Hello everyone!
I am pleased to announce I have started my second (from scratch) tube project!
I have previously made a low voltage line level tube preamp (I"ll insert a link to the thread I'll make here, but you can see a picture of it in my user picture) which I designed and built myself (including the chassis), but now I've decided I'd like to try a tube power amp.
I had purchased two 6CU6's after playing around with a 6CD6 sweep tube on 30V on my bench and I intended to use both 6CU6's to make a big stereo tube amp, with all new components.
Due to budget constraints, I'll be starting a bit smaller, with a single monoblock, which I will design and build myself (including the chassis).
I invite everyone to leave any comments or suggestions about this project right here in this build log, which I will be updating regularly (with pictures 😀 )!!!
I am pleased to announce I have started my second (from scratch) tube project!
I have previously made a low voltage line level tube preamp (I"ll insert a link to the thread I'll make here, but you can see a picture of it in my user picture) which I designed and built myself (including the chassis), but now I've decided I'd like to try a tube power amp.
I had purchased two 6CU6's after playing around with a 6CD6 sweep tube on 30V on my bench and I intended to use both 6CU6's to make a big stereo tube amp, with all new components.
Due to budget constraints, I'll be starting a bit smaller, with a single monoblock, which I will design and build myself (including the chassis).
I invite everyone to leave any comments or suggestions about this project right here in this build log, which I will be updating regularly (with pictures 😀 )!!!
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I've already ordered almost all of the parts I'll need but I won't spoil the surprises until they arrive.
Firstly I'll start out with what I did today, which is starting to build the chassis. I plan to have a single piece of metal that will be the middle of the tube chassis, from the back to the middle to the front, and good looking wood on the sides.
I started with a piece of metal from a scrap computer case and began drawing up my plans:
I then did most of the cutting and bending, so now the metal part of the chassis is mostly done! Also note I'll be adding a metal mesh cage to go over the top of the tube amp and cover everything.
Thank you for looking!
Firstly I'll start out with what I did today, which is starting to build the chassis. I plan to have a single piece of metal that will be the middle of the tube chassis, from the back to the middle to the front, and good looking wood on the sides.
I started with a piece of metal from a scrap computer case and began drawing up my plans:
I then did most of the cutting and bending, so now the metal part of the chassis is mostly done! Also note I'll be adding a metal mesh cage to go over the top of the tube amp and cover everything.
Thank you for looking!
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I will be following along. I have quite a few of the 12v variants of that tube in my stash. Good luck!
Well that may be a while because I'm making this up as I go, using what I have and what I've bought.
I do know however, that I'll be using a single 12au7a to drive a single 6CU6 at about 180VDC.
Today I got a bit more work done on the chassis. Its pretty much done, all I need is wood on the sides now.
Hopefully you can see that the back is at a 90 degree angle while the front is more shallow.
I think for now I'll use some scrap wood and then later on I'll buy some good plywood for the sides. Other than that all I'll have to do is drill out the holes for everything and then paint it and assemble it!
Thanks for looking!
Hopefully you can see that the back is at a 90 degree angle while the front is more shallow.
I think for now I'll use some scrap wood and then later on I'll buy some good plywood for the sides. Other than that all I'll have to do is drill out the holes for everything and then paint it and assemble it!
Thanks for looking!
Today I did a lot of work on this project. I did more work on the chassis, including paint, and I even got started on the wiring!
Hopefully tomorrow I'll get the output transformer and get more work done on the wiring, then maybe I can have an initial power up tomorrow!
Hopefully tomorrow I'll get the output transformer and get more work done on the wiring, then maybe I can have an initial power up tomorrow!
It lives!
Although its not completely finished, and it still has some kinks to be worked out, this amp is working!
Considering I didn't base this amp off of any schematics, I'm very excited that my knowledge coupled with trial and error was enough to get this amp working, and quite well I must say.
Now this is the first tube amp I've heard in person so take this very lightly, but I think this sounds amazing. Due to the small OT there is absolutely no lows, but the mids and highs sound so clear and vibrant!
I'll get some pictures soon!
Although its not completely finished, and it still has some kinks to be worked out, this amp is working!
Considering I didn't base this amp off of any schematics, I'm very excited that my knowledge coupled with trial and error was enough to get this amp working, and quite well I must say.
Now this is the first tube amp I've heard in person so take this very lightly, but I think this sounds amazing. Due to the small OT there is absolutely no lows, but the mids and highs sound so clear and vibrant!
I'll get some pictures soon!
I've run the amp for three hours today and it seems to be working fine! I have yet to add the other side of the 12au7a to the gain stage as well as work out a few other bugs but this amp is working!
Here is some pictures of it. Please note I will make some wooden pieces for the sides as well as a metal mesh cage that is removable to go over the top to protect people from heat and electricity. The front power switch and volume knob are also not currently implemented.
I'll continue to keep updating this log as well as post a schematic at some point after this is completely finished.
Don't hesitate to post any comments or suggestions!
Here is some pictures of it. Please note I will make some wooden pieces for the sides as well as a metal mesh cage that is removable to go over the top to protect people from heat and electricity. The front power switch and volume knob are also not currently implemented.
I'll continue to keep updating this log as well as post a schematic at some point after this is completely finished.
Don't hesitate to post any comments or suggestions!
The real interest is in the electrical design.
Before I have seen the schematic I have not much to comment.
I think some other members think so.
Before I have seen the schematic I have not much to comment.
I think some other members think so.
Agree with artosalo, your build looks good so far, and like many here, I'm curious to see your idea of a sweep tube SE - I have built similiar using a variation of George's (Tubelab) Powerdrive with a triode-strapped 6BC5 IF pentode driver and triode-strapped 6FW5 sweep with a UBT3 o/p trans. Please enlighten us with a schematic yes?
Hello, its time for a bit of an update.
After taking a few months break from tube amps which I spent messing around trying to design my own little 2 transistor class A SS amp (quite successfully I must say!) I have now switched my attention back to this project.
I have made some improvements to my 12AU7A circuit for the gain stage and I may be far enough along that I can draw up a schematic and show you guys, as I expect no more huge design changes, just a few resistor and cap tweaks.
So be on the lookout for more updates soon!
After taking a few months break from tube amps which I spent messing around trying to design my own little 2 transistor class A SS amp (quite successfully I must say!) I have now switched my attention back to this project.
I have made some improvements to my 12AU7A circuit for the gain stage and I may be far enough along that I can draw up a schematic and show you guys, as I expect no more huge design changes, just a few resistor and cap tweaks.
So be on the lookout for more updates soon!
Here is a look at how the mono block currently is configured. Please go easy on me as I really am not all that experienced with tube amps compared to many of you guys here on the forum.
This is just a prototype, and will slowly be improved on as the design is completely derived from my head. I just don't get the same satisfaction (and knowledge) from copying a schematic that a thousand other people use from the internet, but lets not get into that debate.
I appreciate help and suggestions, but try to make me work for it a bit, don't just give me the answer right away 😀
This is just a prototype, and will slowly be improved on as the design is completely derived from my head. I just don't get the same satisfaction (and knowledge) from copying a schematic that a thousand other people use from the internet, but lets not get into that debate.
I appreciate help and suggestions, but try to make me work for it a bit, don't just give me the answer right away 😀
An externally hosted image should be here but it was not working when we last tested it.
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I'm going to be honest, I didn't think it needed it? I hope I'm not embarrassingly wrong.
I followed a chart and basic schematic that I found in a 12AU7 datasheet to setup my 12AU7A gain stage. That schematic and chart called for only what I have on the gain stage for the amount of gain I chose (which is supposed to be a gain of 16 giving me 20V out of the gain stage).
To be more specific, the chart and schematic refers to the cathode resistor as RK, and it specifies for my current configuration my RK should be 0ohms. It also doesn't say anything about applying a negative voltage to the grid....
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you forgot the 220k bias to ground for your 12AU7A
compared 2N5551 vs 12ax7 as VAS stage, 12ax7 was much smoother to my surprise.
does your 2 transistor amp use tube amp topology?
compared 2N5551 vs 12ax7 as VAS stage, 12ax7 was much smoother to my surprise.
does your 2 transistor amp use tube amp topology?
Oh is that what the other person was referring to? If your saying I should have a 220K on the grid of the 12AU7A after the input coupling cap, then I understand what you mean but I'm uncertain as to if it is required. The chart/schematic in the 12AU7 datasheet calls for a 10Meg Ohm resistor there, and since I had none nearly that high resistance, I substituted it with air 🙂
If I do actually need a resistor there, please advise if 220K would be okay, I'm not sure if perhaps that is a general value to use on inputs.
I'd love to be able to know what impediance my OPT is but I bought a cheap used one from eBay (as you might've seen) and I forget what tubes it was used on, and thus have no way of (easily) figuring out its impediance. I almost want to say it was around 3K, but I might be completely wrong. I also never knew what impedance its secondary was made for, In fact I've used this amp with both 6 and 8 ohm speakers, which it seems to be fine with.
As far as my SS amp goes, if you mean tube amp topology as in HV and OPT's, then no my SS amp doesn't follow tube amp topology. It is a simple Class A design, wasteful, yet simple to design. Its simply a single NPN transistor gain stage, driving a large NPN transistor to a resistive load where the output is then capacitive coupled. I'm giving it about 40VDC supply and it pulls about 500MA.
I've yet to order some actual 8ohm resistors to use as a load to test the output power of both my tube and SS amps, but just using speakers on the output with 1KHz input (I know this is a horrible way to measure output considering speakers are not a constant impedance and that impedance is not the same as resistance) I get about 6Watts RMS out of both of the amps (SS measured with 4Ohm speakers, Tube with 6Ohm speakers).
As drawn in your schematic, the 12AU7 is biased through the leakage current of the input coupling cap. Don't have a 10meg, try a 2.2meg at least. 😉
Don't leave the grid 'floating'.
Don't leave the grid 'floating'.
The grid of your 12AU7 has to be biased negatively compared to the cathode.
This can be done by grid leak biasing (using electrons trickling out of the grid) using a high value resistor to ground.
Alternatively, you could use the plain vanilla version with a resistor from cathode to ground. You can then decide if you want to have feedback or not (by bypassing the resistor with a cap, so it does not affect the AC signal).
I hope this makes things clearer (even with my convoluted way of explaining).
Best,
Martin
This can be done by grid leak biasing (using electrons trickling out of the grid) using a high value resistor to ground.
Alternatively, you could use the plain vanilla version with a resistor from cathode to ground. You can then decide if you want to have feedback or not (by bypassing the resistor with a cap, so it does not affect the AC signal).
I hope this makes things clearer (even with my convoluted way of explaining).
Best,
Martin
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