Want to know more about building your own Orange Graphic from scratch? Follow the link below to READ ON…
So how does it sound? After some pretty minimal troubleshooting, great! WOW even with only two EL34s, this thing is insanely loud. My lord. My only (small) complaint: the bass and treble controls have slightly awkward swings to them… even though I used audio-taper pots, 50% of the action seems to occur in the last 10% of the control-movement. As far as the gain: I might actually rewire one of the input stages with a 100k plate load resistor and corresponding 1500 ohm cathode resistor just to lessen the gain a little bit.
Some tips if you plan to build an Orange Graphic: the bass and treble pots should be wired similar to the volume pot; I.E., if the right leg of the volume pot goes to ground, it would be the right leg of the bass and treble pots that go to ground (via a resistor and a capacitor, respectively). I wired them up opposite to the volume pot and now I have very counter-intuitive bass and treble controls, which I certainly can’t be bothered to change. Here’s a link to (basically…) the schematic that I used. This is the non-master-volume model. If you are into the whole master-volume thing, there are plenty of schems online which indicate that iteration as well (for instance, here). One important note: I was having crazy RF problems with the volume pot set to zero. After a little troubleshooting, the fix was adding a ‘grid stopper’ resistor between the wiper of the volume pot and the following tube grid (i used a 9.1k ohm, for no particular reason). This solved the problem with no averse effects. Another note: The Orange schem indicated that the bias voltage should be set to -37v. In practice, with 477 volts on the plates of the EL34s, this was causing the output tubes (new JJ EL34s) to draw a lil too much current. -39v seemed to be the right choice (results in 25 watts/tube plate dissipation).
Like the schematic said, the 80 watt model is exactly the same as the 120 watt model except that it omits two output tubes (and requires a different primary impedance on the output transformer, but if you’ve read this far, you prolly already know that). I rarely build big, fixed bias guitar amps: the several big Fenders, Sunns, and Ampegs I have seem to do the trick for my own studio work, and the parts cost (read: transformer cost) is so high that frankly it’s hard to justify the expense to customers, who mainly want small amps that break up early anyhow. That being said, this Orange came together very easily; trust the schematic, and remember: +/- 20% on component values will yield good results 95% of the time in guitar amps. Just like Leo Fender said. Anyway, If you need a loud guitar amp for some reason, give it a shot. It’s a robust, versatile circuit, and it seems to run a lot quieter than most factory-built Marshalls I have played.
Update 2: I had the chance y’day to try out the effects loop on the Orange 80 clone.
The M300 has a 13K ohm unbalanced input impedance. Based on my success with this unit, I would guess that any effect device with 10K or high input impedance will probably work fine. When I originally bought this unit at Daddys Junky Music (RIP – also – you fkkrs owe me money…), I chose it because it has totally separate reverb and effects sections, a tap tempo button, and… no menus! There is actually a dedicated knob for each function. I have never, ever used a multi-effect unit in a guitar ‘rig’ before (I don’t think I’ve ever had an amp with an FX loop?) but I gotta admit it’s pretty fun.
Anyways… what’s the point… the point is: this simply three-resistor, two-jack ‘effects loop’ could easily be added to any guitar amp that has a voltage amp (e.g., 12A_7 tube) stage following the tone-control-gain-makeup stage. Go wild.
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View Comments
Hey Chris,
I noticed there isn't a stand-by switch on the OR80 Build.
How critical are stand-by switches? Do chokes negate the need for one? Or are they not related in that sense.
How do you calculate how many mA a choke should be rated for? if you know the B+ voltage.
-al
Hi al. The choke situation does not impact the need for a standby switch. rather, it is the presence of the rectifier tube that negates the absolute need for the standby, because it prevents the full B+ voltage from hitting the audio-tube plates before the tubes are heated up. As a general rule, if you use a solid-state rectifier, it's a good idea to have (and use!) a standby switch.
The choke should be rated near (or higher than) the current draw of the audio-portion of the amp. If you don't know how to figure this... you might wanna read up a little more. I can give u some general ballparks tho: a two-6V6 (or EL84) amp is about 100ma, two 6L6 (or EL34) is about 200ma, four 6L6 amp is about 400ma.
Good luck
c.
You mean four 6L6s I suppose...or a pair of KT88s.
YES i meant 6L6, sorry.... and an amp with a pair of KT88 or 6550 will be in the 300ma range, maybe 350 including the preamp.