Building AC-10 clone

[BlueX]

Hello, newcomer to the forum here.

I'm planning to build a clone of Vox AC-10, using the V-1-3 schematics below. Inspiration is the YouTube video below by Johan Segeborn (missed to buy that amp when it was for sale).

Looks like 6 noval sockets: EZ81 (rectifier), EF 86 (or EF 806S), ECF 82, ECC 83, and 2 x EL 84. Seems like EF 86 might need special damping.

Planning to use Marshall-style "flatbed" chassis (instead of L-shaped), and put chassis in headshell (for now). Will probably contact Michael at Modulus first, to discuss parts.

Anyone who has done something similar and can share pictures and info? Any comments or recommendations, so far?


This would be my 4th build after 5E3 kit, 18W (schematics and layout from 18watt.com and sourced parts), and JTM45/100 clone (Marstran schematics of #7026 and sourced parts).

https://www.youtube.com/watch?v=SevP5V6Msrk&t=223s

ac10-v-1-3 schematics.png

[sluckey]

I've done something similar with the AC-15. Lot of similarities. Lot of differences. Take a look. Maybe you can find something useful...

https://sluckeyamps.com/VAC15/ac15.htm
https://sluckeyamps.com/dual_lite/dual_lite.htm

[BlueX]

I've done something similar with the AC-15. Lot of similarities. Lot of differences. Take a look. Maybe you can find something useful...

https://sluckeyamps.com/VAC15/ac15.htm
https://sluckeyamps.com/dual_lite/dual_lite.htm

Thanks a lot! That's really well documented. Need some time to study how you did these.

[BlueX]

I've done something similar with the AC-15. Lot of similarities. Lot of differences. Take a look. Maybe you can find something useful...

https://sluckeyamps.com/VAC15/ac15.htm
https://sluckeyamps.com/dual_lite/dual_lite.htm

I noticed the shielded wires from inputs. Any other measures to avoid interference/oscillation, or would it be sufficient to follow a typical "Marshall turrret board"-style layout?

For grounding I plan to follow Merlin's one-point scheme (sections, cascaded to near the inputs).

[sluckey]

I use shielded cable between input jacks and tube sockets and also between volume controls and tube sockets. The Marshall style layout and careful wiring should give good results. I use the Marshall style on most all of my stuff.

[BlueX]

Anyone who can comment on the wiring of the inputs according to the Vox AC-10, V-1-3, schematics I'm using (see post #1)?

Hi and Lo inputs for each channel (Normal and Vibrato) seems to be identical, i.e. same grid stopper resistance (220k) regardless if plugg into Hi or Lo. What's the point with two inputs, or am I misreading something?

I understand "Marshall 4-holer", where you get 68k to grid in Lo input (and 68k to ground), but two 68k in parallel (34k) to grid and 1M to ground in Hi input.

See enclosed cutouts (Marshall first).

M-U 1986 inputs.jpg

ac10-v-1-3 inputs.jpg

[sluckey]

Both inputs are LOW. By that I mean plugging into either jack sends the signal through a 2:1 voltage divider (two 220Ks). Only one half the guitar signal will reach the tube grid. Believe it or not, when that amp was built people would actually use the dual inputs to connect two instruments to a channel. You and your buddy could both play through the same amp. If you had three friends you could have a four piece band with only one amp.

The Marshall HI/LOW jacks are more useful. If I was building that AC10 I'd rewire the input jacks exactly as Marshall did.

[BlueX]

Both inputs are LOW. By that I mean plugging into either jack sends the signal through a 2:1 voltage divider (two 220Ks). Only one half the guitar signal will reach the tube grid. Believe it or not, when that amp was built people would actually use the dual inputs to connect two instruments to a channel. You and your buddy could both play through the same amp. If you had three friends you could have a four piece band with only one amp.

The Marshall HI/LOW jacks are more useful. If I was building that AC10 I'd rewire the input jacks exactly as Marshall did.

Thanks! Would you also use 68k's, instead of 220k's, into the EF86 and ECF82 grids?

Nowadays my friends could have an amp each, but back in the days the AC-10 setup would have been useful.

[sluckey]

Thanks! Would you also use 68k's, instead of 220k's, into the EF86 and ECF82 grids?

yes

[BlueX]

A question on choke for AC-10, related to my clone build.

Found the enclosed schematics (circuit 05/008, date 9-9-60) where choke is 8 H. In the schematics I've used so far (V-1-3, see post #1) the choke is 5 H. No other difference as I can see (except 0,005 µF instead of 0,0047 µF), even voltage the same.

Any preference for 5 H or 8 H choke?

[BlueX]

Got the parts for my build, most of them from Modulus Amplification. Now it's "dry'fitting" to realise the AC-10 schematics in this "Marshall-style" layout.

Edit: Pic's in reverse order for some reason.

[B Ingram]

A question on choke for AC-10, related to my clone build.

Found the enclosed schematics (circuit 05/008, date 9-9-60) where choke is 8 H. In the schematics I've used so far (V-1-3, see post #1) the choke is 5 H. ...

You already have your parts. That said, the choke on my 1965 AC-10 is a 5H unit.

[BlueX]

A question on choke for AC-10, related to my clone build.

Found the enclosed schematics (circuit 05/008, date 9-9-60) where choke is 8 H. In the schematics I've used so far (V-1-3, see post #1) the choke is 5 H. ...

You already have your parts. That said, the choke on my 1965 AC-10 is a 5H unit.

Thanks, appreciated! It's a valuable confirmation. The schematics with 8 H choke is dated 1960, so that might be an older version.

[cdemike]

Late to the party on this one, but I'm interested to know how it turns out!

Seems like EF 86 might need special damping.

I haven't worked with EF86, but several Dr. Z amps use them and often have the rubber dampers that fit around the bottle. I have wondered about using thick squishy rubber washers to mount the tube socket since that seems like an easier solution and one which would offer better vibration damping. Either way, building it as a head should also help.

Is there a specific reason you'd opt for the ECF82? I might be projecting my own biases, but I'd probably want to convert the "normal" channel's input stage to a 12AX7 both because of availability of spare parts (no new production ECF82/6U8) and because I'd probably want the amp to overdrive more easily than it would with an input stage built around a tube with mu of 40.

[BlueX]

Late to the party on this one, but I'm interested to know how it turns out!

Seems like EF 86 might need special damping.

I haven't worked with EF86, but several Dr. Z amps use them and often have the rubber dampers that fit around the bottle. I have wondered about using thick squishy rubber washers to mount the tube socket since that seems like an easier solution and one which would offer better vibration damping. Either way, building it as a head should also help.

Is there a specific reason you'd opt for the ECF82? I might be projecting my own biases, but I'd probably want to convert the "normal" channel's input stage to a 12AX7 both because of availability of spare parts (no new production ECF82/6U8) and because I'd probably want the amp to overdrive more easily than it would with an input stage built around a tube with mu of 40.

Thanks! Currently working on modifying chassis, but will share pictures and progress.

I put a heat-resistant O-ring on the EF86 socket, to be top mounted, and made rubber washers for the underside, see pic. From what I understand, damping socket is more effective than putting rubber around the glass. Will be interesting to see/hear the result.

The idea is to build an AC-10 clone, following that schematics (with EF86 and ECF82). I built an 18W clone, so I've already got a "3xECC83, 2xEL84, 1xEZ81" amp. Used/NOS ECF82 is still available around here, and I have stocked some already.