Troubleshooting for a Studio Caliber DC-2

[bowery969]

After I received my DC-2 from the seller at Reverb, I noticed it need some fixing upping (they refunded me some of the cost).

The ground prong on the wall plug was damaged and the effects loop didn't work. I took it into a friend to do some TLC.

He fixed the plug and put two new power tubes in. He said all 6 of the preamp tubes tested well. He said that the clean channel wasn't performing as well, and said that the Celestion I had in the amp wasn't that good. He compared with a Greenback of his, and said that the Greenback was so much more warmer. (am I going to be dinged for grammar there?)

I asked about the effects loop and he said that the circuit tested fine.

Took it back home, playing it for a few days now. The lead channel sings, but the clean channel definitely sounds worse, like cottony.

Also, the effects loop worked fine at first, but slowly quieted out so I could hardly hear it. I've been playing without my rack units since then.

There is a professional amp repairman up the road. The nice thing about my friend taking a stab at it, he cleaned it up for a minimal sum. I am sure the pro repairman will charge a premium.

My question here is about the speaker and effects loop.

Will swapping out the speaker solve the clean channel issue?

And as far as the effects loop, another friend said he thought that one of the 6 preamp tubes was devoted to the effects loop. Does that sound right? Or is there some other circuitry involved.


Thanks in advance,

Jason

 

[Spinaltap11]

If you aren't familiar with working with tube amps, let a pro handle it. There's dangerous voltage inside.
I change tubes, but anything else... If you are comfortable move a few tubes, see if the sound changes.

Go to the MB page and DL the manual, it will help you dial in dirt and clean. You should be able to get a great clean sound when dialed in Speaker sounds are subjective...

 

[bowery969]

If you aren't familiar with working with tube amps, let a pro handle it. There's dangerous voltage inside.
I change tubes, but anything else... If you are comfortable move a few tubes, see if the sound changes.

Go to the MB page and DL the manual, it will help you dial in dirt and clean. You should be able to get a great clean sound when dialed in Speaker sounds are subjective...

Roger that, thanks

 

[Monsta-Tone]

The clean channel could easily be a preamp tube
Just because it passes a test doesn’t mean it’s a good sounding tube
Modern tube testers are not all that great either
I have the one that Orange used to make
It’s ok, but not nearly as thorough as a tube tester from the 50’s, 60’s or 70’s
I don’t have the tube chart in front of me, but my memory seems to think V1 and V3 are the clean channel tubes
V1 also affects the lead channel

The FX Loop may be a tube issue as well
I think that’s V4

Also, for the clean channel
Try turning the Master Volume for that channel up and the Gain and EQ knobs down
If the Gain or EQ are past 5, your amp will start to sound much less clean

 

[bowery969]

The clean channel could easily be a preamp tube
Just because it passes a test doesn’t mean it’s a good sounding tube
Modern tube testers are not all that great either
I have the one that Orange used to make
It’s ok, but not nearly as thorough as a tube tester from the 50’s, 60’s or 70’s
I don’t have the tube chart in front of me, but my memory seems to think V1 and V3 are the clean channel tubes
V1 also affects the lead channel

The FX Loop may be a tube issue as well
I think that’s V4

Also, for the clean channel
Try turning the Master Volume for that channel up and the Gain and EQ knobs down
If the Gain or EQ are past 5, your amp will start to sound much less clean

Nice intel, thanks!

 

[Spinaltap11]

DC-2 Manuel link https://mesa-boogie.imgix.net/media/User Manuals/Studio Cal DC-2.pdf

 

[bowery969]

DC-2 Manuel link https://mesa-boogie.imgix.net/media/User Manuals/Studio Cal DC-2.pdf

Thanks. I've got this one.

Is there an EE schematic for this model?

 

[Spinaltap11]

https://schematicheaven.net/boogieamps/boogie_studio_caliber_dc2.pdf

 

[bowery969]

https://schematicheaven.net/boogieamps/boogie_studio_caliber_dc2.pdf

Awesome, thanks.

I was hoping it would be more clear...is there a diagram that indicates which preamp tubes powers what?

I'm wondering specifically about the FX Loop and rhythm channel.

 

[Spinaltap11]

google should be able to help you from here......

 

[bowery969]

google should be able to help you from here......

I have. The best I get is a description for a DC-3's tube positions. That also has 6 12AX7s.

What is the likelihood that the DC-3 and DC-2 have the same positions?

 

[Monsta-Tone]

All of the DC preamp tube layouts are the same
The circuits have slight variations but the DC-3 tube layout is identical to the 2

 

[bowery969]

All of the DC preamp tube layouts are the same
The circuits have slight variations but the DC-3 tube layout is identical to the 2

Awesome, thanks!

 

[bowery969]

All of the DC preamp tube layouts are the same
The circuits have slight variations but the DC-3 tube layout is identical

One more question about this.

Here is that resource for the DC-3 tube positions:

https://www.eurotubes.com/store/pc/Mesa-Boogie-DC3-Standard-Retube-Kit-p381.htm

The first post indicates that V6 should be balanced. I also have a Mesa enthusiast friend who mentioned that the V6 tube is a special tube because it 'regulates' the others.

I've already ordered 6 new Mesa 12AX7s and should receive them shortly.

Do I need to select one of them specially for this V6 position? Do I need to purchase a different one?

 

[Monsta-Tone]

V6 is a funny spot
It’s always overlooked in terms of overall gain
It is the last preamp tube in the circuit but definitely makes a difference in overall tone

I’ve always been on the fence about balanced preamp tubes in any position, but especially in V6
The job of V6 (Phase Inverter) is to split the signal
One side of the split signal is inverted
Then the signal is fed to the power tubes
One side of the signal goes to one of the power tubes
The inverted side of the signal goes to the other power tube

The Phase Inverter in most tube amps is designed to be unbalanced
One side of the circuit has slightly different resistor values

I do see a plus in balanced tubes, but for me it’s more about consistency of tone between tube changes than anything else

 

[bowery969]

V6 is a funny spot
It’s always overlooked in terms of overall gain
It is the last preamp tube in the circuit but definitely makes a difference in overall tone

I’ve always been on the fence about balanced preamp tubes in any position, but especially in V6
The job of V6 (Phase Inverter) is to split the signal
One side of the split signal is inverted
Then the signal is fed to the power tubes
One side of the signal goes to one of the power tubes
The inverted side of the signal goes to the other power tube

The Phase Inverter in most tube amps is designed to be unbalanced
One side of the circuit has slightly different resistor values

I do see a plus in balanced tubes, but for me it’s more about consistency of tone between tube changes than anything else

Ok. Not entirely clear what my action should be, other than make sure the new preamp tubes are consistent.

If I am receiving all 6 new ones from the same place, do I need to do some validation before replacing them all?

 

[Spinaltap11]

So, a phase inverter in the V6 position is often recommended when re tubing a DC amp

From a Tube reseller: This kit contains a matched pair of JJ EL84's for the power section. Five standard ECC83S's for V1 thru V5 and a balanced ECC83S for the phase inverter in V6. A nice upgrade in tone.
The Balanced ECC83S is located in V6, farthest from the input jack.

You don't have to put the phase inverter tube in, and probably wouldn't notice the difference if you didn't

I sent a msg with my last tube order that I am a bedroom player, at low volume, and asked for early breakup....

Just let us know in the comments section if you're looking for an early breakup, a moderate breakup or a later breakup for more headroom in which case we will choose the coolest grades we have available for the power tubes.

Play the amp if there are tube problems, volume drop.... excess noise or hum.... then retube


Where are you located US or...

 

[bowery969]

So, a phase inverter in the V6 position is often recommended when re tubing a DC amp

From a Tube reseller: This kit contains a matched pair of JJ EL84's for the power section. Five standard ECC83S's for V1 thru V5 and a balanced ECC83S for the phase inverter in V6. A nice upgrade in tone.
The Balanced ECC83S is located in V6, farthest from the input jack.

You don't have to put the phase inverter tube in, and probably wouldn't notice the difference if you didn't

I sent a msg with my last tube order that I am a bedroom player, at low volume, and asked for early breakup....

Just let us know in the comments section if you're looking for an early breakup, a moderate breakup or a later breakup for more headroom in which case we will choose the coolest grades we have available for the power tubes.

Play the amp if there are tube problems, volume drop.... excess noise or hum.... then retube


Where are you located US or...

I am in North Carolina, US.

I've already purchased 6 12AX7 tubes (not a kit).

Will I be alright to retube with the 6 I have, or do I need a special tube for the phase inverter?

 

[bowery969]

I am in North Carolina, US.

I've already purchased 6 12AX7 tubes (not a kit).

Will I be alright to retube with the 6 I have, or do I need a special tube for the phase inverter?

by the way, I am a bedroom player, so early breakup would be preferable.

 

[Monsta-Tone]

I didn’t mean to add confusion, the point that I was trying to make is:
The Phase Inverter circuit (V6) is unbalanced by design

The only benefits that I have ever seen from a balanced PI are
1. More money for the tube vendor
2. More easily repeatable tone and output wise when you change tubes again

Chances are, you could just change V1 and V3 and make the clean channel sound much better


In retrospect, I never asked what the clean channel was doing or what it sounded like