Forum: The Ultimate Tone

Hi all,

I would like to build a Power Amp using a preamp tube.
Also because power tubes are getting too expensive for me.
And I am very curious about the sound of course.

I looked at the AX-84 site but like Kevin said there is only one design, the Moonlight.
But it uses a custom transformer.

In TUT5 there is a chapter about AX-84.
There a 125A is used.
As far as I can see, the primaries use colors, like in the schematic.
But the secondaries use numbers.
I don't see them in the schematic.

Wiring should be done in a way that reflects the highest Z.

With an 8 Ohm speaker, it would be 2 & 4 on the secondaries, the highest Z would be 22,500 Ohms then.
Is this correct?

For the Herzog secondaries 1 & 4 are used, giving 11,600 back.


And another question: just for testing, can I use that replacment Reverb TX for our friends over at NewSensor?
I have a few around here.

I will be using an 12AT7.

Kind regards,

Strelok

Hi Guys

Ideally, you use the plate curve of the tube you wish to use and go from there to decide on OT primary impedance.

Yes, you can use a reverb driver transformer and have a low-watt PA. It may be limited to 100mW or so, which is enough to make some sound through an efficient speaker.

The 125-series OTs come with a sheet giving 90 matches of load to reflected primary impedance. Start high and see what works.

Have fun
Kevin

Hi Kevin!

Thanks for your reply!
I have no idea how to do use plate curves. I read some about it and it was understandable so that was nice to learn.
There were two shcematics of the Firefly that I could use.

Then I downloaded some video's that showed the Firefly in use and I did not like the sound.
Too flat.

So that's settled then.

Strelok

Hi Guys

Keep in mind that the firefly is self-split and class-A - part of a minimum-tube-cunt approach. What you do in the preamp makes a lot of difference. This ouptut stage will not colour it too much.

However, you can add a tube and do the splitting separate from the output stage, which gives more degrees of flexibility, just as with a larger conventional power amp.

You asked about using a standard SE reverb transformer, and that will yield a dirtier tone than the push-pull circuit, so maybe more what you were hoping for?

Have fun

Hi Kevin!

True, perhaps I am judging too fast.
I only wabt to use it as a Power Amp anyway.

My dream would be a Herzog with a 12AU7 as power tube.
I can do that with a Firefly schematic.
And then a package I can carry around.

Thanks again!

I will try the Reverb Transformer, very cusious about that.