Ceriatone Chupacabra mods

  • Thread starter Thread starter peterc52
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fusedbrain said:
I was wondering the same thing, but I think he's referring to the .022uf from the tone stack/mv into the pi and the.1uf on the other pi input.
The Friedman Dirty Shirley has a .0022uf on the pi input fwiw....
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That's what it seemed to me too but the context was about the output couplers and bias feeds so that's why I was asking. Since the 0.1uF on the 'other' PI grid is to ground and is just putting that grid at AC ground, the input signal to that triode is thru the cathode. And that signal is affected by the input cap for sure but I didn't know there was a 10:1 'rule'.

But I always try to remember that with guitar amps we are; in the eyes of the great Radiotron, trying to make them sound 'bad'.
 
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glpg80 said:
You’re stuck on 0.1uF/110k. I’m only talking about textbook reasons why the in phase differential input decoupling capacitor should be 10x smaller than the out of phase input. Fuck the resistor. I don’t rightfully care what Marshall are ceriatone or anyone for that matter prefers for tonal reasons.

And you keep quoting “messing with” as if I haven’t explained the theoretical reason why already, if you can’t follow and that’s all you get from my comment then you’re looking for a posting pissing contest. If you want more of an explanation then I’ve also quoted free sources - I don’t need or care about going to ampbook.com
Click to expand...

You're doing exactly what you're accusing me of doing. And I'm not going to put up with it. You are accusing me of "going off". That's what you're doing. You're accusing me of trying to engage in a "pissing contest". That's exactly what you're doing. OP is asking me for advice/my opinion on tweaking this amp. You popped in to start an argument with me. So what do you want out of this exchange? Time to add each other to ignore lists.
 
fusedbrain said:
I was wondering the same thing, but I think he's referring to the .022uf from the tone stack/mv into the pi and the.1uf on the other pi input.
The Friedman Dirty Shirley has a .0022uf on the pi input fwiw....

Seems the majority of this discussion is about the pi OUTPUT couplers and the bias feed resistors. The size of these components affect "bias excursion" as there is a time constant involved. As mentioned, Aiken has written about this, and there is a calculator an ampbooks for these values.
The gist being you have to watch the size of the caps and adjust the resistors accordingly, or the recovery time will be too slow.
I tend to agree with 46&2 that .022uf and 220k is the way to go, although you could go with 150k and leave open the ability to run 6550's if desired.
I don't hear much difference between 150k and 220k, and I like swapping in 6550s in some Marshall style circuits, especially when diode clipping is being used.
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Yes, exactly. You get it.

I don't know why he's hung up on this 10:1 thing. I'm talking about the PI OUTPUT couplers and the gird leak/output resistors. Not the 0.1uF in the PI input. He's being abrasive and talking past me when he knows damn well what I'm saying. And I know what he's saying too, which is why I mentioned looking at the calculator on AmpBooks.com. And yes, we've all read what Aiken has to say on the matter.

That doesn't change the fact that IN THIS AMP, 0.022uF/150K or 220K in the PI is just fine and will sound a million times better than 0.1uF/110K. Who the hell cares about all the theoretical BS. Swap the parts, play the amp, and you'll hear how it sounds. If ya don't like it, try something else. It's not going to hurt the amp.

I've tried every combination of 0.022uF, 0.047uF, 0.1uF, and 82K, 110K, 120K, 150K, 180K, 200K, 220K in the PI output. If someone wants to understand how it actually sounds, screw the theory and bust out the soldering iron.
 
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OP, good luck with the amp and I sincerely hope you have fun tweaking it and getting it to scream. If you have more questions, feel free to PM me directly.
 
fusedbrain said:
I was wondering the same thing, but I think he's referring to the .022uf from the tone stack/mv into the pi and the.1uf on the other pi input.
The Friedman Dirty Shirley has a .0022uf on the pi input fwiw....

Seems the majority of this discussion is about the pi OUTPUT couplers and the bias feed resistors. The size of these components affect "bias excursion" as there is a time constant involved. As mentioned, Aiken has written about this, and there is a calculator an ampbooks for these values.
The gist being you have to watch the size of the caps and adjust the resistors accordingly, or the recovery time will be too slow.
I tend to agree with 46&2 that .022uf and 220k is the way to go, although you could go with 150k and leave open the ability to run 6550's if desired.
I don't hear much difference between 150k and 220k, and I like swapping in 6550s in some Marshall style circuits, especially when diode clipping is being used.
Click to expand...
Yes this is correct and the purpose of my original post - just sharing some guidelines for those that desire to tweak.
 
FourT6and2 said:
Yes, exactly. You get it.

I don't know why he's hung up on this 10:1 thing. I'm talking about the PI OUTPUT couplers and the gird leak/output resistors. Not the 0.1uF in the PI input. He's being abrasive and talking past me when he knows damn well what I'm saying. And I know what he's saying too, which is why I mentioned looking at the calculator on AmpBooks.com. And yes, we've all read what Aiken has to say on the matter.

That doesn't change the fact that IN THIS AMP, 0.022uF/150K or 220K in the PI is just fine and will sound a million times better than 0.1uF/110K. Who the hell cares about all the theoretical BS. Swap the parts, play the amp, and you'll hear how it sounds. If ya don't like it, try something else. It's not going to hurt the amp.

I've tried every combination of 0.022uF, 0.047uF, 0.1uF, and 82K, 110K, 120K, 150K, 180K, 200K, 220K in the PI output. If someone wants to understand how it actually sounds, screw the theory and bust out the soldering iron.
Click to expand...

I’m being abrasive? Have you read your own posts? I absolutely agree the output decoupling capacitors Marshall got right at 0.02uF and 150k. I wasn’t speaking about changing those, you were. I just mentioned a random fact about the ratios of the input decoupling capacitors. Why am I hung up on this? Because not many know the ratio even exists for a reason.
 
Think I might have made a fault somewhere. It doesn’t sound very good atm. Gotta go thru it.

Made the changes suggested here. Depth cap is a .0033

Voltages on the preamp tubes are


V1. V2. V3



Pin 1 172v. 206v. 246v

2

Pin 3 1,6v. 1,4v. 43v

4

5

Pin 6 273V. 371V. 246v.

Pin 7 206v only on V2
Pin 8 2,3v. 207v. 43v

9

IMG_9852.jpeg
IMG_9853.jpeg
IMG_9854.jpeg
IMG_9855.jpeg
 
peterc52 said:
Think I might have made a fault somewhere. It doesn’t sound very good atm. Gotta go thru it.

Made the changes suggested here. Depth cap is a .0033

Voltages on the preamp tubes are


V1. V2. V3



Pin 1 172v. 206v. 246v

2

Pin 3 1,6v. 1,4v. 43v

4

5

Pin 6 273V. 371V. 246v.

Pin 7 206v only on V2
Pin 8 2,3v. 207v. 43v

9

View attachment 375530View attachment 375533View attachment 375536View attachment 375539
Click to expand...

What did you change between when it sounded good and when it didn't?

And what do you mean by it's not sounding good? As in, it's not working properly? Or you just don't like how it sounds after changing something?

I'll take a look at the photos and voltages shortly.
 
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A few cold solder joints: PI output section. Reflow those. NFB resistor toward front panel side. Slope resistor. Just double check every connection you touched. I don't see any obvious mistakes. Maybe a wire got unsoldered somewhere by mistake.

Also where is the missing 10K B+ you said you installed between PI and V2?
 
It's shrill and kinda bossy. No balls. I just finished a jca20 like psychodaves it sounds so much better

the 10k dropping resistor is on one end of the big holy grail (LOL) cap in the middle of the board.

I must go thru all solders again. everything works just sounds bad. Must have made a mistake one place.

Does is it look okay with the things I removed by the input jack?
 
peterc52 said:
It's shrill and kinda bossy. No balls. I just finished a jca20 like psychodaves it sounds so much better

the 10k dropping resistor is on one end of the big holy grail (LOL) cap in the middle of the board.

I must go thru all solders again. everything works just sounds bad. Must have made a mistake one place.

Does is it look okay with the things I removed by the input jack?
Click to expand...

1M to ground on jack: check
33K input grid stopper on pin 2: check

I don't see the 10K dropper on the preamp cap... I see the one bridging both halves, which is good. But the missing dropper... I still don't see it, unless you hid it under the board?

As far as shrill and bassy, again... check all your connections.

Also when did this start? What did you change right before this happened? I presume it sounded good at one point, you changed something, and then it sounded bad. So whatever you changed must be the problem. You started this thread more than 2 years ago, so you'll need to re-trace your steps...

Looks like you removed the bright switch on Gain 1? Check all your connections there as well.
 
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Is this soldered?

IMG_5610.jpeg


Take an ohm meter and measure each of your coax cables from ground to hot to make sure you haven’t shorted them. While measuring also wiggle the coax slightly.

Also I’d start chopsticking with the amp on and see if that bears any fruit.
 
frost822 said:
It looks like in the last few pics that the one PI cap that you see is labeled 2.2nf, that’s a little off from 22nf. Not sure but that’s what it looks like.
Click to expand...

Yeah I saw that and was scratching my head too. That cap is physically the same size as the other 22nF caps. But it's also 630v, so maybe that's why. If it's actually 2.2nF and not 22nF... that's the issue for sure. But I thought maybe I was seeing things, as the photo is blurry.
 
frost822 said:
It looks like in the last few pics that the one PI cap that you see is labeled 2.2nf, that’s a little off from 22nf. Not sure but that’s what it looks like.
Click to expand...

Are they both 2.2nF? They look identical in size. It definitely is 2.2nF.
 
2.2nf is .0022uf. As some other guys have pointed out, that isn't going to sound very good at all. That will make the amp sound very small and thin.

Also want to add that those TAD caps are deceiving because a .022uf looks similar to the .0022uf. Might want to measure them as well to make sure they are the correct value.
 
Thank you guys! Gonna change them to .022 uf. I must have misread it. I’ll be back :)

Of course only had 1 .022 cap laying around! Ordering new parts today! Thank you for your time guys!
 
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FourT6and2 said:
1M to ground on jack: check
33K input grid stopper on pin 2: check

I don't see the 10K dropper on the preamp cap... I see the one bridging both halves, which is good. But the missing dropper... I still don't see it, unless you hid it under the board?

As far as shrill and bassy, again... check all your connections.

Also when did this start? What did you change right before this happened? I presume it sounded good at one point, you changed something, and then it sounded bad. So whatever you changed must be the problem. You started this thread more than 2 years ago, so you'll need to re-trace your steps...

Looks like you removed the bright switch on Gain 1? Check all your connections there as well.
Click to expand...
Is it not this one?
IMG_9854.jpeg
 
peterc52 said:
Is it not this one?View attachment 376100
Click to expand...

Nope lol. Ceriatone left out a 10K B+ dropping resistor. There should be one between the PI and V2. The one you circled is between V2 and V1. These resistors separate each section of the amp so they each get their own filtering. Without it, you have multiple stages sharing the same filter cap.

It's fine if you like that sound/feel. But if it were me, I would install it.
Have a look at one of their superlead layouts and you'll see it: https://ceriatone.com/wp-content/uploads/2016/08/Plexi50BassCeriatone.jpg

Just make sure you get the connections right, so if you do it... really pay attention to how it's wired.
 
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