I'm tired of anemic guitar amps!

[Chuz Life]

Here Chuz Life, just for you.

I don't want you getting mad at me for a little thing like this.

I did like you said, stripped an old AC line cord.

View attachment 1157046

I promise to straighten the wire out before installing the tubes.

Dude that's awesome!

Much respect!

 

[scruffy]

Definitely deburr that hole.

That's original, not one of mine.

There is however a slight problem now. I have to drill an additional hole for that pesky terminal strip, and it has to be done from the chassis side for proper positioning.

I don't want to end up with bits of metal inside the cans. I was thinking.... two sided low-tack painter's tape? I could shape it into a little well around the hole, and hope the tape catches most of the burr. Then lift off the remainder with more tape.

Is there a better way to do this?

 

[Chuz Life]

That's original, not one of mine.

There is however a slight problem now. I have to drill an additional hole for that pesky terminal strip, and it has to be done from the chassis side for proper positioning.

I don't want to end up with bits of metal inside the cans. I was thinking.... two sided low-tack painter's tape? I could shape it into a little well around the hole, and hope the tape catches most of the burr. Then lift off the remainder with more tape.

Is there a better way to do this?

Do you have a can of compressed air or contact cleaner? I'd just drill it and blow it out. (long as power is removed)

 

[toobfreak]

That's original, not one of mine.

Well, I guess like they say, time is money. But you can still deburr them. Actually, I'm starting to notice several holes in your photos that show burrs needing removed. Call me a Sheldon, but I'm of the philosophy that whatever can go wrong often does go wrong.

There is however a slight problem now. I have to drill an additional hole for that pesky terminal strip, and it has to be done from the chassis side for proper positioning.
I don't want to end up with bits of metal inside the cans. I was thinking.... two sided low-tack painter's tape? I could shape it into a little well around the hole, and hope the tape catches most of the burr. Then lift off the remainder with more tape.
Is there a better way to do this?

Hard to say without being able to see it. Sounds to me like I might just remove the cap entirely and just eliminate the problem. Doesn't sound like anything I'd want to gamble on. Lots of power in a tube amp.

 

[Chuz Life]

Well, I guess like they say, time is money. But you can still deburr them. Actually, I'm starting to notice several holes in your photos that show burrs needing removed. Call me a Sheldon, but I'm of the philosophy that whatever can go wrong often does go wrong.


Hard to say without being able to see it. Sounds to me like I might just remove the cap entirely and just eliminate the problem. Doesn't sound like anything I'd want to gamble on. Lots of power in a tube amp.

There are not many caps that are open enough to get a contaminate inside.

A variable, I suppose but those are in radios, not amps.

 

[toobfreak]

There are not many caps that are open enough to get a contaminate inside.

True, but it only takes one little piece to get wedged in the lip where the vinyl outer cover of an electrolytic cap meets the bare metal underneath to then come loose and short something. I can't count how many times I've found pieces of stuff lost in odd locations that are seemingly impossible that I said to myself: "How the hell did you get in there?"

A variable, I suppose but those are in radios, not amps.

View attachment 1157058

I've had a lot of cool things over the years like an old AM transmitter out of a submarine that one of my instructors gave me. Or this radio I saved that I still have put away upstairs--- it was out of a 1919 Eveready AM tube radio, I finally threw the wood cabinet away because it just needed too much work, but I saved the radio and the tubes in it are this odd tapered shape that starts out narrow from a 4-pin base and gets bigger towards the top with a perfectly round dome.

But the tuning capacitor is this huge ganged capacitor in a big brass can. I keep telling myself that one of these days, I'm going to totally rebuild it as a working radio to sit on the table. I even saved the speaker (it is a special speaker that is part of the circuit).

 

[toobfreak]

It's been a few days since we heard anything, so I thought I'd bump the thread. I'm guessing the amp is in some final stages of problem solving/ rework/ and getting the bugs out. I've also considered how fast this amp has come together, a project that probably would have lasted me the entire summer.

I've very fastidious, I tend to lay out drawings and plans and details, laying out parts, testing components, measuring and fitting, fiddling around, then building stages in my mind thinking things through, and making paper templates and laying things out. It takes me forever to get stuff done but I'm painstaking in my approach thinking several steps ahead often detouring to effect elaborate, unique solutions to problems as they are encountered.

I've often told myself this is because I enjoy the process as much (or more) than the end goal itself. I don't know. But I remember back in the 90s building a prototype off the plans of someone at work and other engineers gathering around admiring how I took the complexity of their circuit and laid out the wiring in my head so that when built on board, it was as neat and organized as a button.

Back in the 1980s building a souped up street rod, I contemplated ripping the entire dashboard out, cutting out the panel that held all the gauges, then replacing it with a sheet of brass cut out for the exact instruments I was using (the car had many extraneous Autometer and Sun gauges). It even had a gauge which measured the temperature of the transmission fluid.

But alas, I never did it, I just mounted the gauges on top the dash, steering column and under the dash and wimped out.

 

[scruffy]

It's been a few days since we heard anything, so I thought I'd bump the thread. I'm guessing the amp is in some final stages of problem solving/ rework/ and getting the bugs out.

Yes. And, I was waiting for parts. They took an extra day to arrive because of the holiday.

Let's see, here is the bias fix, it didn't require drilling any extra holes. Now you can see the bottom hole for the reverb posts.

The other fix requires me to drill a new hole for the inverted terminal strip, and I wanted to wait till the parts arrived because there are still a couple of additional holes that need attention.

I checked out the hole you pointed out with the burr. It was the middle hole for one side of the reverb tank. Turns out, the outer two holes are burr free and pretty, whereas this one looks like it was drilled by hand. It was a kloodge, lol.

Maybe they only discovered the tank was moving around after people started complaining, who knows. The fix works, it keeps the tank in place.

Anyway... next step is to complete the replacement of the other terminal strip and then adjust the power chain for the proper voltages. I saved some old tubes for this purpose, and that'll get done "before" installing and biasing the output tubes.

Meanwhile, I haven't done anything about the front panel yet (other than cleaning it). However there are several candidates for cosmetic front panels saved in my bookmarks. Probably that will take some time, and I might have to send them the existing panel to get it done right. While that's in progress, there's still a lot of work - the biggest thing is wiring all the shielded cable between the tubes and the front panel. (Can't really set the audio levels till that's done).

I'll try to drill the rest of the holes tomorrow, there's one more can and a tube socket, plus the power strip and a strip for the negative feedback connections.

 

[Sherlock Holmes]

Yes. And, I was waiting for parts. They took an extra day to arrive because of the holiday.

Let's see, here is the bias fix, it didn't require drilling any extra holes. Now you can see the bottom hole for the reverb posts.

View attachment 1158064

The other fix requires me to drill a new hole for the inverted terminal strip, and I wanted to wait till the parts arrived because there are still a couple of additional holes that need attention.

I checked out the hole you pointed out with the burr. It was the middle hole for one side of the reverb tank. Turns out, the outer two holes are burr free and pretty, whereas this one looks like it was drilled by hand. It was a kloodge, lol.

Maybe they only discovered the tank was moving around after people started complaining, who knows. The fix works, it keeps the tank in place.

Anyway... next step is to complete the replacement of the other terminal strip and then adjust the power chain for the proper voltages. I saved some old tubes for this purpose, and that'll get done "before" installing and biasing the output tubes.

Meanwhile, I haven't done anything about the front panel yet (other than cleaning it). However there are several candidates for cosmetic front panels saved in my bookmarks. Probably that will take some time, and I might have to send them the existing panel to get it done right. While that's in progress, there's still a lot of work - the biggest thing is wiring all the shielded cable between the tubes and the front panel. (Can't really set the audio levels till that's done).

I'll try to drill the rest of the holes tomorrow, there's one more can and a tube socket, plus the power strip and a strip for the negative feedback connections.

Are you certain this is connected the right way around?

 

[scruffy]

Okay, well, here she is. She should be DC happy at this point. (I'll check it thoroughly before beginning testing).

You can see the 5th can and the extra tube socket, and the reverb posts.

 

[scruffy]

From this point forward things get intricate. There will be wires (console cable) all over the place. Part of the point of DC testing is to make sure the underneath (parts) layer works, because it'll be hard to get to after this.

Stage 1 of this amp has a gain of 80, it'll boost a guitar signal up to about half a volt. The signal gets cut in two before the gain control, which feeds stage 2. Stage 2 has another gain of 80, so it takes the 1/4 volt up to about 20 volts. Then there's a tone stack, which is another 50% cut. Stage 3 has a gain of 60, which at full input pushes it way up into overdrive. The first 3 stages are all 12ax7.

The high drive is required for the cold clipper, which is stage 4. It has a gain of about 0.9 when fully clipping. Then that feeds the cathode follower, which is stage 5, it has another gain of 60.

You obviously don't use all this gain in real life. The idea is you're switching stages in and out depending on what kind of sound you want. There are level controls between each stage. Typically you run them about 1/3. At the end of stage 5 the signal level is reduced by a factor of 50, so basically all the gain you get from the various stages ends up around 2 to 5 volts.

That signal then feeds the reverb, and the reverb amp has another gain of 60, which is once again reduced by a factor of about 10, and that then feeds the master volume through another tone stack. So all told the output of the reverb amp is back around 5 volts. Only 0.8 of which is needed to drive the KT-88's to full output.

So you have a remarkable choice of where you want your gain to come from. Each sound is slightly different. You can get a nice clean sound out of the cathode follower if you don't drive it very hard. Or you can get a screaming lead by simply driving it harder. You can switch out both tone stacks and stages 3, 4, and 5 to get a tweed sound with just a volume control and a passive tone control, just like a tweed Deluxe except at 100 watts. The difference is you're pushing KT-88's instead of 6v6's. You can push them as hard as you want. (I recommend four EVM-12L's in Thiele cabs, either a pair of 2x12 Doctor Z's, or four KK audio cabs piled 2 on 2).

The holy grail is a fretless bass through this amp, with just a smidge of cold clipping (and no cathode follower). In that event use two Mesa Diesel cabs with EVM-15L's. They won't complain but they'll be breathing awful hard.

 

[Chuz Life]

From this point forward things get intricate. There will be wires (console cable) all over the place. Part of the point of DC testing is to make sure the underneath (parts) layer works, because it'll be hard to get to after this.

Stage 1 of this amp has a gain of 80, it'll boost a guitar signal up to about half a volt. The signal gets cut in two before the gain control, which feeds stage 2. Stage 2 has another gain of 80, so it takes the 1/4 volt up to about 20 volts. Then there's a tone stack, which is another 50% cut. Stage 3 has a gain of 60, which at full input pushes it way up into overdrive. The first 3 stages are all 12ax7.

The high drive is required for the cold clipper, which is stage 4. It has a gain of about 0.9 when fully clipping. Then that feeds the cathode follower, which is stage 5, it has another gain of 60.

You obviously don't use all this gain in real life. The idea is you're switching stages in and out depending on what kind of sound you want. There are level controls between each stage. Typically you run them about 1/3. At the end of stage 5 the signal level is reduced by a factor of 50, so basically all the gain you get from the various stages ends up around 2 to 5 volts.

That signal then feeds the reverb, and the reverb amp has another gain of 60, which is once again reduced by a factor of about 10, and that then feeds the master volume through another tone stack. So all told the output of the reverb amp is back around 5 volts. Only 0.8 of which is needed to drive the KT-88's to full output.

So you have a remarkable choice of where you want your gain to come from. Each sound is slightly different. You can get a nice clean sound out of the cathode follower if you don't drive it very hard. Or you can get a screaming lead by simply driving it harder. You can switch out both tone stacks and stages 3, 4, and 5 to get a tweed sound with just a volume control and a passive tone control, just like a tweed Deluxe except at 100 watts. The difference is you're pushing KT-88's instead of 6v6's. You can push them as hard as you want. (I recommend four EVM-12L's in Thiele cabs, either a pair of 2x12 Doctor Z's, or four KK audio cabs piled 2 on 2).

The holy grail is a fretless bass through this amp, with just a smidge of cold clipping (and no cathode follower). In that event use two Mesa Diesel cabs with EVM-15L's. They won't complain but they'll be breathing awful hard.

scruffy, do you intend to have all the stages powered all the time, or will the unused (unselected) stages and tone stacks be powered down when not selected? For a little less load on the PS?

 

[toobfreak]

Okay, well, here she is.

Hubba hubba. That's a lot of work. Glad I'm not the one doing it all.

 

[scruffy]

scruffy, do you intend to have all the stages powered all the time, or will the unused (unselected) stages and tone stacks be powered down when not selected? For a little less load on the PS?

All stages powered all the time. There's plenty of juice, and that way you don't have to wait for tubes to warm up.

 

[scruffy]

So... every knob on this amp pulls out.

Example: in the tone stack, you can pull on the treble knob for extra brightness, and pull on the bass knob to bypass the tone stack entirely. When you pull on the midrange knob it shifts the frequency by about 200 Hz, so depending on whether you're playing guitar or bass (or baritone guitar) you can get different emphasis.

Digi-Key has the non standard pullout values in solid shaft pots. I require DPDT, and if you want the normal CTS-type bushing and thread you can get the appropriate Bourns pots for about 5 bucks each.

 

[scruffy]

Two tidbits for today. Two front panel switches. One for the cathode caps in the first stage, the other for the coupling caps. The cathode has about 2vdc on it, so any cap you put there is going to charge. To avoid pops when switching, I charge them ahead of time, by running them through a high value resistor. 47k works, but I use 2.2 meg. That's 1000x the value of the cathode resistor. You can calculate the time constant, it's only a few seconds. To switch a cap in I just short the resistor. There's 0.68 uF like a lead Marshall, 4.7 uF which is delicious for rhythm guitar and gainiac sounds, 25 uF like a Fender, and 220 uF for bass.

The coupling caps are switched like an Orange. It's just a bunch of capacitors in series with taps. It's reasonably important they be of the same type, except perhaps for the last one which is your super-thin sound.

https://schematicheaven.net/newamps/orange_mkii1972.pdf

 

[scruffy]

Stage 1& 2 done.

 

[Sherlock Holmes]

Stage 1& 2 done.

View attachment 1159579

Is there a schematic for this? may we see it?

 

[toobfreak]

Is there a schematic for this? may we see it?

Better yet, maybe for $3500.00, Scruffy will build you one?

 

[Sherlock Holmes]

Better yet, maybe for $3500.00, Scruffy will build you one?

I'm an electronics engineer, if I wanted to build one I would.

I asked if he was sure that electrolytic was wired the right way around, no response, but he'll know soon enough I guess.

The irrational devotion to "tube sound" should have died off by now, its akin to those who obsess over speaker wire, seeking oxygen free silver conductors and other superstitious nonsense.