Vox AC30 head layout

[fabiomayo]

Hi. Can anyone help me check this layout for a Vox build? Any advice is welcome.
EF86 channel, Top Boost channel, tremolo circuit from Vox Pacemaker (per suggestion on the Plexi Palace) and AC15/AC30 Power section.

This is the first(ish ) version:



Here's the new version of the layout, as suggested by Lyle Caldwell from the PlexiPalace Vox forum. One troublesome spot is the grid wire from the volume pot which runs parallell to both the cathode wires and the power supply filter. I'll move that later. How does it look?

One idea I have to keep things neater is to place the tremolo circuit on a separate board and put it on a "second floor" above the top boost tone stack caps. That way I can move the PI and power section closer to the middle of the chassis and keep things more organized. What do you think of that?

[Alf]

Fabio,

I would like to have a closer look at it but the resolution of the drawing is too low, could you send one with a higher resolution ?
This is one of my plans for the future a Vox ac 30 head. This way the tubes have a much better convection as they sometimes get as hot as 200 degrees centigrade.

Alf,

I'll pm you my e-mail address.

[fabiomayo]

Hi Alf. Email sent.

I'm not crazy about the L-shaped chassis. And a head is more practical (though a combo is sexier ).

[Alf]

Thanks Fabio,

Now it 's much better legible.
I'm going to have a good look at it and report back to you.


Alf

[Alf]

Hi Fabio,

Having had a look at it , I must say I like it .
However I would put all four of the Powertubes in one line below the preamp tubes this way you can add a small fanblower if you like to cool the tubes a bit.
I would drop the GZ34 because it gives not very much sag and install diodes.
Putting the topboost on top of the other board doesn't seem such a good idea to me because it will make it harder to service or mod things.

Is there a separate schematic for the topboost ?

Why did you choose for the Pacemaker tremelo ? The regular one sounds very good. I noticed that the Pacemaker is a bias tremelo, must sound good too.

[fabiomayo]

Hi Alf. Thanks for your comments. I'll try to move the power tubes around and see how it looks. I had planned on using a 120vAC fan (don't like to put other things on the 6v winding, maybe I could use the spare 5v if I choose for silicon diodes rectifier).

I understand your suggestion of getting rid of the GZ34 and agree. I'll consider that. One point of having a tube rectifier is to substitute it for a lesser rectifier (current draw and voltage drop compatible of course), especially on the 15w power option (which is likely to be my most frequent choice).

The tremolo was suggested by Beus from the Plexi Palace Vox forum since I had an unused triode and that's what he did in his very similar (and inspiring) project. Should sound good. Most other tremolos requires at least a twin triode tube.

Here's the schematic (I'll email you a higher resolution file). You may find some differences between layout and schem (ie power supply, coupling caps). That's yet to be defined and tweaked. One question regarding the power supply though. What sould be the current draw in B+1 and B+2? Around 200mA and 80mA?

[Alf]

Fabio,

I think the values you mention for the current drawn are okay.
In the schematic the B1 shows as 320 volts in the powersupply while you draw 310 on the plates of the el84's just a small difference. I think this is the ideal voltage for el84's to work at.
For the choke I would not go too high, 5 Henry should be enough but it should be able to withstand the current of 200 mA. This way the sound won´t get too stiff.
I noticed some differences in component values as compared to older schematics but that´s a matter of taste. This is why I stressed the importance of accessability , you must be able to tweak it easily.

I don´t know if you are going to like that mastervolume just give it a go.

Alf

[Richard]

Many people prefer the bias modulating tremolo, In my limited experience, bias tremolos tend to have a smoother, more rounded modulation.

[Alf]

It''s a bit beside the subject but the best tremelo I've heard so far is the Harmonic tremelo (vibrato) in e.g. the super reverb 6G4.
Really superb smooth sound , the way I like it best.


Alf

[fabiomayo]

The only amp I own (or ever owned) with tremolo is a tweed Tremolux 5E9-A replica made by MG Music. It acts on the PI if I'm not mistaken. Even though it has a few strange side effects (Victoria offer a similar amp and explain a little about this) the effect in itself is so sweet. I love it.

[fabiomayo]

Below is the layout with the EL84s in line. I move the OT a bit. I haven't ordered or decided on the trannies yet so this is only an estimate os size and a guess of mount type.

[Alf]

It looks really good Fabio.
One question , were you first planning to use it with a stereo out because it says 2 x ac 15 poweramp ?

Alf

[fabiomayo]

Thanks Alf.

It's mislabeled actually. This project started out with AC15 power amp and then evolved to 4x EL84 though at first I kept AC15 values. I guess in the end experiment will dictate the values.