Building Your Own Tube Amp
[NOTE: This series of articles was originally written by Ralph Power. You may contact him directly at power_ralph@hotmail.com –Ken]
Building Your Own Tube Amp
Ambitious title, eh ? Well the intent of this article is to lay out a logical plan of action for those courageous individuals who are contemplating building their own tube amplifier, but just can’t seem to figure out where to start. As a recent rank beginner myself, I can assist you with information on the thought processes I went through when planning and constructing my own amp. This article will point up important things to consider before you lay out your hard earned cash. Naturally it leans toward creating single-ended and push-pull direct-heated triode amplifiers, which I believe are the best sounding, easiest to build, and give the greatest chance for success, but I think this plan will also work for other types of tube amps and preamps as well.
Tube electronics is generally very simple when compared with the current commercial solid-state microelectronics of today. The real magic goes on inside the tubes themselves. You just mount them on a chassis and provide them with the electricity and audio signal they need to do their jobs. Tube amps are very forgiving and will tolerate incredible abuse and misuse for short periods of time, like during initial power up and debugging.
I believe you can build your own amp that sounds as good or even better than a commercial one for half the cost. And with it comes the immeasurable joy of creating a work of true artistic beauty with your own hands and mind, an amplifier that is as pleasurable to look at as it is to listen to, and one that is so well built, it will be around long after we are all dead and gone. You can’t buy anything like that at Circuit City!
I’m telling you that you don’t have to understand tube amp design or even tube operation theory to build a extremely high performance, state-of-the-art triode amplifier from scratch. Man, this ain’t rocket science! If you are at all experienced with soldering, drilling, and a little painting, you CAN do it. All it takes is a few tools, a schematic, a building plan, and some cash. But above all, what it takes is a sincere desire to create the amplifier of a lifetime.
I’m here to give you a building plan that worked for me. But I warn that this article is very generic in nature and does not attempt to cover all components and situations and does make sweeping generalizations for the sake of brevity. And of course it is all my most humble opinion.
Deciding what kind of amp to build
OK folks, this is absolutely the number one, most important thing of all to consider when building your amp. And you thought it was the wiring! Nope. You must have a firm understanding of your power needs and your output tube and topology options before you can make any intelligent choices for building that dream amp of yours. If you blow this step, you’ll be setting yourself up for a big, expensive, time consuming failure, and a great listening disappointment to boot.
It has been said that the amplifier – speaker interface is the most important in audio and you better believe it if you want to succeed in maximizing your audio enjoyment by building your own personal expression of vacuum tube art. If you don’t already have a pair of efficient, good sounding speakers (generally >90db/watt/meter), you know what you need to do first. Otherwise you are relegated to more conventional push-pull pentode tube and solid-state amps with a higher power output (>25 watts per channel).
Below is chart of common direct-heated triode output tubes and their associated power capabilities. I am one of those audio radicals who believe that direct-heated triode push-pull amplification has just as much potential for giving ultimate musical enjoyment as single-ended amplification does. Therefore I am including push-pull ratings in my chart of common output tubes to give you more options to consider in making that all-important output tube selection based on your power requirements and parts cost. Just remember you have to use push-pull output tubes in pairs, so the tube cost doubles versus single-ended.
Common direct-heated triode output tubes and their average maximum power output at average operating points and their least cost:
|
Type |
SE watts |
PP watts (pair) |
Cost/tube |
|
300B |
8 |
16 |
60 |
|
2A3 |
4 |
8 |
15 |
|
45 |
2 |
4 |
25 (used) |
I recommend that you use the efficiency of your speakers as a guide to your available options as to output tube selection and amplifier topology (single-ended or push-pull). If your speakers’ efficiency is around 90db, then you are pretty much relegated to using the 300B type tubes and their super tube variants (VV32B, VA5300, etc.). This is not a liability at all as the 300B is one of the best sounding tubes ever produced. Even if you have highest efficiency speakers, the golden tone of the 300B tube and extra headroom it provides, are still the safest bet for DHT amplifier success with the most kinds of speakers, especially if they are not horn types.
Push- pull 300B amplification offers the highest output power level of any of the above configurations (up to 40 watts per channel or more in some circuits!).
In the middle of the speaker efficiency range, around 92db/w/m, we have push-pull 2A3 amplification, which is probably the cheapest route to DHT audio enjoyment. With Chinese 2A3 tubes selling for $15 and the availability of used push-pull output transformers from salvage pentode amps selling for pennies on the dollar, there is no economic excuse for not joining the DHT amp party.
For those of you who want to go for that low wattage (< 5 watts) exotic sound, the more esoteric SE 2A3 and 45 tube amplification may just be your ticket to audio nirvana, but you better have a pair of really efficient speakers (>96db/w/m) to have a realistic hope of success, which usually means a speaker with a horn type configuration.
For my initial foray into the world of DIY tube amps, I decided to hedge my bets and go with the 300B single-ended tube topology for higher power and great fidelity.
Building an amp from a kit or from scratch
If you are the type of person that doesn’t like to be hassled with the process of making decisions, locating and purchasing individual parts, drilling, cutting and painting metal chassis, then maybe you should build one of the many excellent complete kits out there which will get you up and running in short order. In the middle ground, there are “parts” kits out there that give you most or all of the parts, but you still have to layout, cut, drill, and finish the chassis yourself. If so, just skip to the appropriate section that you need. But if you’re the type of adventurous soul who wants something beyond what is available in kit form, something that is totally unique in all the world, something that gives the pleasure that only building and owning your own creation can bring, just keep on reading.
Finding a schematic
By now you should know that you want to “do-it-yourself” and also what type of power tube and topology you want to use to build your amp. Getting your hands on a good schematic is the probably the second most important step in the amp building process. Unless you are an experienced experimenter and design your own amps, the safest route is to select a proven schematic from many that are offered for free at sites on the Internet. For instance sites like :
http://www.avvt.com/machmat/tubes/schem.htm
http://www.infomaniak.ch/~bonavolt/audioel.htm
or in magazines like Sound Practices.
A great way to start to learn tube audio is to get hold of as many schematics as you can find and study them closely. If you study them long enough, you will begin to see similarities in circuits and their sections from one schematic to another. Try to view an amp as a combination of different stages (driver stage, output stage, power supply, etc.) and not just a collection of individual parts (resistors, capacitors, tubes, etc.). You can’t see the forest for the trees? Try to see the forest as groups of trees…
Another good way to learn is to get hold of a vintage tube amp and its schematic and spend some time studying the wiring underneath while trying to visualize the circuit flow from input to output. It looks impossible at first, but you’ll be surprised how much you’ll pick up in no time. I’ve found that this is left brain information and sleeping on it will enable you to absorb more than you thought you ever would. Usually commercial push pull designs are much more complicated than what we would normally build, so if you can figure one of them out, our typical DIY amps will be a breeze to understand and build by comparison.
Your amp’s ultimate performance and parts requirements will be dictated by the schematic that you select to build. If you’re not sure which one to pick, try to find one that someone else has built, who can vouch for its performance. Maybe you can even talk them into answering any questions you might encounter as you go along. That’s how I got started. And remember that folks on the Joenet will be glad to help you with any questions also.
(Signal section schematic)
(Power supply schematic)
I’ve always subscribed to the “less is more” and the “keep it simple stupid (KISS)” school of audio design. Luckily both of these prerequisites came together beautifully in a schematic that was given to me by a serious audio experimenter, Gary Dahl. This circuit is exceedingly simple and pure, with no capacitors or resistors in the signal path. And it requires only a hand full of parts to build. I knew the first time I laid my eyes on this schematic that I HAD to build this amplifier. I feel that interstage transformer coupling between the driver and output stages maximizes audio performance while minimizing construction difficulty due to the lower parts count. Please let me know if you need a copy of this interstage coupled 300B schematic or the 2A3, 6B4G, or 45 version of it and I will email it to you. I also have schematics for an interstage-coupled push-pull 2A3 or 6B4G amplifier using the same 5842 driver tube as the single-ended versions. I have built and am currently using the 6B4G version and it is also a wonderful sounding amp. This would be a good choice for those with less efficient speakers or those with PP iron to build with.
In any case, I will also distribute these schematics upon request. These are the same ones that I have offered previously on the Joenet.
There are also many other good schematics that use 2A3s, 6B4Gs, 45s, or other triodes that are capacitor coupled and don’t require interstage transformers to build. There are cap coupled versions of these amps on Angela’s website and on the Aprilsound ‘s website. In any case, you must weigh your options and make your choice before you can begin building. Don’t get hung up here and vacillate endlessly on which one to pick. This article will apply to all of them, as there are only minor differences in building any of them. And ANY triode amp is better than none, so pick the schematic that best meets your needs and budget at this point and let’s get building!
Sourcing parts
Now that you have your schematic in hand, you can start to collect the parts that are called for in your schematic. This step can be as quick as a single trip to a local ham fest or it could take years if your parts include “unobtainium”. Locating and purchasing parts can be as exciting as any step in the building process if you approach it with the correct attitude. Instead of seeing it as a chore, look at it instead as a treasure or bargain hunt. Finding the best, rarest, cheapest, or whatever, can be very exciting in itself and will contribute greatly to the ultimate sound quality of the amplifier. My advice is to buy the best parts you can afford.
I get a lot of my new parts from Handmade Electronics, Angela Instruments, Triode Electronics, Welborne Labs, Mouser Electronics and believe-it-or-not, Radio Shack. I find lots of non-critical parts there and I don’t have to order them.
For used or vintage parts, I get them from other Joenet members and by shopping at hamfests. I’ve gotten some real bargains on tubes at hamfests, a exciting treasure hunt for sure.
Selecting transformers or “iron”, as it is known to the tube audio do-it-yourselfer, is usually the single most expensive category of parts required for any tube amp building project. The quality of the iron greatly affects the ultimate performance capability of the amplifier.
Surplus or “vintage” push-pull iron can usually be found at a much lower price than new or used single-ended iron, just because there was so much more of it made commercially. But don’t think that because it’s cheaper, the old stuff can’t be very good. In fact, some vintage iron is as good as any commercially available iron being produced today, as the art of transformer production was at a very high level at the time. Also be aware that single-ended iron is usually larger, heavier and more expensive because it requires more materials costs to build in the first place. So generally expect to pay more for the output transformers to go with single-ended topology.
I bought new iron for my amp because, at the time, I had proceeds from the sale of my former amp to apply to the new one and I wanted the security of building with new parts. But if you have more time to scrounge and less money to spend, vintage parts can be a great choice for building your ultimate amp.
Be sure to read, understand, and respect the values and ratings of all parts indicated in the schematic that you are using to build your amp. These are design and safety specifications and must be observed even if you substitute other brands of parts. It is usually OK to use a part rated higher than the one it replaces, but you usually can’t safely use one rated lower. For example, if a power supply capacitor is rated at 350 volts, it’s usually OK to substitute one rated higher, at say 450 volts or more. But you could not use one rated for 250 volts safely in this instance. For a resistor rated at 1/4 watt, you can usually safely substitute one rated at a half watt or higher. To capriciously change any parts specifications without knowing what you are doing is inviting catastrophic failure. This could result in shock or fire, or at the very least an expensive component failure.
Use your head and think about this and it will make sense to you. These specifications include the voltage, wattage, capacitance, resistance, impedance, and current ratings for each component and should be specified for all parts on the schematic. When in doubt, or if it is not specified, ask an experienced builder or technician who would know. Safety first!
Power transformers and chokes can be had new or used and will usually be priced accordingly. Be sure to select transformers that have sufficient voltage and current ratings to support all the tubes that will be taking power from it. Over sizing the current capacity of the power transformer is usually a good thing as it will reduce heat buildup and extend longevity. On the other hand, chokes need to be sized fairly close to the normal operating current load to do their filtering job effectively. You can estimate the total current requirement for your amp by adding up the total plate current used by each tube in the amp.
For my amp it is 2 x 20 ma = 40 ma total for the 5842s and 2 x 60 ma = 120 ma total for the VV30Bs or 40 + 120 = 160 ma total for the amp. So I used 200 ma as a minimum rating figure for selection of my power transformer and choke to allow a little overhead. I usually try to pick the power trannie B+ rating for a choke input power supply and then add some cap input if the B+ falls short. So for 300B B+ rating, shoot for 450 volts, and for 2A3, 6B4G, and 45 shoot for a 350 volt B+ rating.
Parts recommendations
First, let’s start with the iron. You can get the readily available Hammond power transformers and chokes from many sources such as Handmade and Angela. For a power transformer for the 300B amp I would recommend the Hammond model 278X or 300BX for a stereo amp or the 275X for a monobloc amp.
For a 2A3, 6B4G, or 45 stereo amp, I would recommend the Hammond 273BX or 302AX, or the 273X for a monobloc amp. For filament transformers for the SE 300B amps, I would recommend the Hammond 166L5, and the 166L2 for the SE 2A3 and the 45, and the 166L6 for the SE 6B4G. For push-pull amps you’ll need twice the filament current for two tubes in parallel, so check the filament requirements for the output tube you’ll be using and size the filament trannie accordingly. For chokes, I can recommend the belled Hammond 193J for most all the above stereo amps and the belled 193G or the unbelled 159P for monoblocs. I usually used the belled chokes and mount them up on top of the chassis with the other trannies.
For output iron, Handmade sells the Hammond and the Magnequest SE trannies. Pick the 2.5K or 3K versions for SE 300B, 2A3, or 6B4G. In the Hammond line, it is the 1627SE and in the Magnequest line it is the DS025, or the bigger RS330. For the SE 45 it is the MQ DS050 at 5K. For push pull amps, Magnequest makes the 5K B21 for PP 300B, 2A3, and 6B4G. And the 6.6K B20 for PP 45. ElectraPrint Audio also sells output iron and Steve Berger at Aprilsound sells the full Tango line of output iron. Take your personal choice here.
For interstage transformers, your choices are a little more limited. Magnequest makes the RIT5 for SE and also a version for PP (5K). ElectraPrint makes a SE version for the 5842 (5K) also. Tango makes several suitable interstage models such as the NC-18 and NC-20. And Lundahl in Sweden makes a full line of power, output and interstage transformers for audio use. I have used belled interstage transformers on top of the chassis and the unbelled ones underneath. Take your choice here.
All the other parts, such as tubes, sockets, 50 watt gold-finned cathode resistors, 450 volt power supply capacitors, carbon composition resistors, and other parts, I get from the previously mentioned sources. If you have any questions here, please ask.
Selecting a chassis
Think “big” here. Why condemn yourself to working inside a small, cramped, dark box? For a few dollars more you can have plenty of real estate to spread all your components out and get a soldering iron in there to boot.
Don’t make building harder than it has to be. For a stereo amp, go ahead and get a full size chassis (17″ by 14″ by 3″, Hammond 1441-38, available at Angela) and don’t think twice. For monoblocs, you can adjust the size accordingly. So unless you have shelf or other space limitations, get a big chassis that will work easily for all the components you’re using. You’ll stay calmer while building it and your amp will look and run cooler too. Also, if you have a lot of heavy transformers, you will probably require the extra strength of a steel chassis versus one that is made from aluminum or other materials. This will prevent flexing and bending under the weight of all the iron.
My interstage-coupled SE VV30B amp weighs about 70 pounds (!), so I used heavy steel for my chassis. Also there are even copper and silver chassis available from specialty retailers, so take your pick. Just use your common sense here and pick the best size and material for your amp.
Laying out the chassis
Here is an area where your artistic side must balance with your practical side in order to get a workable component layout. I suggest looking in audio magazine articles and ads for a picture of an amp that you really like the looks of. If you think about it some, you can probably go a long way towards laying out your amp similar to theirs. You may have to move a few things a little here and there, but the layout worked for them and it can work for you too. I emulated the layout of a Japanese amp I saw in the pages of Sound Practices magazine and it worked beautifully for me. It’s the picture I saw in my head when I envisioned my ultimate amp. Be sure to get this right as you’ll probably be living with this baby for a long time to come.
On the other hand, you can be a original as you dare, but practicality demands that there is a circuit “flow” that must be respected.
The components are wired together from input to output, one to another, so don’t make wiring it more difficult by placing consecutive components on opposite sides of the chassis. Doing a logical flow in your component layout means keeping consecutive components next to each other whenever possible. This will insure that all under chassis wiring will be short, simple, and neat.
Perfect your layout by placing your transformers and tubes on top of the unfinished chassis according to the layout you have decided upon. Move them around some and align them, if needed, to get that perfect balance of looks and practicality that makes this your perfect creation. For my stereo amp, I situated the power supply in the middle of the chassis, on a centerline from front to back, and the audio channels on either side, on a centerline, from front to back. At the rear of the amp, starting at each side, I placed the RCA jack and speaker binding posts, with the IEC power cord jack and fuse holder in the middle, all centered on a horizontal line across the rear. Take plenty of time and measure carefully before and after you mark the holes, checking and rechecking your measurements for alignment and symmetry. Any mistakes at this stage can be expensive and detract from the overall looks of the amp. After you’ve gotten your layout perfected, mark the locations of all the component’s mounting holes with a pencil or marker.
Drilling and cutting the chassis
OK, metalwork can be a joy or a pain depending on how well you relate to power tools. This was the most difficult part for me because I didn’t realize beforehand that metalwork is a major part of making your own amp. I advise you to take your time here. You’ll ultimately do a better job and enjoy the experience more.
I used a 3/4 inch hole saw in my « inch drill to cut the two miniature 9-pin tube socket holes that were centered on the marks that I laid out for them. Next, I drilled three 1 1/8 inch holes for the rectifier and output tube socket holes. I was able to make do with just two sizes of metal hole saws because I was careful to purchase tube sockets that were made for these diameter holes. In addition, you may need to cut other holes in which to mount capacitors and other components. I sprayed a little WD-40 on the hole saws and drill bits during drilling, using it as a cutting oil, and it worked great.
Use the mounting holes in the transformer and tube socket brackets to determine the diameter of the drill bits needed to drill the mounting holes that you marked during the chassis layout. Use the mounting nuts on the toggle switches, RCA jacks, and binding posts to determine the correct size hole to drill to mount them. Also you will need to drill holes between the transformer brackets to allow the transformer lead wires to enter through the chassis. I usually drill these access holes big enough to accept rubber grommets, available at Radio Shack, that protect the transformer lead wires from rubbing against the edge of the chassis hole. Grommets are optional, be sure to drill an ample size hole for this, especially if you decide not to use the grommets. After you select the correct size drill bit, drill the appropriate holes to mount the power and audio transformers, grommets, tube sockets, power switches, RCA jacks, binding posts, fuse holders, capacitors, hum pots, chassis mounted resistors and any other components requiring chassis mounting that you have previously laid out.
You will probably need to cut at least one square hole for the IEC power cord socket and maybe others for horizontal mount power transformers, meters and such. I drilled 1/4 inch holes inside the four corners of the square and then used a power jigsaw or nibbling tool to connect the holes and complete the square cut out. In addition, you must center the bottom plate on the chassis and drill holes through both at once to attach the bottom plate to the chassis, unless it comes predrilled. I usually drill eight holes, one in each corner, and one in the center of each side and use small 1/4″ sheet metal screws to attach the bottom plate and they work nicely. Also, I drill four holes in the corners of the bottom plate in which to later mount four big rubber feet to support the amp. You’ll need to source the rubber feet at a hardware store, ham fest, or Antique Electronic Supply, or such and have them on hand in order to gauge the hole size you need to drill here. Also I recommend putting a flat washer inside the rubber feet to prevent it from pulling off the mounting bolt. You can also use the fancy brass cones or squishy balls for feet if you are so inclined.
After all the mounting holes are drilled and cut, you must then file and sand them smooth and clean, getting rid of all burrs and rough edges. Afterwards make sure that the intended component will fit into its mounting hole. If it is too tight or too rough, go back and file and sand some more until the part fits just right, with no binding. Don’t cheat here as any rough edges on the chassis could nick wiring insulation and cause a short or a give you a nasty cut while mounting or wiring components.
Finishing the chassis
The finesse and artistic touch required of this step stands in sharp contrast to the power and brute force required of the previous step. Let your artistic side have free reign as you decide on and apply the finish of your choice. You have many options for a chassis finish such as paint, chrome, powder coat, anodized, brushed etc., but I will cover only painting here, as it is usually cheaper and easier to do-it-yourself. These other finishes usually require the assistance of a professional to apply or purchase preapplied, usually at additional cost, so be aware.
You will need to apply primer to a raw, unfinished chassis or one that is being refinished, in order to prevent rust and to lay a tacky basecoat for the final painted finish. Some commercial chassis, such as Hammond, come already primed. If you are so lucky, you can skip the priming step. First, lightly sand the whole chassis and bottom plate inside and out to provide a slightly rough base for the primer coats. Next, wipe down the chassis with a good cleaning solvent such as alcohol or even a spray cleaner, such as Formula 409, to remove any grease or oils that might interfere with paint adhesion. Let it dry thoroughly and then spray two or more coats of gray auto primer inside and out to protect the interior from corrosion and provide a good base for the paint on the exterior of the chassis. Follow the painting directions on the can and then let the final coat dry overnight.
I decided early on that I wanted a nice metallic gold look for my chassis, so I used a metallic gold lacquer with matching lacquer clear coat that I selected from the auto parts store. I have found Pep Boys to be a source of many different attractive auto body colors to select from. I have also used metallic silver and metallic graphite gray with good results. Other paint options include Hammertite “hammer finish” paints and speckled “faux marble” finishes. Let your artistic side choose your preference for finish choice. Following the directions on the can, spay several coats of the paint on the outside of the chassis and bottom plate, while waiting the directed time between coats. Later spray several clear coats over the paint, again waiting the directed time between coats. Please follow the directions on the paint can as close as possible for the best finish. Be very careful in handling the newly painted finish to prevent smudges and fingerprints. Try to handle it by the bottom edges or by the tube holes if possible.
I advise that you wait several days and let the finish paint cure well before you handle the chassis and continue with the next step. If you rush it here you will create smears, tears, and scratches in the beautiful soft finish which will cause you great distress.
Trust me, I learned the hard way. Let the finish cure and harden for several days before going on to the next step, especially if you used many coats of paint. You’ll be glad you did.
Finishing the transformers and other exterior parts
You may need to sand off and refinish the power and/or the audio transformers if you are using vintage iron or if the new ones don’t look like you want. I usually need to sand smooth and repaint new Hammond iron because it comes sloppily dipped in varnish and I usually want my iron to be a flat or semi gloss black to complement my chassis color. Use the above chassis finishing directions to refinish any iron or other external parts that you need to get the look you’re after for your dream amp. Mounting parts on the chassis
This is a really fun step because you feel a great sense of accomplishment and excitement as you mount the grommets, transformers, tube sockets, switches, jacks, binding posts, etc. onto the beautiful chassis that you just finished preparing. Use screws and nuts obtained from Home Depot or other hardware stores to attach any hardware.
I used mostly 10-32 and 8-32 size screws, nuts, and flat and lock washers to do the job, but use the sizes YOU need to do the job. You can be creative here and use chrome or even brass nuts and bolts for that classy touch. Take care with component orientation and positioning as you mount the components. Also be careful not to scratch your chassis when doing this, as you will have to touch it up later if you do. This step goes fairly quickly and when you’re through, it looks just like that amp you’ve been dreaming about.
Wiring the amplifier
This step is where your practical side comes in and one that makes this amp your unique creation. This is the step that most people can’t envision beforehand and understandably so. Wiring an amplifier is just a series of simple steps, taken one at a time. The sum of them looks complex when you are finished, but taken individually they are quite simple. You must have the faith to go forward with the confidence that it WILL work out.
I have discovered that you can wire an amp exactly like a schematic is drawn and it will work. I used to think there were schematics and then there were real amp layouts, but now I realize that they are one and the same. It’s just that there are many practical ways to translate a schematic into a parts layout and still remain true to the schematic.
Whenever possible, you should wire directly between two components. If you have taken time laying out the components logically, wiring between them should be easy and direct. If you have parts that are not usually mounted directly on the chassis (resistors, capacitors, etc.), that come between two other mounted components (tube sockets, transformers, jacks, etc.), you will need to mount them on an adjacent terminal strip in order to bridge the two mounted components. You can do as I do, and mount them on the bolts that you used to mount the tube sockets, transformers, etc. whenever possible. In my amp, I mounted a five lug terminal strip (from Radio Shack ) adjacent to every tube socket using the bolt that mounted the tube socket to the chassis. I used it to attach the opposite ends of the grid and cathode resistors, bypass caps, and filament dropping resistors and such that were attached to their appropriate lug of the tube socket. If you think about what I just said it will make sense to you
First I connected the AC power socket to the power transformer and the fuse and power switch. Then I twisted and ran the 5842 and 300B filament supply wiring and used cable clamps to hold it down so that it would lie close to the chassis. Next, I installed the 5842 and 300B cathode resistors and bypass caps and the 300B hum pots. After that I wired the power supply caps and choke and the 5842 dropping resistors. Finally, I installed the wiring from the input jacks to the 5842 tube sockets.
Sorry, folks, that’s all I’ve got! If you’ve got any questions, email Ralph directly… He’s a great guy and will be glad to help you out.
also, check out Vacuum Tube Amplifier Theory for some additional beginner DIY info, particularly the articles by henry pasternack on vacuum tube fundamentals, tube amp power supplies, and electromagnetics. the trouble tracing guide by norman crowhurst is also highly recommended.
