Dumble clone (Ceritone) OTS50

[foreverstrung]

I've just received a kit to build a Ceritone Overtone Special 50. I'm trying, without luck, to find a schematic. Ceritone has the layout and amp manual online, but I'm having a real hard time chasing down the schematic. Appreciate any direction someone might have.
I'll upload status as I'm putting this together.

[dbharris]

That looks like what we call a high plate skyline circuit on a 50W version. Here is a thread with info including layout and schematic (for a 100W).

https://ampgarage.com/forum/viewtopic.php?f=5&t=12873

Good luck!

[foreverstrung]

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[foreverstrung]

Main boards installed tomorrow

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[dbharris]

Looking good! You may want to use some RTV to secure the LNFB cap at V1b to the chassis. You also might consider running the two power wires along the side and back of the chassis so they are tucked up and out of the way.

-Dan

[foreverstrung]

Looking good! You may want to use some RTV to secure the LNFB cap at V1b to the chassis. You also might consider running the two power wires along the side and back of the chassis so they are tucked up and out of the way.

RTV is coming. It'll be in multiple locations.
The wire running diagonal I cut short. It's for the footswitch. Do you think it'll really be a problem run like this? Noise? I figured it just being the foot pedal it might not be an issue. Just takes a nudge and I'll reroute it. LOL

[dbharris]

Looking good! You may want to use some RTV to secure the LNFB cap at V1b to the chassis. You also might consider running the two power wires along the side and back of the chassis so they are tucked up and out of the way.

RTV is coming. It'll be in multiple locations.
The wire running diagonal I cut short. It's for the footswitch. Do you think it'll really be a problem run like this? Noise? I figured it just being the foot pedal it might not be an issue. Just takes a nudge and I'll reroute it. LOL

It will probably be fine, being low voltage DC. These amps are really complicated and generally you will get the best results by copying the part composition and lead dress that Dumble used. You can look of pictures of ODS #124, which is probably the best documented example, and try to mimic that.

[foreverstrung]

It will probably be fine, being low voltage DC. These amps are really complicated and generally you will get the best results by copying the part composition and lead dress that Dumble used. You can look of pictures of ODS #124, which is probably the best documented example, and try to mimic that.

Well I rerouted the footswitch wires.
Finished putting it together today.
Went through and ran a highlighter through the layout. Found 2 discrepancies.
I'll do a voltage chart in the morning.
Hopefully send a sound check sometime tomorrow.

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[Bieworm]

If it were me I would have waited to add all that silicone supporting goo until after the build was 100% ready and operational. When you need to tweak and troubleshoot it will work against you. It’s bitchin’ and messy to remove. But.. fingers crossed and who knows

[dbharris]

That's a lot of progress, the build looks good!

It looks like you may have forgotten the grid wire from board to grid stopper at V2a. When you do make this connection, fly this lead up from the board and then over and down to the terminal strip. This connection is not shielded.

For V1 and V2, you may want to run your cathode wires and V_b plate wire closer together. Part of "the sound" comes from how Dumble played with the lead dress to take advantage of phase relationships sometimes causing positive feedback for portions of the circuit.

Here is ODS #124 as an example. You can also see the grid wire on V2b.

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I see this amp had the OD trigger as an external pot. You may want to start with this set at 25K from wiper to ground (it is a 100k pot right?) with the amp on and in overdrive mode.

Good luck with the start up procedure.

-Dan

[foreverstrung]

It looks like you may have forgotten the grid wire from board to grid stopper at V2a. When you do make this connection, fly this lead up from the board and then over and down to the terminal strip. This connection is not shielded.

For V1 and V2, you may want to run your cathode wires and V_b plate wire closer together. Part of "the sound" comes from how Dumble played with the lead dress to take advantage of phase relationships sometimes causing positive feedback for portions of the circuit.

This is good stuff. I'm pretty sure I've got the V2a grid wire together as in the layout. If I'm missing something, I'd sure appreciate some clarity. I've quadruple checked and it's wired as it should be as per layout. If it's the same wire your describing, my layout has it as a shielded wire and that's what I've run. Like I said, if you see or don't see something, please confim and clarify for me.

Dressing out V1 and V2 as you described is good stuff to know.

I see this amp had the OD trigger as an external pot. You may want to start with this set at 25K from wiper to ground (it is a 100k pot right?) with the amp on and in overdrive mode.

Yes, 100k pot
Again, good stuff to know.

[dbharris]

It looks like you may have forgotten the grid wire from board to grid stopper at V2a. When you do make this connection, fly this lead up from the board and then over and down to the terminal strip. This connection is not shielded.

For V1 and V2, you may want to run your cathode wires and V_b plate wire closer together. Part of "the sound" comes from how Dumble played with the lead dress to take advantage of phase relationships sometimes causing positive feedback for portions of the circuit.

This is good stuff. I'm pretty sure I've got the V2a grid wire together as in the layout. If I'm missing something, I'd sure appreciate some clarity. I've quadruple checked and it's wired as it should be as per layout. If it's the same wire your describing, my layout has it as a shielded wire and that's what I've run. Like I said, if you see or don't see something, please confim and clarify for me.

Dressing out V1 and V2 as you described is good stuff to know.

I see this amp had the OD trigger as an external pot. You may want to start with this set at 25K from wiper to ground (it is a 100k pot right?) with the amp on and in overdrive mode.

Yes, 100k pot
Again, good stuff to know.

I do see it now coming from the back of the chassis where the trigger pot is. I missed it the first time looking at the photos

I personally wouldn't find the external trigger pot very useful, just my opinion. Dumble did have this feature on some amps, but the vast majority it was an internal trim pot. This will set the amount of overdrive, but more so the timbre of the overdrive. With the cascading gain design, there is a ton of gain available. Most folks will set the trigger as low as possible while still having a nice overdrive sound. This approach will make the overdrive channel the least buzzy sounding and more an extension of the clean channel, which is the goal. Very small changes to this control will result in a very different timbre to the OD. Experimenting is fun!

-Dan

[foreverstrung]

Status Update
Voltages checked out well. Had some issues at first with AC side I needed to chase down. Once I did and then checked the voltages, I plugged in my guitar. At first, I got no sound so I broke out the scope. It showed my signal traveling through nicely so I tried again and it was the OD pot in the back. On 0 it shuts down the signal.......So now I've been playing it for a bit tonight, getting to know it, but I'm getting some unwanted noise on the OD channel. Light sporadic crackle.
Just did the chopstick and I'm getting a lot of noise at V1. Something loose or grounding out. I'll go searching, cleaning up shortly..........I've got a lot of E caps in this rig. I'd appreciate suggestions on quickest bleed of stored voltage. One cap at a time will be tiresome.

If it were me I would have waited to add all that silicone supporting goo until after the build was 100% ready and operational. When you need to tweak and troubleshoot it will work against you. It’s bitchin’ and messy to remove. But.. fingers crossed and who knows

This good advise. Fortunately I did't (so far) have an issue with this, but next time, I will wait till I'm a 100%.

I personally wouldn't find the external trigger pot very useful, just my opinion. Dumble did have this feature on some amps, but the vast majority it was an internal trim pot. This will set the amount of overdrive, but more so the timbre of the overdrive. With the cascading gain design, there is a ton of gain available. Most folks will set the trigger as low as possible while still having a nice overdrive sound. This approach will make the overdrive channel the least buzzy sounding and more an extension of the clean channel, which is the goal. Very small changes to this control will result in a very different timbre to the OD. Experimenting is fun!

Agree with this. That 100K OD pot is way aggressive. An internal trim pot would have been more efficient as far as I'm concerned

[dbharris]

I use a nice insulated alligator clip lead with a 3W 220K metal oxide resistor soldered between the clips. Connect one end to the hot side of B+ filter caps (right before the choke) and the other end to your ground bus bar. It will drain everything down in about a minute. But always double check with the DMM first.

Glad you got it up and running. Takes a while to get all of the trimmers adjusted...just keep playing and tweaking while everything settles in.

What guitar/pickups are you using? Try setting the bass pot pretty high like 6-7 it tends to open up the skyline eq stack. Treble around 4.5. Mids I set based on the guitar I'm playing...scoop for strat and boost for LP.

-Dan

[foreverstrung]

So now I've been playing it for a bit tonight, getting to know it, but I'm getting some unwanted noise on the OD channel. Light sporadic crackle.
Just did the chopstick and I'm getting a lot of noise at V1. Something loose or grounding out. I'll go searching, cleaning up shortly

Bad tube. Replaced. Sounding good

[dbharris]

So now I've been playing it for a bit tonight, getting to know it, but I'm getting some unwanted noise on the OD channel. Light sporadic crackle.
Just did the chopstick and I'm getting a lot of noise at V1. Something loose or grounding out. I'll go searching, cleaning up shortly

Bad tube. Replaced. Sounding good

Glad you got it sorted out. Just as an FYI in case you aren't familiar, the FET trimmer is usually set to provide about a 10db of boost. OD trigger usually in the 23K to 35K range. The PI trimmer is a more complicated endeavor. Are you using a matched tube in V3? Do you have a signal generator? Just DMM or Scope too?

-Dan

[foreverstrung]

Glad you got it sorted out. Just as an FYI in case you aren't familiar, the FET trimmer is usually set to provide about a 10db of boost. OD trigger usually in the 23K to 35K range. The PI trimmer is a more complicated endeavor. Are you using a matched tube in V3? Do you have a signal generator? Just DMM or Scope too?

-Dan

I'm waiting on new tubes to arrive. Pre amp and Power. I picked up a pair of matching NOS NIB RCA 6L6GC tubes and 3 NOS Sovtek pre amp tubes and 2 extra NOS RCA pre amp (12AX7)
I figured the FET trimmer was a boost and have it set now where I like it.
As for the PI trim pot, the Ceritone manual on this says the A side is 6DCV less than the B side, but I was going to wait till I got these new tubes to really get it where it should be. I have a signal generator and a scope. What are you suggesting?

I've started getting everything together to build my head cab and then speaker cab.

[dbharris]

Glad you got it sorted out. Just as an FYI in case you aren't familiar, the FET trimmer is usually set to provide about a 10db of boost. OD trigger usually in the 23K to 35K range. The PI trimmer is a more complicated endeavor. Are you using a matched tube in V3? Do you have a signal generator? Just DMM or Scope too?

-Dan

I'm waiting on new tubes to arrive. Pre amp and Power. I picked up a pair of matching NOS NIB RCA 6L6GC tubes and 3 NOS Sovtek pre amp tubes and 2 extra NOS RCA pre amp (12AX7)
I figured the FET trimmer was a boost and have it set now where I like it.
As for the PI trim pot, the Ceritone manual on this says the A side is 6DCV less than the B side, but I was going to wait till I got these new tubes to really get it where it should be. I have a signal generator and a scope. What are you suggesting?

I've started getting everything together to build my head cab and then speaker cab.

Those RCA tubes will sound great! The point of the PI trimmer is to balance the whole power amp (including PI, power tubes, and OT) for the least harmonic distortion. You can insert a signal into the return jack, sine wave anything from 100 hz to 1khz is fine. I think you want about 2V of signal. Set the master volume where you plan to use it most. You can scope the cathodes of the power tubes at the red test points and then adjust the PI trimmer for those signals to match. If it is hard to tell from the scope (for instance my digital scope doesn't do a good job for this task), then you can use a DMM with a probe in each of the red test points, set to mv. You adjust the trimmer until the DMM reads 0. This is the "ampeg method."

-Dan

[JMPGuitars]

for instance my digital scope doesn't do a good job for this task

What scope are you using that can't handle that?

[foreverstrung]

As for the PI trim pot, the Ceritone manual on this says the A side is 6DCV less than the B side, but I was going to wait till I got these new tubes to really get it where it should be.

Correction. The manual Ceritone puts out for this amp says the opposite of this statement.
A side is 6 DCV higher than the B side