High Voltage Hijinks

[Feral Feline]

A set of bamboo chopsticks.

Not just for poking around but for help grabbing things: components, moving wires...
If not adept at using chopsticks in the manner they're meant to be used, practice a little — eat more asian foods.


Or practice on spaghetti/other pasta...




PS: Once you've used the chopsticks in the amp's spaghetti, don't use them to eat with anymore...

 

[Paradox916]

@Hal Harvey @Asdrael thankfully there are assembly instructions with start up and testing protocol and this project also has multiple fuses involved, 630ma on the mains 4a on the heaters and relays and 100ma on the HV and first start up the HV circuit the fuse is not installed and the HV circuit is not energized. But building a limiter is definitely on the agenda

 

[Hal Harvey]

light bulb limiter + Rob Robinette’s startup protocol and nothing bad can happen.

Yep. Rob should put all that stuff on his site in a book.

I like this drawing because it shows how simple the concept is:



I think if I ever change mine up I'll get rid of the outlet receptacle and just go wall plug>lamp>extension cord socket.

As long as you wear protection googles and keep your hands out of the chassis ofc.

Googles?! I thought all nerds (like those in this thread) wear glasses as standard.

Take your time. Don't rush. Doing a first startup when you just finished your last solder joint at 2:00 AM is not a great idea no matter how excited you are. Don't be lazy. I've never been injured working on tube stuff. I have gotten injuries at the drill press or whatever though. Almost always it's because I was too lazy to go get the correct tool etc.

Anyway, back to fun stuff

 

[Asdrael]

Seriously running out of things to do while I wait for the transformers.



And the layout for the chassis inside and component is done in DIYLC too. And the facegrill - will likely go with a laser engraved plexiglass with LEDs in the headshell that change color based on the channel.

Yes, I went there, sized the PT for it and have a couple of 3 pin headers on the PCB for it

 

[Paradox916]

Seriously running out of things to do while I wait for the transformers.

View attachment 105796

And the layout for the chassis inside and component is done in DIYLC too. And the facegrill - will likely go with a laser engraved plexiglass with LEDs in the headshell that change color based on the channel.

Yes, I went there, sized the PT for it and have a couple of 3 pin headers on the PCB for it

That’s going to be pretty cool.

 

[Feral Feline]

DIYLC

When you run out of things to do it's time to either make popcorn, bake brownies or both (to cover both food groups — Savoury & Sweet).

 

[Hal Harvey]

or build.

 

[JohnnyCreepy]

GUESS WHAT? I found it, finally found it. Measured voltages yesterday and V2b cathode gave odd readings. Today noticed resistor leg had snapped just where it enters into board. That was causing cutoff when raising gain and making resistor move with sound pressure.

 

[Hal Harvey]

GUESS WHAT? I found it, finally found it. Measured voltages yesterday and V2b cathode gave odd readings. Today noticed resistor leg had snapped just where it enters into board. That was causing cutoff when raising gain and making resistor move with sound pressure.

Awesome!!

 

[Hal Harvey]

X88R preamp (crunch and lead channels) is done. I'm pretty happy with this one.





I may reduce the coupling cap after the first stage to tighten it up, but for now I'm leaving it stock. I used a Mesa SPAX7 in the first tube position and JJ ECC83S in the remaining spots. I think the SPAX7 is just a test selected ECC83S but in any case the preamp is very quiet, I may pick up a few more.

On to the Model T. I need to make a mini board with MOVs and flyback diodes, and drill a few last holes in the chassis.

 

[JohnnyCreepy]

MOVs and flyback diodes

How you’re planning to add these? For OT protection?

 

[Paradox916]

X88R preamp (crunch and lead channels) is done. I'm pretty happy with this one.

View attachment 105972
View attachment 105973
View attachment 105974

I may reduce the coupling cap after the first stage to tighten it up, but for now I'm leaving it stock. I used a Mesa SPAX7 in the first tube position and JJ ECC83S in the remaining spots. I think the SPAX7 is just a test selected ECC83S but in any case the preamp is very quiet, I may pick up a few more.

On to the Model T. I need to make a mini board with MOVs and flyback diodes, and drill a few last holes in the chassis.

Very cool! how did you end up handling the channel switching (nevermind I think I figured that out) and what are your B+ voltages just out of curiosity

 

[Hal Harvey]

How you’re planning to add these? For OT protection?

Yeah OT protection. Two series of three MOVs (to minimize capacitance), on each side of the primary. Two series of 1N4007s from primary ends to ground. Just like Merlin mentioned in his new book, and Tim Robbin's paper on OT protection too.

I have that same MOV setup in my GT120 build already but without the flyback diodes. I may circle back and get the flyback diodes in that one too.

 

[Hal Harvey]

Very cool! how did you end up handling the channel switching and what are your B+ voltages just out of curiosity

The channel switch just grounds the 3rd stage grid in each channel like in the X88R.

With tubes installed I have 430V right after the rectifier. The schematic I have has 432V there so I hit the bullseye. Past the rectifier my power supply matches the original 100%. I can take more measurements if you want them for comparison to your build.

 

[Asdrael]

X88R preamp (crunch and lead channels) is done. I'm pretty happy with this one.

View attachment 105972
View attachment 105973
View attachment 105974

I may reduce the coupling cap after the first stage to tighten it up, but for now I'm leaving it stock. I used a Mesa SPAX7 in the first tube position and JJ ECC83S in the remaining spots. I think the SPAX7 is just a test selected ECC83S but in any case the preamp is very quiet, I may pick up a few more.

On to the Model T. I need to make a mini board with MOVs and flyback diodes, and drill a few last holes in the chassis.

Clean. Good work! And no arcing then But... why is the middle tube retainer shiny while the others are not? WHY???

 

[Hal Harvey]

Clean. Good work! And no arcing then But... why is the middle tube retainer shiny while the others are not? WHY???

Pfft arcing.

The tube retainers... I don't actually leave those on. They are just there so I can flip it over on the workbench. I think Belton makes some for PCB mount, do you use those? I have one from a Mesa, longer spring with ridge and o-ring that mounts to the chassis.

Edit:

 

[Paradox916]

The channel switch just grounds the 3rd stage grid in each channel like in the X88R.

With tubes installed I have 430V right after the rectifier. The schematic I have has 432V there so I hit the bullseye. Past the rectifier my power supply matches the original 100%. I can take more measurements if you want them for comparison to your build.

Nice!… more measurements aren’t necessary, I was mostly curious what it was right after rectification. My project is ( according to the schematic is about 50v less) I was just wondering how close they were.

 

[Asdrael]

Pfft arcing.

The tube retainers... I don't actually leave those on. They are just there so I can flip it over on the workbench. I think Belton makes some for PCB mount, do you use those? I have one from a Mesa, longer spring with ridge and o-ring that mounts to the chassis.

Edit:
View attachment 105983

I don’t use any of these. Never felt the need to with modern equipment, proper tube/wire/transformer layout and decent lead dress. And a noise gate in the loop sometimes

 

[JohnnyCreepy]

Yeah OT protection. Two series of three MOVs (to minimize capacitance), on each side of the primary. Two series of 1N4007s from primary ends to ground. Just like Merlin mentioned in his new book, and Tim Robbin's paper on OT protection too.

I have that same MOV setup in my GT120 build already but without the flyback diodes. I may circle back and get the flyback diodes in that one too.

I added flyback diodes for my amp, but left out MOVs. Former caused no negative effects on tone!

Have you lifted heaters from PI?

 

[Hal Harvey]

I added flyback diodes for my amp, but left out MOVs. Former caused no negative effects on tone!

Have you lifted heaters from PI?

Yeah I can’t tell the difference with or without MOVs. I think if HiFi guys are using them they are likely more than fine in guitar amps. In the GT120 I put MOVs on the mains input too. I think if you are playing bars or whatever with sketchy power it’s a good idea. I’m leaving the mains MOVs off the Model T (because my audience is cats).

I have elevated heaters in everything I have built so far. I wire my heaters Soldano style. Elevating heaters is healthy for cathode follower tubes, gotta watch the heater to cathode limits. Especially for non-12AX7s.