Superlite TMB chassis layout - will this fly?

[gkwallace]

I would make some pics of the build in all possible angles and details. Looking at pics somehow shows irregularities that I didn’t notice/ overlooked while looking at the actual build.
Post them images here too, so we can help you.

That's a great idea. I know exactly what you mean. I used my phone and zoomed in and looked at every part but that would provide different angles.

On a side note I remember i dropped that output transformer right on the concrete from about 4 ft high. There is some sort of abrasion on the coil wrapping. There's continuity on the output side of it, but I can't really check the input side of it while it's wired up.
There was so little smoke. I wondered if I imagined it. I did smell it. It could be that the amp was upside down and couldn't see the transformer and it was just burning some enamel or something.

This is the first time I've ever hoped it was a burnt transformer because Im at a loss.

[JMPGuitars]

Too bad the transformer manufacturer didn't think to put a "Do Not Drop" warning label on it.

[gkwallace]

Too bad the transformer manufacturer didn't think to put a "Do Not Drop" warning label on it.

Might be a dumb question, but do you think that is most likely my issue?

[JMPGuitars]

I don't like guessing. It could be that, sure. But you need to safety check everything, and observe. Try with the power tubes removed, and see what happens.

I also don't like having any wires under the board, because that makes it difficult to observe them.

Check for unwanted shorts first.

Check the capacitance values of both halves of the can cap referenced to ground, also check resistance.

[Bieworm]

The fact that you state you’re not sure if you even saw smoke makes me wonder if it even happened.
When using an aluminium chassis there are reflections from lights around you that might give you the impression something moved. Also, firing up a new build is always kind of exciting, and that makes you nervously careful. Even the slightest sound will be interpreted as something wrong.
When starting up a new amp there are parts that will make some kind of sound while filling up with electricity.
Why don’t you just start up the amp using a lightbulb current limiter or variac? Troubleshoot from that point if necessary.

[gkwallace]

The fact that you state you’re not sure if you even saw smoke makes me wonder if it even happened.
When using an aluminium chassis there are reflections from lights around you that might give you the impression something moved. Also, firing up a new build is always kind of exciting, and that makes you nervously careful. Even the slightest sound will be interpreted as something wrong.
When starting up a new amp there are parts that will make some kind of sound while filling up with electricity.
Why don’t you just start up the amp using a lightbulb current limiter or variac? Troubleshoot from that point if necessary.

Good idea and that's what I did. With the variac at around 80v nothing happened for 5 min or so. I took some measurements and everything was measuring something sane. Once I put full power it took another few minutes and there was a light smoke. I have crazy high voltage where there shouldn't be. All of my voltages are very high but in aprrox the correct ratio on all the pins.

[gkwallace]

Reworked some wiring and didn't get anywhere really.
Here are my voltages on V1:
1: 357v, should be 100v
3: 48v, should be 1.15v
6: 352v, should be 100v

My ABCD voltages
A:376, should be 345
B:374, should be 310
C:365, should be 280
D:360, should be 210

Hence the smoke I would guess.

[Bieworm]

Reworked some wiring and didn't get anywhere really.
Here are my voltages on V1:
1: 357v, should be 100v
3: 48v, should be 1.15v
6: 352v, should be 100v

My ABCD voltages
A:376, should be 345
B:374, should be 310
C:365, should be 280
D:360, should be 210

Hence the smoke I would guess.

Check the plate resistor of V1. It looks like it has zero resistance instead of 100k. Is it wired correctly? Pics sure would help
Do you have pics from the underside of the board? Is the B+ for V1 correctly routed to the correct node/turret?

[gkwallace]

You are correct. I believe it is an underboard wire. I'm unsoldering the tone stack now to get a good look.
Stand by!

[gkwallace]

Check the plate resistor of V1. It looks like it has zero resistance instead of 100k. Is it wired correctly? Pics sure would help
Do you have pics from the underside of the board? Is the B+ for V1 correctly routed to the correct node/turret?

Bingo!
I have sound!!! My finger on the end of an input cord anyhow!

It goes from an above board ground to an underboard ground on the same turret. The layout had some optional diodes and I thought the wire was included in the option.
Looking at it now, it's obvious.

I really needed a win, thanks for the help.

[gkwallace]

gregs volts.pdf

Here's my new voltages attached

[Bieworm]

Did you overwrite the target voltages on the sheet? You’re supposed to write YOUR voltages down in the blank white boxes. the orange boxes are for reference.. what are you comparing now?

[gkwallace]

this is the original

[JMPGuitars]

this is the original

He wants you to fill out the PDF correctly so we can see both the reference voltages, and your latest updated voltages that you see right now in your amp, including the bottom row.

He's asking you to make it easier for us to help you.

[gkwallace]

this is the original

He wants you to fill out the PDF correctly so we can see both the reference voltages, and your latest updated voltages that you see right now in your amp, including the bottom row.

He's asking you to make it easier for us to help you.

I'm mentally challenged. I'll get that done as soon as I can.

[gkwallace]

acrobat web sucks.
here is my voltage file.
I replaced the 100ohm 10v with a 150. It brought my voltages more in line, but v1a and v1b are high. I also didn't realize how high my ac HV was.

PS -It's a 290v HV. I measured the HV when it was first turned on. I'm sure it would have dropped from 300 to 290 when it warmed up.

[JMPGuitars]

PS -It's a 290v HV. I measured the HV when it was first turned on. I'm sure it would have dropped from 300 to 290 when it warmed up.

Probably not. The 290V rating is based on older (lower) wall AC levels. Around 300V is normal.

Assuming your cathode resistor is 180Ω, your power tubes are biased too hot. We target 85%, and you're at 94%. That's technically okay, but your tubes won't last as long. I'd suggest going up to 200Ω cathode resistor.

After your power tubes are corrected, you should test your voltages again. Assuming V1 plates are still high, you can adjust that also, but it isn't necessary. If you like how it sounds, cool. If you want it a little dirtier in the preamp, then increase the V1 plate resistors to 120kΩ and see how that sounds (and check voltages again).

Thanks,
Josh

[gkwallace]

Assuming your cathode resistor is 180Ω, your power tubes are biased too hot.

My power tubes are 2v - 5v higher than the voltage chart.
Is this what voltage you are saying is too high?

If so, I had no idea that voltage was so critical. In my mind I feel you are correct and that's what is making the disturbing flubby distorted lows when it's dimed. I know my speakers can handle 18w dimed.


PS - while i wait for a 200ohm resistor I thought I'd experiment.
I put a 180ohm in series with a 100ohm and the 9 and 7 went up. I put a 100ohm in and the plate went down to 300 and 324. Makes sense to me.

What am I missing? There must be something I'm misunderstanding when you say they are biased hot.

[JMPGuitars]

What am I missing? There must be something I'm misunderstanding when you say they are biased hot.

Yes, math.

Cheat and use the calculator: https://robrobinette.com/Tube_Bias_Calculator.htm

First select EL84 from the list and put in the plate to cathode voltage (Example: Plate 343 minus Cathode 13 = 330). Then scroll down to cathode bias section, and put in your values. That will tell you the actual tube dissipation. 85% is the target.

Thanks,
Josh

[gkwallace]

Cheat and use the calculator: https://robrobinette.com/Tube_Bias_Calculator.htm

First select EL84 from the list and put in the plate to cathode voltage (Example: Plate 343 minus Cathode 13 = 330). Then scroll down to cathode bias section, and put in your values. That will tell you the actual tube dissipation. 85% is the target.

I kind of understand that part, what I don't understand is how increasing the cathode resistor is going to lower the bias or "hotness".