First build, Ceriatone 18w TMB EF86, no output

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ievans
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First build, Ceriatone 18w TMB EF86, no output

Post by ievans »

Hi. A million years ago I started ordered and started on a Ceriatone 18w TMB EF86 kit build, but put it aside (had kids, you can fill in the blanks). I decided to try to bring it over the line again, and dug it out of the box I had packed it away in.

I had stopped after doing the initial heater, pots, and PT wiring/soldering. In the intervening years I can see that my previous lead dress/heater wiring, especially, is not great. But I figured in the interest of getting it done it would be better to see what I had rather than pull it all apart again.

I'd read up on here how to implement better grounding techniques, so I deviated somewhat from the Ceriatone layout document on the board ground bus star ground (near the input jack).

I followed Rob Robinette's startup procedure, using a lightbulb limiter, and it all seemed ok. Voltages all seemed in spec. Tube heaters and filament wires were working on Standby, and all was well taking it off Standby. I added output tubes and connected a speaker with all the pots all the way off, and everything still seemed good.

But I got no sound output at all. Diming the Volume and MV produced no hum or white noise at all, and the same for the EF86 channel. Plugged in a guitar with no change.

I thought maybe the OT was the issue, and measured resistance with the rectifier and output tubes pulled and the amp off. It's a Classic Tone 40-18037.

OT primary
  • Red - Brown: 316 ohms
  • Red - Blue: 337 ohms
  • Brown - Blue: 365 ohms
OT secondary
  • Black (COM) - Orange (16 ohm): 0.6 ohm
  • Black (COM) - Green (8 ohm): 0.7 ohm
  • Black (COM) - Yellow (4 ohm): 0.5 ohm
I don't see anything alarming there, so I don't think it's a bad OT.

I took it off the lightbulb limiter to measure the real voltages/resistance at the PT, tube pins, and OT.

The PT is a Classic Tone 40-18035.

PT Primary
Black (COM) - Black/White(120): 121v

PT Secondary
GND - Red1: 301v
GND - Red2: 302v
GND - Green1: 3.41v
GND - Green2: 3.42v
Yellow - White: 6.9v

I'll post the tube pin voltages next.
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Last edited by ievans on Tue 05/03/22 4:32 pm, edited 1 time in total.
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by ievans »

Here are the pin voltages. The speaker sometimes made a crackle noise when I measured some pins, and I noted it.

V0 (EF86)
1. 91.2v
2. 0v
3. 2.09v
4. 3.23vAC
5. 3.23vAC
6. 73.8v
7. 0v
8. 2.08v
9. 0v

V1 (12AX7)
1. 118.4v (made noise in the speaker)
2. -8mv
3. 0.95v
4. 3.25vAC
5. 3.25vAC
6. 118v (made noise)
7. -8mv
8. 0.95v
9. 2.35vAC

V2 (12AX7)
1. 269v (made noise)
2. 0.2mv
3. 5.87v (made noise)
4. 3.25vAC
5. 3.25vAC
6. 269v
7. 0.7mv
8. 5.85v (made noise)
9. 3.25vAC

V3 (12AX7)
1. 134v
2. -44mv
3. 5.85v (made noise)
4. 3.27vAC
5. 3.27vAC
6. 258v
7. 134v
8. 135v (made noise)
9. 3.27vAC

V4 (EF84)
1.
2. 30mv
3. 11.69v
4. 3.25vAC
5. 3.25vAC
6.
7. 341v (made noise)
8.
9. 332v (made noise)

V5 (EF84)
1.
2. 22mv
3. 11.71v
4. 3.26vAC
5. 3.26vAC
6.
7. 342v (made noise)
8.
9. 332v (made noise)

V6 (EZ81 rectifier)
1. 117vAC
2.
3. 355v
4. 6.6vAC
5. 6.6vAC
6.
7. 117vAC
8.
9.
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by ievans »

So that's all the data. I don't know enough to tell if some of the voltages are way out of line, though I think I remember reading I should be getting negative voltage on the preamp tubes on pin 2. Any tips on how to troubleshoot this amp?
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by ievans »

ievans wrote:
Tue 05/03/22 4:12 pm
OT secondary
  • Black (COM) - Orange (16 ohm): 0.6 ohm
  • Black (COM) - Green (8 ohm): 0.7 ohm
  • Black (COM) - Yellow (4 ohm): 0.5 ohm
Actually, is this a problem? Shouldn't the resistance be a lot higher?
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by Bieworm »

A couple wourds of advice:

print the schematic and layout on a sheet of paper. Take a highlighter and verify every connection and part value, starting from the input. Only mark the area on the schematic and layout AFTER you verified it's done correctly in the amp.
You clearly must have missed something or made a mistake in the wiring. I have no clue about your knowledge on amp circuits, but it helps to mentally crawl inside the signal chain.. realising what does what, and what should follow to what. Being able to read a schematic is crucial, don't forget that. Sometimes people have a successful build by just following the plan (layout) like a Lego build... but more so often people make mistakes, layouts are faulty to begin with.. so use the schematic as your guideline and use the layout just for topology's sake.

That standby switch wiring is very dangerously connected, leaving a lot of bare wire to be touched by accident. I would use heat shrink...
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by Bieworm »

ievans wrote:
Tue 05/03/22 8:53 pm
ievans wrote:
Tue 05/03/22 4:12 pm
OT secondary
  • Black (COM) - Orange (16 ohm): 0.6 ohm
  • Black (COM) - Green (8 ohm): 0.7 ohm
  • Black (COM) - Yellow (4 ohm): 0.5 ohm
Actually, is this a problem? Shouldn't the resistance be a lot higher?
I wouldn't say a lot higher. The datasheet of a Hammond 1750PA 18W OT gives us 1.4 Ohm between comm and 16R. I do find it odd you measure less resistance on the 16R tap than the other 2. It should be higher for it's the whole coil, where the other 2 are taps in between...

AND.. how accurate is your measuring equipment?
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by Daviedawg »

Getting noise from the testing tells you a lot. Not getting noise at the EF86 may also tell you something. If you are getting noise from the speaker your issue is not with the output but is in front of where you first get noise. Simple, but reduces the likely issues.

I would check the EF86 wiring but first check your input jack is good and that the wiring is right. Stick your guitar cable in it and test for continuity from centre to first amp connection and sleeve to ground. Then move forward.

Dd

Edit. I would also wrap the connections at your mains input receptacle and fuse. Too easy to accidentally touch those or short them.
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by Unit_1 »

With power disconnected, and caps drained, plug a cable into the input jack and check for continuity and resistance from the tip of the plug to pins 2 and 7 on V1.

It's the first step in establishing the signal path..... plus you're getting scratchy sounds, meaning the output chain is working at that point. The problem would most likely be in between that and the input.
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by ViperDoc »

Double check to make sure your inputs are wired correctly, and that your preamp ground buss is grounded.
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by gbranzell »

Be sure resistor R13 is proper value. 820 not 820K. Check all your Phase inverter values and connections. You probably have an improper resistor value or cold solder joint.
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by JMPGuitars »

Please watch the soldering technique videos in my signature. You definitely have some bad solder joints, the ones standing out the most are on your ground bus wire. Some of your solder joints look like the soldering iron tip melted the solder, rather than the metal that was soldered.

I only use pre-tinned wire, and for my bus wire I use pre-tinned/bonded 18AWG wire. Dirty copper wire is hard to solder to, and needs to be well cleaned and well heated for a good connection.

It's possible the solder issues on your ground bus are contributing to your sound issue, but it's more likely that you need to do a highlighter test (like Bieworm said) with a schematic and follow the signal path from the input jack to the OT. Only highlight after confirming both connections and values are correct.

Since you said you heard noise through the speaker, it's not likely the OT is the issue.

At some point, you should also desolder your heater wiring and do that over more carefully. This is what my heater wiring typically looks like:
jmpguitars-heater-wiring.png

Messy heater wiring can lead to a lot of noise issues...once you have sound.

Thanks,
Josh
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by ievans »

Ok, thanks everyone. There's some progress.

I'd done the highlighter check with the layout (there's no published schematic for this model, and the only one I can find is a modified version where the values of many of the caps & resistors are different, but between the two I can recreate it). But redid it. I discovered one problem, which was a wire that had broken loose from the bottom of the board going to the treble pot that was attached on the incorrect post, which I think explains the complete lack of output, as it was going mistakenly to ground.

I fixed that and redid the input and standby wiring with some heatshrink to make it safer. I traced the rest of the signal path with my multimeter, and I have continuity at least through the signal path.

I think the EF86 tube is bad, so I'll order another one.

After going back through the startup with my lightbulb limiter, I put the rectifier and power tubes back in, and this time I got some faint signal with the MV and Volume pots dimed, quiet but crunchy notes. I noticed one of the power tubes was microphonic, so I rolled the power tubes with some old Sovteks. But no dice. Same faint, but high gain, sound with MV and V all the way up.

But I feel like I've narrowed down the causes and made some headway, as I'm getting signal.
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by ievans »

JMPGuitars wrote:
Thu 05/05/22 12:49 pm
I only use pre-tinned wire, and for my bus wire I use pre-tinned/bonded 18AWG wire. Dirty copper wire is hard to solder to, and needs to be well cleaned and well heated for a good connection.
Roger that. The board came prepopulated with the bare copper ground bus. I added some flux and reflowed the joints
At some point, you should also desolder your heater wiring and do that over more carefully.
...
Messy heater wiring can lead to a lot of noise issues...once you have sound.
I intend to, for sure. It's Not Fun confronting your messy, ignorant past now that you know better.
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by Unit_1 »

"OT primary

Red - Brown: 316 ohms
Red - Blue: 337 ohms
Brown - Blue: 365 ohms"

I just measured an OT I have from Mojo, red is the centertap and should be about half of the brown to blue. On mine brown to blue is 627 ohms, the red to either other is 315ish.

I have a similar problem with a 5e3 I started on 10 years ago and shelved due to cancer. Better now. I was just measuring a good OT (by removing the tubes to remove the ot from the circuit) and it has almost exactly the same ohms.

So did the one that's not working. I did find a missing ground wire in the input jack, but still no joy after fixing that.
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by ievans »

Ok, we've got sound! On the TMB channel at least. V2's screen grid resistor wire was wrong. I kept measuring 760ohm on the connection to ground across a 56k resistor, so I thought it was blown, but it measured correctly off the board. Which led me to find the wrong wire off pin 8 of V2.

It's a bit noisy (as I expected), but working. Now to optimize....

For anyone searching for similar problems, the other posters in here were helpful in pointing out that getting scratchy sound when taking measurements off the tube socket pins meant that the output stage wasn't the likely source of the problem. Tracing the signal path and connections, either on a schematic or layout was the key.
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by Bieworm »

What I find really useful is that when you are wiring an amp, you call the connections by their names. On a 12AX7 I don't see pin 2 and 7, but the grid. or pin 1 and 6, but the plates/anodes.. that makes me know what I'm doing. Etc for coupling caps, filter caps, tone caps...
I also don't wire anything to the pots or tube sockets that come from the board until I actually mount the board. Once the board is put in I start wiring the circuit systematically in the actual sequence of the schematic.
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Re: First build, Ceriatone 18w TMB EF86, no output

Post by Unit_1 »

What I find really useful is that when you are wiring an amp, you call the connections by their names.
As a programmer analyst and manufacturing expert, one of my consultant jobs was working for Advanced Bionics for a number of years. The engineers were not good when it came to assembling microscopic cochlear implants (which are literally assembled under stereo microscopes), but of course knew the audio design inside and out.

The assembly people had very little if any knowledge of the function of the circuits, but knew exactly what went where. Of course they were all dressed in bunny suits... :lol:

My point is that knowledge of the circuit has no effect on your assembly abilities and people that have no idea what they are building, can be successful at putting together half million dollar audio circuits.

I call it by pin number because I want to count the pins before I attach the wire because all the engineering was done long ago on my computer and I just need to keep my mind on the shape of what I'm doing! 8)
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