Superlite TMB chassis layout - will this fly?

[Bieworm]

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".

Ohms law. By increasing the resistance you will be lowering the current. Bias is what we call the current draw of a tube. The higher the current draw, te hotter the bias.

[gkwallace]

I get it now. So the current is actually more important than the voltage is. We just used the voltage to get the proper current?

[Bieworm]

I get it now. So the current is actually more important than the voltage is. We just used the voltage to get the proper current?

Yes.. voltage is of a lesser importance (within limits) than current draw. You can have a too high voltage than is good for the plates, resulting in shorter lifespan of the tubes. Too low voltage will affect the headroom in a negative way. But the main target is the current draw of the output tubes.

[gkwallace]

So when you build an amp presumably accurate to the schematic and the voltages aren't what the schematic suggests, is it unusual to have to play with the current and voltages to get it biased correctly?

[Bieworm]

So when you build an amp presumably accurate to the schematic and the voltages aren't what the schematic suggests, is it unusual to have to play with the current and voltages to get it biased correctly?

Yes

[JMPGuitars]

Voltage will vary from amp to amp. You can build 5 of the same, and you will see differences. There will be variances from transformer to transformer. The wall voltage may be different depending on the time of day.

We used to say to target 12V for cathode voltage because, with older voltages, that came pretty close to what we wanted. Now it's simply better to focus on the actual dissipation.

[gkwallace]

Now it's simply better to focus on the actual dissipation.

Sweet! I'm glad we have that cleared up.
So what your saying is you design an amp schematic with theoretical voltages and current, build it and f around 'till it's correct. (with your vast experience as a guide, of course, Obi Wan)

[JMPGuitars]

Sure, but at this point Bieworm has probably built more amps than me. Pick his brain too.

[gkwallace]

I don't play favorites. I'm thrilled to get any help from anywhere!

[Bieworm]

So when you build an amp presumably accurate to the schematic and the voltages aren't what the schematic suggests, is it unusual to have to play with the current and voltages to get it biased correctly?

Yes

Correction: no, it is not unusual. I misread your post previously

[gkwallace]

Now that I have a better understanding of what I'm trying to do I decided to take the amp back to stock components according to the schematic. I put the 100ohm sag resistor after the rectifier back in (I had put in a 150) and put a couple coupling capacitors back to stock. I also rewired my tone stack, because why not, I didn't like the tone. Maybe I made a mistake.

My voltages look pretty sane compared to the voltage chart except V1 is a bit high making v2 a bit low.
(in my simple mind)

Here's my brand spanking new voltages 100% stock components.

[Bieworm]

Looking good