KLB
02-23-2006, 02:35 PM
I wanted more compression, earlier breakup and lower volume with a Germino Club 40 1x12 combo compared with with EL-34. I subbed 6V6 and rebiased, which resulted in a "Masonette on Steroids." It was closer to my goal, but still too loud and punchy.
With a 5AR4, JJ 6V6 tubes can produce about 30 watts in the Club 40! This is due to the larger power supply capacitance and bigger, more "open" sounding output transformer (OT) vs. the Masonette. The power transformer is the same in both amps, putting about 440-450v on the 6V6 plates at 70% dissipation, depending on AC line voltage.
Here are some Club 40 mods for 6V6 which will make it feel significantly less loud than with EL34:
POWER SUPPLY
The stock Club 40 power supply capacitance is Plate-32mf + Screen-32mf in a dual-cap can, PI-32mf + V2-32mf in a dual-cap can, V1-30mf on the circuit board. Change the V3 (phase inverter) + V2 cap to a dual 16mf F&T, which is the same size. Also, change the V1 cap to a 16mf/475v Sprague Atom. I also like this power supply setup with EL-34. It is the same as the Classic 45. The result is better touch response -- less stiff with a more bouncy feel.
Replace the stock 5AR4 with a quality 5Y3GT (RCA, etc.). This reduces the plate volts by about 50v to about 390v, and gives a more compressed touch response. The amp remains lively, but in a more "up close and personal way." A 5U4GB would put the plate voltage between the 5Y3 and 5AR4. For some creamy distorted tones, try running JJ or other stout 6V6 at 12 watts idle bias dissipation.
PHASE INVERTER (PI)
Substitute a 12AT7 for the 12AX7, which reduces the output from the PI. 6V6 input grids saturate easily, and don't require as much signal as EL34. This tube swap helps tame the preamp output, letting you increase the preamp volume so it can breathe better without overly saturating the 6V6.
Optionally replace the stock .1mf PI caps with .022mf. IMO, EL-34 don't really need the .1mf caps, but 5881/KT-66 sound better with them. This mod further reduces the PI output by cutting excessive deep bass. You will still have plenty of bass and drive for the 6V6. Depending on the cab and other factors, you can change the .022mf PI input cap to a .01mf.
You can replace the 10K "tail" resistor with a 27K (stock Deluxe Reverb value), which further reduces the PI output and contributes to slightly better push-pull balance.
It's all about scaling the PI circuit to match the capabilities of 6V6.
PREAMP
Experiment with removing the .68 cap on the 2nd gain stage. With these mods, you may find that you don't need the slight boost in gain/treble that this cap gives. It depends on the guitar, speaker, effects, volume level, etc. You can put it on a push-pull switch on the 1m bass pot.
If you use a 5Y3 rectifier, you may want to remove one of the two 8.2k/10K power supply resistors in a row that go between the screen and PI. Replace with straight wire, or leave the resistor in place and jumper with wire. This will increase the preamp voltages closer to the level with a 5AR4. Otherwise, you may have too much preamp breakup and sag.
NEGATIVE FEEDBACK - NFB
I am using a 16 ohm Cannabis Rex speaker on the 8 ohm tap to properly load the OT for 6V6. Like many others, I like the way the C-Rex colors the tone, at least with this amp. The NFB resistor is 56K in my amp, but you may like 47K or smaller for more NFB, or 68K or larger for less NFB. More NFB will tighten the amp, smooth the high end, and reduce apparent gain. Note that if you use the 4 ohm tap (for an 8 ohm speaker), you will have less NFB than the 8 or 16 ohm tap. One way around this is to move the NFB wire from the speaker jack to the 8 ohm tap so it remains the same regarless of output impedence used.
These 6V6 mods are also suitable for the Low Voltage 55. If you plan to use a 5Y3 or 5U4 rectifier, you will want to replace the first dual 50mf filter cap with a dual 32mf. Otherwise, you may stress the rectifier too much, causing early failure.
Cheers,
Ken
PS - Have fun and don't accidently discharge the filter caps into yourself!
With a 5AR4, JJ 6V6 tubes can produce about 30 watts in the Club 40! This is due to the larger power supply capacitance and bigger, more "open" sounding output transformer (OT) vs. the Masonette. The power transformer is the same in both amps, putting about 440-450v on the 6V6 plates at 70% dissipation, depending on AC line voltage.
Here are some Club 40 mods for 6V6 which will make it feel significantly less loud than with EL34:
POWER SUPPLY
The stock Club 40 power supply capacitance is Plate-32mf + Screen-32mf in a dual-cap can, PI-32mf + V2-32mf in a dual-cap can, V1-30mf on the circuit board. Change the V3 (phase inverter) + V2 cap to a dual 16mf F&T, which is the same size. Also, change the V1 cap to a 16mf/475v Sprague Atom. I also like this power supply setup with EL-34. It is the same as the Classic 45. The result is better touch response -- less stiff with a more bouncy feel.
Replace the stock 5AR4 with a quality 5Y3GT (RCA, etc.). This reduces the plate volts by about 50v to about 390v, and gives a more compressed touch response. The amp remains lively, but in a more "up close and personal way." A 5U4GB would put the plate voltage between the 5Y3 and 5AR4. For some creamy distorted tones, try running JJ or other stout 6V6 at 12 watts idle bias dissipation.
PHASE INVERTER (PI)
Substitute a 12AT7 for the 12AX7, which reduces the output from the PI. 6V6 input grids saturate easily, and don't require as much signal as EL34. This tube swap helps tame the preamp output, letting you increase the preamp volume so it can breathe better without overly saturating the 6V6.
Optionally replace the stock .1mf PI caps with .022mf. IMO, EL-34 don't really need the .1mf caps, but 5881/KT-66 sound better with them. This mod further reduces the PI output by cutting excessive deep bass. You will still have plenty of bass and drive for the 6V6. Depending on the cab and other factors, you can change the .022mf PI input cap to a .01mf.
You can replace the 10K "tail" resistor with a 27K (stock Deluxe Reverb value), which further reduces the PI output and contributes to slightly better push-pull balance.
It's all about scaling the PI circuit to match the capabilities of 6V6.
PREAMP
Experiment with removing the .68 cap on the 2nd gain stage. With these mods, you may find that you don't need the slight boost in gain/treble that this cap gives. It depends on the guitar, speaker, effects, volume level, etc. You can put it on a push-pull switch on the 1m bass pot.
If you use a 5Y3 rectifier, you may want to remove one of the two 8.2k/10K power supply resistors in a row that go between the screen and PI. Replace with straight wire, or leave the resistor in place and jumper with wire. This will increase the preamp voltages closer to the level with a 5AR4. Otherwise, you may have too much preamp breakup and sag.
NEGATIVE FEEDBACK - NFB
I am using a 16 ohm Cannabis Rex speaker on the 8 ohm tap to properly load the OT for 6V6. Like many others, I like the way the C-Rex colors the tone, at least with this amp. The NFB resistor is 56K in my amp, but you may like 47K or smaller for more NFB, or 68K or larger for less NFB. More NFB will tighten the amp, smooth the high end, and reduce apparent gain. Note that if you use the 4 ohm tap (for an 8 ohm speaker), you will have less NFB than the 8 or 16 ohm tap. One way around this is to move the NFB wire from the speaker jack to the 8 ohm tap so it remains the same regarless of output impedence used.
These 6V6 mods are also suitable for the Low Voltage 55. If you plan to use a 5Y3 or 5U4 rectifier, you will want to replace the first dual 50mf filter cap with a dual 32mf. Otherwise, you may stress the rectifier too much, causing early failure.
Cheers,
Ken
PS - Have fun and don't accidently discharge the filter caps into yourself!