I'm tired of anemic guitar amps!

[Chuz Life]

And here it is with my new PT and OT in place. This is why I chose this particular chassis. 10" from front to back.

View attachment 1148546

Curious, what are the specks on the Toroid PT?

 

[Leo123]

I'm going to build an amp. And post the whole thing on YouTube. Show the world how it's done.

My ear has had it with anemic amps. I like thump, I like an authoritative sound. I like the power tubes to break up at full volume, none of that saggy blues stuff.

My other requirement is it has to be bulletproof. It has to be able to fall out the back of a truck and survive. So no PC boards, all old school point to point wiring. The worst thing that happens is a tube blows and then you replace it and you're done.

If you're into guitar amps, check out the schematic of this 200 watt Marshall. Notice the 12AU7 driver, in front of the power tubes. That's there because the KT-88's require 50 V rms to reach full power. They sound great when they do, they're thumpy and they have great dynamics, but they need some beef backing them up.

https://schematicheaven.net/marshallamps/major_1967u_lead_200w.pdf

So I'm going to have a 400 VA toroid that can supply almost an amp at 560 volts (the tubes draw 640 mils at full power), but it weighs less than half as much as a big metal power transformer.

And I'm going to make it a dial-an-amp, so you can get any sound you want just by flipping a few switches. If you want a Fender sound with reverb and the tone stack up front you can get that, and if you want a Marshall sound with the tone stack in back you can get that too. And anything in between, and above and beyond.

By using a 12AU7 as a phase inverter, ahead of the driver, I get a combined gain of about 60 for the power amp, which is just about perfect, that means about 0.8 volts will drive it to full power. With a long tailed pair, it'll have the same sparkle as a Marshall Major about halfway up, and then it'll get really aggressive when it's cranked.

I want to blow some windows out this year. It's one of my New Year's resolutions.

That's so cool!! I have played through monster amps but now, I gravitate to my Mesa Boogie 35W/215W/5W. It's good for the club gigs and parties I play. I bet your amp will be awesome!!!

As far as lots of different sounds, my Mesa Boogie has so many modes It can get confusing. Sometimes I think I need an amp with just one knob!!! LOL

 

[toobfreak]

Well, the good news is, most of the paint came off the back panel. Took about an hour. The bad news is, it didn't work at all on the front panel. In both cases I'll have to do some sanding.

I'm guessing the front is hard anodized.

Got some of the major holes drilled, you can see both transformers mounted along with the punch holes for the capacitors.

Might be overkill, but where I have high power wires going through holes in a chassis, I like to protect the edges by using one of those push-in rubber grommets so there is no chance of anything ever rubbing and shorting out due to shock and vibration.

Worst case: I will paint the inside of the holes with Plastic Dip.

I always operate from the position of worst case scenario and design stuff to hold up for at least 50 years.

 

[scruffy]

Curious, what are the specks on the Toroid PT?

Antek as4t400 with 70v bias tap

120/230 4 wire primary (two coils)
2x 400v/500 mA each tapped at 70v
2x 6.3v 4A

DC output full wave = 560 volts

Two KT-88's at full power deliver 312 v each to the OT for a total of 625v RMS, which is then stepped down by the OT to 28v at an 8 ohm speaker. Total current draw at full power is 318 mA, split between the tubes.

Ultralinear KT-88's require about -85 volts bias to get 50 mA quiescent current, at which point they're dissipating about 28 watts each. Total push pull gain is about 12.5 from a 50 V RMS input. You get about -95 volts DC out of the 70 v transformer tap which you then need to filter because it's half wave.

Total heater current is 3.2 amps for the power tubes and 2.1 amps for the rest. So with these specs, the power transformer never gets stressed, and the OT is operating at top of spec. A 2A HT fuse will protect the output stage in the event of a shorted tube or capacitor. Since there are huge power capacitors there is considerable surge current at power on so we need a Slo-Blo fuse on the mains.

The 12AU7 driver stage has a gain of 10 and an output impedance of only 15k ohms, so we use 100k bias resistors to supply sufficient current to the KT-88 grids. To capture the 31 Hz from the low B on a bass we can use .1 uF coupling caps from the driver to the KT-88's.

When I bring this up I'm going to make sure it's DC-hapoy first. We want 50 mA on the KT-88's, and we want exactly 450 volts supplying the driver stage. To do this I'm going to have to wire up all the rest of the tubes too (for DC only, so leaving out all the coupling caps), because this is the only way I can trim the resistors in the power supply. The reverb wants 420 volts, the PI wants 390, and the cathode follower wants 375. Then 360 and 350 for the preamp tubes.

So that's the plan. Wire everything up for DC, bias the power tubes, trim the power supply resistors, and then start installing the audio.

In the pic of the underside of the chassis, the entire upper right quadrant is power only, no audio whatsoever. It's the hot zone where the AC and all the power transformer wires run. Everything south of the main ground though, is absolutely pristine and clean. The only thing in the upper left quadrant is the output transformer, the speaker wires run along the edge of the chassis to the speaker jacks. On the other side the primary drops straight down to the power tubes, it's just an inch or two.

This arrangement will end up hum free at 100 watts. You can see where the reverb transformer divides the first 5 preamp tubes from the PI and driver, that point there has an audio signal >= 0.8 volts at full power, and it's 5 inches away from anything that has to do with the power supply.

 

[scruffy]

I'm guessing the front is hard anodized.

What does that mean?

Will it come off?

 

[toobfreak]

What does that mean?
Will it come off?

If it is hard anodized, no, the anodizing penetrates into the metal pretty deep and also makes the metal harder too.
If it is anodized, you'll have to try painting over it I guess, or make a whole new panel.

If it is anodized, scratching it with a scribe will leave a scratch but even a scratch below the surface will not leave plain shiny metal showing, the scratch will still be black.

Anodizing provides a very durable but somewhat dull wear surface.

 

[GMCGeneral]

I'm going to build an amp. And post the whole thing on YouTube. Show the world how it's done.

My ear has had it with anemic amps. I like thump, I like an authoritative sound. I like the power tubes to break up at full volume, none of that saggy blues stuff.

My other requirement is it has to be bulletproof. It has to be able to fall out the back of a truck and survive. So no PC boards, all old school point to point wiring. The worst thing that happens is a tube blows and then you replace it and you're done.

If you're into guitar amps, check out the schematic of this 200 watt Marshall. Notice the 12AU7 driver, in front of the power tubes. That's there because the KT-88's require 50 V rms to reach full power. They sound great when they do, they're thumpy and they have great dynamics, but they need some beef backing them up.

https://schematicheaven.net/marshallamps/major_1967u_lead_200w.pdf

So I'm going to have a 400 VA toroid that can supply almost an amp at 560 volts (the tubes draw 640 mils at full power), but it weighs less than half as much as a big metal power transformer.

And I'm going to make it a dial-an-amp, so you can get any sound you want just by flipping a few switches. If you want a Fender sound with reverb and the tone stack up front you can get that, and if you want a Marshall sound with the tone stack in back you can get that too. And anything in between, and above and beyond.

By using a 12AU7 as a phase inverter, ahead of the driver, I get a combined gain of about 60 for the power amp, which is just about perfect, that means about 0.8 volts will drive it to full power. With a long tailed pair, it'll have the same sparkle as a Marshall Major about halfway up, and then it'll get really aggressive when it's cranked.

I want to blow some windows out this year. It's one of my New Year's resolutions.

Just get a Fender Twin Reverb amp and you're done! In any event, as a bassist myself, I went from a 6X10 700 watt 3/4 Hartke stack with SWR head to a Fender Rumble 500. All the power, all the tone, and none of the heft.

 

[scruffy]

I'm guessing the front is hard anodized.


Might be overkill, but where I have high power wires going through holes in a chassis, I like to protect the edges by using one of those push-in rubber grommets so there is no chance of anything ever rubbing and shorting out due to shock and vibration.

Worst case: I will paint the inside of the holes with Plastic Dip.

I always operate from the position of worst case scenario and design stuff to hold up for at least 50 years.

Yes. All that is coming. My amp will be bulletproof. Example: the terminal strip next to the power tubes socket. That's held in by a #6 kep nut, and the power tube socket has a pair of #4 screws. What happens if the amp falls off the back of a truck and one or the other comes loose? You don't want 560 volts floating around inside your chassis. So you provide structural support in the form of big fat bare wires between pin 1 and the ground on the terminal strip. This way if one comes loose, it'll be held in place by the other one. In the unlikely event they both come loose at the same time they'll stay together as a unit, and it won't migrate very far because of all the other wiring attached to it.

The same principle applies to the PT, which is held in place by a single highly torqued bolt. If that ever comes loose, you want the PT to be held in place by the wiring. If you examine the pic of the top of the PT you'll see that the back to front motion is limited by the heater wires on one side and the OT on the other. The only way it can slide is side to side. So underneath the chassis I have the AC and HT wires crisscrossed to provide an equal amount of side to side tension. The transformer would have to rip out the power switch and the main ground lug before it could move. And since it's right up against the side of the case, we're only really concerned about movement "inward" towards the reverb tank, and in that case the structural support provided by the wiring is the last resort. I'm pretty sure if the PT starts moving around you'd know about it, and bring the amp to "qualified personnel for servicing" lol.

I think about these things a lot. Because I've actually seen amps fall out of trucks. And jump three feet high when the truck goes over a pothole. Not to mention being dropped by drunk roadies (or even sober ones). I torque the hell out of the transformer mountings but one never knows, all kinds of strange things happen to amps. People put them in road cases to protect them from the airline baggage carousels but it doesn't always work. I like to lock down my amps good and hard. Grommets are good, solder lugs are good, all of the above. Turret boards are bad, PC boards are the worst. IMO the only thing PC boards are good for is to prevent caps and trannies from touching each other.

 

[scruffy]

Just get a Fender Twin Reverb amp and you're done!

Nah. Too clean. I want grit.

My amp is going to be a dial-an-amp.

You want Fender? Sure, you can have that - lush reverb and all, identical tone stack, the whole nine yards.

But flip a switch, and you turn into a high gain Marshall. The reverb drops out, the up front tone stack goes away, and instead you get an overdriven cathode follower with a Marshall tone stack right after it, just like the real thing

But sometimes I want an SLO, where I can send the overdriven lead sound into my outboard effects, then come back and use the reverb.

And sometimes I want a weirdo thin sound like you can get out of an Orange if you turn the bass cut all the way up.

Imagine all that inside a single amp. You want a different amp? Just flip a switch. If I have enough room I'll build a midi circuit for it so you can control it with a footswitch.

It's a different philosophy from modeling, for sure. Modeling amps sound great if you use them the way they were intended, but guitar players never do what's intended. Richie Blackmore's famous quote is "it sounded great just before it blew up". Spill a beer on it, "hey that sounds great". Spill another one and see what happens (try to spill it the same way the second time).

 

[GMCGeneral]

Nah. Too clean. I want grit.

My amp is going to be a dial-an-amp.

You want Fender? Sure, you can have that - lush reverb and all, identical tone stack, the whole nine yards.

But flip a switch, and you turn into a high gain Marshall. The reverb drops out, the up front tone stack goes away, and instead you get an overdriven cathode follower with a Marshall tone stack right after it, just like the real thing

But sometimes I want an SLO, where I can send the overdriven lead sound into my outboard effects, then come back and use the reverb.

And sometimes I want a weirdo thin sound like you can get out of an Orange if you turn the bass cut all the way up.

Imagine all that inside a single amp. You want a different amp? Just flip a switch. If I have enough room I'll build a midi circuit for it so you can control it with a footswitch.

It's a different philosophy from modeling, for sure. Modeling amps sound great if you use them the way they were intended, but guitar players never do what's intended. Richie Blackmore's famous quote is "it sounded great just before it blew up". Spill a beer on it, "hey that sounds great". Spill another one and see what happens (try to spill it the same way the second time).

Well as I noted, I'm a bassist myself so I need a clean amp. I get my sound out of three basses I use in my toolbox. My 2011 American Standard Precision which I have strung with Ernie Ball Cobalt flats, my MiM Player Series fretless Jazz, and my Sterling by Music Man StingRay (Ray34) which is my active bass. Both of those I use D'Addario 165XL Nickels.

 

[scruffy]

Well as I noted, I'm a bassist myself so I need a clean amp. I get my sound out of three basses I use in my toolbox. My 2011 American Standard Precision which I have strung with Ernie Ball Cobalt flats, my MiM Player Series fretless Jazz, and my Sterling by Music Man StingRay (Ray34) which is my active bass. Both of those I use D'Addario 165XL Nickels.

Well here's a trick - take your StingRay to your local Guitar Center and plug it into a Soldano SLO lead channel. Turn down all the gains, and tell me if it isn't easier to play.

I have a Music Man pickup in the bridge position of my Form Factor Wombat, it has great mids coming out of it. I built a tube preamp for it that has Soldano's stage 3 in it (the one that uses the 39k cathode resistor, except I switch it to 22k, 10k, and 4.7k). With that setup, the bass is so responsive I barely have to touch the strings. Lets me do Jaco all night long without getting tired.

The secret is the mids in the amp work with the mids coming out of the pickup. Where you get the articulation is from the mids, not the bass. Fender amps cut the mids, it's what they're known for. This trick is the exact opposite, you boost the mids to articulate your fingerstyle.

I used to use a Walter Woods blue-light through Bag End's, and got tired of the cleanliness. And I don't like pedals for bass (except for the MXR bass synth I just got, I like that very much), things like BassBalls turn me off because they're so cheesy sounding. I want gritty bass thump without having to pound the strings. After lots of experimentation the answer turned out to be Soldano's stage 3.

It's a strange concept electronically, it's a "half rectifier". One half of your signal stays clean while the other half turns into a square wave. It's very unique, no one else has it and no one else uses it for bass (that I know of). But after gigging with it a couple of times, I'll never go back, and this capability will be in all my amps.

I'm not even sure it's possible to accomplish this with transistors. Maybe it is, I don't know. But the tube version works perfectly. When you're playing with a pick you get near-perfect pick articulation and you don't have to pound the strings to get a thump.

 

[GMCGeneral]

Well here's a trick - take your StingRay to your local Guitar Center and plug it into a Soldano SLO lead channel. Turn down all the gains, and tell me if it isn't easier to play.

I have a Music Man pickup in the bridge position of my Form Factor Wombat, it has great mids coming out of it. I built a tube preamp for it that has Soldano's stage 3 in it (the one that uses the 39k cathode resistor, except I switch it to 22k, 10k, and 4.7k). With that setup, the bass is so responsive I barely have to touch the strings. Lets me do Jaco all night long without getting tired.

The secret is the mids in the amp work with the mids coming out of the pickup. Where you get the articulation is from the mids, not the bass. Fender amps cut the mids, it's what they're known for. This trick is the exact opposite, you boost the mids to articulate your fingerstyle.

I used to use a Walter Woods blue-light through Bag End's, and got tired of the cleanliness. And I don't like pedals for bass (except for the MXR bass synth I just got, I like that very much), things like BassBalls turn me off because they're so cheesy sounding. I want gritty bass thump without having to pound the strings. After lots of experimentation the answer turned out to be Soldano's stage 3.

It's a strange concept electronically, it's a "half rectifier". One half of your signal stays clean while the other half turns into a square wave. It's very unique, no one else has it and no one else uses it for bass (that I know of). But after gigging with it a couple of times, I'll never go back, and this capability will be in all my amps.

I'm not even sure it's possible to accomplish this with transistors. Maybe it is, I don't know. But the tube version works perfectly. When you're playing with a pick you get near-perfect pick articulation and you don't have to pound the strings to get a thump.

I like how my basses sound now. And the only time I use any type of preamp is at my church as we go directly to the board. There I use a GK Flex for that purpose.

 

[scruffy]

This is what the operating point of Soldano's stage 3 looks like:

 

[scruffy]

I like how my basses sound now. And the only time I use any type of preamp is at my church as we go directly to the board. There I use a GK Flex for that purpose.

Aha. Okay well, church music is kind the opposite of what I do.

I'm an old school rocker who acquired jazz chops. But I use a fretless for jazz - for rock I want to be loud and proud.

I'd get bored to tears playing church music all day (or even for a few hours lol). Fretless "mwah" is good for church sometimes, if your music director doesn't get mad at you for drawing attention to yourself.

 

[Chuz Life]

Antek as4t400 with 70v bias tap

120/230 4 wire primary (two coils)
2x 400v/500 mA each tapped at 70v
2x 6.3v 4A

DC output full wave = 560 volts

Two KT-88's at full power deliver 312 v each to the OT for a total of 625v RMS, which is then stepped down by the OT to 28v at an 8 ohm speaker. Total current draw at full power is 318 mA, split between the tubes.

Ultralinear KT-88's require about -85 volts bias to get 50 mA quiescent current, at which point they're dissipating about 28 watts each. Total push pull gain is about 12.5 from a 50 V RMS input. You get about -95 volts DC out of the 70 v transformer tap which you then need to filter because it's half wave.

Total heater current is 3.2 amps for the power tubes and 2.1 amps for the rest. So with these specs, the power transformer never gets stressed, and the OT is operating at top of spec. A 2A HT fuse will protect the output stage in the event of a shorted tube or capacitor. Since there are huge power capacitors there is considerable surge current at power on so we need a Slo-Blo fuse on the mains.

The 12AU7 driver stage has a gain of 10 and an output impedance of only 15k ohms, so we use 100k bias resistors to supply sufficient current to the KT-88 grids. To capture the 31 Hz from the low B on a bass we can use .1 uF coupling caps from the driver to the KT-88's.

When I bring this up I'm going to make sure it's DC-hapoy first. We want 50 mA on the KT-88's, and we want exactly 450 volts supplying the driver stage. To do this I'm going to have to wire up all the rest of the tubes too (for DC only, so leaving out all the coupling caps), because this is the only way I can trim the resistors in the power supply. The reverb wants 420 volts, the PI wants 390, and the cathode follower wants 375. Then 360 and 350 for the preamp tubes.

So that's the plan. Wire everything up for DC, bias the power tubes, trim the power supply resistors, and then start installing the audio.

In the pic of the underside of the chassis, the entire upper right quadrant is power only, no audio whatsoever. It's the hot zone where the AC and all the power transformer wires run. Everything south of the main ground though, is absolutely pristine and clean. The only thing in the upper left quadrant is the output transformer, the speaker wires run along the edge of the chassis to the speaker jacks. On the other side the primary drops straight down to the power tubes, it's just an inch or two.

This arrangement will end up hum free at 100 watts. You can see where the reverb transformer divides the first 5 preamp tubes from the PI and driver, that point there has an audio signal >= 0.8 volts at full power, and it's 5 inches away from anything that has to do with the power supply.

I definately need to brush up on my tube theory. Is there an advantage to using tubes in the power supply section (rectifier tubes vs. Diodes)?

It seems a solid state power supply would be cleaner and add less noise to the audio path.

 

[toobfreak]

My amp will be bulletproof. Example: the terminal strip next to the power tubes socket. That's held in by a #6 kep nut,

Wow, I have not met many people who know what a KEPS locknut is.

 

[Chuz Life]

Wow, I have not met many people who know what a KEPS locknut is.

Nylocks are good too

 

[toobfreak]

Nylocks are good too

Nylon-insert locknuts are great. Maybe better than KEPS. They will never loosen even in an atomic blast. Another great L/N is an Ovalock. I generally go traditional washer and nut and just apply a drop of Loctite 271. But grade 2 steel is weak. I like stainless or grade 5 or something as pound for pound, they are far stronger against breakage than plain steel.

 

[Chuz Life]

I definately need to brush up on my tube theory. Is there an advantage to using tubes in the power supply section (rectifier tubes vs. Diodes)?

It seems a solid state power supply would be cleaner and add less noise to the audio path.

Replying to my own post to share this. I used to be a maintenance tech for a local factory that had several "RF Welder/ Sealers." They were Tube type and had very high voltages and were also high wattages. (40kW was very common.) In the power supplies, the machines used diode stacks to rectify the high voltage ac from the step up transformer (1200 Vac or so) to 900+ Vdc. The stacks looked like this.

If you zoom in, you can see the diodes are actually in series on the strips. It would still mostly work, even if a diode shorted.

Just sharing for maybe some inspiration or brainstorming.

The Oscillation Tubes were about the size of a cantaloupe.

 

[scruffy]

Replying to my own post to share this. I used to be a maintenance tech for a local factory that had several "RF Welder/ Sealers." They were Tube type and had very high voltages and were also high wattages. (40kW was very common.) In the power supplies, the machines used diode stacks to rectify the high voltage ac from the step up transformer (1200 Vac or so) to 900+ Vdc. The stacks looked like this. View attachment 1151006If you zoom in, you can see the diodes are actually in series on the strips. It would still mostly work, even if a diode shorted.

Just sharing for maybe some inspiration or brainstorming.

The Oscillation Tubes were about the size of a cantaloupe.

View attachment 1151011

That looks like a 3-1000Z or some such thing.