New build but no output

[armandodiaz]

I put together a new 18w build. Decided to go on it, on my own, rather than buying a kit. This is my 2nd build. My 1st was a MJT 800 and it was very successful, even with added mods.
I decided to use the Ceriatone 18w TMB EF86 layout. It seemed easy enough. Toughest part was forgetting to order something and having to pay extra shipping.
So anyway, got all together, took a couple of voltage readings (even though I don't have a voltage chart) and seemed ok. I hooked it up to the speakers, plug in my guitar, put up the volume and..... nothing. I'm just getting a very low hum from the speakers that does not change as I make changes.
So my question is; where is a good place to start?
I'll try to upload the layout and a pic.
Thanks all!

[Daviedawg]

Hi
If you are hearing hum then there is some sort of output from the amp. So I would start at the output and work back through to see where the signal is being lost. To do that you need to inject a signal into the circuit at various nodes. Or you can use a probe from your meter to tap and make noise in the signal path to see where it stops. This will give you a limited section to look for issues in. The amp needs to be on to do that so care is needed and one hand behind your back type of approach.

There is an awful lot going on in a small space at the input and pots area in your build which could cause the issue so I would also take a non conductive probe ("chopstick") and move some of the connections in that area while the amp is running and listen for noises or changes in the output.

But even before that I would check that the input jacks are wired correctly.

Alternatively if not happy working on the amp live you will need to make copies of your schematic and layout both of which you mark up with a highlighter as you work through comparing the diagrams with what you have actually built. Look carefully for shorts in the signal path as there is none of the wanted signal getting to the speakers.
I would start at the inputs and follow the signal path.

Dd

[Bieworm]

Although I seriously doubt the build..
I notice you don’t have a cap at V2 pin 2. It’s there on the layout (a.022uf) but not on the build. It would mean you lose the signal right there.
Without a schematic it will be a very hard job troubleshooting this.

[armandodiaz]

Thanks for the replies.
Its hard to see but there is a connection between V2 pin1 and the cap on the board.
Is there some sort of generic voltage chart for an 18W?

[Bieworm]

Taking a second look makes me wonder how much your build resembles the drawn layout. That makes it pretty impossible to track down any issues. Without a schematic the voltage chart will be of little use imho.
Check the downloads area.. there are charts, but if they’re useable is a good question.

[JMPGuitars]

Voltage charts are always usable if you know which tube is which, and you're matching the correct tube type.

I would guess V1 of the EF86 Modern Classic is probably closest to his circuit: files/JMPGuitars_18W_EF86_TMB_Modern_Cl ... ltages.pdf

That's a guess, assuming they follow the similar values as the original EF86 Lite variants for the EF86 tube.

[armandodiaz]

So far I found a cold solder on the bus going across the output jacks. But that wasn't it.
I began following the pwr from the pwr transform and throughout the board, working from left to right. I found no pwr after the 8K2 2W resistor (the teal colored resistor) on the board. Unfortunately, I don't have an extra so had to order some.

[Bieworm]

So far I found a cold solder on the bus going across the output jacks. But that wasn't it.
I began following the pwr from the pwr transform and throughout the board, working from left to right. I found no pwr after the 8K2 2W resistor (the teal colored resistor) on the board. Unfortunately, I don't have an extra so had to order some.

Maybe the resistor is ok, and there is something grounded after it that shouldn’t be. You can unsolder one side of the 8k2 and check its resistance to rule that one out.

[JMPGuitars]

I suggest also taking a look at the soldering and ground scheme threads in my signature.

Also do a full highlighter test before powering the amp on again.

Thanks,
Josh

[armandodiaz]

So far I found a cold solder on the bus going across the output jacks. But that wasn't it.
I began following the pwr from the pwr transform and throughout the board, working from left to right. I found no pwr after the 8K2 2W resistor (the teal colored resistor) on the board. Unfortunately, I don't have an extra so had to order some.

Maybe the resistor is ok, and there is something grounded after it that shouldn’t be. You can unsolder one side of the 8k2 and check its resistance to rule that one out.

When I noticed no pwr after the ressistor, I unsoldered it and tested.... got zero reading.

[Bieworm]

Well, if it reads infinite then you have a bad resistor. I always check resistors before they go in. And never push the hot iron longer than necessary to the connection. When even a 2W resistor gets smoked by the soldering technique there will be a lot of other stuff that will likely be dead.

[armandodiaz]

New findings.....

I couldn't wait for my 8K2 resistors to come in, so I went into my inventory and had plenty of 10K resistors. So let's try that for testing. That resistor started smoking immediately.
So started doing continuity testing. I came up with having continuity on either side of the big 450V capacitors that have positive and negative polarity (yes they are installed correctly). I've checked the other capacitors with polarity and they had no continuity.
So does that mean they are bad?
So if they are bad, my big question is why? Also do they need to be polarized? Can I change them to the mustard capacitors?
Or maybe I need to update to better capacitors... like Jupiter or Sprague?

[Bieworm]

Stop this right now! Pull out the tubes and measure the B+. Again, you should never get 500+ V on the plates. There’s something really wrong.
By the way.. those 450V caps are most likely the filter caps, which should be 500V caps for safety’s sake. You can’t get those values in non polarised tyoes without them being physically gigantic in size.
First thing to know is why your B+ is over 500V.
Second thing is to check for shorts. If there is, you should get at least a blown fuse. This makes no sense.
So, pull the tubes. What are the voltages on the 290 V wires (measure between each wire and ground) if they’re giving the 290 V +/- 10%, then you put in the rectifier tube. Remeasure those wires and additionally measure the B+. This is the wire going from pin 3 of the EZ81 to the standby switch. What are these values?
Also, is the center tap of the 290V winding grounded or not? It’s all hard to see on the photo. You changed the color of the wires when adding more length to it.

[armandodiaz]

OK found the problem... and yes I screwed up....

On the top right of the board there's a jump wire from the 2nd terminal to the 9th terminal. I had it connected to the 3rd terminal, which is grounded. So I was grounding the whole board.
I fixed it and it sounds awesome and quiet! It didn't even screw anything up, other than the resistor. I may still install the Jupiter capacitors.
That Fat Cap is incredible. I put it with a switch but I don't think I'll ever turn it off.
Once I get the correct resistors in the mail, I'll install it and it will be complete.
Thanks for everyone's help!

[armandodiaz]

Stop this right now! Pull out the tubes and measure the B+. Again, you should never get 500+ V on the plates. There’s something really wrong.
By the way.. those 450V caps are most likely the filter caps, which should be 500V caps for safety’s sake. You can’t get those values in non polarised tyoes without them being physically gigantic in size.
First thing to know is why your B+ is over 500V.
Second thing is to check for shorts. If there is, you should get at least a blown fuse. This makes no sense.
So, pull the tubes. What are the voltages on the 290 V wires (measure between each wire and ground) if they’re giving the 290 V +/- 10%, then you put in the rectifier tube. Remeasure those wires and additionally measure the B+. This is the wire going from pin 3 of the EZ81 to the standby switch. What are these values?
Also, is the center tap of the 290V winding grounded or not? It’s all hard to see on the photo. You changed the color of the wires when adding more length to it.

Never said I got 500V. The most I have is 351V on one side of the 32uf/32uf capacitor. The other side of the capacitor is 292V.
But yes you are correct, I found a short.
Thanks

[Bieworm]

Ow sorry.. was confusing you for another member. Where was the short?

[armandodiaz]

Ow sorry.. was confusing you for another member. Where was the short?

On the top right of the board there's a jump wire from the 2nd terminal to the 9th terminal. I had it connected to the 3rd terminal, which is grounded. So I was grounding the whole board.

[Daviedawg]

Well done finding the issue.

Many more times it is a wiring problem than it is a component failure. We all do it. Systematic checking of your work as you go can save time later. My system is to stop for a cup of tea at intervals and go over what I have done since the last break.

Enjoy your amp.

Dd