Tips For Improving Vox AC4TV?

[The New Steve H]

Tonight I took out my Vox AC4TV and fiddled with it. I ended up putting a 12AY7 in the preamp, and I'm ordering an Eminence Ragin' Cajun. I have a Ragin' Cajun in a cabinet, and the Vox sounds better with the Eminence than the Celestion it came with.

I'm trying to give it a clearer, sweeter sound. More like a Fender. Let's face it. I want ALL amps to sound like a 5F6A. Any suggestions, other than buying a Fender? The Vox seems to have kind of a fuzzy sound.

I tried an EL844 in it, and it sounded disgusting. I'm going to put a JJ EL84 in it as soon as I can get one. It has a Sovtek in it now, and I've read that the JJ is a little better.

If anyone could suggest something that has more gain than a 12AY7, without the harshness of a 12AX7, I would be interested.

When I opened it up, it actually didn't look too bad. I liked what I saw better than the PCB maze inside the Chinese AC30 I worked on.

[selloutrr]

http://endofthegame.net/2011/09/02/vox-ac4tv-mods/

5751 tube maybe more to your liking

changing out the tone caps will greatly improve the tone. if you want a smoother fender tone consider sozo or jupiter molded reissue caps.

changing the OT will also give tonal results.

[endofthegame]

Cheers for the plug! Like I mentioned in my guide, a speaker change is absolutely essential with this amp (the stock speaker is rubbish). As for your tubes, a 12AT7 tube is exactly what you are after (not sure if 5751s fit in an AC4TV). The preamp tube ranking from highest to lowest gain is:

12AX7 - 100
5751 - 70
12AT7 - 60
12AY7 - 45
12AV7 - 41
12AU7 - 19

I wouldn't recommend JJs, they are hit and miss, about 50% of their tubes don't even work. I would strongly suggest you get NOS Tesla EL84s instead of JJs, Tesla was the original tube factory that JJ ended up buying, and they've done a poor job of keeping up with their tradition. These tubes are only $38 a pop, which might seem pricey, but are very good value for an excellent NOS tube. As for your 12AT7, see if you can get a (NOS preferably) RCA Black Plate tube, these sound the most Fendery in my opinion.

Hope that helps, Good luck!

[endofthegame]

Oh, almost forgot. Here is where I buy my NOS Tesla tubes: http://www.kcanostubes.com/content/nos- ... t-jj-el84s

[10thTx]

I'm trying to give it a clearer, sweeter sound. More like a Fender.

Looking at the schematic, do you think you can get it to sound clearer like a Fender?

Having said that, you could consider changing the EL84 out for a 6V6 & change the V1 plate and cathode values to something more like 150k/2.7k. Then change the V2 plate and cathode to 120k/1.8k.

C5 & C18 could be changed to something more in the .01-.02 range.

That should give it somewhat a clearer tone.

With respect, 10thtx

[10thTx]

Maybe something like this?

[The New Steve H]

The 12AT7 sounds like a neat idea. I already ordered 4 12AY7s, but I'll need them for my other amps.

[Phil_S]

See if you can find a 6CM6 and rewire the EL84 socket (better, get an adapter.) 6CM6 is the noval 6V6.

[The New Steve H]

It occurs to me that it wouldn't be hard to remove the entire Vox board and stick something homegrown in there. Maybe I could stick a Champ circuit in there and call it a Vump.

[The New Steve H]

I notice the Champ has no bypass caps on the preamp. Am I asking for tonal hell if I lift the caps on the Vox?

I found a Mesa 12AT7 at Guitar Center, so I'll be trying that shortly.

[Reeltarded]

Might make it dull. Try it. It actually might make it just what you want.

[The New Steve H]

Tubedepot sells a 5F1 PCB, and it has a nice piece of literature that goes along with it. It says they added a 22uF cap to the preamp to bring out the bass. I might just copy that.

I could make a whole new board using the Vox schematic, and I could add and subtract at will. That would take about two days, and I already have most of the stuff. Maybe that's a good approach, because I won't wreck the China stuff that's already in it.

[Reeltarded]

removing a higher bypass will soften the peak in the frequency response, and detract from the gain some.

How about adding a 22uF over the preexisting cathode bypass? (whatever is already there) That will leave everything as is, but more lowend.. and it's a 10 minute trip from cold iron to hawt mess.

[The New Steve H]

That's a good idea. I could probably mash one in there without soldering it, just to get the flavor.

I'm off to the garage to see what the new tube does.

[The New Steve H]

I'm mystified by the huge mess of capacitors and resistors on the second half of the preamp. It's like it has plain old filter on the cathode, plus a second filter on the input. Are they trying to increase the bass by killing high frequencies or what?