5c1 champ - reduce wattage?

[knifeinthesink]

Is it possible to do this by only changing component values?

I want a quiet practice amp I can get some subtle break up out of without waking up family. 5 watts is going to be too loud but I can live with it if I can't adjust easily.

Haven't committed to Champ yet but the quantity of discussion and documentation and its simplicity makes it look like the best choice.

This is my first guitar amp build.

 

[doozerdave]

5C1 Champ certainly is a very simple option. The 6V6 is cathode biased, so you could have a switchable cathode resistor to move the bias point around, push it into cut-off for more break up. You could also play with different screen voltages.

5E1 Champ gets you into a 12AX7 (more tonal options with more tubes readily available) without too much more complexity. It also gives you the option to add a buffered tone stack in the future.

 

[nazaroo]

Since its such a low wattage amp already, why not just put in a series-parallel dummy speaker load? Then the amp would act the same, but the speaker would be taking 1/4 the power (and half the voltage) it was before.

---T-----[ 8 ohm resistor]------*-----[ 8 ohm resistor]------------T----------
. . |. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
. . L-----[ 8 ohm resistor]-----*-----[ original speaker] -----------|


Make these 10 watt resistors and mount them inside the speaker cabinet with a switch.

Then you haven't messed up the amp in any way. It would still be the champ!

 

[knifeinthesink]

Thanks for the replies.

I'll experiment with these suggestions.

I like the dummy load. Any downside to this?

 

[nazaroo]

Thanks for the replies.

I'll experiment with these suggestions.

I like the dummy load. Any downside to this?

Mount them where kids' fingers won't reach in and get burned.

There is no downside provided the speaker and resistors/switch are mechanically/electrically connected (soldered) properly.

Add one more safety item to EVERY amp:

Permanently wire a 100 - 150 ohm 2 watt resistor across the speaker leads to prevent high voltage spikes from blowing the output transformer if the speaker is accidentally disconnected when the amp is on and playing, or a tube shorts.

This won't affect the sound at all (the resistance is too high to pull any current), but can save you $100 for a transformer.

 

[Enzo]

The 5C1 has a pentode input stage, on to the volume control, then direct to the grid of the 6V6 output tube. Unless you are driving the heck out of it, I don't think the breakup you get is from the power amp stage. Which leads me to ask, what is lacking with just turning it down? The preamp stage is operating the same no matter what the control setting, so any preamp tube breakup should remain.

Later versions like the 5E1 replaced the single pentode with a 12AX7 dual triode with volume control between triodes. IN those cases, one could add a "master" volume control by turning the 6V6 grid resistor into a pot.

 

[Printer2]

The 5C1 has a pentode input stage, on to the volume control, then direct to the grid of the 6V6 output tube. Unless you are driving the heck out of it, I don't think the breakup you get is from the power amp stage. Which leads me to ask, what is lacking with just turning it down? The preamp stage is operating the same no matter what the control setting, so any preamp tube breakup should remain.

Later versions like the 5E1 replaced the single pentode with a 12AX7 dual triode with volume control between triodes. IN those cases, one could add a "master" volume control by turning the 6V6 grid resistor into a pot.

Has a point, not enough gain in a 5C1 to get really dirty. Mind you, you could use a booster to hit the input tube harder and then use the volume control to set the level. Then again it all depends on how much you want.

With a dual triode setup you can have a master, I did this on one of my amps and it works well enough. Not the ultimate in tone but pretty good and still have low volume.

 

[knifeinthesink]

Interesting.

I like mild breakup on expressive notes and I like to use the guitar volume pot to control the breakup. Most of the guys I like to listen to have a fairly clean tone. I have another amp that does that well but I don't need this to get too dirty.

Guess I'll try it stock and see. Sounds like it might be right for me as it is.

 

[chrispenycate]

Thanks for the replies.

I'll experiment with these suggestions.

I like the dummy load. Any downside to this?

Much as I hate to disagree with he who suggests this (I love dummy loads, even on stage), it does change the sound a bit (note, I haven't said it makes it worse) I think it's the amp appreciating the constant impedance rather than the mess the speaker reflects back, but it could be the speaker reacting to less damping. But, if you use high wattage resistors you can use the same box on stage for smaller gigs when the sound man's accusing you of overwhelming the mix (It's not true, of course. We just enjoy the feeling of total control. Oh, the power, the power!) and it's reasonably easy to put a headphone output and combine the blast of sound in your eardrums with total non annoyance of neighbours.

 

[Enzo]

Oh it changes the sound alright. If nothing else, your ears respond to a different frequency range at lower volumes. Look up Fletcher-Munson. That is why stereo receivers add that tone boost loudness control. And at louder play, the speaker can mechanically react differently than at low levels.

And food for thought, output power is not the best way to control volume. To make a 5 watt amp half as loud, you must reduce it to 0.5 watts. Half a watt.