After 5 years, help me finish my AC15

[Willabe]

Do you have two input jacks? If so, just wire them exactly like the schematic you posted.

One thing that occurred to me, I do not have a Hi and Low input on my amp. On all my past amps I only used the Hi input so I left it out. Could I simply add in the 1M resistor (or play with values to see what I like) to lower the signal?

[Willabe]

Or... should I play with lowering the G2 Screen Input resistor. (I know... try both). The Screen Input resistor is currently 1M. If I put another 1M in parallel than that will cut the value in half. Would that be too low (as in would it do damage)?

I'd play with the EF86 screen R 1st.

This will help you;

http://www.valvewizard.co.uk/EF86.html

And this;

http://www.valvewizard.co.uk/pentode.html

What you are asking about the screen R is in there and he talks about using a screen stopper R too, I would definitely try that.

[dbishopbliss]

Do you have two input jacks? If so, just wire them exactly like the schematic you posted.

No, just one. Both channels are permanently jumpered to the single input jack and I wired them as the Hi input.

[sluckey]

See the pic if you want to wire your input jack as a "LO" jack. I think you could just turn the vol knob on your guitar to accomplish the same thing.

[dbishopbliss]

I think you could just turn the vol knob on your guitar to accomplish the same thing.

I noticed my guitar losing a lot of highs when rolling back the volume knob. Maybe I need to add a treble bleed circuit but that is a lot of work since I have a ES335-style (Eastman T386). Not to mention, it seems like every guitar that gets plugged in has the same effect. Zero clean, highs roll off with the volume down.


I played around with clipping resistors in parallel with the screen grid resistor (R20) and really didn't hear much difference. I will keep trying different things.

[PRR]

> highs roll off with the volume down.

How long is your cable?

[dbishopbliss]

> highs roll off with the volume down.

How long is your cable?

4 feet, or 10 feet. Happens with both.

[HotBluePlates]

I think you could just turn the vol knob on your guitar to accomplish the same thing.

I noticed my guitar losing a lot of highs when rolling back the volume knob. ... Not to mention, it seems like every guitar that gets plugged in has the same effect. Zero clean, highs roll off with the volume down.

The 50% signal loss due to the input jack wiring is the same as turning your guitar's Volume from 10 to 9.

Regardless, the first thing that comes to mind if you're unhappy with treble loss due to turning down your guitar's Volume is to turn the Cut control for more treble.  Depending on your speaker choice, you could have more treble than you want anyway.

I wound up trying to work around a 1964 Deluxe Reverb's bright cap by turning the amp's Volume up to 7-8, then turning my guitar's Volume near-off to get the room-loudness I wanted (late-night apartment playing).  Worked fine for me with a Tele with what's generally called "50's wiring" when applied to a Les Paul (retains highs when both Vol and Tone controls are rolled back).

[dbishopbliss]

I understand about rolling back on the volume, etc. but that doesn't really help me if I want to play with a drummer. If I turn the amp up to where it can be heard (call that 3) then it is very overdriven. If I roll back on the guitar volume then I am below drummer level. I'm not necessarily looking for sparkly clean fender tones... I like a little edge on everything but it would be nice if I could have that tone AND be able to play with a drummer.

[HotBluePlates]

... doesn't really help me if I want to play with a drummer. If I turn the amp up to where it can be heard (call that 3) then it is very overdriven. ...

This is where you have to figure out whether the amp is distorting because the EL84s are distorting (and the EF86 is clean), or because the EF86 is distorting (and the EL84s are clean).

Fastest way to do that is measure the d.c. volts across the EL84 cathode resistor:  that's your bias voltage.  Now attach your meter to the EL84 control grid, set for a "peak a.c." measurement.  Play until distortion just-starts, then back off a hair on volume.  You might need to reset the meter's peak-hold function to capture the peak signal driving the EL84s just-before distortion starts.

Compare the measured peak to the EL84 bias voltage.  If the peak voltage is about the same as the EL84 bias, you're hearing the EL84s distort; you'll need a bigger output section for louder-clean.  If the peak voltage is well below the EL84 bias, you're hearing the EF86 distort (or much less likely, the phase inverter distort); adjust the screen voltage to reduce distortion.

"Which way, or how do I adjust the screen voltage?"

Put a pot somewhere: might be as a variable resistor in place of the resistor from B+ to screen.  Or it might be that you keep the screen resistor as-is, and add a variable resistor from screen to ground/cathode (somewhat like the vintage AC10).

You're adjusting by-ear to your-taste, so no one can really help you out with what to do.  Just gotta do it, make a choice aligned to your preference.

[dbishopbliss]

Here’s the finished amp in the head cabinet. The logo is just a paper cut out. If you know of a good laser engraver please le me know.

[Willabe]

Looks really great!