New build problems

[Tfultz]

This is my third build. Every build has had some trouble shooting but this one has me stumped. The signal on TMB and normal are intermittent. I strum a chord and it’s buzzy harsh and then gets louder. Strum again same thing. I went over all connections. Chopsticked. The only difference was the brown and white output wires from output transformer causes some static chop sticking. I resoldered but same. I’m using a mercury output. I need a place to start to diagnose. Also gain is really high than other builds but can’t tell since signal is way low and in and out.

[Daviedawg]

Those are the symptoms of a poor solder joint where you are making partial contact. Or a whisker style short also making a partial contact. I also once had those symptoms where I had crammed wires into a small space. You have been doing the right thing. So all I can suggest is to start again and mark up a schematic as you progress to make sure you are getting everything. You can also check if the controls affect the symptoms to see if you can pinpoint where in the circuit the problem(s?) lies.
I am not sure if we looked at them before for this build but you could post a current set of voltages on the standard form from the downloads just so we can have a looksee.

Dd

[Tfultz]

My voltages attached. Something isn’t right. I’m in ballpark for some and way off on others.

[Tfultz]

Pics of build

[Tfultz]

I went to test it out again. TMB is whisper quiet now and normal channel is scratchy and definitely not as loud as should be. The ohm selector increases volume. All the pots function as should changing the high mids and low. Not sure what’s going on.

[JMPGuitars]

the Solder Technique and Modern Ground Schemes posts.

Then make a few changes for cleanliness/safety. For example, IF you're going to keep that ground bus across the back of the pots, cut it short at the ends so it isn't coming close to things like the standby switch or input jacks.

Clip some or all of the unused turrets so they're not close to the leads coming off of other things like your filter cap there.

Another thing you'll probably learn about if you watch enough of the solder technique videos is that your wires shouldn't look the way they do. There should be a small gap of exposed wire between the turrets and the insulation.

Regarding your voltages: you're comparing to the classic 18 watt with tremolo. V1 is your regular channel, V2 is your PI, V3 is your TMB channel. Print this chart, and add an extra row somewhere for your V3 and mark it TMB. files/JMPGuitars_18_Watt_Lite_2b_Voltage_Test_Chart.pdf

Thanks,
Josh

[Tfultz]

Voltages are off. Maybe someone can point me in right direction

[JMPGuitars]

Voltages are off. Maybe someone can point me in right direction

You need to measure every pin of your TMB tube except the heaters.

Most of your voltages so far don't concern me. The PI looks very well balanced, just biased differently than my targets.

Pin 3 of your rectifier shows your B+, and it's probably fine at 347, but it would have more overdrive closer to 340. If you like the way the amp sounds, don't worry about it.

What does concern me a little is that your transformer voltages are farther off than I would expect. 16V difference on the OT, and 5V on the PT. I would try cleaning the solder joints there and then redoing them, or at least reflow them a bit and see if you can get better joints there. My transformer voltages are usually equal on the PT, and within 1 or 2 volts for the OT.

You should also 1. check the voltages at pin 2 of the power tubes, and 2. try and get the pin 3 voltage up to 12. This is one of the most important values to match.

Are you still having signal issues?

Thanks,
Josh

[JMPGuitars]

Here, I made a new voltage test chart: files/JMPGuitars_18_Watt_TMB_Voltage_Test_Chart.pdf

The voltages there should be good enough targets, if I find out otherwise at some point I'll update it.

Thanks,
Josh

[Tfultz]

I completely took out the board and going to rewire everything. You said some space is needed with cloth. First two builds didn’t use cloth. Also have grounded wire as suggested. I’ll rebuild and check and get back to you. How do I minupulate the voltages. I’m still new and learning. Once put back together. Thanks so much. Tom

[Tfultz]

Mercury output. The white is my center tap wire that goes to filter cap. If so I wired it wrong thinking red was to cap like other ot’s

[crgfrench]

Maybe check the secondary side too, those colors are not typical either.

[JMPGuitars]

I completely took out the board and going to rewire everything. You said some space is needed with cloth. First two builds didn’t use cloth. Also have grounded wire as suggested. I’ll rebuild and check and get back to you. How do I minupulate the voltages. I’m still new and learning. Once put back together. Thanks so much. Tom

Please watch the soldering videos I linked before you redo the board. The gap isn't just for cloth wire, it's for any wire type.

To raise the cathode voltage on the power tubes (pin 3), you need to slightly raise the cathode resistor value. If you're running 150 ohm, try 180 instead.

[Tfultz]

Your right the output has totally different colors on wiring. And I totally wired it up wrong. Hope I didn’t blow something up before I took board out. Before the TMB channel was whisper quiet and regular channel was very buzzy but loud. Did I possibly hurt something. I had black 4ohm wired common on output jack. White to pin 7 on v4 instead of to cap and red which is centertap to cap.

[Tfultz]

Update. Amp is up and running. All voltages are all close or spot on with voltage chart. Next time I’ll actually read the schematic for different transformers cause the color wires are not universal. Thanks for the help and replies. Tom

[Daviedawg]

Great that you got it all sorted.

Dd