You are having TOO much fun!!1 I cracked up when the transformer fell off the stool, and you said "nothing broke" like it was nothing.... FUNNY! I live in a historic district too here in Pomona, CA., and we have 2-3K kids on Halloween also! Tons of fun! Love your videos! So much information, and just plain fun!
Hi Bill, I am still having fun. I have recently been going pretty slow on audio amplifiers but some are starting to come to my interest and I want to start building. I have been into my astronomy hobby lately and watching lots of YT videos on amateur astronomy. I bought a star tracking device and am using good telephoto lens and getting some amazing results and able to go out by myself without having to deal with the size and weight of the 10" Meade scope. That one is too much for me along. Anyway... This amp in the video morphed into a standard Williamson driver (I removed the driver board, cut a piece of aluminum and mounted two octal sockets on it for a pair of 6SN7s) and changed the 1625s to KT88s. Increased the power considerably. I think I made a later video of it - not too sure unless I look... Good to hear from you and thanks for your comments.
This is so cool. I sit here now having just stopped for the day working on my amplifier. And let me tell you, if you saw this thing your head would spin. It weighs like 200 pounds, has a 15 tube power supply, another 14 in the power amp including instrumentation... 6 modes of operation... Solid oak, custom CNC top plates...I mean it makes your little project seem really small... But here's the thing - I've been working on my amp since 1997 or even earlier. And it's still not finished. I have scrutinized over every single detail, scrounged absolutely the highest grade components, I even hired a renowned engineer to design most of the circuit and schematic. And you'll be sitting there listening to that sweet little thing you're building before I'm finished with my project for sure. With any luck, I should have first music out of this thing in Feb. after 20+ years. There's something really good to be said about being decisive like you're doing. You're building that amp very much by freehand, and that will come with some mistakes and some learning, but you'll have an awesome hand-crafted amp in no time. If you do like I do, you spend $15K in parts and it'll take you 20 years to finish.
It sounds like you are building a beauty. Some of my projects weigh in close to the 200 pound mark also. Actually, my biggest KW level transmitter is probably more like 400 pounds as it is built in a 1947 steel cabinet. Fortunately, it does have nice rollers or I wouldn't be able to move it at all. I have been building for a long time and have much of it in my head. I used to take the time to draw nice schematics, long hand, but now I usually only take notes on the specialties of the equipment I build and keep it with the instrument so when it needs repair or modification, I don't have to "reinvent the wheel" so to speak. I have already changed this one from the Poseidon board driver to a genuine Williamson driver design with 6SN7 and it does perform better. I also keep Lots of parts on hand so I don't have to discover that I am missing something and then have to order it and wait for it to ship to me and lastly... I am pretty obsessive on my building and will put fourteen hours a day into it if time permits. Thanks for sharing your experience and if you have a RUclips channel, or want to start one, please share your experience and amplifier with the world. You will meet like-minded and nice people.
@@ElPasoTubeAmps I'd love to see some video of the monster. I suppose I really should upload a video about this amp. The power supply is finished and functional, and I'm making progress with the amp every day now. I spent a TON of money on the CNC made top plate, but I have to add a few screw holes by hand to accommodate some terminal strips. The aluminum is pretty thick, and I'm having a hell of a time keeping the drill bit from walking around, even with a hole guide. Got any tricks up your sleeve for that? Luckily my first holes are hidden under transformers, but now I need to drill ones that are going to be visible. Anyway, I'll give you a quick rundown of the topology. Standard Push-Pull Parallel (or not parallel if you want) output sections, 2 or 4 tubes. It's based for KT-88, etc., designed around KT-90, and it uses Harmon Kardon Cit II OPTs. Lundahl 1660 interstage transformers handle driving the outputs and phase splitting. By turning a knob, it can run either Push-Pull or Single-End, each one in either triode, pentode, or ultralinear mode for a total of 6 operating modes. All biasing is set with 10 turn precision pots, as well as all the instrumentation and calibration pots. Drivers are 6SN7. Gas tubes, OB2, OA3, etc. are used in several places including voltage for the instrumentation. Feedback and input attenuation are adjustable via stepped attenuators, and all the 10-turn precision pots have counters with locks on them. All the octal sockets are vintage Amphenol ceramics. Meanwhile, the power supply has a HV transformer putting out 630VAC @1A into an 8 tube bridge rectifier made with 6AX4/6AU4 (TV damper rectifiers). There's a big mil surplus potted transformer putting out 30 amps of 6v filament, plus a smaller 6v filament referenced to high voltage via center tap... There are OD3 and OA3 gas tubes stabilizing the screen and bias voltages, a pair of massive 10H chokes, massive oil filter caps as well as electrolytic, and all sorts of other odds and ends. The power amp chassis contains all the metering which allows you to set bias, check voltages, check driver stage and output stage signals, etc. The whole thing connects with umbilical cords. There's also a safety circuit that shuts off HV+ and drains all the caps to ground via power resistors if either a bias fault or unplugging of the umbilical happens. But yeah - do you have any advice for keeping a drill bit from wandering when you really can't use a drill press?
@@hugeshows I spend plenty of money on new drill bits just to keep the bits from "walking around" as you say. If the hole is critical, I start with a small bit and go up in size slowly. You will end up with less burr to remove that way. Holes under the transformer is OK. It is hard to not have some "mystery" holes. But you may be able to just fill some of them with a screw and nut or a "goof" plug and it will look great. I love the fact that you are using 10 turn pots and VR tubes. I have thought of installing a switch to change between UL, triode and tetrode (beam power) mode but I would have to also come up with proper screen voltage and would likely use VR tubes. I may do just that now that we are discussing it. Something a little more special than just the Williamson designs that I keep building... I have made my NFB adjustable before but nowadays just leave it at a set value. I have noticed that with NFB turned completely out, the amplifier sounds really "alive" but THD rises sharply. I have read about using the TV damper tubes and I can not tell you off the top of my head, but check the maximum current rating of these tubes and make sure your amplifier does not need more current than they can provide. In this last amp I posted, I quickly saw that at high power, the sag in voltage from using a single 5U4 was not acceptable and the high end power suffered a lot. It is amazing how 10 cent diodes solves all these PS sag problems... I have some massive 10H 400 and 500 mA chokes but they are so huge. I just got in an order from Mouser for 1H, 300 mA and 1.5H, 500 mA chokes new from Hammond. I usually need higher current than can be easily found and 10H is not necessary but nice if we have them and room for them on our chassis. Sure sounds like you have built a beauty. As for umbilical cords - I would suggest adding an external, flexible braid ground between the chassis just for safety. I am sure you have taken proper precautions in multiple ground connections in your cords but in the event of electrical separation of the PS and amplifier, you know there would be full potential between the chassis. Just my thought on that aspect. It would be really nice to see your build on RUclips. Say safe...
@@ElPasoTubeAmps Thanks for the advice. I've made a little video for you showing the amp and how the drilling all worked out. Thanks again, and that video should be up in a couple hours.
Great! I'm very excited to see building of this amp. Nice selection of power tubes. 1625 / 807 tubes are great. But I am a little confused about the G2 of this tube. How to really calculate the voltage of this G2. Really anxious to see how you do this.
In this amplifier the tubes will be running UL because of the taps on the output transformer so the screen voltage will be the same as the plate voltage and the tube can be seen in a triode connection. I have included a link to a book by Eimac that discusses how screen voltage in tetrodes affects cathode current you might enjoy. www.cpii.com/docs/related/22/C&F2Web.pdf
I use 807s in my designs and for HiFi a pair in UL will produce in excess of 30W at 5% THD. In the guitar world, I use four in parallel push pull, class AB2 and achieve just over 130W. Nice valves. They are a 6L6 with a top cap for the anode, so it will work at 750volts without destroying the IO base..
I agree the 807/1625 is very much overlooked in the audio world but the vintage 6L6GC's can bring such a high price. As you say, the plate cap allows much higher plate voltages and as much as 120 watts output running them as a tetrode with proper screen voltage. Maybe after seeing this video, others will choose to start building with these grand old tubes just like you have been doing. Thanks for your comments.
I start with either a hole and a nibbler tool (with the lines of the hole drawn out on the chassis) or just go to a Dremel tool cut-off disk and then smooth down the side with a file. I don't have any specific tool for square or rectangular holes. It is not the easiest part of preparing holes in a chassis.
Just wondering.... Will there be a parts list and schematic so that we could build our own based on your videos? Thanks for the videos Dave. Always look forward to them, and now even more.
Hi Steve, I have never, that i can remember, posted schematics and parts list unless I just show it in the video. I do try to show the over-all schematic of the amplifiers but since I generally stick to the tried-and-true designs like the Williamson, or Dynaco or McIntosh, etc. those schematics can usually be found with a little Internet research. One set of schematics I often show are the five books that can be downloaded. Here is a link to one - lilienthalengineering.com/100-amplifiers-chapter-1/100-amplifiers-part-4 Just search for, 100 Amplifiers - Part X where X is the number 1 thru 5. They are absolutely amazing books on amplifiers. I liked these books so much I actually printed each book and bound it for my library for ease of viewing them. Hope this helps.
@@ElPasoTubeAmps I re-watched the video and saw the schematic. Thank you. I am far from a skilled wizard like yourself, but hope someday to build an amp from scratch and your videos make that dream come closer.
This one will be the Poseidon board and it is not Williamson but does deliver a drive voltage that is sufficient for the 6L6/EL34/6550 family of beam power tubes. When I start on the amps with the Svetlana SVT572-10 tubes, I am going to go to a voltage amplifier that will deliver much more drive voltage as the bias level is much higher on the low mu triodes. Those amplifiers will either be classic transformer driven (assuming I have two matching transformers for two amplifiers) or some form of CT inductor.
Hi Dave, Where do you source your chassis? I'm looking for an enclosure to house two 50A Megawatt power supplies. Nice start to the audio amp. 73 WB3BJU
Don, I order them from www.mouser.com. Here are a couple of part numbers to get you in the ball park so you will know what to type in to find them. I just ordered two 17x17x4 chassis today. They are about $60 each but the smaller ones are a bit cheaper more in the $40 range. Try these part numbers 1444-14103 or 1444-17134 You can then browse around for the size you want. I have got to tell you what just dawned on me. I assume you might know that I have already build a 833A class-B amplifier that I use on 20M SSB. I can change the bias to meet class-C operation and then use one of the huge KW level transformers I have, as a modulation transformer, that will match 8 ohms primary impedance to a secondary impedance (using the transformer what me might think of as "backwards") anywhere between 5K and 20K and then drive the 8 ohm winding of this transformer with a 400 watt solid state McIntosh amplifier. This is crazy but I think I can make it work. I will have a full, high-level, plate modulated KW of AM on 20M. I love it. That should put out a serious amount of carrier. :-) I bet everyone will just love me all at 14.286 MHz Your thoughts? 73 WA4QGA
I’m kind of confused, are you building an 807 guitar/audio amp? Or will this be part of an am transmitter ? I love 4-400’s and 4-1000’s the design of 4-400 am transmitter reminds me of the Johnson 500 (single tube) or Collins 20V (pair)
Maybe Stephen got it right below... :-) This amp with the Triad transformer will be just a HiFi amp. Mostly I like to see for myself and document the performance of some of this vintage "iron" that claim such fantastic performance. We shall see. Also, some viewers want to see how amplifiers are built so I will post a few videos on the progress as it occurs, which I hope will help others. The AM transmitter is a separate project. I have now thought that maybe all I need to do is change the bias and plate tank Z of the 833A amp I have already built and then build a large modulator for that amplifier. Maybe even use a McIntosh MC2205 that I already have that will deliver over 400 watts of audio. I have the transformers to match 8 ohms to the high Z that the plate of the 833A class-C amplifier will need. Now that would be a novel approach to AM...
@@Dukers2300 I have been charmed by the MV type 83 rectifier before. I know they use it in the TV-7 tube testers as the voltage drop is low and constant and I think I have a couple. I will have to think about it.
I’ve wanted to build a KT88 audio amplifier for a long time. What always stops me is getting the right transformers. Where do you procure yours from? Thanks!
Edcore CXSE25-8-5K for the 8 ohm output.. Edcore makes hi quality transformers.. this transformer is for Class A..if your interested I have lots of tested information.
I see dan dee below has given you a nice source. In general, I just find transformers at estate sales and from parting out military equipment. I have also been doing this for more than 50 years so I have ended up with quite a nice stash of power transformers. Output transformers are, for sure, a more difficult item to fine. However, keep in mind that, for example, a 5K to 8 ohm OPT can also be used as a 2.5K primary with a 4 ohm load (on the 8 ohm winding) or 10K primary with a 16 ohm load (on the 8 ohm winding) and so on. The amplifier in this video is a perfect example of using a 4K primary as a 8K primary by putting the 8 ohm load on the 4 ohm winding. Similarly, for example, a 500 volt CT power transformer can be used as a conventional CT full-wave for about 300 VDC or you can wire it in a bridge mode for about 600 VDC or even a voltage doubler for about 1200 volts. If you are lucky enough for your transformer to have dual primary windings, you can double (or half) the values I just mentioned. So, you may have an option with transformers that you just haven't thought of yet. Hope this helps.
I have finished all the drilling and painting and I did rotate the OPT several times looking at it but ended up laying out and cutting the holes like it is laid out in the picture. The reason is primarily to give the 5U4 a little more room as it is a very hot tube and will heat up the transformers close to it and hopefully, the wires will be long enough from the OPT transformer to reach the 1625 tube sockets without having to lengthen them. One of the things that I don't like, and it is completely unimportant, is the label on the UTC power transformer is upside down when the transformer is mounted with the connections under the chassis. I don't know why they put the UTC label on that way. Oh well...
@@ElPasoTubeAmps Thanks for your reply! Yep, an upside down sticker would annoy me too! Yes, those 5U4's get hot alright so plenty of air around them is a good thing. Looking forward to seeing it finished. Thanks..
@@paulbione5267 It is getting there. Chassis is drilled and painted and all components are mounted so just a little hook-up and we will see how it performs.
The one thing I'd emphasize as one who has built a fair number of amps; Maybe it seems obvious, but you want to get all your metalwork out of the way before you start to mount sockets & trannies and especially before you start soldering wires. Usually it's kind of awkward to drill holes with a 15-20 pound transformer (or two of them) mounted to the main surface. Usually not so bad if you are hand drilling; But on a drill press it can be irritating. Then again....If you need to drill a "forgotten" hole close to a mounted transformer, you might need an aircraft (super long) drill bit to get to it. You sure don't want to carve out 1"+ holes for tube sockets with trannies mounted. Yeah, if you have the right size punch, not the biggest of big deals, but beginners do not have the right punches. Right? And you generally don't want to drill holes in the chassis after you've placed wires, because you could injure the wires. When you look at an amp schematic and start thinking about building it; you have to realize that some parts are NOT going to be on the schematic, in many cases. Dave shows these but it's very common for a beginner to overlook the mechanical and layout considerations when the schematic does not show: an AC on-off switch; the type of AC entry, fuseholder, pilot light. What kind of pilot light? A little LED or a big #47 holder that requires a (I think) 3/4" or 7/8" hole? What if you want a standby switch? And how are you gonna handle the output connectors? Dual banana posts? Fine. You don't want those right near your 450+ volt power supply. You have to carefully drill the holes for banana plug posts if you are using separate ones or else a mating dual banana plug won't fit right. And you don't want those right next to the inputs, either. And where are the input jacks? Front or back? You sure don't want those near your big power transformer. Dave is using a PC board for the preamp section, which IMO is the way to go. If you want an input "volume" control you have to consider how close to the edge of the chassis you cut the rectangular hole for that board. (This is a lot more true if you are going to mount some tone controls) If you don't leave enough room around the preamp section, your tone controls get shoved down towards the power tubes and that's likely to be a problem noise-wise. A lot of people like to convert old tube hi-fi amps for guitar use. Many of these present problems because often there ends up being no room for tone controls; or maybe you want to add another tube stage (or two, maybe you want to add reverb or tremolo---oh, and by the way, those require some extra jacks, usually on the back) ) and you can't do it in a mechanically neat way. Or there isn't room for a parts board or tag strip and you're forced to build P2P. What about some misc tie points under the chassis, barrier strip thingys? NO SCHEMATIC SHOWS THEM! Or you want to add pin jacks for bias-adjust test points. So I apologize for spewing out all the unpleasant issues I have encountered building tube stuff. All I can say is; most "surprises" end up creating awkward, uneven, hodgepodge mounting of parts, while at the same time, it is very very difficult for a beginner to anticipate all the tomfoolery that can happen. You want to build something that looks perfect but for your first few builds, regrettably, that's almost impossible!
I think you have done a marvelous job of describing so many of the issues of homebrew equipment building, especially for the new-builder and never too late for us old-builders also to get reminded of how complicated things can get. Lastly, I might add that after a piece of equipment is built and something needs to be added it is really important to make darn sure there is nothing beneath the chassis before drilling from above the chassis. Seems pretty obvious, but stupid things can happen if one is not really careful and end up drilling a hole thru an inductor (or whatever) from getting in a hurry. Thank you for your time and your reply.
@@ElPasoTubeAmps Thanks, Dave! Just trying to share some experience tidbits. Y'know, there are big differences between building a Fender-like guitar amp (with tone controls and possibly reverb/trem controls) and a "monobloc" type amp like you show in this video. The difference revolves around; with a Fender-type amp you are usually trying to build something kind of long left-to-right and not very deep as it is at least pictured as going into a cabinet. That's completely different than building a nearly-square item like you're doing in the video. You don't that much care about how big the chassis footprint is. That has tremendous implications for parts layout. Even in a bloc type amp, it's almost a requirement to sprinkle some terminal strips around the tube sockets. You are gonna need them to mount stopper and screen resistors & coupling caps. Again; no schematic EVER shows how many tie point strips you're gonna need. By the time you have say 6-place tie point strips, these usually have two chassis mounting holes. I wish I could tell you how many times I have figured on needing a 3-place tie point strip which only needs one mounting hole, but I really need 6 or 8-place, and then the hole I drilled for the small term strip is no good and then other hole I need runs into another tube or is under a tranny. *And it's THESE holes you discover you need AFTER the wiring has been placed. Solution: There is never a penalty for over-specifying the number of tie point strips you will need and leaving a few lugs blank.* Back when you & I started building stuff, all the parts were 25 cents each. Now, every stinking part is $3 or $7 and while that isn't all that much money, 57 of them are. I move on to building Fender-type amps. You can buy stuffed or empty tag strips that carry all the R's & C's that are not mounted right between the tone control lugs. In general, those make your life easier; but to use those strips, you have to have (meaning, you have to plan for) a fair amount of room where no chassis mounted stuff is located between a tube lineup along the back edge and the tone pots on the front edge. This is a HUGE deal converting an old dual 6V6 or 6L6 PA or mono amp to guitar. With these conversions, unless you are building a "primitive" guitar amp (with only a pot or two) the layout you make with the tracing paper when you are first placing the big parts on top of the chassis *also has to show where the tag strip will go UNDER the chassis* or you're bound to create interferences. I have tried to convert some of these amps where in the end, it was easier to cut out the entire top surface of the old chassis and replace it with a blank piece of sheet metal. Many of these amps, the controls will be so close to the tube sockets you're bound to create noise issues. Best of luck, builders!
@@pneumatic00 I sure agree with you about size and shape of what we build. If you notice that most of my amplifiers look like vintage McIntosh models for power amps. I tend to run into issues when having to cram parts into a small space and it isn't fun for me to build anymore so I don't build equipment like preamps and such. Same experience here with the terminal strips under the chassis. I remember a RF amp I build not too long ago and posted it and commented that there was only One "mystery hole" in the chassis. I have found that just putting a screw, or goof-plug, as required, tends to dress up these mistakes of too many holes. And, indeed, sometimes things like terminal strips do need to be drilled and mounted after other components are already on the chassis. In this case, as I have done in the past, I will drill all the holes I need, then a cleaning and coating of primer on the chassis followed by grey wrinkle paint. I guess I will be old-fashioned to the end.
Another thing that never appears in the diagrams is the filament connections, which will take up space and still have to avoid being near connections where there is low signal.
Please do NOT run any tube in a audio amplifier at ICAS values. CCC is stressful enough. Where do you obtain your DIY Poseidon printed wiring boards? The sources seemed to have dried up.
I think the source has dried up but I have had mine for years. Here is where I used to get them. www.triodeelectronics.com/diytubemk3.html Possibly they still have PCA replacements for Dynaco MarkIII and MarkIV, etc that can be helpful - They did recently re-post a link to the manual for the Poseidon board but the other Dynaco type boards are probably just as good for home brew.
You are having TOO much fun!!1
I cracked up when the transformer fell off the stool, and you said "nothing broke" like it was nothing.... FUNNY!
I live in a historic district too here in Pomona, CA., and we have 2-3K kids on Halloween also! Tons of fun!
Love your videos! So much information, and just plain fun!
Hi Bill,
I am still having fun. I have recently been going pretty slow on audio amplifiers but some are starting to come to my interest and I want to start building.
I have been into my astronomy hobby lately and watching lots of YT videos on amateur astronomy. I bought a star tracking device and am using good telephoto lens and getting some amazing results and able to go out by myself without having to deal with the size and weight of the 10" Meade scope. That one is too much for me along. Anyway...
This amp in the video morphed into a standard Williamson driver (I removed the driver board, cut a piece of aluminum and mounted two octal sockets on it for a pair of 6SN7s) and changed the 1625s to KT88s. Increased the power considerably. I think I made a later video of it - not too sure unless I look...
Good to hear from you and thanks for your comments.
This is so cool. I sit here now having just stopped for the day working on my amplifier. And let me tell you, if you saw this thing your head would spin. It weighs like 200 pounds, has a 15 tube power supply, another 14 in the power amp including instrumentation... 6 modes of operation... Solid oak, custom CNC top plates...I mean it makes your little project seem really small... But here's the thing - I've been working on my amp since 1997 or even earlier. And it's still not finished. I have scrutinized over every single detail, scrounged absolutely the highest grade components, I even hired a renowned engineer to design most of the circuit and schematic. And you'll be sitting there listening to that sweet little thing you're building before I'm finished with my project for sure. With any luck, I should have first music out of this thing in Feb. after 20+ years. There's something really good to be said about being decisive like you're doing. You're building that amp very much by freehand, and that will come with some mistakes and some learning, but you'll have an awesome hand-crafted amp in no time. If you do like I do, you spend $15K in parts and it'll take you 20 years to finish.
It sounds like you are building a beauty. Some of my projects weigh in close to the 200 pound mark also. Actually, my biggest KW level transmitter is probably more like 400 pounds as it is built in a 1947 steel cabinet. Fortunately, it does have nice rollers or I wouldn't be able to move it at all.
I have been building for a long time and have much of it in my head. I used to take the time to draw nice schematics, long hand, but now I usually only take notes on the specialties of the equipment I build and keep it with the instrument so when it needs repair or modification, I don't have to "reinvent the wheel" so to speak.
I have already changed this one from the Poseidon board driver to a genuine Williamson driver design with 6SN7 and it does perform better.
I also keep Lots of parts on hand so I don't have to discover that I am missing something and then have to order it and wait for it to ship to me and lastly... I am pretty obsessive on my building and will put fourteen hours a day into it if time permits.
Thanks for sharing your experience and if you have a RUclips channel, or want to start one, please share your experience and amplifier with the world. You will meet like-minded and nice people.
@@ElPasoTubeAmps I'd love to see some video of the monster. I suppose I really should upload a video about this amp. The power supply is finished and functional, and I'm making progress with the amp every day now. I spent a TON of money on the CNC made top plate, but I have to add a few screw holes by hand to accommodate some terminal strips. The aluminum is pretty thick, and I'm having a hell of a time keeping the drill bit from walking around, even with a hole guide. Got any tricks up your sleeve for that? Luckily my first holes are hidden under transformers, but now I need to drill ones that are going to be visible.
Anyway, I'll give you a quick rundown of the topology. Standard Push-Pull Parallel (or not parallel if you want) output sections, 2 or 4 tubes. It's based for KT-88, etc., designed around KT-90, and it uses Harmon Kardon Cit II OPTs. Lundahl 1660 interstage transformers handle driving the outputs and phase splitting. By turning a knob, it can run either Push-Pull or Single-End, each one in either triode, pentode, or ultralinear mode for a total of 6 operating modes. All biasing is set with 10 turn precision pots, as well as all the instrumentation and calibration pots. Drivers are 6SN7. Gas tubes, OB2, OA3, etc. are used in several places including voltage for the instrumentation. Feedback and input attenuation are adjustable via stepped attenuators, and all the 10-turn precision pots have counters with locks on them. All the octal sockets are vintage Amphenol ceramics.
Meanwhile, the power supply has a HV transformer putting out 630VAC @1A into an 8 tube bridge rectifier made with 6AX4/6AU4 (TV damper rectifiers). There's a big mil surplus potted transformer putting out 30 amps of 6v filament, plus a smaller 6v filament referenced to high voltage via center tap... There are OD3 and OA3 gas tubes stabilizing the screen and bias voltages, a pair of massive 10H chokes, massive oil filter caps as well as electrolytic, and all sorts of other odds and ends. The power amp chassis contains all the metering which allows you to set bias, check voltages, check driver stage and output stage signals, etc. The whole thing connects with umbilical cords. There's also a safety circuit that shuts off HV+ and drains all the caps to ground via power resistors if either a bias fault or unplugging of the umbilical happens.
But yeah - do you have any advice for keeping a drill bit from wandering when you really can't use a drill press?
@@hugeshows I spend plenty of money on new drill bits just to keep the bits from "walking around" as you say. If the hole is critical, I start with a small bit and go up in size slowly. You will end up with less burr to remove that way. Holes under the transformer is OK. It is hard to not have some "mystery" holes. But you may be able to just fill some of them with a screw and nut or a "goof" plug and it will look great.
I love the fact that you are using 10 turn pots and VR tubes. I have thought of installing a switch to change between UL, triode and tetrode (beam power) mode but I would have to also come up with proper screen voltage and would likely use VR tubes. I may do just that now that we are discussing it. Something a little more special than just the Williamson designs that I keep building...
I have made my NFB adjustable before but nowadays just leave it at a set value. I have noticed that with NFB turned completely out, the amplifier sounds really "alive" but THD rises sharply.
I have read about using the TV damper tubes and I can not tell you off the top of my head, but check the maximum current rating of these tubes and make sure your amplifier does not need more current than they can provide. In this last amp I posted, I quickly saw that at high power, the sag in voltage from using a single 5U4 was not acceptable and the high end power suffered a lot. It is amazing how 10 cent diodes solves all these PS sag problems...
I have some massive 10H 400 and 500 mA chokes but they are so huge. I just got in an order from Mouser for 1H, 300 mA and 1.5H, 500 mA chokes new from Hammond. I usually need higher current than can be easily found and 10H is not necessary but nice if we have them and room for them on our chassis.
Sure sounds like you have built a beauty.
As for umbilical cords - I would suggest adding an external, flexible braid ground between the chassis just for safety. I am sure you have taken proper precautions in multiple ground connections in your cords but in the event of electrical separation of the PS and amplifier, you know there would be full potential between the chassis. Just my thought on that aspect.
It would be really nice to see your build on RUclips. Say safe...
@@ElPasoTubeAmps Thanks for the advice. I've made a little video for you showing the amp and how the drilling all worked out. Thanks again, and that video should be up in a couple hours.
Great! I'm very excited to see building of this amp. Nice selection of power tubes. 1625 / 807 tubes are great. But I am a little confused about the G2 of this tube. How to really calculate the voltage of this G2. Really anxious to see how you do this.
In this amplifier the tubes will be running UL because of the taps on the output transformer so the screen voltage will be the same as the plate voltage and the tube can be seen in a triode connection.
I have included a link to a book by Eimac that discusses how screen voltage in tetrodes affects cathode current you might enjoy.
www.cpii.com/docs/related/22/C&F2Web.pdf
I use 807s in my designs and for HiFi a pair in UL will produce in excess of 30W at 5% THD. In the guitar world, I use four in parallel push pull, class AB2 and achieve just over 130W. Nice valves. They are a 6L6 with a top cap for the anode, so it will work at 750volts without destroying the IO base..
I agree the 807/1625 is very much overlooked in the audio world but the vintage 6L6GC's can bring such a high price. As you say, the plate cap allows much higher plate voltages and as much as 120 watts output running them as a tetrode with proper screen voltage. Maybe after seeing this video, others will choose to start building with these grand old tubes just like you have been doing. Thanks for your comments.
what do you use to cut rectangular holes?
I start with either a hole and a nibbler tool (with the lines of the hole drawn out on the chassis) or just go to a Dremel tool cut-off disk and then smooth down the side with a file. I don't have any specific tool for square or rectangular holes. It is not the easiest part of preparing holes in a chassis.
Just wondering.... Will there be a parts list and schematic so that we could build our own based on your videos? Thanks for the videos Dave. Always look forward to them, and now even more.
Hi Steve,
I have never, that i can remember, posted schematics and parts list unless I just show it in the video. I do try to show the over-all schematic of the amplifiers but since I generally stick to the tried-and-true designs like the Williamson, or Dynaco or McIntosh, etc. those schematics can usually be found with a little Internet research. One set of schematics I often show are the five books that can be downloaded. Here is a link to one - lilienthalengineering.com/100-amplifiers-chapter-1/100-amplifiers-part-4
Just search for, 100 Amplifiers - Part X where X is the number 1 thru 5. They are absolutely amazing books on amplifiers. I liked these books so much I actually printed each book and bound it for my library for ease of viewing them. Hope this helps.
@@ElPasoTubeAmps I re-watched the video and saw the schematic. Thank you. I am far from a skilled wizard like yourself, but hope someday to build an amp from scratch and your videos make that dream come closer.
Nice! You didn't really state what you are building. It seems to be the classic williamson design. is that right?
This one will be the Poseidon board and it is not Williamson but does deliver a drive voltage that is sufficient for the 6L6/EL34/6550 family of beam power tubes. When I start on the amps with the Svetlana SVT572-10 tubes, I am going to go to a voltage amplifier that will deliver much more drive voltage as the bias level is much higher on the low mu triodes. Those amplifiers will either be classic transformer driven (assuming I have two matching transformers for two amplifiers) or some form of CT inductor.
Hi Dave,
Where do you source your chassis? I'm looking for an enclosure to house two 50A Megawatt power supplies. Nice start to the audio amp. 73 WB3BJU
Don,
I order them from www.mouser.com.
Here are a couple of part numbers to get you in the ball park so you will know what to type in to find them. I just ordered two 17x17x4 chassis today. They are about $60 each but the smaller ones are a bit cheaper more in the $40 range. Try these part numbers 1444-14103 or 1444-17134 You can then browse around for the size you want.
I have got to tell you what just dawned on me. I assume you might know that I have already build a 833A class-B amplifier that I use on 20M SSB. I can change the bias to meet class-C operation and then use one of the huge KW level transformers I have, as a modulation transformer, that will match 8 ohms primary impedance to a secondary impedance (using the transformer what me might think of as "backwards") anywhere between 5K and 20K and then drive the 8 ohm winding of this transformer with a 400 watt solid state McIntosh amplifier. This is crazy but I think I can make it work. I will have a full, high-level, plate modulated KW of AM on 20M. I love it. That should put out a serious amount of carrier. :-) I bet everyone will just love me all at 14.286 MHz
Your thoughts? 73 WA4QGA
I’m kind of confused, are you building an 807 guitar/audio amp? Or will this be part of an am transmitter ? I love 4-400’s and 4-1000’s the design of 4-400 am transmitter reminds me of the Johnson 500 (single tube) or Collins 20V (pair)
Maybe Stephen got it right below... :-)
This amp with the Triad transformer will be just a HiFi amp. Mostly I like to see for myself and document the performance of some of this vintage "iron" that claim such fantastic performance. We shall see. Also, some viewers want to see how amplifiers are built so I will post a few videos on the progress as it occurs, which I hope will help others.
The AM transmitter is a separate project. I have now thought that maybe all I need to do is change the bias and plate tank Z of the 833A amp I have already built and then build a large modulator for that amplifier. Maybe even use a McIntosh MC2205 that I already have that will deliver over 400 watts of audio. I have the transformers to match 8 ohms to the high Z that the plate of the 833A class-C amplifier will need. Now that would be a novel approach to AM...
Hey! Weird suggestion: use a type 83 vapor rectifier and a 30 second delay relay tube for your B+ onset after the filament warms up
@@Dukers2300 I have been charmed by the MV type 83 rectifier before. I know they use it in the TV-7 tube testers as the voltage drop is low and constant and I think I have a couple. I will have to think about it.
I’ve wanted to build a KT88 audio amplifier for a long time. What always stops me is getting the right transformers. Where do you procure yours from? Thanks!
Edcore CXSE25-8-5K for the 8 ohm output.. Edcore makes hi quality transformers.. this transformer is for Class A..if your interested I have lots of tested information.
I see dan dee below has given you a nice source.
In general, I just find transformers at estate sales and from parting out military equipment. I have also been doing this for more than 50 years so I have ended up with quite a nice stash of power transformers. Output transformers are, for sure, a more difficult item to fine.
However, keep in mind that, for example, a 5K to 8 ohm OPT can also be used as a 2.5K primary with a 4 ohm load (on the 8 ohm winding) or 10K primary with a 16 ohm load (on the 8 ohm winding) and so on. The amplifier in this video is a perfect example of using a 4K primary as a 8K primary by putting the 8 ohm load on the 4 ohm winding.
Similarly, for example, a 500 volt CT power transformer can be used as a conventional CT full-wave for about 300 VDC or you can wire it in a bridge mode for about 600 VDC or even a voltage doubler for about 1200 volts. If you are lucky enough for your transformer to have dual primary windings, you can double (or half) the values I just mentioned. So, you may have an option with transformers that you just haven't thought of yet. Hope this helps.
Don't you need to rotate one of the transformers 90 degrees?
I have finished all the drilling and painting and I did rotate the OPT several times looking at it but ended up laying out and cutting the holes like it is laid out in the picture. The reason is primarily to give the 5U4 a little more room as it is a very hot tube and will heat up the transformers close to it and hopefully, the wires will be long enough from the OPT transformer to reach the 1625 tube sockets without having to lengthen them. One of the things that I don't like, and it is completely unimportant, is the label on the UTC power transformer is upside down when the transformer is mounted with the connections under the chassis. I don't know why they put the UTC label on that way. Oh well...
@@ElPasoTubeAmps
Thanks for your reply! Yep, an upside down sticker would annoy me too! Yes, those 5U4's get hot alright so plenty of air around them is a good thing. Looking forward to seeing it finished. Thanks..
@@paulbione5267 It is getting there. Chassis is drilled and painted and all components are mounted so just a little hook-up and we will see how it performs.
@@ElPasoTubeAmps
Excellent!
The one thing I'd emphasize as one who has built a fair number of amps; Maybe it seems obvious, but you want to get all your metalwork out of the way before you start to mount sockets & trannies and especially before you start soldering wires. Usually it's kind of awkward to drill holes with a 15-20 pound transformer (or two of them) mounted to the main surface. Usually not so bad if you are hand drilling; But on a drill press it can be irritating. Then again....If you need to drill a "forgotten" hole close to a mounted transformer, you might need an aircraft (super long) drill bit to get to it. You sure don't want to carve out 1"+ holes for tube sockets with trannies mounted. Yeah, if you have the right size punch, not the biggest of big deals, but beginners do not have the right punches. Right?
And you generally don't want to drill holes in the chassis after you've placed wires, because you could injure the wires.
When you look at an amp schematic and start thinking about building it; you have to realize that some parts are NOT going to be on the schematic, in many cases. Dave shows these but it's very common for a beginner to overlook the mechanical and layout considerations when the schematic does not show: an AC on-off switch; the type of AC entry, fuseholder, pilot light. What kind of pilot light? A little LED or a big #47 holder that requires a (I think) 3/4" or 7/8" hole? What if you want a standby switch?
And how are you gonna handle the output connectors? Dual banana posts? Fine. You don't want those right near your 450+ volt power supply. You have to carefully drill the holes for banana plug posts if you are using separate ones or else a mating dual banana plug won't fit right. And you don't want those right next to the inputs, either.
And where are the input jacks? Front or back? You sure don't want those near your big power transformer.
Dave is using a PC board for the preamp section, which IMO is the way to go. If you want an input "volume" control you have to consider how close to the edge of the chassis you cut the rectangular hole for that board. (This is a lot more true if you are going to mount some tone controls) If you don't leave enough room around the preamp section, your tone controls get shoved down towards the power tubes and that's likely to be a problem noise-wise.
A lot of people like to convert old tube hi-fi amps for guitar use. Many of these present problems because often there ends up being no room for tone controls; or maybe you want to add another tube stage (or two, maybe you want to add reverb or tremolo---oh, and by the way, those require some extra jacks, usually on the back) ) and you can't do it in a mechanically neat way. Or there isn't room for a parts board or tag strip and you're forced to build P2P.
What about some misc tie points under the chassis, barrier strip thingys? NO SCHEMATIC SHOWS THEM!
Or you want to add pin jacks for bias-adjust test points.
So I apologize for spewing out all the unpleasant issues I have encountered building tube stuff. All I can say is; most "surprises" end up creating awkward, uneven, hodgepodge mounting of parts, while at the same time, it is very very difficult for a beginner to anticipate all the tomfoolery that can happen.
You want to build something that looks perfect but for your first few builds, regrettably, that's almost impossible!
I think you have done a marvelous job of describing so many of the issues of homebrew equipment building, especially for the new-builder and never too late for us old-builders also to get reminded of how complicated things can get. Lastly, I might add that after a piece of equipment is built and something needs to be added it is really important to make darn sure there is nothing beneath the chassis before drilling from above the chassis. Seems pretty obvious, but stupid things can happen if one is not really careful and end up drilling a hole thru an inductor (or whatever) from getting in a hurry. Thank you for your time and your reply.
@@ElPasoTubeAmps Thanks, Dave! Just trying to share some experience tidbits. Y'know, there are big differences between building a Fender-like guitar amp (with tone controls and possibly reverb/trem controls) and a "monobloc" type amp like you show in this video. The difference revolves around; with a Fender-type amp you are usually trying to build something kind of long left-to-right and not very deep as it is at least pictured as going into a cabinet. That's completely different than building a nearly-square item like you're doing in the video. You don't that much care about how big the chassis footprint is. That has tremendous implications for parts layout. Even in a bloc type amp, it's almost a requirement to sprinkle some terminal strips around the tube sockets. You are gonna need them to mount stopper and screen resistors & coupling caps. Again; no schematic EVER shows how many tie point strips you're gonna need. By the time you have say 6-place tie point strips, these usually have two chassis mounting holes. I wish I could tell you how many times I have figured on needing a 3-place tie point strip which only needs one mounting hole, but I really need 6 or 8-place, and then the hole I drilled for the small term strip is no good and then other hole I need runs into another tube or is under a tranny. *And it's THESE holes you discover you need AFTER the wiring has been placed. Solution: There is never a penalty for over-specifying the number of tie point strips you will need and leaving a few lugs blank.*
Back when you & I started building stuff, all the parts were 25 cents each. Now, every stinking part is $3 or $7 and while that isn't all that much money, 57 of them are.
I move on to building Fender-type amps. You can buy stuffed or empty tag strips that carry all the R's & C's that are not mounted right between the tone control lugs. In general, those make your life easier; but to use those strips, you have to have (meaning, you have to plan for) a fair amount of room where no chassis mounted stuff is located between a tube lineup along the back edge and the tone pots on the front edge. This is a HUGE deal converting an old dual 6V6 or 6L6 PA or mono amp to guitar. With these conversions, unless you are building a "primitive" guitar amp (with only a pot or two) the layout you make with the tracing paper when you are first placing the big parts on top of the chassis *also has to show where the tag strip will go UNDER the chassis* or you're bound to create interferences. I have tried to convert some of these amps where in the end, it was easier to cut out the entire top surface of the old chassis and replace it with a blank piece of sheet metal. Many of these amps, the controls will be so close to the tube sockets you're bound to create noise issues.
Best of luck, builders!
@@pneumatic00 I sure agree with you about size and shape of what we build. If you notice that most of my amplifiers look like vintage McIntosh models for power amps. I tend to run into issues when having to cram parts into a small space and it isn't fun for me to build anymore so I don't build equipment like preamps and such.
Same experience here with the terminal strips under the chassis. I remember a RF amp I build not too long ago and posted it and commented that there was only One "mystery hole" in the chassis. I have found that just putting a screw, or goof-plug, as required, tends to dress up these mistakes of too many holes. And, indeed, sometimes things like terminal strips do need to be drilled and mounted after other components are already on the chassis.
In this case, as I have done in the past, I will drill all the holes I need, then a cleaning and coating of primer on the chassis followed by grey wrinkle paint. I guess I will be old-fashioned to the end.
Another thing that never appears in the diagrams is the filament connections, which will take up space and still have to avoid being near connections where there is low signal.
Please do NOT run any tube in a audio amplifier at ICAS values. CCC is stressful enough.
Where do you obtain your DIY Poseidon printed wiring boards? The sources seemed to have dried up.
I think the source has dried up but I have had mine for years. Here is where I used to get them. www.triodeelectronics.com/diytubemk3.html
Possibly they still have PCA replacements for Dynaco MarkIII and MarkIV, etc that can be helpful -
They did recently re-post a link to the manual for the Poseidon board but the other Dynaco type boards are probably just as good for home brew.
V