This is my first tube build and I would like the members opinion of this design.
6EM7 Single-Ended Triode (SET) Vertical Amplifier
I am going to build a more conventional case and have everything to start except the transformers which should be here today. My first newbie question is, will there be a problem building the power supply section first and testing it without a load as I always do with SS circuits? I understand you need a load before turning on a tube amplifier. I have very efficient horn speakers and have heard so much about the SET that I wanted to at least hear one on my speakers. I recently build an Firstwatt F6 and am enjoying it but I really want to hear a SE SET without spending a lot of money to start with.
6EM7 Single-Ended Triode (SET) Vertical Amplifier
I am going to build a more conventional case and have everything to start except the transformers which should be here today. My first newbie question is, will there be a problem building the power supply section first and testing it without a load as I always do with SS circuits? I understand you need a load before turning on a tube amplifier. I have very efficient horn speakers and have heard so much about the SET that I wanted to at least hear one on my speakers. I recently build an Firstwatt F6 and am enjoying it but I really want to hear a SE SET without spending a lot of money to start with.
Hello wdecho 
I know you from another forum, I am "thesloth" on that forum. Yes I know how clever of me to use Phish songs for my handles.
I use large resistors to load power supplies. You would want a 50 watt resistor around the 3k value for 86mA. I am looking forward to you getting your transformers from Edcor!
http://www.ebay.com/itm/like/251299367303?ul_noapp=true&chn=ps&lpid=82
I know you from another forum, I am "thesloth" on that forum. Yes I know how clever of me to use Phish songs for my handles. I use large resistors to load power supplies. You would want a 50 watt resistor around the 3k value for 86mA. I am looking forward to you getting your transformers from Edcor!
http://www.ebay.com/itm/like/251299367303?ul_noapp=true&chn=ps&lpid=82
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I received my transformers from Edcor and I am impressed with the quality and especially the packaging. It will be a few days before I use them though.
What is your opinion famousmokingbird of testing the power supply before hooking it up to the amplifier circuit?
By the way it only took 2 weeks from the time I ordered until they were shipped.
What is your opinion famousmokingbird of testing the power supply before hooking it up to the amplifier circuit?
By the way it only took 2 weeks from the time I ordered until they were shipped.
Yes I am very impressed with Edcor too!!! 2 weeks is really good.....the last time I ordered I had to wait 2 months! But I did order like 12 transformers.
I like to test power supplies before using them with a particular circuit. I have a few high powered resistors like the one I linked in my last post that I use. Since you are building a Class A amp the current shouldn't change much during operation so a resistive load is a good approximation of the actual circuit it will be hooked up to, i.e. constant current draw. The current draw will be at it's highest during idle.
I am not a huge fan of the rheostat in the power supply. It's probably best to just calculate the exact value.
I like to test power supplies before using them with a particular circuit. I have a few high powered resistors like the one I linked in my last post that I use. Since you are building a Class A amp the current shouldn't change much during operation so a resistive load is a good approximation of the actual circuit it will be hooked up to, i.e. constant current draw. The current draw will be at it's highest during idle.
I am not a huge fan of the rheostat in the power supply. It's probably best to just calculate the exact value.
Balanced class A draws constant current (if properly balanced). SE does not.
Looking at the load lines at the link in the first post, the output section swings about 60mA of current when fully driven. Not at all constant current draw.
It will be highest when grid approaches 0V, getting close to 75mA from 42mA idle.
MrCurwen, sorry to burst your bubble but my statement is correct. Or maybe you need some new reading glasses 
Let me reiterate;
I never once said SE.
Here it is from someone much smarter than the both of us combined:
Valve Wizard: "If the amplifer runs in class A then its current demand does not change much with drive level, so as far as the power supply is concerned it looks like a constant resistance"
When looking at load lines that is the AC impedance. There is very little DC resistance in the primary of the output transformer so the DC current draw will cause very little drop in voltage.
I stand by what I said in that a resistive load is a perfectly good approximation to test the power supply for this circuit.
Let me reiterate;I never once said SE.
Here it is from someone much smarter than the both of us combined:
Valve Wizard: "If the amplifer runs in class A then its current demand does not change much with drive level, so as far as the power supply is concerned it looks like a constant resistance"
When looking at load lines that is the AC impedance. There is very little DC resistance in the primary of the output transformer so the DC current draw will cause very little drop in voltage.
I stand by what I said in that a resistive load is a perfectly good approximation to test the power supply for this circuit.
May i ask why? Datasheet limitation or some other consideration? Sorry i am on the phone so i can't check 6EM7 datasheet yet. I thought 5x the plate resistor of the preceeding stage (100k) is a good value to not overload it?
Seriously I question why but I didn't really want to ask. I usually shoot for 10x for best results. I believe the output Z of first stage is somewhere around 28k, I wouldn't go lower then 270k. But then you got to go with a bigger coupling cap. Personally I would use 470k (I don't know the reason for the 500k value in original schematic).
Thanks everyone.
I have noticed a big difference already in building tube vs SS, drilling holes. A lot more for a tube build. I bought a CL90 to install on the mains but I also have a CL60 on hand. Any thoughts on using one and which one would be better. From what I have read the CL90 is 2 amps vs CL60 5 amps. Also I am a little confused about grounding. I notice on the schematic that the amplifier ground is not connected to the chassis ground. On the SS amps I have built I have always connected both sometimes with a CL60 from Amp ground to chassis ground for Class A. Are they kept separate on this amp?
I have noticed a big difference already in building tube vs SS, drilling holes. A lot more for a tube build. I bought a CL90 to install on the mains but I also have a CL60 on hand. Any thoughts on using one and which one would be better. From what I have read the CL90 is 2 amps vs CL60 5 amps. Also I am a little confused about grounding. I notice on the schematic that the amplifier ground is not connected to the chassis ground. On the SS amps I have built I have always connected both sometimes with a CL60 from Amp ground to chassis ground for Class A. Are they kept separate on this amp?
Hi wdecho, I just built the same amp using 13em7 tubes and posted it on diyaudioprojects. I was unsure of my power supply so I breadboarded the whole thing first, which turned out to be a good move. I originally followed Tom McNally's version and parts values but this didn't work out well. I switched to Suncalc's amp and parts values and it works fine. I don't know if lowering the grid leak resistor would improve this or not. Larger value coupling caps didn't improve mine so I kept my parts like Suncalc's design. I'm using a SS bridge rectifier without a CL90 and it works fine. I also have separate safety and circuit grounds. It's a good sounding amp, you'll like it!
Are you making that exact chassis? He doesn't ground the chassis because, well it's wood, it's not conductive.
If you are using a different chassis can you take some pictures and post them. Also if you are using a different chassis do you have a layout down yet? Basically keep the power supply away from the input stage. Orient the magnetics on different planes. Twist all heater wires tightly and keep them short and away from sensitive wiring. As for grounding what has consistently worked out well for me is to imagine all the currents and keep the the sensitive stage currents "upstream" in a bus ground configuration. So I ground the beginning of the bus at the input and the end usually at the power supply C1 ground. Keep the large currents like power supply and power tube as close to the C1 side ground and then keep all the first triode grounds near the input. Ask 5 different people how they ground and you might get 5 different answers. But in short just try and avoid current loops.
I have never used an inrush current limiter so I have no comment. With such low capacitance in the power supply and the 6EM7 heater current is less than an amp I wouldn't even bother. If your amp had SS rectification with 20,000uF input C then yeah maybe install a current limiter
If you are using a different chassis can you take some pictures and post them. Also if you are using a different chassis do you have a layout down yet? Basically keep the power supply away from the input stage. Orient the magnetics on different planes. Twist all heater wires tightly and keep them short and away from sensitive wiring. As for grounding what has consistently worked out well for me is to imagine all the currents and keep the the sensitive stage currents "upstream" in a bus ground configuration. So I ground the beginning of the bus at the input and the end usually at the power supply C1 ground. Keep the large currents like power supply and power tube as close to the C1 side ground and then keep all the first triode grounds near the input. Ask 5 different people how they ground and you might get 5 different answers. But in short just try and avoid current loops.
I have never used an inrush current limiter so I have no comment. With such low capacitance in the power supply and the 6EM7 heater current is less than an amp I wouldn't even bother. If your amp had SS rectification with 20,000uF input C then yeah maybe install a current limiter
I am using a conventional chassis. I just finished installing all the hardware on my chassis so the next part is the electronic parts. From my research on the net I found what you say about grounding true, different methods. On solid state everything goes to a star ground and pretty much that is it. I will leave off the inrush current limiter on this amp. I am not building this amp for a showpiece but for hearing a SE SET in my system. I am using a large baking pan for the chassis and a piece of wood for the pan to sit on. Cheap DIY is me.
Other consideration.
However I take my recommendation back; the resistor should be a big value.
Explanation: That resistor has two things to consider. I was only thinking of one, and not the other.
1) Like you say, it presents a load for the preceding stage. 5x value is indeed wise.
2) It's in the grid current loop. For this, the ideal impedance to drive the grid is as low as possible. I've found that pretty much all tubes benefit from proper grid drive, some more, some less. I use source followers to drive output stage grids always.
Since it's been years since I last built audio reproduction with resistor plate loads, I simply forgot the first point. The plate loads I use are ok with whatever so it didn't occur to me.
Tubes that have a very large pulse current capability (6EM7 is intended to drive the vertical deflection circuits in larger televisions) often in my experience eat a lot of grid current. That was the reasoning behind my suggestion. But since the first stage has such a high output impedance, it must remain 500k or so.
I would still make the cathode cap bigger. Or replace it with a LED, fed extea current via resistor from B+.
You can star ground a tube amp, or anything for that matter. I never like star grounding or maybe I just never understood it
My understanding is that you isolate different sections of the amp and then bring all of their grounds to one single point, usually at the chassis ground. This method still has no guarantees that you won't run into a ground loop. BTW I like the baking pan chassis, cheap, sturdy, and effective.I finished my 6EM7 amp yesterday and am impressed with the sound. The 2 watts are more than enough for my 103 db horns and even sound real good with a pair of 87 db test speakers. A very large soundstage with pinpoint centering of the vocals. Decent bass with a very smooth midrange and treble. I have a 5.5 cubic inch sub with a sealed 15 inch subwoofer for low bass anyway. The cost was around $250 which is as cheap as you can build a Class A SE SET. I am now officially a tubehead.
And I take it you must mean 5.5 cubic foot sub rather than cubic inch?[/QUOTE]
Yes, my mistake.
I have not held a camera in years but it did happen. It really is not much to look at on a baking pan and no way will I show my bird nest wiring underneath. I admire builders that take the time and effort to make a neat wiring job and show case chassis but I am more after the sound and do not really think I will use it as my main amplifier but that may change. About as cheap as you can build a SET if you can get by with 2 watts.
Yes, my mistake.
I have not held a camera in years but it did happen. It really is not much to look at on a baking pan and no way will I show my bird nest wiring underneath. I admire builders that take the time and effort to make a neat wiring job and show case chassis but I am more after the sound and do not really think I will use it as my main amplifier but that may change. About as cheap as you can build a SET if you can get by with 2 watts.
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