I have been collecting parts for this project for several years. It started when I went to the next town over with my friend, to look at some McIntosh 40s, which he bought and the seller tossed in 2 Heathkit Williamson amplifiers because I asked what he was going to do with em.
The McIntosh 40s are now rebuilt and he and his neighbors all love them!
I didn't want to build another Williamson amplifier with these because that's already been done, alot... luckily, within the Acrosound transformer catalog there's another schematic for a 6L6 amp using the TO-300. Perfect, I'll build the one that nobody else has done.
I started by slapping some parts I already had, together into a working prototype proof of concept. B+ was about 100v low. A few resistors were glossed together to make values, but once it worked it sounded good. Best of all the bass was tight and clear. Gotta have good tight clean bass.
At that point I made a list of the components I didn't have and got them coming from mouser. Just resistors and caps... I never ordered the chassis.
At that point the project languished while I got my 1972 toyota put back together and driveable. Now that it's going into amp building season again I've got them pulled back out and I'm making chips.
I ordered 4x 12x7x3 hammond boxes for chassis, I made 4 reinforcement struts out of 1.5" angle aluminum. I acquired 4 8 Henry, 150 miliamp chokes also from mouser. Drew it all out on graph paper and then transfered it to the chassis using a center punch. The chassis are all drilled out and finished now, the reinforcement struts are responsible for a lot in these amps, they keep the chassis rigid, but also provide a mounting point for terminal strips, and they act as a nut, meaning I tap holes in them so I don't need to use nuts on my hardware. The cathode resistor for the cathode biased output stage is attached directly to the strut with 4-40 stainless screws so the strut will act as a heat sink as well. There's also a row of convection holes which allow the heat to rise out of the chassis. Last night I began wiring up the first if 4. Yes there will be 4. Two are for me, and 2 are for my friend Izeck.
Because I'm weird, I like to style my builds to keep people guessing as to when the amplifier was put together. When it looks like I built something out of Radio and television news in 1956, I'll have reached my goal. Along those lines, I've decided to build these with octal sockets for a companion preamp, which were common back in the day. Preamps often robbed their miniscule power from the power amp they were driving. I'll set mine up to run my McIntosh C8, and C8s because that's what I've got. Reconfiguring the plug is simple and it has a rca in case you wanted to use some other self powered Preamp...
Overall very fun and relaxing experience and I'm not done yet. I'll try and get a photo of the schematic up today, it's a simple one, but I've never seen, much less heard one...
Questions comments?
I missed Burning amp this year but I'll bring these next year for sure.
The McIntosh 40s are now rebuilt and he and his neighbors all love them!
I didn't want to build another Williamson amplifier with these because that's already been done, alot... luckily, within the Acrosound transformer catalog there's another schematic for a 6L6 amp using the TO-300. Perfect, I'll build the one that nobody else has done.
I started by slapping some parts I already had, together into a working prototype proof of concept. B+ was about 100v low. A few resistors were glossed together to make values, but once it worked it sounded good. Best of all the bass was tight and clear. Gotta have good tight clean bass.
At that point I made a list of the components I didn't have and got them coming from mouser. Just resistors and caps... I never ordered the chassis.
At that point the project languished while I got my 1972 toyota put back together and driveable. Now that it's going into amp building season again I've got them pulled back out and I'm making chips.
I ordered 4x 12x7x3 hammond boxes for chassis, I made 4 reinforcement struts out of 1.5" angle aluminum. I acquired 4 8 Henry, 150 miliamp chokes also from mouser. Drew it all out on graph paper and then transfered it to the chassis using a center punch. The chassis are all drilled out and finished now, the reinforcement struts are responsible for a lot in these amps, they keep the chassis rigid, but also provide a mounting point for terminal strips, and they act as a nut, meaning I tap holes in them so I don't need to use nuts on my hardware. The cathode resistor for the cathode biased output stage is attached directly to the strut with 4-40 stainless screws so the strut will act as a heat sink as well. There's also a row of convection holes which allow the heat to rise out of the chassis. Last night I began wiring up the first if 4. Yes there will be 4. Two are for me, and 2 are for my friend Izeck.
Because I'm weird, I like to style my builds to keep people guessing as to when the amplifier was put together. When it looks like I built something out of Radio and television news in 1956, I'll have reached my goal. Along those lines, I've decided to build these with octal sockets for a companion preamp, which were common back in the day. Preamps often robbed their miniscule power from the power amp they were driving. I'll set mine up to run my McIntosh C8, and C8s because that's what I've got. Reconfiguring the plug is simple and it has a rca in case you wanted to use some other self powered Preamp...
Overall very fun and relaxing experience and I'm not done yet. I'll try and get a photo of the schematic up today, it's a simple one, but I've never seen, much less heard one...
Questions comments?
I missed Burning amp this year but I'll bring these next year for sure.
I draw it on graph paper first which may seem primitive and time consuming but it's not. You can use the same graph paper to transfer the drill points to the chassis box and the strut, then they'll line up perfectly once together, or that's the theory. Also the same drawing is used to mark all 4 amplifiers in the production run. We call this process CAD.
Cardboard assisted development.
Cardboard assisted development.
"We call this process CAD. Cardboard assisted development."
I used to call it PCAD (paper CAD) There was a software program called P-CAD at the same time period but it got eaten up by a bigger fish.
Those have got to be the biggest power transformers that I have ever seen in a tube audio amp.
I used to call it PCAD (paper CAD) There was a software program called P-CAD at the same time period but it got eaten up by a bigger fish.
Those have got to be the biggest power transformers that I have ever seen in a tube audio amp.
In response to the transformers being huge...
I had 2 of them already and found 2 more on ebay, salvaged from Baldwin organs. They're very heavy and have lots of reserve power. Initially they ran a push pull 6l6 amp and about 60 small signal tubes. I did away with the 5u4 in favor of some diodes. Why would a person ever go to the effort to design and build a tube power amplifier from scratch only to cheap out on an anemic power supply.
Tube amplifier aren't cheap, and good tube amplifiers require good iron which is not cheap. What I am attempting is not expensive necessarily, but also I'm not simply buying the minimum required. I dont mind paying for the extra capacity where it matters. I already had 2 of em and I ordered the other 2 on ebay for well under what a single hammond would have cost.
There's no replacement for displacement, and there's no substitute for big heavy EI power transformers on tube amplifiers.
I've even got a few transformers that are bigger than these stashed for other projects.
I had 2 of them already and found 2 more on ebay, salvaged from Baldwin organs. They're very heavy and have lots of reserve power. Initially they ran a push pull 6l6 amp and about 60 small signal tubes. I did away with the 5u4 in favor of some diodes. Why would a person ever go to the effort to design and build a tube power amplifier from scratch only to cheap out on an anemic power supply.
Tube amplifier aren't cheap, and good tube amplifiers require good iron which is not cheap. What I am attempting is not expensive necessarily, but also I'm not simply buying the minimum required. I dont mind paying for the extra capacity where it matters. I already had 2 of em and I ordered the other 2 on ebay for well under what a single hammond would have cost.
There's no replacement for displacement, and there's no substitute for big heavy EI power transformers on tube amplifiers.
I've even got a few transformers that are bigger than these stashed for other projects.
The first thought when I saw those pictures was a memory of the Baldwin organ I restored in high school. It had been donated to the school as scrap from Victor Pianos and Organs, an old school keyboard shop in Miami that's still in business. The organ had a "tone chassis" that ran the full width of the organ and had 60+ 6SN7s on it. The power transformer on that chassis was huge and had a pair of FAT wires for the heater bus. There was an amp chassis in the bottom of the organ that I don't remember much about since it worked. Most of the wax coated paper caps in the tone cabinet had lost their wax and were leaky enough to upset the frequency dividers. I replaced them all. Changed a lot of old carbon comp resistors too.
The 3 year long vocational electronics program in my high school had a policy that if you fixed up any donated "junk" with your own parts or purchased all of the parts from the school you got a grade on your work, then got to take the "project" home. I took the organ home in 11th grade and a 1957 vintage Emerson color TV in 12th grade. It was the only color TV in the neighborhood when the moon walk that was broadcast in color happened in 1971.
That high school class was where I really learned how to melt vacuum tubes.
The 3 year long vocational electronics program in my high school had a policy that if you fixed up any donated "junk" with your own parts or purchased all of the parts from the school you got a grade on your work, then got to take the "project" home. I took the organ home in 11th grade and a 1957 vintage Emerson color TV in 12th grade. It was the only color TV in the neighborhood when the moon walk that was broadcast in color happened in 1971.
That high school class was where I really learned how to melt vacuum tubes.
If you have them and they work for your purposes….
Big EI’s look nice on tube amps. I’ve built using toroids and they are never as pretty.
But I might also be inclined to see how much power I can wring out of one of them, though. I’ll bet you could get one to pump out 300+ watts, with an appropriate OPT and tubes to drive it. Especially if I had more than one of them to play with. But then the ”appropriate OPT” would cost a pretty penny (Unless you cheat and use a power toroid). So many tube amps, so little (time*money).
Big EI’s look nice on tube amps. I’ve built using toroids and they are never as pretty.
But I might also be inclined to see how much power I can wring out of one of them, though. I’ll bet you could get one to pump out 300+ watts, with an appropriate OPT and tubes to drive it. Especially if I had more than one of them to play with. But then the ”appropriate OPT” would cost a pretty penny (Unless you cheat and use a power toroid). So many tube amps, so little (time*money).
That's why my Challenger had a 440 CID and the Camaro had a 350 CID. The Mustang looked nice, but a tired old 289 ain't going to beat a big block.......but the little FWD Dodge only had 135 CID and it was almost as fast as the Camaro. Too bad there is no equivalent for the turbocharger in the tube amp world.
A typical vacuum tube organ uses one or two triode sections as a frequency divider (divide by 2) 12 more sections are tunable oscillators. None of these stages need more than a few mA but there is an oscillator or a divider for every key on the keyboard. My old Baldwin used 6SN7s which draw 600 mA each for the heaters. Later organs used 12AU7s or specialized tubes designed expressly for organ divider use, until someone figured out how to do the frequency divider with NE-2 neon lamps. Depending on when the organ was made most of the transformer's power could have been used for making heat.
These had dual 5u4 rectifiers so we have to assume they're good for enough current to run a single channel of 6l6...
There's an unused filament winding at 12v and another at 5v for rectifier.
I may wire one or both of them into a bucking arrangement to get my 6v filament a bit lower.
It's at 6.6v iirc. Anyway here's the schematic and I should be listening to #1 by the end of the day.
I've got to finish the power supply and then I'll fire it up...
There's an unused filament winding at 12v and another at 5v for rectifier.
I may wire one or both of them into a bucking arrangement to get my 6v filament a bit lower.
It's at 6.6v iirc. Anyway here's the schematic and I should be listening to #1 by the end of the day.
I've got to finish the power supply and then I'll fire it up...
Yes, I intend to look at the amplifier a little closer today, hook up the feedback and see what sort of baseline performance it will achieve.
As I was thinking about it last night I've got a massive hum from leaving the heaters floating without ground reference. I'll need to button those up before measuring distortion.
As I was thinking about it last night I've got a massive hum from leaving the heaters floating without ground reference. I'll need to button those up before measuring distortion.