Vox AC4 build

[andyfromdenver]

Hello!!
I'm going to turn a Vox Pathfinder 15r into the mysterious (and from an exotic far off island) Vox AC4. I've never heard an original and hopefully they rule! This will start out stock except for a Tremolo "Depth" which is absent from the original.
Will the MDF (or whatever) cab try and steal it's soul? Do I need a "bling-y" speaker? Will the ef86 tube give me a tasty cranked crunch? These questions and more.... :)
I'm gonna make a layout from the schematic and I'll post items as this progresses.

[andyfromdenver]

$80 on Craigslist.
A tip of my beer for the 15r. I gutted this poor thing :( Not bad for so little money and sort of full sounding, but crank it and turn up a little treble and you're heading for a divorce, blech... And the reverb....just. no good...
The PT maaay be reused in a somethin' or other, but not for this; I gave it to my friend.

[waparker4]

Cool project! This reminds me of forum member Jaybird's less-than-wordy posts about his 5f1 build in a pathfinder (http://www.tdpri.com/forum/amp-centr...er-15-amp.html) that I have always silently admired.

[hackworth1]

Right On, Andy. Bring on the Pics and deets, please.

[andyfromdenver]

Mike Tyson's Punch Out. (I'm drawing a generational line in the sand here:))
1. Drill to 3/8" (for this particular punch).
2. Snug on the punch out.
3. Remember that you left your wrench @ the shop....
4. Improvise in DIY fashion with a clamp!!!
5. Voila, a 3/4" hole for my 9 pin sockets.

[andyfromdenver]

Layout finished. It will take a little experimentation when built to add a trem depth (may leave off, not sure).
Need a 25 per side turret board (may have 1-2 extra lugs, but filter caps may hog a couple each).
Single inpt. as the original AC4 schematic makes one superfluous (I think...)

[andyfromdenver]

Oops. I don't know if the layout is legible or too blurry, but if someone is looking at it or god forbid saving it (though it's a rough draft). Erase the dotted line to nowhere between the two .01 caps. That was a leftover from an erasure. Also, you may not be able to see my teeny little el84 cathode cap and resistor to ground. I ran out of space on my board drawing.

[muchxs]

You might want to use an isolation socket for your EF86. Mount it solid to the chassis in a combo, it may kick yer ass. Just sayin'...

Look up the "Vox" board at the top of the page.

https://taweber.powweb.com/store/termord.htm

Weber sells an isolation socket, too.

[andyfromdenver]

much xpreciated!!

Hopefully sticking to a 8" speaker will minimize microphonics too.

I was wondering where to get those cool turret boards, thank you very much!

[celeste]

As I recall, Webers iso sockets are crap. The socket does not float, it is spring loaded in only one direction which makes it useless for vibration isolation

[andyfromdenver]

Wait, the wizards of Tdpri, whom I admire greatly, weren't looking @ my layout and junk
j/k.
I forgot to ground the ef86 cathode cap and resistor.
So here's the new pic, for anyone playing along @ home, see the 25/25 and 1.5k off pin 8 of the ef86, those need to ground (I can also just add a line to the adjacent 1M lug). I had it right in the scribble-y version my boss walked me through.
@Celeste, thank you for the input, I guess I'll leave that TBD.

[muchxs]

Originally Posted by celeste

As I recall, Webers iso sockets are crap. The socket does not float, it is spring loaded in only one direction which makes it useless for vibration isolation

I came up with a really cool design that really does float. The socket is on its own little sub chassis which is in turn suspended via "o" rings stretched to little machined posts. Pop a 1.125" hole in the chassis which is normal for an octal, float the .750" miniature inside an air gap.

The Weber socket like it or not is available. I can't think of another one available from commercial sources. I have a couple isolation sockets in tape decks in my junk pile. I'm fortunate, it's a spectacular pile.

[tubeswell]

FWIW, I use the o-ring and grommet method

[hackworth1]

Nice Pic, tubeswell. The EF 86 preamp tubes have a microphonic reputation. I suppose they offer a tonal coloration and amplification that makes them worthwhile to use.

[celeste]

Originally Posted by muchxs

I came up with a really cool design that really does float. The socket is on its own little sub chassis which is in turn suspended via "o" rings stretched to little machined posts. Pop a 1.125" hole in the chassis which is normal for an octal, float the .750" miniature inside an air gap.

The Weber socket like it or not is available. I can't think of another one available from commercial sources. I have a couple isolation sockets in tape decks in my junk pile. I'm fortunate, it's a spectacular pile.

Pearl Isosockets. Bill still lists them, but I can't find a vendor.

I float my sockets on O-rings on the turret board,

Then trap them with an upper shield

Then suspend the whole thing on resilient mounts from the chassis. The holes in the chassis for the tubes are guides, not holes for the sockets.
The back of the turret board looks sort of normal except for my use of Gothik Ring layout.

[tubeswell]

If you look, you can still find good NOS examples of EF86s, which are more robust at coping with microphonics. Between that and shock-mounting, you can go a long way to overcoming this issue.

[muchxs]

Originally Posted by celeste

The back of the turret board looks sort of normal except for my use of Gothik Ring layout.

Hit a few Hamfests in search of Lavoie (think I spelled it right) boat anchors. They used those funky Cinch sockets with the little terminal strip "stalk" on them. I had a coffee can full of them. Now if I could only remember where I put them...

They're not isolation sockets. They are cool little problem solvers.

If you want some I may still have a chassis with half a dozen on there. They used nice Gudeman .1 @ 400 PIOs, too.

There are enough tie points to wire relatively complicated circuits at each socket.

Angela had the sockets for a while. Steve thought they were worth Big Dough.

Originally Posted by tubeswell

If you look, you can still find good NOS examples of EF86s, which are more robust at coping with microphonics. Between that and shock-mounting, you can go a long way to overcoming this issue.

They're surprisingly affordable compared to 12AX7s. I'm surprised because 12AX7s are a lot more common.

[TheNewSteveH]

I have an AC4TV. Not the world's greatest amp. Changing the speaker and putting a 12AT7 in V1 made a big difference. The new speaker is 8 ohms, but nothing has exploded yet.

[littlericky]

Originally Posted by TheNewSteveH

I have an AC4TV. Not the world's greatest amp. Changing the speaker and putting a 12AT7 in V1 made a big difference. The new speaker is 8 ohms, but nothing has exploded yet.

Have you upgraded.the attenuator resistors? Seems to be all that is needed for safe 8ohm use.

[andyfromdenver]

Celeste and Tubeswell, thanks for those great pics! I was going to wait to post in here when I had something going, but I didn't want to not acknowledge (didn't want to not...I should be a politician!) your valued input.
Now i'm going to have to look up Gothik Ring layout!! I'm scared it's going to take me to a dark and foreboding Myspace page!! j/k.
I guess I can let the cat out of the bag that I bought Merc Mag trannys; should arrive Thursday. There aren't a whole lot of options that I can tell. I get the 25+ friend price, which softened the blow.
I know of one cool scavenge option from a device from the 70's which will give me all the trannys and tubes for peanuts, but I don't want to spoil it for those in the know...ebay prices are already climbing.