watt finally builds an amp (results TBD)

Some progress, some tribulations.

I painted the end bell, but I'm leaving the upside down C on the laminations. (Hey, it's a good letter.)

The base is just a stand-in, pieced together just to see. That stink bug on the right seems to like it, though.

Still some holes to be drilled--for attaching terminal strips and output transformers, which I plan to mount underneath. And probably a big-ish hole for the 200 uF cap in the power supply. Still thinking about where to mount the choke.

Then, to soldering!

IMG_2380.JPG
 
Thinking about next steps, and I could use some feedback, if you're willing.

First, about grounding. I think I've picked up a bit from some of the other build threads here, but I want to ask (since it makes a difference for where I'll drill to mount terminal strips).

I'm planning to route a length of solid copper as a ground bus.
It should connect to chassis ground at one end but not the other, correct?

I was planning to mount a terminal strip close to the large power supply capacitor and run the ground bus through the common terminal, the one connected to the hole that I'll use to affix the strip to the chassis.

At the signal end, I could solder the bus to an unused terminal in one of the strips I'll use to connect components there. Or is that a bad idea? Something like below. (The terminal strips and bus will be underneath, of course. I'm not trying for some kind of deconstructionist design.)

IMG_2381.JPG

With that image in view, is that an OK orientation for the choke? It, and the output transformers, will be underneath.
 
After some thinking and a little intenet research, I think I've answered my questions from the prior post. Gonna mount the choke on one of the wooden panels of the base, underneath the multisection JJ cap. And I've read a bit more about star ground procedures, so I think that I have a handle on the ground bus.

But questions keep coming up, all the time.

I've been puzzling over this part of the power supply schematic (I added the socket numbers in red in an attempt to make everything as obvious as possible for myself):

Screen Shot 2020-04-04 at 10.17.45 PM.png

Maybe not a puzzle for those who have done this before, but as I understand it so far, the 5R4 has four connections: pins 2, 8, 4, and 6.

Is the schematic simply trying to show that one leg of the 5V winding also connects to L1 and C1?

Another way of putting it: there are no pins other than 2, 8, 4, and 6 to connect, correct?
 

Thermionics

Post Whore In Training
Are you mounting the choke and OPTs 'below deck' as it were? I've found that helps with the whole inverse square aspect of magnetic fields as it adds a third dimension to the whole orientation / distancing thing.
 
Are you mounting the choke and OPTs 'below deck' as it were? I've found that helps with the whole inverse square aspect of magnetic fields as it adds a third dimension to the whole orientation / distancing thing.

Yep, OPTs and choke below deck.

This is another dry fit. Still need to drill some holes at the corners of the plate to attach to the wooden base. (Also made another base.)

2AD92486-33A2-4941-873E-3E50B0848EA4.jpeg
 

Redboy

Knobophobe
Maybe not a puzzle for those who have done this before, but as I understand it so far, the 5R4 has four connections: pins 2, 8, 4, and 6.

Is the schematic simply trying to show that one leg of the 5V winding also connects to L1 and C1?

Another way of putting it: there are no pins other than 2, 8, 4, and 6 to connect, correct?
You're correct about this.

Here's another schematic that shows this more clearly.

5R4 schema.png
 
One more question (or a question and two related questions), and hopefully I'll be able to make some progress today.

As you can see in post 45's pic, the PT's 6V leads are long enough for me to reach either the 12AT7's or one of the EL84's sockets. But doing so will run that 6V lead down the middle of the amplifier.
  • Would that be, as they say in Ghostbuters, "bad"?
  • Would it be better to connect the 6V lead to the terminal strip at the lower left of the PT, then run a twisted pair along the edge of the plate?
  • In either case, should I connect those 6 volts to one of the EL84s first?
 
One more question (or a question and two related questions), and hopefully I'll be able to make some progress today.

As you can see in post 45's pic, the PT's 6V leads are long enough for me to reach either the 12AT7's or one of the EL84's sockets. But doing so will run that 6V lead down the middle of the amplifier.
  • Would that be, as they say in Ghostbuters, "bad"?
  • Would it be better to connect the 6V lead to the terminal strip at the lower left of the PT, then run a twisted pair along the edge of the plate?
  • In either case, should I connect those 6 volts to one of the EL84s first?

Depending on where you inputs are I would try to do the following:

Keep heater wiring as far as possible from low-level signal, ie: inputs
If heater wiring and signal wiring (low-level, or speaker-level) have to cross, do so at 90 degrees.


Ssshh.....smell that?
 
Depending on where you inputs are I would try to do the following:

Keep heater wiring as far as possible from low-level signal, ie: inputs
If heater wiring and signal wiring (low-level, or speaker-level) have to cross, do so at 90 degrees.

Thanks for this guidance.

I'm likely going to locate both inputs on (using the image from 45 as a reference) the left side of the amplifier, attached to the wooden base. Planning to create two circular recesses with a Forstner bit to hide them a bit inside the base plane.

I like the idea of keeping the heater wiring away from signal wiring, where possible. So I'll likely connect the 6V leads to the terminal strip and route a twisted pair to the EL84 on that side. After that, I suppose there are a few different ways to do it, but I'll keep the 90 degree rule in mind whatever I do.

(I guess there is a way to cross the streams.)
 
I appreciate Redboy's watchful eye. My tube sockets, mounted from the bottom, could use some reinforcement. These are readymade (not bespoke :smile: ) washers. I did have to drill them a little, though.

IMG_2402.jpg
 
"Progress."

FullSizeRender 2.jpg

If I started this by framing it as an educational experience, one thing I've learned is that it's difficult--even with some forethought and the best intentions--to make the layout look like anything other than a pile of parts. At least for me, on this first try.
 
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You can see that there's a little more to be done in both the power supply and the audio part of the circuit. Which leads to the question below.

Another tube pinout question, this time about the EL84 connections. The RH84 schematic's representation of the EL84 shows two grids.

Screen Shot 2020-04-12 at 6.33.20 PM.png

But other representations show three.

Screen Shot 2020-04-12 at 6.23.45 PM.png

This matters for me at the moment because I want to be sure that I connect D1, the zener diode, to the correct pin. Is the RH84 schematic simply omitting the suppressor grid, since it shares pin 3 with the cathode?
 
Regarding your ground bus. I believe I was instructed to ground my bus(s) as close to the input socket as possible.

Sorry I missed this when you first posted it.

The ground scheme could be something that I have to revisit/revise. As I have it now, the bus is grounded to the chassis back in the power supply. That's also where the ground from the IEC will go. I'm planning to run a ground wire from the RCA inputs to the bus, but it will make contact--at least as I was planning to do it--closer to the signal end, which is the opposite end from chassis ground.
 

Wntrmute2

Not So Mediocre Member
Seems weird to me too when I thought about it. I would think that grounding the PS caps would allow for a quieter bus but I was convinced by multiple sources to ground between the input jacks. That is what I did. I also put a switch in line so I could float the bus if needed. No difference at this point. This was in my phono stage, but I also grounded at the inputs on my Radiotron 2A3s (300Bs).
 
This matters for me at the moment because I want to be sure that I connect D1, the zener diode, to the correct pin. Is the RH84 schematic simply omitting the suppressor grid, since it shares pin 3 with the cathode?

I went ahead, making this assumption. If you out there think differently, please do let me know.
 
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