Polski (PL) 
English (United Kingdom) 
Damian 'Ghost' Smółka
(Published on the TRIODA-Grzegorz Makarewicz website on May 9, 2021)
Hello. In this article, I'd like to present a piece of equipment I recently had the pleasure of making – the Soldano SLO-100. This is my fourth tube project I've completed, and I consider it the best one I've ever made with my soldering iron.
Technical data:
- Power – 100W
- Power tubes – 4 x 6L6WXT+ Sovtek
- Preamp tubes – 5 x ECC83 RFT
Transformers:
- TS – IGMT-SLO100
- TG – IGOT-SLO100
- Choke – IGCH-SLO100
Channels:
- Normal Channel – Controls: Preamp Volume, Master Volume, Bass, Middle, Treble, Presence, Depth, Switches: Normal/Bright, Clean/Crunch,
- Overdrive Channel – Controls: Preamp Volume, Master Volume, Bass, Middle, Treble, Presence, Depth,
- Equalizer – Common for both channels, additionally Presence and Depth adjustments,
- Channel switching – Available from both the footswitch and the front panel switch. LED indicates Overdrive channel operation.
Other:
- FX Loop – Tube, non-adjustable,
- BIAS Adjustment – External measuring points, trimmer for adjustment,
- Speaker output – 2 x Jack, Impedance switch 4/8/16 Ohm.
Diagrams and layout I used:
The PCBs were purchased from Tube-Town - https://www.tube-town.net/ttstore/product_info.php/info/p935_Soldano-SLO100-PCB-Set.html.
As for the execution itself, I divided the work into individual stages, as always.
Day 1
With all the necessary components in place, the first step was adapting the chassis to the existing components and drilling mounting holes for the transformers and PCBs. Protective tape proved helpful, and after aligning the components, I drew out their layout. I usually do this directly on the chassis, but this time I was working with a powder-coated chassis, where the pencil marks were faint and easily rubbed off.
To drill the holes, I used a stepped drill bit—the popular "Christmas tree" drill bit. Additionally, I had to ream out the holes in the knobs because it turned out that, even though I'd planned for them to be the correct diameter for the potentiometers, they were still too small and wouldn't fit onto the shafts. This completed the first stage of work. It was time to install the first components in the chassis.
As you can see, I've placed a mounting block under the power supply PCB. I saw this in someone's SLO copy and liked it because it allows for relatively neat cabling. This will be visible in the photos to follow.
To summarize the first day of assembly, I installed the control panel, Power and Standby switches, power socket, mains fuse, preamp and output tube sockets, BIAS measurement points, and the mains transformer. I've also connected some components. Everything can be seen in the photos below.
As you can see, the connections on the switches and the mains power socket are made using connectors. These connections are additionally protected by heat-shrink tubing for safety reasons. A similar procedure is performed on the fuse sockets. All connections in this area are made using tight twisted pairs, further simplifying cable routing within the chassis.
Day 2
With the mains transformer connection already preliminarily completed, I decided to start the next day by assembling the power supply board. The first thing I had to do was slightly enlarge the holes where the incoming wires would be soldered. This was justified by the fact that I decided to use Turret pins in these locations, as this allowed me to later solder the wires from the top of the board, which significantly simplified assembly.
With all the components prepared, I began fitting them to the board. After a few minutes, everything was ready and soldering could begin.
Fifteen minutes with a soldering iron in hand and the result is visible below. At this point, I freely admit that, despite trying to keep reasonably meticulous photographic documentation, I didn't take a single photo showing the underside of the board (the same with the preamp board) – I'll try to remember that next time, but for now, "bird's eye" photos will have to suffice.
Next, I decided to run the filaments to the output tubes. This is where the first difference between my version and the original becomes immediately apparent – I run all the filaments with a twisted pair, while the original uses straight lengths of wire. Why? I didn't have wire thick enough to handle 9A of filament current, and besides, I didn't want to risk any potential negative side effects – my rule is to always run the filaments with a tight twisted pair.
The wires going to the sockets were connected to the wires from the mains transformer in a terminal sleeve and then placed in a "distribution box".
Next, I installed the output transformer and choke because I decided that I first had to deal with the issue of running power to all the points that required it.
I started by connecting the anode fuse with the choke and the TG. Then, I connected the power supply for the indicator light and the constant filament voltage to the connector. I also connected the choke to the connector, which powers the secondary grids of the output tubes and the preamp power supply board.
Then, as a way to relax from fighting with cables, I assembled a trimmer system for external BIAS adjustment.
The next step was to finish wiring the "switchboard." I ran the necessary ground wires from it, and connected one end to the chassis.
The maneuver performed with the purple wire will probably be puzzling. The reason is simple – I cut it too short while in a hurry, and after installing the power supply board, it didn't reach the point it was supposed to. Fortunately, I had one spot left on the connector, otherwise I would have had to extend it differently.
At this point, I considered the power supply wiring stage complete. I checked to see if the power supply board fit easily into place and then checked the clearance between the connector and the board.
I considered the distance satisfactory, but as a precaution, I also taped the top of the cube with duct tape. At this point, I decided to end day two.
Day 3
I came to the conclusion that at this stage I could easily mount the power supply board in the chassis, but to do so I first had to wire the filaments for the preamp tubes.
Next, I soldered resistors for the filament voltage under the power supply board (visible under the white and purple wires in the photo). In this design, only the preamp, which is filament-fed with direct current, is filament-fed. The output stage is filament-fed with unbalanced alternating current. This solution has been discussed several times on the forum, so I decided to test how it performs in practice.
Before installing the power supply board, I decided to connect the power supply to the anodes of the power tubes.
Next, I placed the power supply board in place and soldered all the necessary leads. It turned out that all the dimensions were perfect – the board slotted into place without any problems and without interference with other components. It was possible to remove the connectors from the switches and power socket without removing the board.
Unfortunately, due to time constraints, I had to stop assembling the elements for that day.
Day 4
I decided that the next thing I would do would be to get rid of the last untamed tangle of cables, i.e. the output from the speaker transformer.
After preparing the mains power sockets and then installing them together with the switch, I was able to cut the TG cables to the appropriate length and then started soldering them.
Later in the installation process, I discovered that I had accidentally cut the yellow cable too short and had to replace it with a longer one. Fortunately, this wasn't a problem. That concluded another day of installation.
Day 5
The next day, I decided to assemble the power amplifier. I installed the power tube sockets with the intention of assembling the entire system exactly as it appears in the photos below.
The next step was to assemble the external BIAS measurement system. I know it's already visible in the photos above – this is because I didn't always take continuous photos, but rather shot a whole series of them in bulk. Because of this, the photos sometimes show that something I haven't mentioned yet is assembled.
Then I installed the Footswitch socket and the channel selector switch on the front of the amplifier.
At this point, I had assembled practically everything that didn't require connection to the preamp PCB. It was time to assemble it, but I decided to do so the next day. That day, I also prepared all the components to the appropriate dimensions so I could begin the next step by soldering the components onto the board.
Day 6
As with the power supply, I also used solder pins on the preamp board where it would be easier to solder the wires from above. The next step was to solder the jumpers into the appropriate locations. Next came the resistors, the bridge rectifier for the switching circuit, small capacitors, and finally the VTL5C1. At this point, the board looked like the photos below.
The red wire at the top of the board that connects point B2 to GND is the power supply to point B2. I'm writing about this because I've already received a question about it via email, so I decided to clarify this issue to avoid any potential misunderstandings.
Then I installed all the remaining capacitors.
And I also connected the wires that I had already cut to the appropriate length.
I finished the day by connecting the power supply for the Overdrive channel LED, connecting the Bright/Normal and Clean/Crunch switches, mounting all the potentiometers on the chassis, assembling the input jack and connecting the ground rail on the potentiometers.
At this point, I had to put editing on hold for two weeks because I was away at university. However, upon returning home the next day, I finished the piece.
Day 7
Before leaving, I had all the amplifier components ready; all that was left was to mount the preamp PCB in place, make the necessary connections, and the first tests could begin.
First, I powered up the power amp and inverter to check if I'd connected the anode power supply from the TG to the output tubes correctly. The squeal that appeared after switching on the anode voltage quickly answered that question. A moment with the soldering iron to improve the connection, a second attempt, and... the silence I'd been waiting for. Then I inserted the return tube for the FX loop, plugged the guitar into the Return input, and performed my first sound test. As expected, a nice, clean sound. I checked the EQ and other controls. Everything was fine.
All that was left was to insert the remaining tubes and test the amplifier's full potential. An hour of testing with a guitar revealed that everything worked as it should. As for the sound, "amazing" perfectly fits the description. The clean channel has a nice, classic tone. Engaging the Bright setting allows for a nice "glassy" effect. Switching to Crunch mode gives you the perfect channel for playing blues and rock ballads. However, the real power of this monster is undoubtedly the Overdrive channel. This beast reaches my required gain level around 6-7 on the scale, so there's still some headroom up to 11 for true rock-throwing enthusiasts.
I set the bias current to 42-44mA (this is the discrepancy between the measurement points). The next day, I performed an endurance test on the equipment. After eight hours of continuous use – playing music from a CD player interspersed with playing the guitar – the mains transformer had warmed up, but was still comfortable to hold, and the speaker transformer was only slightly warm. I conducted the test with the amplifier housed in its enclosure, thus operating in the conditions it would be exposed to.
At this point, I consider the project complete. To summarize, the assembly went smoothly without any major problems, except for the anode power supply being connected backwards and the footswitch socket wires being mixed up (I soldered red as ground and black as power on the board. I only realized the mistake during a final check of the system before powering it up, so it was quicker to swap the two wires on the socket than to try to do it on the board). If you have any comments or suggestions that might be useful for me in the future, please leave comments and ask questions on the forum in this thread: - http://www.trioda.com/forum/viewtopic.php?f=19&t=26189
A few more photos to finish.
And sound samples – files with the prefix "slo" are this amp. Please don't comment on the instrumental abilities :) the recordings are so-so, but I can't produce anything better.
http://www.soundclick.com/bands/page_music.cfm?bandID=1244201
At the beginning of the year, the amplifier received a new housing - here it is, in all its glory.
Prepared by: Damian "Ghost" Smółka