Crazy like a Vox (aka "Sligh Vox")

[Geezer]

This started out as a Valve Junior rebuild for a friend to use as a power amp for his Digitech GNX3000 amp modeler, but turned into much more.
The starting circuit was basically a Deluxe 6G3, but it quickly evolved way past that.
2 gain stages (with a trim pot between the last gain stage & the PI), LTP PI, no NFB, Hi-Cut control.

Fantastic, touch responsive tone.......probably the best sounding amp I've built so far.

The schematic>>

[Geezer]

And the Layout>>

[Geezer]

Here are Jpeg versions>>>

The schematic
http://img.photobucket.com/albums/v325/jallenshaw/Voxy%20thing/6G3Daleproject-2.jpg


The Layout
http://img.photobucket.com/albums/v325/jallenshaw/Voxy%20thing/6G3Daleproject-1.jpg

[tubenit]

Given DaGeezer's positive comments, I thought someone might want to build this as a scratch build vs. a gutted and modded Valve Jr.

So I drew this up. I also indicated a Hammond PT that would be suitable I think for this build and then using a GZ34 rectifier tube. If that was done, the last couple of dropping resistors on the B+ rail would need lower values to get closer to DaGeezer's voltages on the 12AX7 tubes.

With respect, Tubenit

[dnator]

Hi,

This is my first time posting here but i've lurked here enough to download this schematic and layouts and I built this amp.  It's only my second build and I just got it done last night. So far I've been having a great time playing it. 

This forum is great resource and thanks for sharing this design!

Dave

[Geezer]

Here's a new layout for the Crazy Vox.

This is pretty much true "point-to-point" (my 1st attempt at such) using terminal strips.

The circuit is highly sensitive and can have oscillation if the lead dress is too long. It is very "Trainwreck"-like in that respect, so I thought that the more direct & short leads would help to calm it a bit....we'll see.

I'll be starting on this shortly, as I get the $ together for the parts (although I already have pretty much everything but the Mallory 150's & the PT). For the PT, I'm going to use the $25 Weber RVBPT (260-0 @100mA, 6.3v @3A) which I have had tremendous success with in the past (Little Wing).

Please check for errors......Geez'r

EDIT: I added pictures of Geezer's finished chassis & another layout which is the same as his but simply with straighter lines drawn.
With respect, Tubenit

[Geezer]

Fixed a few mistakes & did a few tweaks, as follows:

*V1, pin 3 " changed Rk from 2.7k to 2.3k, and corrected the value of the bypass cap from .01uf to the correct 0.1uf.

*Changed the Rk of the output tubes from 185R to 100R. The tubes are now biased @ 100% & have much better definition & clarity....it was biased way too cold with the original 185R. NOTE: the PT I used is 250-0 using a SS bridge recto, so the plate-to-cathode voltage is ~307v. If you use a higher voltage PT, you will have to take that into consideration & calculate the bias current accordingly & adjust you Rk resistor for proper plate dissipation.

*Did away with the "5th" B+ node....the (2) V1 plates now share a common node.

*Added a "normal/medium/low" input switch. on/off/on mini switch gives "normal" input in middle position, "medium" attenuation in the "up" position, & "low" input signal from the guitar in the "down" position. Very useful.

*moved the controls around for a more natural arrangement.

There may be other small changes (i'll post if I remember any), but thoses are the main ones.....G

ps....sorry for all the different "names" of this amp.  :-[
"Vox on the Run"/"Crazy Like A Vox"/"Sligh Vox"/"Vista 12" are ALL the same basic design. I just played around with the names for fun. Sorry if there is any confusion.  G

NOTE: DaGeezer is hereby deducted 3&1/2 points off his all time high unblemished score for confusing the bejeebers out of all of us with the name changes.  Sorry Geezer but it's an unavoidable penalty! You had racked up so many points for innovation and creativity it's sad to see this happen.
 ;D        With regret and respect, Tubenit

[Geezer]

Updated schematic......made some mods to cut down on Bass responce (too much Bass w/ certain closed back cabs)

[Geezer]

More mods to the circuit.....added a 5879 pentode.

Here's the thread on the mod.
http://www.el34world.com/Forum/index.php?topic=8366.msg74827#msg74827

EDIT: updated the files to correct a slight error @ the V1 cathode bypass caps.

[Geezer]

More mods & tweaks.......cleaned it up a bit with some local NFB on 2nd gain stage.
Also, I raised the B+ rail voltages to all preamp tubes by decreasing some of the dropping resistor values.


Oh, also now able to put a 12AT7 in the PI slot (was 12AU7) & removed the cathode bypass caps from the triodes......a switchable Ck on at least one of those stages would be good as a "boost" for those who want more gain.