3rd Gen started

[Reeltarded]

WOW! That looks insanely great! Stunning!

Thanks for the tip on the choke. I have always wondered!

[ijedouglas]

Thanks guys, appreciate the kind words.

[dorrisant]

Wow!!

[Smitty]

Very nice solder joints. No flux mess. Which solder did you use?

Thanks for the choke tip.

[ijedouglas]

Very nice solder joints. No flux mess. Which solder did you use?

Thank you. I use Kester 63/37 44 activated. I do spend time afterwards with q-tips and isopropyl though

[VolkerStaub]

I see you using these era correct, yellow, Spragues lytics.
Do these bypass caps make a big difference in terms of sound compared to modern equivalents?

[ijedouglas]

I see you using these era correct, yellow, Spragues lytics.
Do these bypass caps make a big difference in terms of sound compared to modern equivalents?

By modern equivalents do you mean the current sprague TVA?

[VolkerStaub]

I see you using these era correct, yellow, Spragues lytics.
Do these bypass caps make a big difference in terms of sound compared to modern equivalents?

By modern equivalents do you mean the current sprague TVA?

Nope, I mean any available electrolytic 5uF/63V at Mouser

[ijedouglas]

I see you using these era correct, yellow, Spragues lytics.
Do these bypass caps make a big difference in terms of sound compared to modern equivalents?

By modern equivalents do you mean the current sprague TVA?

Nope, I mean any available electrolytic 5uF/63V at Mouser

Yes. Without knowing which ones and testing them, I can't really comment though. There are a few posts on this forum that discuss the differences in some of the more modern caps. I would recommend getting a few different brands/types and listening for yourself as some may be better suited to the amp you are working on

[Stephen1966]

Hi Ian,

The idea of reversing the choke is really interesting, I will be trying it this weekend if I get time.

The problem is always the amount of time between an AB test so I've made a version of your box.

It's a simple circuit but given the voltages involved coming off the B+ it should come with a disclaimer:

THESE VOLTAGES CAN KILL YOU.
DO NOT TRY THIS IF YOU DON'T KNOW EXACTLY WHAT YOU ARE DEALING WITH.

It should go without saying; you try this at your own risk.

This is the schematic:

DipTrace Schematic - Voltage inverter - 01.pdf

And here's a couple of pics to show the internals:

IMG_20230421_222604.jpg

IMG_20230421_222629.jpg

I've used a heavy duty APEM DPDT switch and the internal wiring is AWG18 solid core for the current carrying wires (IN - from the B+ and back, and OUT to the choke and back). The DMM tap allows you to see the polarity of the voltage - plus or minus - and is wired up using AWG20 solid core. I tested it using a 9V battery and it works. I also double checked the GND to ensure it doesn't have continuity with any part of the switched circuit. The GND is essential and is only for the case. It does not connect to any part of the switched circuit.

[ijedouglas]

Very nice!!! Good idea on the DMM test points.

Interested to hear your results

[jazzbass]

Hi Stephen1966,

I'm following your construction and your experience with the Choke. I need to ask you some questions (which demonstrate how little I know about this fascinating matter ) the DMM outputs are in parallel with the OUT outputs, maybe two holes and two bushings on the case can be avoided?
Forgive my ignorance but what does DMM mean and why did you provide a bushing for the earth?

A hug.

Franco

[timrobertson100]

Hey Franco

DMM: Digital Multimeter

[Stephen1966]

Hi Stephen1966,

I'm following your construction and your experience with the Choke. I need to ask you some questions (which demonstrate how little I know about this fascinating matter ) the DMM outputs are in parallel with the OUT outputs, maybe two holes and two bushings on the case can be avoided?
Forgive my ignorance but what does DMM mean and why did you provide a bushing for the earth?

A hug.

Franco

DMM - ditto Tim. A DMM can measure positive and negative voltages - it provides a visual confirmation of the polarity. Yes, it's in parallel with the OUT outputs. Strictly speaking, you don't need it, this device is for a listening test after all and your ears are what matter but the position of the switch along with a positive (parallel) or negative (inverted) volt reading will tell you whether the choke wires should be reversed (inverted) or not when you connect it back up to the power board. It's important you know which wire is which on the choke, they are commonly both black and look identical so before desoldering from the power board it will be useful to mark them in some way. You shouldn't swap any board B+ points or wires. To begin though, I will be desoldering the choke wires and connecting them up to the box in the order they came off the board.

For connections to and from the board and the choke, I am using AWG18 (1.5mm^) stranded cables with a 4mm banana jack on one end (for connecting to the box) and some heavier duty alligator clips on the other. No one here should need reminding that before you start messing around with any of this, your caps should be fully discharged.

The GND lug is for your protection. If 400+ volts are going to arc across any of the internal circuitry and into the box or switch toggle, I want a solid connection to Earth that doesn't look for a path to ground through my soft tissues. Or yours, for that matter. Don't leave it out.

[Stephen1966]

Very nice!!! Good idea on the DMM test points.

Interested to hear your results

Thanks Ian, it isn't too pretty but it should do the job.