Vajra 18 watt layout rev.1

fpena · Post by **fpena** » Mon 03/31/03 10:29 pm

The layout (rev1) is *done*.

You can check it out at

http://www.tonepad.com/project.asp?id=24

I'd like to hear your comments on this one, as it's my first published tube amp layout.

*Fp

AC · Post by AC » Wed 04/02/03 9:05 pm

Hi guys,I was checking the 18W layout and I think the bias switch is wired wrong(I might be wrong also).
If you look at the Blues Express Plus version A8a for example,the positive end of the bypass cap/resistor is lifted when in fixed bias mode.In yours the cathode is always connected to ground through the cap/resistor.In order to have it like that you would have to lift the ground connection of the cathode cap/resistor when in fixed bias mode,maybe using a 3P2T switch.
Maybe I'm interpreting wrong but check it when you can and let me know.
Aharon(AC)

fpena · Post by **fpena** » Thu 04/03/03 11:48 am

I did the layout according to the schematic and I also find this bias switch arrangement to be *questionable* (In all my ignorance)

Check out this other amp that has bias switch (AX84 California Dreamer)

Could it be that the Vajra 18 watt schem is wrong or is that another way to have switchable fixed/cathode bias?

Fp

Robal · Post by **Robal** » Sat 10/04/03 2:46 am

BTT. Anyone build with this layout? Is it on the 18watt.com site somewhere, or only at tonepad? http://www.tonepad.com/project.asp?id=24

dboul · Post by **dboul** » Sun 10/05/03 12:45 am

Looks interesting . . .

My comment may be a little off topic, I'm getting really curious about the EF86 mod on this circuit. I've read the other threads about it, but left not feeling like I knew what the EF86 does in the this amp.

I have a JMI AC30 that has an EF86 tone stack and it's almost a religious experience cranking that amp up! The chime and smooth breakup will give anyone goose bumps. The thought of adding a little of that flavor to this amp is very intriguing.

What's the general feeling about doing this?

All the best!

Post by **zaphod_phil** » Sun 10/05/03 11:34 am

Pentodes naturally distort more than triodes, leading to a warmer/fatter sound. Looks like you've already discovered what the EF86 will do for your 18W. You just have to buy EF86s carefully, so you don't get microphonic tubes.

dboul · Post by **dboul** » Sun 10/05/03 3:15 pm

Thanks Phil!

Your input is always great!

Is there an agreed upon layout diagram here for an EF86 tone stack?

I've seen the schematic, but I'm so "home grown" that I'm only comfortable with layout diagrams.

Not good at translating schematics into reality . . . yet!

Indeed, if I can put some of that Vox "life" into this circuit, I might just break down and cry. I love the Marshall sound and I love the true Vox sound . . . having both in one amp would just be too good!

Thanks again Phil!

Post by **Plexi** » Sun 10/05/03 5:57 pm

On the head version..or could be used in the combo..The led is on the back of the head for the trem on and off..You could add an led to your footswitch,so you could see when its on or off{if needed}
Just put an led in your footswitch,and use a stereo jack,and cable.
Just a thought if someone wanted to use it.
Richie

Post by **Plexi** » Sun 10/05/03 5:59 pm

woops i clicked reply instead of "new thread" sorry..

Richie

Post by **Gabi** » Mon 10/06/03 10:41 am

Fp...

I am not sure if it's me, but I am getting a white blank page when clicking on http://www.tonepad.com/getFile.asp?id=45 (that is the "To Download File... Click here" link for the pdf)

Am I doing something wrong? I have Acrobat and all that in my browser...

gabi.

dboul · Post by **dboul** » Fri 10/10/03 3:04 pm

When you get to the website . . . right click on the "download" link and choose "save targer as" and save it locally and it will come up fine. I ran into the same problem.

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Vajra 18 watt layout rev.1

Vajra 18 watt layout rev.1

Just an idea