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Angela Instruments Super Single-Ended 6V6 Guitar Amplifier Project

So, you dig the single-ended 6V6 sound but a Champ or Princeton just isn't loud enough for your needs? Here's a project for you! The Angela Super Single-Ended amp! This little beast is more than twice as loud as a single 6V6 amp, and more than twice as nasty when cranked. Basically, the circuit is very similar to the Princeton project on this site but we've pumped up the output stage and the power supply. If one 6V6 sounds good, WHY NOT USE TWO OF 'EM IN PARALLEL SINGLE-ENDED? If one 5Y3 is enough for the power supply, let's try two of 'em parallel like some of the old hi-fi amps used. This amp also has yet another unique feature you have a choice between two different input tube types. Go for a classic, cutting 12AX7 sound OR an extra fat, smooth octal 5691/6SL7. No, you don't have to rewire the amp; just pull out one type and put in the other in the 'alternative' socket you've installed right next door. We've also given you some more tonal choices: there's a BRIGHT/DEEP switch as well as a cathode bypass switch that lets you choose between a tight, classic twangy Fender sound and a more full bodied cranked VOX tone. In our prototype amp we used an Audio Note EXPERIMENTER 2.5K single-ended 15W output but you can use anything that fits, between 2.5K and 4K or so with good (but different...) results. Hammond and other suppliers make output iron that'll work great. Check out the NEW 125ESE, etc on our Hammond pages; compared to the old 125E, the much larger, air-gapped 125ESE offers better bass and more headroom but still gives up plenty of harmonic distortion when cranked, especially with a hot P-90 or humbucker. I used the "2.5K" primary tap on the 125ESE but you can experiment with the other taps and pick the one that works best for you. If you're really, really broke you can scrounge suitable iron from old radio/phono junkers or even use half of a push-pull transformer. Just remember that the primary impedance required is around half that of a Champ, since there are two output tubes in parallel. We've used a Fender Deluxe reissue power transformer, putting out 337VAC per side under load, resulting in around 370VDC on the plates of the 6V6GT output tubes. Any 'combined plate and filament' type with similar specs will work. Look for close to 335VAC on the high voltage tap if you want the amp to "growl" but not much more unless you've got a barn full of good 6V6GT socked away. A transformer with a high voltage current rating of about 150-200mA is adequate, with 5V/3A for the rectifier tubes and 6.3V/3-4A for the other filaments. See the TRANSFORMER pages of this Web site for other choices. Most of the other parts for this project are similar to those used in the single 6V6 amp project shown in our '96 Catalog. I recommend using vintage style parts at first; electroltyics, carbon resistors and such. Later, you can try film caps and more exotic stuff.

Test Voltages

Measurements were taken at the 6V6GT sockets with the following tubes installed: two 5Y3GT, two 6V6GT, one 12AX7. Output transformer was the 125ESE output transformer but similar measurements were recorded with the Audio Note 15W Experimenter and the Hammond 125E.
1. Plate (pin 3) of the 6V6GT to chassis ground 362VDC.
2. Plate (pin 3) to cathode (pin 8) 339VDC.
3. Screen (pin 4) to cathode (pin 8) 348VDC.
4. Cathode (pin 8) to chassis ground 22.15VDC.

Mods

1. Mod Number One. Worried about burning up 6V6GT power tubes? No problem! Just yank out one of the 5Y3GT rectifier tubes and the B+ will drop twenty volts or so down to around 340VDC, plus you'll get a softer sound with less "drive."
2. Mod Number Two. Lower the hum inherent in this sort of SE circuit by jacking up the value of the first filter cap (before the choke...) from 40uf to 80uf/450VDC.

Connections Between The 6SL7 And 12AX7 Tube Sockets

6SL7 SOCKET LUG #1. A green wire runs between the 6SL7 lug #1 and 12AX7 socket lug #2, where you will also find the hot wire from a shielded two-conductor cable. Note that there is no connection of the shield in this area, the wire is simply stripped back and the shield braid is cut flush, well away (.25 inch or so) from the inner hot wire. This shielded cable runs under the left side of the circuit board up toward the volume pot where it connects.

6SL7 SOCKET LUG #2. You will find two blue wires soldered to this lug. One blue wire runs between the 6SL7 lug #2 and 12AX7 socket lug #1. The other blue wire runs between 6SL7 lug #2 and the turret terminal board junction of a .022 signal capacitor and the 150K 1W resistor. 6SL7 SOCKET LUG #3. You will find two yellow wires soldered to this lug. One yellow wire runs between the 6SL7 lug #3 and 12AX7 lug #3. The other yellow wire runs between 6SL7 lug #3 and the turret terminal board junction of the positive end of a 25uF/50VDC capacitor and a 1.5K .5W resistor. 6SL7 SOCKET LUG #4. You will find one green wire and the hot wire from a shielded two-conductor cable connected here. Note that, here again, there is no connection of the cable shield in this area, the wire is simply stripped back and the shield braid is cut flush well away (.25 inch or so) from the inner hot wire. This shielded cable runs under the turret terminal circuit board up to the volume pot where it connects. The green wire runs from 6SL7 socket lug #4 to 12AX7 socket lug #7.

6SL7 SOCKET LUG #5. You will find two blue wires soldered to this lug. One blue wire runs from 6SL7 lug #5 to the top end (from underneath) of the turret terminal board where it connects with a .022 signal capacitor and a 100K .5W resistor. The other blue wire runs between 6SL7 lug #5 and 12AX7 lug #6.

6SL7 SOCKET LUG #6. You will find two yellow wires soldered to this lug. One yellow wire runs between 6SL7 lug #6 and 12AX7 lug #8. The other yellow wire runs between 6SL7 lug #6 and the bottom end of the turret terminal board where it connects with a 2.7K .5W resistor and a short ground ÔbussÕ to three other turret terminals.

6SL7 SOCKET LUG #7. You will find two green wires solderd to this lug. One green wire runs between 6SL7 lug #7 to 6V6GT socket lug #7. The other green wire runs from 6SL7 socket lug #7 to 12AX7 socket lugs #4 and #5 (yes, this wire is soldered to BOTH of these lugs).

6SL7 SOCKET LUG #8. You will find two green wires soldered to this lug. One green wire runs between 6SL7 lug #8 and 12AX7 socket lug #9. The other green wire runs between 6SL7 socket lug #8 and 6V6GT socket lug #2.

Some Of You Have Asked Us For A 'Parts List'...Here's How The Parts On the Board Run From Left To Right (Starting With The Filter Cap Nearest The Power Transformer)...Also The Lone Resistor At The Bottom Of The Board...
1. Sprague Atom 80uF/450VDC polarized axial lead electroltyic, anything close will work fine but make sure that the rating is 450VDC or greater. Please note from our commentary above that we started with a 40uF capacitor in this position on our prototype, so you may want to try that value first and see if you prefer the sound. Actually, any value between 40uF and 100uF will work fine, with different sonic results. A higher value cap here will give a 'tighter sound' with a bit more bass and less hum, a lower value cap will result in more 'slop' and harmonic content.
2. Sprague 16uF/475VDC polarized axial lead electrolytic. 20uF, 22uF or anything 'in the ballpark with a voltage rating equal to or greater than 475VDC will work fine. You can also use metalized film caps like Angela Fast Caps, SCR, Solen, etc.
3. Another Sprague 16uF/475VDC or something close.
4. 10uF/100V polarized axial (radials are OK if the leads will reach...) electroltyic, any OK brand will do. You can also use Black Gate, ELNA CERAFINE, Nichicon Muse or other audionut capacitors.
5. 250 ohm 5W resistors. Wirewounds are cool; try to find something that says BROWN DEVIL on it for the karma, right? Metal oxide will do if that's all you can find.
6. 220K .5W resistor, carbon composition, Riken, whatever.
7. .022/600VDC signal capacitor, old Mylars are cool, Angela Tin Foil signal caps, paper in oil caps if you're rich, etc.
8. 100K .5W resistor, carbon composition, Riken etc.
9. 150K 1W resistor, carbon composition, Riken etc.
10. Another .022/600VDC signal capacitor.
11. 1.5K .5W resistor, carbon composition, Riken etc.
12. Sprague Atom 25uF/50VDC polarized axial lead electrolytic.
13. 2.7K .5W resistor, carbon composition, Riken etc.
14. Another 25uF/50VDC Sprague Atom.
15. .68/250VDC signal capacitor. Old Sprague Mylar, Angela Tin Foil, SBE, etc. 600VDC caps are probably the easiest to source so don't hesitate to use those.
16. 10K .5W resistor, carbon composition, Riken, any other good resistor.

There's a couple of 1.5K .5W resistors on the power tube sockets. Carbon composition, Riken, etc. will do just fine.

You'll also need a .0047/600VDC and a 47pf/500VDC for the tone circuit. I prefer old Mylar Spragues but if you're forced by circumstance to use modern silver mica, SBE, etc. it's OK. It really doesn't matter that much. This is a good circuit and it'll sound fine no matter what type of signal caps you'll use. 

The Schematic Directly Below Originally Appeared In The Angela Instruments 1996 Catalog.

schematic
 

Below find Jesse Quitsland's more artistic interpretation of our schematic.