4 Tube Amp From Scratch

[TubeNoob]

Hey überfuzz -

well i'm making the schematics in CircuitMaker 2000 but it won't run simulations because as i recall it says the tube definitions aren't valid or something like that.

which program is decent and free out there?

or can i download correct tube definitions from somewhere? i did some searches but came up short.

thanks for the post

[überfuzz]

I don't think there's any freeware with tubes in them... You probably have to find them or define them yourself. I use LTSpice, it's a freeware and quite ok. Sniff the net if you're interested, there's heaps of tutorials and videos. Further, you'll find tubes, transformers and shit to go with it. If you try it, let me know if there's a gnarly and I'll try to help.

[TubeNoob]

Hey überfuzz -

I looked around and it seems LTSpice is one of the better options (especially free). And i did find that they had some tube definitions and demo schematics using them on Duncan Amps.

I am going to try to rebuild the schematic with it and see how it goes, so thanks for the suggestion! That will be a big help in confirming which components need to be high voltage tolerant, too, which is cool.

Also need to research using .inc files with LTSpice because i did find definitions for all the more popular tubes, but not sure how to implement those yet with this program.



Also, wanted to check back with everyone/anyone on my OT transformer questions which were:

1) How does this transformer look for this project?
https://taweber.powweb.com/store/lopo_ot.jpg
("Flea OT" - 4k and 1.5k primaries, 8 and 4 ohm outs, 3 watts)

2) I do have the OT that came on the radio, it's only about a 1/4" smaller than this Weber one. Is it suspected that it won't sound good given that it was for a cheap old radio and not a guitar amp or some other reason? Just curious, I'm still looking at getting a new one.

[TubeNoob]

Hi überfuzz,

So I did the schematic using LTSpice and ran the simulator. It is 'running' but threw up a few errors I haven't figured out yet. I am able to poke around for voltages etc.

Errors are:

"Questionable use of curly braces" etc etc

AND

WARNING: Node U1:HB is floating.
WARNING: Node U2:HB is floating.
WARNING: Node U3:HB is floating.

(I do have power hooked up to the heaters on those valves, by the way in case that's what its ref'ing to).

Meanwhile, i'm tinkering away...

Let me know if you have time to take a look, i can export the .net list or something for you maybe? Not sure how that works.

Screenshot attached.

[JoeM]

I havent played around with any spice programs for years, but I dont recall even having seen the heaters connected, maybe it was just assumed they were connected. It does look like that's the problem with your sim. I might have a tube amp sim on my old computer, I'll check and see. The particular spice program I had did have some tube sims, and a complete tube power amp sample.

[TubeNoob]

Hey JoeM,

Thanks for posting.
Yeah they have ones with and without heaters available on Duncan Amps now. I tried the one without heaters and it said the instance had fewer connections than the component definition, and when i added the heaters, that error went away.

I have prodded around to find the nodes this new error refers to but haven't found them yet.

A tube amp sim? cool! keep me posted!

Cheers

[überfuzz]

I don't use the tubes with heaters. They simulate heating up, so you'll not get any signal through until they warm. You know like a real tube. This forces the user to widen the time span of the simulation. Annoying if you ask me. :-)

Did you try the 'normal' tubes? In your schematic there's a couple of tubes named triode. If you link to a file called; koren_tubes.inc, you'll be able to simulate say a 12ax7 triode. Google the file, I don't remember where I found it. Also, I see you've found a potentiometer. That's something I haven't used, I used two resistors. I'm going to look it up.

[JoeM]

Hey JoeM,

Thanks for posting.
Yeah they have ones with and without heaters available on Duncan Amps now. I tried the one without heaters and it said the instance had fewer connections than the component definition, and when i added the heaters, that error went away.

I have prodded around to find the nodes this new error refers to but haven't found them yet.

A tube amp sim? cool! keep me posted!

Cheers

OK, I found the program on my old laptop, it has a sample tube power amp sim. I also found the complete spice program as a zip file.

[TubeNoob]

@ überfuzz: Ah i didn't know that about longer sim time. Yes, i did try the basic triode/pentode, i guess i figured if i could put in more specific models it might be better, but i'm just learning this stuff so maybe that's not really the case? I couldn't find a sim for the 6at6 so i stuck a 12ax7 there as the first stage. That potentiometer is on the Yahoo LTSpice group under 'files'. Or i can email them to you if you want (there are two).

@ JoeM: Hmmm, very cool! Don't suppose that might be a post-able or email-able file by any chance?? Thanks a lot for checking your old computer for that!


The transformer arrived so I'll be testing its voltages and working on a schematic for the power supply today, and will post that and the layout i did...


Other than those things, I'm basically waiting to start building this thing for 3 other reasons -

1) need to figure out if i'm correct in my power ratings for the resistors and caps (which i'm hoping the sim will help on)
2) if that transformer i mentioned from Weber will be right for this
3) placing an order for the parts i'm missing!

[überfuzz]

Thenoob - No need to mail them, I looked them up. Thanks! The circuit you're going to use. Is it taylor made by you or is it some known circuit. If not, it's definitely a good idea to simulate the amp. Calculate might not be so necessary cause the simulation will reveal any funky stages. Set up two voltage with a 400mV sine signal in each and alter their frequency. This way you'll see if and where the signal is breaking up. And... you know the rest, different styles guitarists aim for different break ups and voicing. (Personally I lean against the clean side of the spectrum. And use negative feed back to rough things up.)

[TubeNoob]

Cool, glad u got them!

The circuit is one i 'pieced together' and have been debugging and fine-tuning with the help of the pros on this forum. Its basically a Fender Champ type circuit with a Kalamazoo tremolo and a 6at6 as the first stage (like a Harvard or Matchless). A frankenstein for sure!

So i do have one sine wave at 400hz as the 'input signal'. U mentioned a 2nd one, where would that go?

And i'm new to sims, so how do you look for breakup? Would that be monitoring the tube stages to see where distortion starts happening?

Regarding NFB, i had thought that was to reduce distortion, not correct?

Thanks for the info, sir!

[überfuzz]

Cool, glad u got them!

The circuit is one i 'pieced together' and have been debugging and fine-tuning with the help of the pros on this forum. Its basically a Fender Champ type circuit with a Kalamazoo tremolo and a 6at6 as the first stage (like a Harvard or Matchless). A frankenstein for sure!

So i do have one sine wave at 400hz as the 'input signal'. U mentioned a 2nd one, where would that go?

They go in series. You can add how many you like. Two is a good way of detecting any unbalance in the voicing. That is, you'll see if one wave, with the same amplitude, is amplified more than the other. The amplitude will be different if so.

And i'm new to sims, so how do you look for breakup? Would that be monitoring the tube stages to see where distortion starts happening?

If you get the simulator going you'll be able to alter the amplitude of the in-signal, done in the voltage gizmo. Raise the signal till the sine shape is messed up. Or even better work out how to use wave files as in-signals. The you'll hear it. (Like I said, not 100% accurate but you get a fair idea.)

Regarding NFB, i had thought that was to reduce distortion, not correct?

Thanks for the info, sir!

Spot on, with a negative feedback in the circuit the distortion in the power stage is somewhat controllable. More nfb less break up, less NFB more break up. Imagen what you'll be able to do with a potentiometer controlling it. You should google it!

[TubeNoob]

Ok, thanks for that info, überfuzz. I will look into using a wav file, too.

As for the NFB on a pot, on my Princeton build i put it on a switch as an option. I like options!!

SO, i put a fuse on the powersupply unit i got and tested it out. To my surprise, the guy who sold it to me didn't get it right in his description which said there were two 12v outputs on it. Here's what it tested out as:

195v / 14.2v / 63.4v


Hmmm, wondering about using that 50B5 again instead of the 6V6! Muhahaa! I do also have several NOS 50EH5's.


Attached is the power supply schematic...


(i wrote 12v on this schematic but it actually tests as 14.2v)

[Bruce / Mission Amps]

Wow this is quite a thread... and I'm not going to read every post or reply either.
However, there is such a thing as a 12V6GT by GE.
Send me your snail mail address and I'll send you some parts to end this thing....

[TubeNoob]

Well, life took a bit of a turn in the past 2.5 yrs since my last post to put it mildly, but i do find myself back in the states with all my lovely electronics gear out of storage and this project has been revived!

(i know that may not be a happy thought for some of you!)

I'm back to figuring out the power supply for this amp now.

I have this PT on hand: P-TF227722 (https://www.tubesandmore.com/products/P-TF22772).

I have tried simulating the power supply using a spice program and Duncan amps simulator; not getting results i can really make sense of.

The spice program is telling me that after the 10k resisitor on the B+ that the voltage goes from 320v to the millivolt range, i'm assuming this is my lack of skills at using spice.


Here's an updated schematic which includes the watt and volt ratings of the components i have on hand.


I'm trying to double check a few things:

1) Are these component ratings safe?

2) Are the component values in the ball park for getting me the correct power requirements for the tubes?

3) Does this seem like an adequate amount of B+ filtering?






Here's a preview of what it's lookin like - I've got the "chassis" almost fully drilled up. Some cool knobs, to boot - sonically essential!




Hope you have all be doing well...