High Voltage Hijinks

I forgot to mention the grounding scheme in the Wilbury amp. I made a lot of effort on this build to be careful with the grounding points and it really paid off with ridiculously low noise.

Other than the mains safety, there are only two points of chassis ground, with the power and preamp grounds separated. The HV center tap, heater center tap and power amp caps are grounded to a bolt near the power transformer. The preamp grounds, including the pots, are connected to the negative end of the preamp filter caps with a wire going from there to another ground bolt near the input jack. I used an isolation washer on the input jack to separate the sleeve from the chassis and ran the ground wire from the jack to the ground lug of the first stage filter cap.

Writing it out makes it sound more complicated than it really is. I'm definitely going to be doing this for future builds.

Another little trick I used was a 470R, 5W resistor from the 16Ω tap of the output transformer to ground. The idea is a hard-wire protection if the amp is turned on with no speaker connected.
 
jubal81 said:
I forgot to mention the grounding scheme in the Wilbury amp. I made a lot of effort on this build to be careful with the grounding points and it really paid off with ridiculously low noise.

Other than the mains safety, there are only two points of chassis ground, with the power and preamp grounds separated. The HV center tap, heater center tap and power amp caps are grounded to a bolt near the power transformer. The preamp grounds, including the pots, are connected to the negative end of the preamp filter caps with a wire going from there to another ground bolt near the input jack. I used an isolation washer on the input jack to separate the sleeve from the chassis and ran the ground wire from the jack to the ground lug of the first stage filter cap.

Writing it out makes it sound more complicated than it really is. I'm definitely going to be doing this for future builds.

Another little trick I used was a 470R, 5W resistor from the 16Ω tap of the output transformer to ground. The idea is a hard-wire protection if the amp is turned on with no speaker connected.
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It's a good looking build @jubal81 you are in the right place.

My ground method is similar, except one chassis ground in the power section, the "one true ground". This is my last full amp build https://forum.pedalpcb.com/threads/it-lives-matamp-gt120-clone.26449/

You mentioned your input jacks are isolated, is your output jack isolated too? That would be another chassis ground point. I isolate the output jacks too. Also of note most 1/4" jacks are not rated for speaker output, including the common open frame Switchcraft jacks. Switchcraft makes a proper speaker output jack, the Z15J:

1763866095347.png

You can isolate it using the same isolation washer kits Switchcraft makes for the open frame jacks.

Looks like you have a MOV in there too, on the tube rectifier?

What are you building next?
 
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Hal Harvey said:
It's good looking build @jubal81 you are in the right place.

My ground method is similar, except one chassis ground in the power section, the "one true ground". This is my last full amp build https://forum.pedalpcb.com/threads/it-lives-matamp-gt120-clone.26449/

You mentioned your input jacks are isolated, is your output jack isolated too? That would be another ground point. I isolate the output jacks too. Also of note most 1/4" jacks are not rated for speaker output, including the common open frame Switchcraft jacks. Switchcraft makes a proper speaker output jack, the Z15J:

View attachment 106599

You can isolate it using the same isolation washer kits Switchcraft makes for the open frame jacks.

Looks like you have a MOV in there too, on the tube rectifier?

What are you building next?
Click to expand...

I didn't isolate the speaker jacks, but I think I'm going to go back and do that, too.
I've got protection diodes and an MOV on the rectifier from RG's famous "immortal amp mods."
Dunno how clear the picture is, but I mounted terminal strips at each tube to get the grid and screen resistors mounted directly on the tube sockets.
I was just playing it and the PPIMV is so good, though I'm wondering if anyone's ever slapped some little treble bypass caps on that dual pot ...

I've got the fever, so next up is another rebuild on a Princeton head kit I got from Mojotone. I did my own turret board layout for it where I ditched the tremolo and used the tube for a long-tail pair phase inverter. I've been looking around for ideas and I'm really tempted by a build I found on EL34World Forum for a Dumble-inspired Bluesmeister with a 1-tube reverb. Wondering if I have enough real estate on the panel for all the knobs, lol.

4 tube dumble with reverb.gif
 
jubal81 said:
I didn't isolate the speaker jacks, but I think I'm going to go back and do that, too.
I've got protection diodes and an MOV on the rectifier from RG's famous "immortal amp mods."
Dunno how clear the picture is, but I mounted terminal strips at each tube to get the grid and screen resistors mounted directly on the tube sockets.
I was just playing it and the PPIMV is so good, though I'm wondering if anyone's ever slapped some little treble bypass caps on that dual pot ...

I've got the fever, so next up is another rebuild on a Princeton head kit I got from Mojotone. I did my own turret board layout for it where I ditched the tremolo and used the tube for a long-tail pair phase inverter. I've been looking around for ideas and I'm really tempted by a build I found on EL34World Forum for a Dumble-inspired Bluesmeister with a 1-tube reverb. Wondering if I have enough real estate on the panel for all the knobs, lol.

View attachment 106617
Click to expand...

Very cool :) I have a Dumble ODS build in my queue as well. I have the chassis (Amplified Nation) and transformers already. Power amp section will be like the Park 75: pair of KT88s hitting a 50W output transformer).
 
Messing with OT didn’t redeem it, but changing V2b section back to how it was when I got this amp. Maybe preamp tubes at 70s behaved good with cathode arrangement shown at left on the drawing and now it just causes leaky buzzing mayhem?

IMG_7484.jpeg

So 50Hz problem solved, but now preamp hiss is audible. Gonna tweak input grid as I have too much resistance there! :D
 
JohnnyCreepy said:
Messing with OT didn’t redeem it, but changing V2b section back to how it was when I got this amp. Maybe preamp tubes at 70s behaved good with cathode arrangement shown at left on the drawing and now it just causes leaky buzzing mayhem?

View attachment 106623

So 50Hz problem solved, but now preamp hiss is audible. Gonna tweak input grid as I have too much resistance there! :D
Click to expand...
For what it's worth, the cathode on the parallel V1 and V2B on the Deliverance is set up like the right schematic.

For the hiss, have you tried moving wires around with a chopstick? Otherwise, maybe increase the grid resistors?
 
Asdrael said:
For what it's worth, the cathode on the parallel V1 and V2B on the Deliverance is set up like the right schematic.

For the hiss, have you tried moving wires around with a chopstick? Otherwise, maybe increase the grid resistors?
Click to expand...
Yeah, cathode bypass was modded at sime point and changed it to back how it was presented in schematic. Played like that for many months and had a hum problem worseninng. Wrong choice!

I have 60k grid stops on input jacks, added extra 10k right to grid socket pin. This whole combined grid resistance might now cause extra hiss too. But god damn working with old pcb is frustrating as copper tracks are so prone to lift with heat. I really need to finish new layout with P2P scheme…
 
Momentary stop for complaining 70s PCBs and time to bash this sucker down. Like WTF what were they thinking at Peavey about fitting a folded pcb into crammed space? It was just awful getting the pcb out just to replace one leaky eCap. Volume pot had drift and avoided removing PCB with jumpering a new pot into leftovers of the bad one.

IMG_7486.jpeg

Now mates 6505 roars again!
 
I am going to try staying calm but FUCKING HELL HOW CAN GLS SUCK SO BADLY

They managed to change the name on the shipping label to a mix of my first name and the sender's last name even though the initial label was 100% correct. So I had to play tricks to get the package.

But it was also apparently dropped from the 10th floor or something. The package was built like a tank - I mean triple packed etc - but the PT still looked like that on arrival:

PT1.JPEG

PT2.JPEG

Yes. Not even talking about the legs, part of the EI core are actually fucking pushed in and bent. I mean... what the fuck. Choke and PT show a bit of damage to the legs but the core seems intact.

Choke.png

OT.png


I am in contact with Thermionic to find a solution. At least they seem to be of very good quality, everything looks great and smells new :D
 
Asdrael said:
I am in contact with Thermionic to find a solution. At least they seem to be of very good quality, everything looks great and smells new :D
Click to expand...

Man that is a bummer. You are right though, aside from the damage they do look great :)

I love that fresh varnish smell a new transformer has.
 

Hot of the press, this one covering the Jose 3 in 1 mod. It was interesting to hear Jose liked the older higher voltage amps, my (very limited compared to Jose) experience has been the same. I think it's another reason 100W amps sound better than 50W amps, they tend to be higher voltage too.

I need to get back to my tube projects, I got sucked into a video game, and then was working a bit on a guitar. I have been thinking a lot about what is next after I finish my current projects. Thinking more seriously about a standalone trem and spring reverb, something like the Soldano Surf Box (in addition to a couple of more preamps).
 
Hal Harvey said:

Hot of the press, this one covering the Jose 3 in 1 mod. It was interesting to hear Jose liked the older higher voltage amps, my (very limited compared to Jose) experience has been the same. I think it's another reason 100W amps sound better than 50W amps, they tend to be higher voltage too.

I need to get back to my tube projects, I got sucked into a video game, and then was working a bit on a guitar. I have been thinking a lot about what is next after I finish my current projects. Thinking more seriously about a standalone trem and spring reverb, something like the Soldano Surf Box (in addition to a couple of more preamps).
Click to expand...

I have been trying to catch up on those, it's pretty interesting and funny at the same time.

Also Thermionic lab just answered my email and they will ship end bell replacements so I can try everything out. If it doesn't work due to internal damage, they will rebuild for me. So there is that.

In the meanwhile, I have been busy with Fusion.

To be ordered from JLC (haha 15€)

1765228035335.png

With transformers on (left is OT, right is PT at 90° and Choke at 90° of it too).

1765228047677.png

Since JLC is doing the chassis I will be ordering some cleaner PCB as well fixing up the mistakes I did.
 
I hope this is the right thread to ask... If not, I'll start a separate thread....

I've built a Mojotone VibroChamp several years ago. It is set up to accommodate a 4 Ohm speaker. I also made a Mojotone NC30 which has an 8 Ohm speaker. Since I play later at night, I found a cheaper 8 Ohm Two Notes attenuator. I'd like to use the attenuator for both amps, but recongize the impedance mismatch for the VibroChamp. When I was looking at the schematics for the VIbroChamp, I realized that the impedance might be determined by the output transformer (see picture)
1765638260134.png

The speaker is wired with the yellow, 4 Ohm, wire, but there is an 8 Ohm option.

  • Is it safe to use a toggle switch, selecting either the 8 Ohm or 4 Ohm output from the output transformer? When using the attenuator, I'll use the 8 Ohm setting and switch to the 4 Ohm setting when the speaker is connected.
Thanks for the advice.
 
Synchrony Pedalworks said:
I hope this is the right thread to ask... If not, I'll start a separate thread....

I've built a Mojotone VibroChamp several years ago. It is set up to accommodate a 4 Ohm speaker. I also made a Mojotone NC30 which has an 8 Ohm speaker. Since I play later at night, I found a cheaper 8 Ohm Two Notes attenuator. I'd like to use the attenuator for both amps, but recongize the impedance mismatch for the VibroChamp. When I was looking at the schematics for the VIbroChamp, I realized that the impedance might be determined by the output transformer (see picture)
View attachment 107630

The speaker is wired with the yellow, 4 Ohm, wire, but there is an 8 Ohm option.

  • Is it safe to use a toggle switch, selecting either the 8 Ohm or 4 Ohm output from the output transformer? When using the attenuator, I'll use the 8 Ohm setting and switch to the 4 Ohm setting when the speaker is connected.
Thanks for the advice.
Click to expand...
Yes, but make sure your toggle switch is rated for the application. I've seen (and own) more than a few amps with a rotary switch for 4/8/16ohm output, no reason a toggle wouldn't work for two options.
 
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