Build This Tube Amp With A Screwdriver

[FlaCharlie]

So a few years ago I picked up a Switch Mode Power Supply (SMPS) that's designed for tube circuits. It has separate outputs for 6.3v and 12.6v heaters and a 300v output for the B+. But other projects took precedence so it sat on the shelf for a long time. Some folks over at DIYAudio had messed around with them with varying results. I culled as much info as I could from them and I finally got around to using it on my breadboard setup to power a basic SE circuit. The obvious attractions are low cost and simplicity.

This piqued my interest in extending that element of simplicity to the rest of the amp. I get the sense that there are a lot of folks who might be interested in building a DIY tube amp but are hesitant to take the plunge because they are overwhelmed by the complexity. My goal here is to present something that is far less intimidating for newbies.

This is a project that anyone CAN build. Not just a simple circuit but something that is extremely easy to assemble while still using point to point wiring.

So I've dubbed this one the Simplissimo. I'm not sure if that's a real word or not but I like it.

The result is a design whose construction requires no soldering. You can build this amp with a screwdriver and a few basic hand tools. It's nothing earth shattering. The same construction techniques are commonly used when breadboarding which is the experimental process I always use when I build a DIY project from scratch. It's a simple technique where all the parts are mounted to a wooden board. So no chassis fabrication skills are needed either.

My breadboard experiments always end up looking like a rat's nest with so many clip leads running everywhere that it's scary. So I've eliminated that aspect. And while my experiments typically do have some soldered connections, this just takes the next step and eliminates them. I plan on posting a few designs that use breadboard style construction and this SMPS.

Just to be clear, this build isn't so much about using a particular tube or circuit. I'm just using this SMPS as a turn-key power supply solution and combining it with simplified build techniques. Any design that can be powered with ~300v B+ can be built like this and it's easy to experiment since everything is wired point to point. Want to compare pentode, triode and UL? Try a boutique coupling cap? A different feedback resistor value? A different biasing method? A screwdriver is all you need.

Of course, if a more traditional build is preferred, the same construction techniques can be combined with a conventional power supply and some type of chassis. Eventually, I'll be posting a different circuit that combines these breadboard techniques and SMPS with the same type of bamboo box that I used for a chassis with my Boogie Factor 1626 preamp.

Glo-Tone Boogie Factor 1626 Tube Preamp

I mentioned this preamp in the thread about Class D amps and a couple of people seemed interested so this thread will offer some details. What I'll do here is to present an updated version of a thread I posted elsewhere in 2020, when I built this. Some background: I first got interested in...

www.hifivision.com

Those who have read my previous build threads know that I like to keep costs low by using repurposed materials and I often use inexpensive, "under the radar", tubes. I've strayed from that formula just a bit here in that this design uses tubes that are common and in current production.

I have not abandoned the low budget, bang for the buck, approach. You should be able to build it for ~$300 if you forego the use of boutique coupling caps. A considerably less expensive version could be built if you go with a SE circuit that runs 6V6s or 12V6s in triode or pentode (not UL) that uses less expensive output transformers.

I'm not a designer or an engineer. I'm just a hobbyist / copy and paste builder. I try to incorporate elements from other designs and combine them in different ways. There are many popular SE circuits out there which use a triode to drive a variety of output tubes. So you'll find many of the same elements I'm using here elsewhere. Truth is, there's not much new under the sun when it comes to tube amps.

For simplicity I decided to stick with octal tubes only and to save space I opted to use a single, dual triode, input tube. So I experimented with both the 6SN7 or 6SL7 as inputs in combination with numerous output tubes including the 6V6, EL34, 6L6GC, the Russian 6n3ce and the 7591. I tried running triode, pentode, UL and E-Linear, though not all combinations with every different tube. I also tried a variety of biasing methods for the input tube and some other circuit variations.

In the end I chose the EL34 which offers a good combination of power and affordability with a 6SL7 on the input. No, I haven't abandoned the use of oddball tubes and the versions that follow will likely use some.

Building the same circuits over and over again is not my style. I usually try to incorporate at least a few "new to me" elements in my DIY projects. Gotta keep it fresh and interesting.

Although I have some vintage PP EL34 amps that I've restored, I've never built anything from scratch with an EL34 or a 6SL7. I've also never built an Ultra Linear (UL) amp or anything that uses local, plate-to-plate (aka Schade), feedback. And, though I used SMPSs to heat the tubes in my most recent amp, the Cockeyed Monkey, the use of a SMPS to power everything is also new to me.

https://www.hifivision.com/threads/glotone-cockeyed-monkey-a-directly-coupled-set.94233/

The output section is just a basic UL EL34 design using local, plate-to-plate (aka Schade), feedback. The current popularity of Schade FB is often traced to the RH amp designs but it's really nothing new. I recently came across a schematic for a "house brand" radio that was sold in Western Auto stores starting in 1947. It uses Schade FB in its amplifier section, which consists of a 6SQ7 driving a 6V6 output tube.

This basic output section is now very common. One example is the Skunkie Designs EL34 amp. She is now selling handcrafted, custom built amps using the same basic output section for ~$2000 to $2500. The most expensive version uses the legendary ISO Tango OTs! Of course she also has a series of step-by-step videos on her YouTube channel for those who want to build it themselves.

And Analog Ethos sells SE EL34 kits using the same UL output section design for ~$1300 to $1600. Their instructions are superb and this is a great option for those who would rather not deal with chassis fabrication. I've also seen some schematics that use the same circuit with different output tubes, such as the 6V6. So the basic design is well known and respected.

For the input I'm using the 6SL7, which is a dual triode. And just like the amps mentioned above, I'm using one triode to drive each EL34.

Besides the use of a SMPS and breadboard construction techniques there are two main differences between the designs mentioned and this one. The most obvious one is that this PS only puts out ~300v, so I'm running the outputs at lower voltage and higher current while the others run higher voltage and lower current.

The other is that I use a AA battery to bias the 6SL7. I've used the same battery grid bias scheme for input tubes in other builds too. It's simple to implement and I like how it sounds. Because the tube does not draw current from the battery, the battery will last as long as its shelf life. For a common Alkaline that should be at least 3 to 4 years. For a lithium it's probably 8 to 10 years. You must use regular batteries in this application. You can not use rechargeables.

Of course you can try other bias schemes. For example, Stephe's Skunkie Designs amp uses a combination of a resistor and an LED to bias the dual triode 5751 input tube in her amp. The 5751 is a 9 pin miniature that has the same amplification factor (mu 70) as the 6SL7, BTW. The Analog Ethos kit uses the more traditional combination of a cathode resistor and bypass cap to bias a dual triode 12AT7, another 9 pin miniature.

I tried both of these alternatives and preferred the battery method but YMMV. I encourage prospective builders to take full advantage of the breadboard and point-to-point construction methods used here. Break out the screwdriver and experiment!

Anyway, here's a pic of the finished amp. Yeah, it's not much to look at:



And here's the schematic:



Since most people who can't solder or fabricate a chassis probably can't read and build from a schematic either, I'll add some (hopefully) easy to follow wiring diagrams, a few in-progress pics and some construction notes, along with a basic parts list later. Oh, and if you're concerned about using breadboard construction because of the high voltages that are present, that will be addressed too. I'll do my best to try to present all this in a newbie friendly manner.

Again, my goal here is to encourage people to get into the DIY aspect of this hobby we all enjoy.

If you're DIY curious I encourage you to check out the excellent Skunkie Designs videos (as well as other build channels) on YouTube, the kits available from Analog Ethos and others, as well as threads on other forums, such as Audio Karma, that focus on restoring and modding amps pulled from old console stereos. What I'm presenting here is just another "intro to DIY" option.

 

[FlaCharlie]

So here's a pic that shows the basic bits mounted to the board:



The board itself is just particle board that's typically used for shelving. It's easier to screw into than solid wood. I use a drill to start the holes but if you don't have a drill a hammer and a nail should work fine too.

One reason I wanted to go with octal tubes is that the breadboard sockets for them are very inexpensive. If you shop around you can find them on eBay for ~$3 each shipped or about half that on Amazon for the parts themselves. They are used for electrical relays and are usually listed as octal relay sockets, not as tube sockets. Since they're quite common the price is low. Other types of tube sockets that are designed for breadboard / experimental use can also be found (7 and 9 pin miniature, octals, loctals, 4, 5, 6, 7 pins for use with older tubes, compactrons too) but they are typically at least 2x to 3x more expensive. These types are generally mounted on a small circuit board.

While I use a variety of connectors on my experimental breadboard, for a more finished build like this I prefer these barrier strips. Their screws are easy to access and, on these, the metal strip that connects each pair of screws can also be removed if necessary, which increases their versatility.

These, and several other parts used in this project, were from AliExpress. As I understand it, India has restrictions on direct trade with China so AliExpress may not be a viable source but you should be able to find similar items elsewhere. At least some of them can also be found on eBay and Amazon, though prices will likely be a bit higher.

The SMPS I'm using is advertised as HiFi 250w Switch Power Supply DC300v 0.6A +12.6v@4A +6.3v@4A For Tube Amplifier PSU.

If anyone wants to delve into the technical aspects of this, or other SMPS, please start your own thread or go over to DIYAudio where there are numerous threads about SMPS in general and at least one thread about this particular unit. That's how I became aware of them.

I don't know anything at all about SMPS design and I don't claim to have a high level of expertise with these but I'll make a few comments based on my experiences.

They don't seem to be branded but they have a label on one side and there seem to be two model numbers being sold. The first one I bought was found on eBay some years ago. It has a number that ends in -52. More recently I picked some up on AliExpress, where they are a bit cheaper (under $40 shipped). Their model numbers end in -U1.

They (both versions) have a delay to the B+ (high voltage) startup. They claim that it starts 30 sec after the heater voltage but the delay on the ones I have is more like 10 or 12 sec, which seems to be plenty. There is a slight click when the B+ starts but it's not loud enough to be a concern.

One quirk I found with the -52 version was that it went into protection (hiccup) mode whenever I had anything connected to the 12.6v heater output. It would immediately shut down and then try to restart. That was disappointing because I was hoping to have the option of running 12SN7 or 12SL7 tubes since they're cheaper than 6SN7s and 6SL7s. I was also considering a 6V6 design that could also run 12V6s. It's possible that I had it hooked up wrong, I suppose. It's also possible that this issue has been fixed. As I said, I bought this -52 version years ago.

And it might eventually start. I say that because another user who experienced hiccup issues seemed to be content to just let it go through this cycle repeatedly because it would eventually start up. I'm not so patient. The -52 version works fine with only 6.3v tubes though. And there seem to be some other solutions which are discussed over in the DIYAudio thread.

I suspect that the -U1 version may be an updated model because it works fine with any combination of 6.3v and 12.6v tubes. I did notice, however, that the B+ voltage at startup is more controlled if you have some type of load on the 12.6v output. I'm using a resistor but using a 12.6v tube or even a 12v pilot light works too. I have not tried to use only 12.6v tubes so I don't know if the 6.3v output should also be kept loaded in that situation.

Though not commonly used in tube amps, switch mode supplies are widely used in all sorts of applications. Everyone has equipment that runs off of external SMPS "wall warts" or internal supplies. Apparently they can, and usually do, generate noise at their switching frequency. I have no way to measure such things and I really only care about noise I can hear, unless it results in damage.

Perhaps the most interesting comment I've read on this was in a post by renowned designer Pete Millet over on DIYAudio where he said, "most of the worry about noise when using switchers in audio is pure superstition. 60Hz rectifiers inject a lot more junk than a properly designed SMPS."

I have no idea if this particular supply is "properly designed" but, in practice, it seems to work well enough. I have a very large number of tube amps, both DIY and vintage, all of which use traditional power supplies. While this amp is not dead silent with ear to speaker it isn't any noisier than they tend to be. It's actually quieter than many of them.

I mounted the SMPS using a 1" L bracket (aka corner brace) with a nylon spacer so that the unit is suspended above the surface of the board. The metal shell of the SMPS acts as a heat sink so this allows air flow underneath. A couple of thinner nylon spacers are placed underneath to add support. The copper bit is an electrical ground lug. These parts are all available in the U.S. at Lowe's or Home Depot. You can likely find them at your local hardware store.

The heat sink / metal shell does get hot just as a normal power transformer does. Of course the tubes get even hotter. While I was experimenting with it there was no air flow under it. It was just sitting on the board with a piece of non-slip shelf liner foam underneath it. It did not get hot enough to cause problems, even after running it continuously for 12 hours.

The SMPS has a voltage adjustment but it affects the high voltage and heater voltage outputs simultaneously. So I just adjust it to get the 6.3v heater voltage right and then use whatever B+ that provides. All the output voltages are DC and remain rock steady after startup. The metal shell is tied internally to the safety ground of the AC input and I'm isolating it from signal ground as is often done with a normal PS.

This pic shows a few parts mounted to the 6SL7 socket and the heater wiring:



I ran separate wires from the 6.3v output to the 6SL7 and the pair of EL34s. This allows me to switch to a 12SL7 by simply moving one wire over to the 12.6v output. I think I made some changes after I took this pic so you might notice some differences in pics I'll post later.

One suggestion I'd make is to install all the wires first and then go back and add the various parts. I didn't do that and it took me longer to build than it should have. Trying to run wires underneath other parts that have already been installed is kind of a pain. It's much easier if you do it in layers starting with the wires.

I'm using solid core wire instead of stranded wire as it's much easier to work with. Much of it is cloth covered "vintage style" wire from Antique Electronics and some is Military spec silver plated copper with teflon insulation, that I got from Apex Jr. Both of these suppliers sell it by the foot.

I'll post info on the connections later . . .

 

[sadik]

You did excellent Job.

 

[FlaCharlie]

You did excellent Job.

Thanks! As with most things it helps to just take it one step at a time.

 

[FlaCharlie]

So for those who can't read schematics, I'll try to explain all the connections using the following wiring diagrams. While they're not step-by-step instructions like you'd find in a kit, they should be fairly easy to follow.

Here's the wiring diagram for the 6SL7 input tube which plugs into the center socket:


The connections close to the center of the diagram are numbered. They're the screws on the octal socket that go to the tube pins. You can see the orientation of the locator pin / keyway. The locator pin prevents the tube from being inserted the wrong way. Notice that, unlike the diagrams found in tube data sheets, the sequence here is counter-clockwise since we're looking at the top of the socket. The sockets have numbers molded into the plastic but they're tiny and difficult to see.

The connections further from the center are on the terminal strips. For simplicity, only one connection ( O ) is shown but each one actually represents a pair and connections can be made to either one of the pair since they are connected to each other.

Note that parts from Pins 4 and 5 of the 6SL7 go to 3 connections. Those 3 are on the larger 8 position terminal strip that's located in the center / on the rear side of the amp. I'll post a diagram of the entire 8 position strip later. Obviously, there will be some redundancy as some connections will appear on two different diagrams.

The parts / connections on Pins 1 and 2 of the 6SL7 go to a smaller terminal strip which only has 3 terminals. That strip is located in the center / on the front side of the amp.

Here's an in-progress pic that shows some of that. I meant to take more of them but once I started wiring things up I got on a roll and didn't take many pics.



Here's the wiring diagram for the Left Channel EL34. The connections on the right side are on the 3 position barrier strip mounted on the front side of the amp. The connections on the left side are on the 4 position barrier strip mounted towards the rear of the amp.



Here's an in-progress pic of that:



Similarly, here's the wiring diagram for the Right Channel EL34. Again, the connections on the right side are on the 3 position barrier strip mounted on the front side of the amp and the connections on the left side are on the 4 position barrier strip mounted towards the rear of the amp.



Note that Pin 8 (the cathode) and Pin 1 (G3) must be connected at the socket with a wire. Some tubes make this connection internally but the EL34 does not so the jumper wire is necessary. Also, the EL34 does not have a Pin 6. So I'm using that connection (Pin 6) on the socket as a tie point. This makes it easier to mount the grid stopper resistor since the resistor body should be mounted as close to the grid pin as possible. The grid stopper is the dark brown resistor in the pic. Pin 5 is the grid pin.

Here's an in-progress pic of the 6SL7 and the Right EL34:



Here's the wiring diagram for the SMPS terminal strip, which has 6 positions:



And here's a pic of it wired up:



The SMPS terminal strip is mounted with nylon spacers so there's a gap between the bottom of the terminal strip and the board. This allows the green wires in the pic, which are the 6.3v heater wires, to run underneath the terminal strip on their way to the tube sockets. The orange wire, which is the heater ground, connects to the SMPS terminal strip as shown in the diagram.

Here's the wiring diagram for the 8 position terminal strip, which is mounted in the center / rear of the amp. Again, some of these connections are also described on other diagrams.



Here's a pic of the amp from the rear showing how I've mounted the IEC socket that connects the SMPS to the AC supply coming from the wall. I've used a combination IEC connector / fuse / switch and mounted it with a pair of 2" L brackets.



I think there may be a limit to the number of pics in a single post so I'll continue in another post . . .

 

[FlaCharlie]

Here's a pic of the connections between the IEC socket and the SMPS. I'm using crimp / push on connectors on the switch. Those were sourced from AliExpress but I'm sure you can find them elsewhere too. The connection to the SMPS is made with crimp on spade connectors but you could just make these connections with the bare wires.



Prospective builders can use a variety of methods to wire up the AC connection from the wall to the input of the SMPS.

IEC sockets just allow you to use a removable power cord. They are available in a variety of configurations. You could use an IEC that also houses a fuse but has no switch or an IEC connector that has no switch and no fuse.

Of course, you don't need to use an IEC at all, it's just a convenience. You could just connect the bare wires of a 3 wire cord directly to the SMPS, plug the other end into a power strip and switch it on and off using the power strip.

The SMPS has an internal fuse and various protection circuitry so it will go into protection mode if there is an issue. I just wanted to be doubly sure so I used an additional fuse. I'm using a 2A fast blow. You can also use a chassis mount fuse holder that uses crimp connections if you only want to add a fuse.

Here are pics of the speaker connections and the RCA inputs:




For the RCA inputs and speaker outputs I'm using a wall plate that's typically used for home theater installations. There are a couple different types of these. Some plates have small square holes and use connectors that snap into place. I'm using the type that has the speaker binding posts and RCA jacks fastened to the wall plate with nuts. Either type should work fine.

You'll usually find these plates with either all speaker connections or all RCA already installed. The one here originally had 8 speaker connections. I removed 4 of them and filled two of the empty holes with RCA jacks that were removed from some of the square snap-in types. So now I've got 4 speaker connections and 2 RCAs mounted onto a single plate. The RCA jacks are female to female.

The 8 position terminal strip diagram that I posted earlier shows how the RCA inputs are wired.

You could use a plate that has 6 connections instead of 8. I bought the 8 connection plate so that I would have 4 extra speaker connectors that I could use later for other projects.

If you want to build it like I have here (without solder) you want to make sure that the connectors themselves do not require solder. Some listings for these only show the outside connections and you can't tell if the inside connections require solder or not. You need to be able to see pics that show both sides of the connectors so you can confirm that they're the right type.

For the speaker connections I'm using banana plugs on speaker side. They also use screws to attach the speaker wires. On the amp side of the wall plate the bare wires from the OT (output transformer) are screwed into the binding posts.

Here's the wiring diagram:


Here's a pic of the speaker posts that are used in the wall plates and the handy RCA plugs with screw connectors that I'm using on the amp side of the wall plate.



This is just one method of making these connections. You don't need to use one of these wall plates. For example, the OT (output transformer) secondary wires and the speaker wires could be connected with screws using one of the same type of terminal strips that are used elsewhere. Vintage amps typically use screw terminals to connect the speakers.

For the RCA inputs you could just cut an interconnect cable and use the screw connections / terminal strips on the wire end. The end that still has a plug can either be left long enough to connect to a source or it could be kept very short. If kept short you could then use a female to female RCA adapter to connect separate / longer cables.

These days I mostly stream audio or play CDs through a DAC that has a volume control. So I've just built this as a power amp with no volume control. Volume controls with screw connections are available if you want to add one.

Coming up next . . . Safety issues

 

[FlaCharlie]

One of the concerns about building on a breadboard is that there are high voltages present. Of course the most popular tube amp ever made, the Dynaco ST-70 uses an exposed circuit board and, from what I've seen, not many owners seem concerned.

Still I would encourage prospective builders to use a cage.

So where can you find a suitable cage? I often find metal mesh baskets at thrift stores for a few dollars and I've collected several of them on the odd chance that they can be repurposed. But, for this project, I wanted to be able to suggest something that can be more reliably sourced.

Since I live in the U.S. I don't know what's available in India but the solution I found was purchased at Target, which is a "big box" store like Walmart. I assume there are similar stores in India. At $20, it was more costly than I'd like but then I'm used to buying used stuff at thrift stores. It's a metal mesh slide out storage drawer. Something similar can likely be found online too.



If you're planning on using a cage you really want to buy the cage first and then use it to determine the dimensions of your breadboard. That's what I did here. The actual size of the board I'm using is 8.5" x 13.75". I normally like to have a bit more space. I made it work but, as you can see, everything is pretty tightly spaced.

I opted to simply flip the drawer section over and set it over the amp as seen in this pic:



Another option would be to either place or secure the breadboard inside the drawer and access the amp by pulling the drawer open.



If you want to use that method you will need to be sure that there is enough clearance for the speaker / input connections so the drawer can slide in and out. They stick out too much in the one I built so I would need to reposition them in order to use the in-drawer option.

In either case, those connections should not be allowed to come in contact with the vertical metal bars. The bars on this cage are spaced so that an IEC plug fits neatly between them if you position the connector correctly. You'll notice that the speaker / RCA jacks have a bar going right between them. So you need to cover that section of the bar with some type of insulation. I haven't added that yet but I'll probably use heat shrink or maybe just electrical tape.

Coming up next I'll discuss which parts I used . . .

 

[FlaCharlie]

I'll start by listing the parts used according to which part of the circuit they're associated with and what their function is.

Resistors are 1/2w (0.5w) carbon film unless noted. You can use metal film if you prefer. The ones marked * are used as grid stoppers. For those I prefer to use carbon comp types which are non-inductive. They should be mounted so that the body of the resistor is as close as possible to the tube pin. The exact values are not so important.

You might even be able to omit them. They are used to prevent possible oscillation. Some tube types (those with high transconductance) are more susceptible to this and others not so much. I usually include them "just in case". On the other hand, I have a lot of vintage tube amps and I don't think any of them use grid stoppers. And most schematics for modern commercially available amps don't have them either.

6SL7 or 12SL7
Triode section #1:
100k grid leak resistor
220 Ω grid stopper resistor*
AA Battery
Battery Holder w/wire leads
100k plate load resistor (I'm using 1w but 1/2w is OK too)
330k feedback resistor
39k feedback resistor

Triode section #2:
100k grid leak resistor
220 Ω grid stopper resistor*
AA Battery
Battery Holder w/wire leads
100k plate load resistor (I'm using 1w but 1/2w is OK too)
330k feedback resistor
39k feedback resistor

EL34 x 2
Each tube requires:
470k grid leak resistor
680 Ω grid stopper resistor*
200 Ω 5w cathode resistor (wirewound)
220uf 25v cathode bypass capacitor (electrolytic)
1.8k screen resistor
0.22uf coupling capacitor (400v or higher)

Note on coupling caps: Obviously, you can go down the boutique rabbit hole if you like but basic caps from reputable sources are fine. I splurged a bit because I wanted to try the Mundorf Aluminum Oils that Stephe recommends. They are available from Parts Connexion in Canada and cost ~$48 shipped to the U.S. I assume they sell internationally.

I don't typically spend a lot of time trying different caps but I had tried several types that I had on hand when I was breadboarding this experimentally with a similar circuit. The ones that sounded best in that comparison - before I ordered the Mundorfs - were probably the cheapest I had in stock. I think I must have bought them 20 years ago when I was first stocking my shop. I don't remember where I got them. They are unbranded but the drawer they were in was labelled Metallized Polyester and they were the last two left in that value. The Mundorfs did sound better to me but I didn't think they were head and shoulders better. The concept of diminishing returns is quite real, IMO. I often find that spending considerably more results in only an incremental improvement and sometimes no improvement at all.

That said, part of the fun of a breadboard style build is that it makes it very easy to experiment with different parts. So have fun with it. It's a subjective hobby so YMMV.

Power Supply
SMPS - listed as "250w / 300v 0.6A / 6.3v 4A / 12.6v 4A" on eBay and AliExpress
Model # ending in -U1 is preferred / see earlier post
for comments on Model # ending in -52

1k dropping resistor
22uf 450v electrolytic capacitor
250 Ω 5w resistor (wirewound) (omit if using 12SL7 instead of 6SL7)
100 Ω resistor (isolates the heater supply ground from signal ground)
100 Ω resistor (1w metal oxide) (isolates the signal ground from safety ground)
0.1uf 630v capacitor (isolates the signal ground from safety ground)
2A Fuse

Tubes
I haven't done any serious tube rolling in this build.

I'm using some JJ E34L output tubes. I had a quad of them that I bought years ago. I had used them in some vintage PP amps (Pilot 260, Eico HF-87) but they still test as new. They're easy to find. Antique Electronic Supply (tubesandmore.com) lists them for $24 each. They're a reliable source for other items too. I'm not sure if they ship internationally.

The only types of 6SL7s I've tried are a USA Raytheon with black glass and an RCA short bottle with clear glass. Both are used tubes but test as new on my Hickok with well balanced triodes. The big dealer near me, Radio Electric Supply (vacuumtubes.net), lists NOS Raytheons for $25 and the RCAs for $40, also NOS. I've also used a Raytheon branded Japanese 12SL7, which also sounds fine. They list 12SL7s for $5 each. They're probably the largest tube dealer in the world. They have millions of tubes and they ship internationally.

Another very large dealer is vacuumtubesinc.com in Orlando. They probably also ship internationally.

I prefer using old production tubes but there are new production 6SL7s available. Oddly, they seem to cost more. There is also a Russian version that I've heard is decent.

I avoid the "boutique" dealers who write flowery descriptions of how a tube sounds. And I have no problem using strong or new testing used tubes.

Output Transformers
Should have 3.5k or 5k primary with an UL tap
rated for at least 10w

Obviously, you can use any OT you prefer, even ones that cost $1000. The cost of OTs will be the biggest variable when it comes to total build cost. Check physical sizes and adjust your build accordingly.

The OTs I'm using were purchased from AliExpress. They're not "branded", at least not in English.

As I understand it, Indians do not have direct access to AliExpress so I won't offer any tips on buying from them. I sometimes find the same items on Amazon, but typically at a slightly higher price. Can you obtain the same items through other sources? If not, I'm sure you can find suitable substitutes.

I mostly chose the ones I'm using based on price and the claim that they have 38H of inductance, which is higher than many of the others sold there. Inductance supposedly affects bass response and higher is better. They cost ~$80 for the pair including shipping. I also bought some that are 5k for a different project. They're apparently from the same manufacturer (based on a label on the bottom) and they cost me ~$90 shipped.

Slightly larger ones, rated at 13w are also available. I think I saw some of those for ~$110 shipped. And higher wattage ones are listed too but prices are higher.

Bottom line . . . I'm very happy with the sound I'm hearing using them. My last project, the Cockeyed Monkey, used the 15w GXSE OTs from Edcor, which are a popular choice for DIY builders in the U.S.

GloTone Cockeyed Monkey - A Directly Coupled SET

So here's my latest DIY amp, the Cockeyed Monkey . . . I always like to try some things that are "new to me" in my builds and this one has several elements that I've been meaning to try for a while. I had never built a directly coupled amp so I figured it was time. I decided on using...

www.hifivision.com

I believe that Stephe and Analog Ethos use the Edcors. They cost about twice as much (~$160). Shipping transformers is expensive. If you can source them domestically or from another nearby country that's probably your best option.

Here are pics of the OT listing and some of the other items that were purchased from places like eBay and AliExpress. The descriptions can be used to search. These are not links and prices shown may not be current or the best deal. All I can say is "shop around". Buy from whatever source you're comfortable with.

 

[mahaaprasaad]

I'll start by listing the parts used according to which part of the circuit they're associated with and what their function is. .....

Though I am not Electronics guy and do not understand most of the things you explained, I can understand its value for the DIY amp build for beginners. Thank you very much for your detailed write-up particularly addressing the Indian community of Audio Enthusiasts, covering all the significant aspects of DIY with images.

 

[FlaCharlie]

Though I am not Electronics guy and do not understand most of the things you explained, I can understand its value for the DIY amp build for beginners. Thank you very much for your detailed write-up particularly addressing the Indian community of Audio Enthusiasts, covering all the significant aspects of DIY with images.

Thanks! The thing about a build like this or a well documented kit is that you really don't need to understand electronics in order to build something.

I've been messing around with tube amps for almost 25 years and my technical understanding is still quite limited. I started by collecting vintage gear and learned to simply replace the old resistors and capacitors with new ones using the same parts values. Eventually I got into DIY.

Earlier I mentioned kits sold by Analog Ethos. While I have no affiliation and do not own one of their kits, their build manuals (which can be downloaded free from their website) are the best I've seen in terms of step-by-step procedures. In addition, they include a fantastic explanation of how tube amps work. So, purely from an educational perspective, their manuals are an excellent resource for anyone who is interested in tube amps.

 

[Amarendra]

Thanks! The thing about a build like this or a well documented kit is that you really don't need to understand electronics in order to build something.

I've been messing around with tube amps for almost 25 years and my technical understanding is still quite limited. I started by collecting vintage gear and learned to simply replace the old resistors and capacitors with new ones using the same parts values. Eventually I got into DIY.

Earlier I mentioned kits sold by Analog Ethos. While I have no affiliation and do not own one of their kits, their build manuals (which can be downloaded free from their website) are the best I've seen in terms of step-by-step procedures. In addition, they include a fantastic explanation of how tube amps work. So, purely from an educational perspective, their manuals are an excellent resource for anyone who is interested in tube amps.

I will have to take print of your post and read it multiple times. Thank you for the same.