50W Plexi, Dual Rectifier, PPIMV Budget Build

[Guitarnut]

Well, in the face of progress flies a stupid mistake. I labeled the face plate upside down. Working on this amp with its reversed layout and upside down chassis is like reading a book in a mirror.

Easy enough to fix but costly time wise.

Peace,
Mark

[Guitarnut]

As I start to wire the chassis, I want to make sure I have a handle on the dual rectifier circuits. My layout got a bit cluttered a so I drew out what I have in the layout.

Comments or suggestions welcome.

[IMG:800:600]http://www.crenshawweb.com/plexi50/recto_circuits.jpg[/img]

Peace,
Mark

[martin manning]

You can save 10W by taking the 5VAC wire off of the rectifier pin8 and moving it to the unused center terminal of the switch, and jumper the wire coming from pin 8 over to the unused switch contact next to it. You'll get a slow start switching from the SS to a cold vacuum rectifier, but I'd rather reduce the heat.

[Guitarnut]

You can save 10W by taking the 5VAC wire off of the rectifier pin8 and moving it to the unused center terminal of the switch, and jumper the wire coming from pin 8 over to the unused switch contact next to it. You'll get a slow start switching from the SS to a cold vacuum rectifier, but I'd rather reduce the heat.

Clever. That way the tube doesn't heat until it's selected. Thanks!

Like so?

[img:800:600]http://www.crenshawweb.com/plexi50/recto_circuits_2.jpg[/img]

[martin manning]

That's it. Can't draw on my phone... yet...

[Guitarnut]

That's it. Can't draw on my phone... yet...

Cool! I'll add this to the design. Thanks again for your input.

Mark

[Guitarnut]

More progress. I have most everything wired up. I still need to add the bias adjust, AC connections, OT secondaries and output jacks.

I had already cut the 5V wire so I didn't move it to the switch but I think I will eventually.

[IMG:800:600]http://www.crenshawweb.com/plexi50/build90.jpg[/img]

[IMG:800:600]http://www.crenshawweb.com/plexi50/build91.jpg[/img]

[IMG:800:600]http://www.crenshawweb.com/plexi50/build92.jpg[/img]

[IMG:800:600]http://www.crenshawweb.com/plexi50/build93.jpg[/img]

[IMG:800:600]http://www.crenshawweb.com/plexi50/build94.jpg[/img]

[IMG:800:600]http://www.crenshawweb.com/plexi50/build95.jpg[/img]

[IMG:800:600]http://www.crenshawweb.com/plexi50/build96.jpg[/img]

[IMG:800:600]http://www.crenshawweb.com/plexi50/build97.jpg[/img]

[IMG:800:600]http://www.crenshawweb.com/plexi50/build98.jpg[/img]

[IMG:800:600]http://www.crenshawweb.com/plexi50/build99.jpg[/img]

[IMG:800:600]http://www.crenshawweb.com/plexi50/build100.jpg[/img]

[johnnyreece]

Looks like it's getting there! One thing I couldn't see: Do you have your 1 ohm resistors in your bias measuring circuit?

[xtian]

Oof. I want to say good luck with your build. But all these long runs to and from your preamp tubes are going to cause trouble, and they're even mixed in with the signal wire running to your power tube grids. Not even Fender was this wild with the lead dress. Keeping my fingers crossed for you, man!

[johnnyreece]

Oof. I want to say good luck with your build. But all these long runs to and from your preamp tubes are going to cause trouble, and they're even mixed in with the signal wire running to your power tube grids. Not even Fender was this wild with the lead dress. Keeping my fingers crossed for you, man!

I wondered about that, too. If it does turn out to be noisey, do you think you can get away with some terminal strips, or maybe some PTP on V1 and V2? I'm just an amateur, so feel free to ignore me.

[xtian]

I'm an amateur, too!

Trouble, if it happens, is going to come from parasitic oscillation. That is, oscillation (heard as squeal or "feedback") caused by wires from different parts of the circuit being too close to each other.

It's ok to bundle together the three wires from each triode (anode, cathode and grid) but you should keep each triode's wires separate, and away from other wires, too, like unfiltered HT voltage, heater wires, OT wires, etc.

[Guitarnut]

Looks like it's getting there! One thing I couldn't see: Do you have your 1 ohm resistors in your bias measuring circuit?

They're in there. The lower Rs coming off the sockets and running to the central ground point.

Peace,
Mark

[Guitarnut]

Yeah, when I started wiring it up I knew it was far from conventional. Hopefully, it's acceptable.

Only one way to find out!

Peace,
Mark

[johnnyreece]

Looks like it's getting there! One thing I couldn't see: Do you have your 1 ohm resistors in your bias measuring circuit?

They're in there. The lower Rs coming off the sockets and running to the central ground point.

Peace,
Mark

Yeah, don't know what I was looking at...Saw the connection from pin 1 to 8...completely ignored the giant resistor coming from pin 8...

[Reeltarded]

(screams like a little girl) AAACK!

Wires!