Thanks Tom, but I would only consider building something like this for a friend I've made at the DIY events, and they would have to do all the tedious wood working....
Ive been wanting one of these for a long time. They are kind of pricey so i haven't invested in it yet. Some day i definitely need too do it. The wiring portion is my least favorite portion of this hobby. Thats why ive had a finalist center channel sitting there for 1.5 years waiting to solder the leads up and glue front baffle on. The sure 4x amp board is sitting too. The speaker selector switch is sitting as well. I enjoy the woodworking part!
What are the dimensions of the wood portion of the amp? If you have a rough dimension of the holes and stuff i can atleast draw it in a cad program amd dimension it out.
Ive been meaning to make a spline jig for a router table or table saw maybe this is a good opportunity to make it.
I enjoy the soldering piece, which if I ever find time I'll bother the crap out of Craig and build one. The part that has stopped me is the testing and setting the bias.
Mike I am the opposite. I love bending and soldering leads and wires. I don't hate the wood working part, but finishing it is by far my least favorite part.
For anybody interested in tube audio - I just stumbled across this site - http://http//vinylsavor.blogspot.com/ He has a Tube of the month column, but sadly I don't think he's covered the 6V6.
I like the woodworking part, as most of my recent builds have been a geometrical challenge. The finishing is a lot of "will this come out okay?" The xover is the most fun part for me. I have currently about 5 xovers laid out and the cabs aren't even built for them yet.
I just started the internal wiring. This first step is probably the most important. A solid earth ground to the top aluminum plate is absolutely MANDATORY for safety. A star washer that cuts into the metal is required. I do this on every project, even lower voltage stuff like the class D project. There will be one more very important safety step (a low impedance connection from the B+ power supply common to the case) which I will show/explain later.
Also notice there is a rubber grommet where the transformer leads pass through.
I forgot to mention, I am using a all in one IEC power jack and fuse. The Hot lead is strapped directly to the fuse (you can see the strap above and to the left of the green ground terminal. If I had chosen to use a standard power jack and separate fuse holder it is important that you wire directly from the Hot terminal to the fuse first, then over to the power switch. I have seen projects that were wired from the jack to the switch first, then to the fuse. This leaves all the wiring before the fuse unprotected! Not safe. On a tube project the input current required is pretty low, less than 1 amp for this project. So I will choose a 1 amp fuse. That allows the use of smaller gauge wire which is much easier to work with. If I miswired it like I mentioned before and a short circuit happened in front of the little fuse, the current available before the house circuit breaker tripped could be 15 or 20 amps x 150% for up to 1 second. Using 20 awg or smaller wire means fire!!!
Making a little progress on this day off work. Twisting these leads are not a necessity but it helps keep things looking a lot tidier. The green wires from the transformer to the terminal strip are the 6.3 VAC tube filament (heater) wires. I will tightly twist the wires from that terminal strip over to the 6V6 tubes' sockets to eliminate any 120 Hz hum. In my experience DC heating is not required for a quiet tube project. I build my projects large enough that I don't have to cram everything in tight quarters. I can have the entire Power Supply on one half of the amp and the sensitive high gain circuits generously spaced apart on the other half. Works for me...
Just for info: - The black wires are 120 VAC from the jack/fuse to the front power switch and to the primary of the transformer. - The yellow wires are the 5 VAC heater leads for the rectifier tube. - The red wires are the HT (high tension) 275 - 0 -275 VAC to the rectifier (so 550 VAC between them!!!). Can you say "Lethal voltage"? The unattached red lead is the center tap of the HT, it becomes the ground point of the power supply.
I'm surprised no one has asked why the bottom side of the top aluminum plate looks tan instead of shiny aluminum. I forgot to mention that I chem-filmed the top plate with Alodine 600 before I painted the top side. Totally not necessary, but what the heck, I work at a metal finishing/plating company. One of these days I'm going to chrome, cad, or nickel plate amp parts... just because I can
I loved following your threads on PETT and now, what can I say? You go man!! The fact that you're documenting your tube greatness here, makes me blush like a hot tube. Wait is that not PC? #tubes #pwrryd
Thanks Bryan! I love looking at other people's project pictures and thus enjoy sharing mine with you guys. Obviously I do not create step by step instructional pictures that are good enough to follow along and build your own. But my hope is that simple progress pictures might make someone think "Hey, that's not so difficult. I could build that". Broken into small chunks it really isn't any harder than soldering up speaker crossovers. A single "under the hood" picture of a completely finished tube amp can look way more complicated than it really is.
Back in town and I have some time today before heading back to work tomorrow.
I just finished up the power supply section of this preamp. Coming off the rectifier tube I have a capacitor input C-L-C-L-C filter. The inductors are 1.5 Henry and the caps are 100 uF (first cap only 22 uF, limited by tubes peak current capability). The inductors are quite a bit more expensive ($17 each) than simple power resistors but they work much better in filtering out the AC ripple without dropping so much B+ voltage. Their DC resistance is only 56 ohms, so at 44 mA load current they only drop about 2.5 volts each. But at the 120 Hz ripple (full wave rectification) they have an XL of 1131 ohms.
I commented earlier in the thread that I was going for a little cleaner looking top this time. So instead of drilling a bunch of holes and having the fastener heads showing that hold terminal strips, I opted to use epoxy. Should be plenty strong, the electrical components don't really weigh much. Four 3-position terminals is all I need for this simple circuit.
Soldered in a few components today. The beauty of vacuum tube preamps is the simplicity (lack of parts) of the design.
The blue resistors are the plate loads, 5Kohm 10W resistors. The red Audyn caps are the output decoupling caps. The little 2 watt green resistors are the cathode bias resistors (680 ohm). In parallel with them are the two brown electrolytic 1000 uF bypass caps.
Craig , you make it look easy . Very professional and clean sir ! I have an old HH Scott amp from a console radio that I would like to get going. Pretty sure its a mono amp but this gets me pumped and wanting to see if I can get it going.
Comments
I want to hear it.
I vote black knob as well
What are the dimensions of the wood portion of the amp? If you have a rough dimension of the holes and stuff i can atleast draw it in a cad program amd dimension it out.
Ive been meaning to make a spline jig for a router table or table saw maybe this is a good opportunity to make it.
He has a Tube of the month column, but sadly I don't think he's covered the 6V6.
InDIYana Event Website
Also notice there is a rubber grommet where the transformer leads pass through.
Just for info:
- The black wires are 120 VAC from the jack/fuse to the front power switch and to the primary of the transformer.
- The yellow wires are the 5 VAC heater leads for the rectifier tube.
- The red wires are the HT (high tension) 275 - 0 -275 VAC to the rectifier (so 550 VAC between them!!!). Can you say "Lethal voltage"? The unattached red lead is the center tap of the HT, it becomes the ground point of the power supply.
I loved following your threads on PETT and now, what can I say? You go man!! The fact that you're documenting your tube greatness here, makes me blush like a hot tube. Wait is that not PC? #tubes #pwrryd
I just finished up the power supply section of this preamp. Coming off the rectifier tube I have a capacitor input C-L-C-L-C filter. The inductors are 1.5 Henry and the caps are 100 uF (first cap only 22 uF, limited by tubes peak current capability). The inductors are quite a bit more expensive ($17 each) than simple power resistors but they work much better in filtering out the AC ripple without dropping so much B+ voltage. Their DC resistance is only 56 ohms, so at 44 mA load current they only drop about 2.5 volts each. But at the 120 Hz ripple (full wave rectification) they have an XL of 1131 ohms.
The blue resistors are the plate loads, 5Kohm 10W resistors. The red Audyn caps are the output decoupling caps. The little 2 watt green resistors are the cathode bias resistors (680 ohm). In parallel with them are the two brown electrolytic 1000 uF bypass caps.
https://www.tubedepot.com/products/p-ts-825