DIY 300B Redux

[MrEd]

Not quite. Probably wait until winter. Source parts and fiddle around with layout until then.

Looks like it was drunk when posted that... but I was at work. Lol
I studder when type 😅
It's amazing how a project can take but worth it when completed.

 

[Punker X]

Got hear these yesterday. Thanks for having me over. Off to a great start. Heard a couple odd things, may have been recording related. Overall loved them.

 

[Wntrmute2]

Thanks for the kind words. Been focused on the internal layout today.

Not happy with the second choke and 300B filament transformer crammed next to each other. The first choke is planned to be right above those two components.
Wondering if an aluminum divider will provide any isolation for the input and power tubes and circuitry?

 

[paul_b]

Aluminum can provide a barrier to RF, but not so much for magnetic fields. Definitely be sure to check which orientation of the PT/OT gives the lowest coupled AC voltage onto the primary of the output transformer.

 

[Wntrmute2]

Yup. Done that but will reconfirm. Have any thoughts about the choke and filament transformer being right next to each other?

 

[paul_b]

That wouldn't be particularly concerning to me. I would be concerned that the filament PT has its coil aligned with the grid of the 300B though. If you can swap those two pieces of iron for the black box caps at the rear of the chassis, that physical separation might be helpful, but then again it may not matter too!

 

[Wntrmute2]

Look any better?

 

[paul_b]

Yeah, I think that's a better bet. If you can drill holes in the side panel, you could also probably align it with the power transformer and mount it close to the bottom of the chassis to eat up space that's usually just not used for a lot.

 

[Wntrmute2]

So the bobbin is pointing in the same direction as the PT? Like below? I'll listen for hum before committing of course.


And not like below, correct?

 

[paul_b]

The top two pictures have the coils aligned. The bottom one is not.

I do tend to point my bobbins forward on the power transformers of my builds, then I will put power supply related parts in front of the PT.

 

[Wntrmute2]

This was the quietest arrangement when I tested things a few weeks ago.

 

[MrEd]

This was the quietest arrangement when I tested things a few weeks ago.View attachment 78978View attachment 78979View attachment 78980

Is it the blue tape or the rubber band.. tell us your secrets 😅

 

[Wntrmute2]

Just plain old painters tape.