Short iPhone clip of my JCA20 Jose mod

[311boogieman]

Dave always gets fantastic tones in his clips. This $450 amp sounds unbelievably good! I love it!

+311


Sounds awesome and great playing too Dave!

 

[JerEvil]

Sounds great man. I honestly have never liked the clips I have heard of unmoved JCA's but this is killer.

 

[dstroud]

jeez loise that sounds wicked!

 

[FourT6and2]

I lowered the voltages in the power section a bit

you mean plate and screen voltage?

Yes. If memory serves me I put a 10k 2 watt resistor at R51 and removed the jumper. It wasnt a big change. I need to put it on a switch so I can go back and fourth between high and low voltages. I was just a little paranoid throwing that voltage on a little switch. It should be okay though.


Thanks for the kind comments everyone.

What is R51? You talking about B+ dropper?

 

[psychodave]

I lowered the voltages in the power section a bit

you mean plate and screen voltage?

Yes. If memory serves me I put a 10k 2 watt resistor at R51 and removed the jumper. It wasnt a big change. I need to put it on a switch so I can go back and fourth between high and low voltages. I was just a little paranoid throwing that voltage on a little switch. It should be okay though.


Thanks for the kind comments everyone.

What is R51? You talking about B+ dropper?

I don’t have the schematic and am too lazy to look.

 

[nico22]

it's not R51 does not exist, it's R49 power dropper before the PI
jumper factory.

 

[FourT6and2]

it's not R51 does not exist, it's R49 power dropper before the PI
jumper factory.

So it's the first B+ dropper? If that's the case how does that drop the voltage on the power tubes? The power tube voltage is fed from before the dropper, isn't it? Changing that resistor changes the voltages in the preamp, not the power amp. Lowering its value increases voltages in the preamp, making the amp tighter/stiffer and less gainy. Increasing it lowers voltages, making the amp looser, fizzier, and more gainy/hairy. Common values are 10K - 20K. I try to tune an amp to get no less than 160v on V1a plate.

Dave, try a 25K, 5-watt pot instead of a switch. That way you can use it as another tone control lol

 

[psychodave]

it's not R51 does not exist, it's R49 power dropper before the PI
jumper factory.

So it's the first B+ dropper? If that's the case how does that drop the voltage on the power tubes? The power tube voltage is fed from before the dropper, isn't it? Changing that resistor changes the voltages in the preamp, not the power amp. Lowering its value increases voltages in the preamp, making the amp tighter/stiffer and less gainy. Increasing it lowers voltages, making the amp looser, fizzier, and more gainy/hairy. Common values are 10K - 20K. I try to tune an amp to get no less than 160v on V1a plate.

Dave, try a 25K, 5-watt pot instead of a switch. That way you can use it as another tone control lol

It was a mod Cameron gave me. The voltage to the power tubes dropped like 25 volts.

That’s an interesting idea about using a 5 watt pot.

 

[FourT6and2]

it's not R51 does not exist, it's R49 power dropper before the PI
jumper factory.

So it's the first B+ dropper? If that's the case how does that drop the voltage on the power tubes? The power tube voltage is fed from before the dropper, isn't it? Changing that resistor changes the voltages in the preamp, not the power amp. Lowering its value increases voltages in the preamp, making the amp tighter/stiffer and less gainy. Increasing it lowers voltages, making the amp looser, fizzier, and more gainy/hairy. Common values are 10K - 20K. I try to tune an amp to get no less than 160v on V1a plate.

Dave, try a 25K, 5-watt pot instead of a switch. That way you can use it as another tone control lol

It was a mod Cameron gave me. The voltage to the power tubes dropped like 25 volts.

That’s an interesting idea about using a 5 watt pot.

That's how I tune every amp I build. I clip in a 5-watt pot and dial in the B+ line with that. Then when I find a setting I like, I solder in a resistor matching whatever value the pot is set to. Theoretically, you could do that for every resistor in an amp

 

[gibson5413]

Sounds fantastic!

 

[Jeff Hilligan]

it's not R51 does not exist, it's R49 power dropper before the PI
jumper factory.

So it's the first B+ dropper? If that's the case how does that drop the voltage on the power tubes? The power tube voltage is fed from before the dropper, isn't it? Changing that resistor changes the voltages in the preamp, not the power amp. Lowering its value increases voltages in the preamp, making the amp tighter/stiffer and less gainy. Increasing it lowers voltages, making the amp looser, fizzier, and more gainy/hairy. Common values are 10K - 20K. I try to tune an amp to get no less than 160v on V1a plate.

Dave, try a 25K, 5-watt pot instead of a switch. That way you can use it as another tone control lol

It was a mod Cameron gave me. The voltage to the power tubes dropped like 25 volts.

That’s an interesting idea about using a 5 watt pot.

Any chance we could chat?
2threeone5four7zero000

 

[jasonP]

Awesome Dave!

 

[jcmlespaul]

Awesome tone! What pups are you sporting in your guitar?

 

[psychodave]

Awesome tone! What pups are you sporting in your guitar?

It's a Charvel with a Suhr Aldrich pickup. The guitar is a freak though. It has a lot of natural compression, but doesn't sound choked or sterile. Best guitar I've owned.

 

[V2a]

For a self-professed psycho, you sure do make some good tones...

 

[Kapo_Polenton]

Sounds great! But I think your stockers with a nudge from a pedal sound better. Less buzzy, more natural. Bit more sag and less tight. That's why i just boost!

 

[psychodave]

Sounds great! But I think your stockers with a nudge from a pedal sound better. Less buzzy, more natural. Bit more sag and less tight. That's why i just boost!

I hear ya regarding the big amps, but no pedal is giving a stock Jet City 20 to sound like my modded one.

 

[sluice]

That sounds freaking amazing! My kind of tone!