SKYLINER build - inspired by ODS #124 and #060

[Stephen1966]

Greetings tubaholics!

This topic picks up where I left off in 'ODS 124 - revisited for the 21C'
https://ampgarage.com/forum/viewtopic.p ... &start=360

The prior topic was focused on the possibilities for updating and refining the ODS124 amp to include reverb and a few extras. Where it was exploratory, this topic will include the build, testing and final project files.

To get us started, I include my working schematic: SKYLINER 2.0
[Edit; updated 18/12/2021 to SKYLINER 2.1 - observed voltages added]

SKYLINER 2.1.pdf

A note about the PSU: When working inside the amp, I always ensure my caps are drained before starting any procedure. Resistors in parallel with the caps in the PSU naturally discharge all the caps when the amp is switched off (but still plugged in) to a safe working level within about 2 minutes.

And also, my layout: SKYLINER, low plate custom reverb

SKYLINER layout.pdf

Please note that the SKYLINER 2.0 schematic is largely untested. The only tests I can confirm at the moment are that the relay system works and that the FET has been biased using two 9V batteries in series. As I write, the amp circuit has not yet been powered up and I'm following the discussion on forming new electrolytic caps before I proceed with further testing.

A word about the structure of the layout pdf. I was very impressed by user coolidge's '#183 build attempt' topic: https://ampgarage.com/forum/viewtopic.p ... 26#p423326 and noted especially that he had built his amp in layers. This is true of the #124, too. We can see it in the photos hosted on Rob Livesey's site https://thesubjectmatter.com/dumblearchive.html and so, when constructing the pdf it was done in layers with the first stages at the bottom and the final stages at the top. This provided the blueprint for the build. When you open the pdf, you will see all the appropriate build layers on top of one another. Use adobe acrobat (or reader) to hide the layers to 'Hardware base, back and side panels' which was my start point, integrating the components with the chassis.

Some layers are you start and finish before moving to the next and others (later on) are combined to include a bit of this and a bit of that. And I already have some notes about what works and what doesn't work so well but following this layout pdf, you have a kind of build manual for how you might put this amp together yourself.

I've tried to keep the build as faithful to to Dumble's methods as possible and so at the very first layer, you will find the layout made from the files in https://ampgarage.com/forum/viewtopic.php?t=5719 - Ayan Gill, Martin Manning, Tony Albany, ic-racer, "Billy" all deserve special mention and my profound thanks for their historical contribution to the #124 documentation and study. The photos and sketches became my primary source, backed up by the 1.6 (1988) layout [correction: the schematic is 1.6 and another vital point of reference, but the layout by Tony and Martin was my main go to]. If you compare the original photos with my build, you will see there are many similarities, but some differences as well, this is an updated and modified version, after all.

When it came to the reverb, I owe a special debt of gratitude to Baz for his study and Spice simulations of the #060 reverb circuit which is incorporated in this build. Frustratingly, Chris Barnett, who documented the #060 with schematic sketches and photos didn't offer much for the reverb part of the circuit so we used Aaron's schematic of the #060 and the photos, and Baz's simulation to piece it all together. As it stands, you will find some components are coloured red as a memo to self to test these components for their values but if I were to include all the supposed values for completeness, the whole reverb circuit would be in red perhaps. However, the testing to be performed will be to reduce the -6dB loss Baz simulated and that will probably hone in on the mixing and grid resistors as outlined in my previous post by Martin Manning.

Baz, if you're listening, I have the components for the other reverb circuits you put together but they deserve whole new amps for testing

The pdf layout is largely illustrative, meaning that some views are made for clarity, as you will see from the photos I will be posting, in real life, the lead dress was slightly different. I do think lead dress is very important to the SNR and so I've done everything I can to be as faithful to the Maestro as possible.

Forgive the omission if I haven't mentioned you by name, I've listened and learned so much from you. Thank you.

Stephen

[Stephen1966]

Here are some more constructor's files for the SKYLINER

This is the drawing for marking up and drilling the chassis, the 2019 version of the TT-Chassis 003 - 590 x 190 x 64 (mm) from Tube-Town in Germany

Skyliner - CHASSIS DRILL CENTRES.pdf

Again, the pdf is in layers.Front back and sides are shown with all the dimensions in view but you should open the layers panel in Acrobat or Reader to get the dimensions of the component fittings for the base.

Then, there are the boards, there are nine [correction: 10] boards to make altogether. The Rectifier and Relay Filter boards were combined in one due to the narrow space left over after I had chosen the power module and front face fittings (LED and power switch). I'm not offering a BOM here because I figure you will want to use your own selected components though some, will probably end up the same. I get end of life notices all the time and some of the parts that went into this amp are already obsolete, though perfectly workable in my view.

Five of the boards are PCBs I made myself. This sheet can be printed (at 100% scale!) onto copper sided blanks and then etched using an etching agent like ferric chloride - fairly benign stuff but my advice is follow the safety instructions and dispose of it sensibly. The solution can be stored and used again. It takes about ten minutes to etch these boards.

PCB print 17-08-2021.pdf

I'm already thinking of replacing the FET board in the amp with one using precision trimpots for the voltage source resistor and the drain resistor. Martin Manning mentioned that when he was designing his version of the FET board he had considered using trimmers in these locations. I think it's a good idea especially for biasing the FET source resistor since mine - under test - required 3.9k to get the correct bias so I ended up replacing the fixed (2.32k) resistor with a 5k trimpot which gave the correct bias. My upgrade will use 10k Rs and 25k Rd which should provide the scope for some nice experimentation. I'm using the modded board to get things started and if the Rd voltage is off, it is easier just to replace the whole board.

Here's a picture of the current board:

SAM_7537.JPG

The etched boards look like this:

SAM_7420.JPG

[Stephen1966]

... then there are the main boards

All of these have backing boards as well. Actually, apart from the power board, the blank boards were meant to be 2mm thick but Tube-Town sent 3mm by mistake and by the time I noticed it, it was too late to do anything about it. So they ended being quite chunky but I'm gong to call it MIL-SPEC

In no particular order, here are the board drawings:

FET board 17-08-2021.pdf

FET relay 16-08-2021.pdf

OD relay 16-08-2021.pdf

PAB relay 16-08-2021.pdf

PI board 16-08-2021.pdf

Power supply board 21-08-2021.pdf

Preamp board 16-08-2021.pdf

Rectifier and Relay Filter board 18-08-2021 copy.pdf

Reverb board 16-08-2021.pdf

RVB relay 16-08-2021.pdf

Again, printing at 100% and sticking the template to the boards is quicker and easier than marking them up individually.

[Stephen1966]

Here is my start up procedure using a variac and a light bulb limiter (LBL). Between stages 7-10 I will be forming the caps and it gives me a chance to think about the B+ voltages and if they're off by an excess of 20% with tubes out, what to do with the dropping resistors.

I've kept the procedure as brief as possible and along the way I'll be checking for the usual suspects, smoke, heat, arching, red-plating and so forth.

1. Double check diode, cap and LED polarities against schematic
2. Install 500mA slo-blo fuse
3. All switches off, tubes out
4. Check GND continuity from Gtr input to Power input.
5. Plug in the amp. Attach amp to LBL – low watt bulb, LBL to variac
6. Voltmeter to first cap,
7. Power and Standby switches on
8. Slowly raise variac to 20V for 10 minutes.
9. Slowly raise variac from 20V to 40V for 10 minutes
10. Repeat 40-60V, 60-80V etc. until variac reaches 240V
11. Power and Stby off
12. Replace 500mA slo-blo fuse with 2A slo-blo
13. Install preamp tubes
14. Power switch on – monitor heaters’ response and measure voltage on pins 4/5 and 9 all tubes
15. Standby switch on
16. Record voltages on each tube’s pins
17. Clip voltmeter to power tube grid pin 5
18. Measure negative voltage and adjust bias for lowest (-60V) voltage
19. Power and Stby off
20. Connect dummy load, install power tubes
21. Volume and master at 0
22. Power on
23. Check LBL
24. Stby on
25. Check LBL
26. Power and Stby off
27. Repeat 20-25 with speaker in place of dummy load
28. Test and play.
29. Power and Stby off
30. Remove LBL

Then it will be on to biasing the amp - touch wood!

Stephen

[Aaron]

Wow, great posts! Nice work mate.

Aaron

[Stephen1966]

Wow, great posts! Nice work mate.

Aaron

Wait! There's more

I was watching interviews with Elon Musk recently talking about his Starliner and he said something to the effect that it takes 10,000% more time to put the infrastructure in place around a project than it does to make and execute the design. I can confirm that, the build took about 100 hours over two weeks but the planning and design took over a year. New technologies and new skills have to be developed along the way.

the first real task of design was to determine the placement of the transformers. Here I'm playing with the position of the output transformer:

SAM_7353.JPG

SAM_7354.JPG

And with the choke

SAM_7357.JPG

You will notice a pair of headphones in the background. The headphone trick, yes it does work but it is either my hearing or the crappy headphones I didn't get a really definitive indicator of hum except when the OT was really close to the PT. The DVM wasn't so conclusive either. So, in the end I opted for the signal from the scope in which it's easy to see the difference. A note about that. We have LED lighting in a room about 10 ft away from where this shot was taken and with the lights switched on the waveform picked them up. The OT was doing its job acting as an antennae. Side note: next project - man-sized Faraday cage

All this was pretty academic however, because the final position of the OT was practically the same as found in the original by Martin in his topic 'ODS #124 Chassis Layout - https://ampgarage.com/forum/viewtopic.php?f=5&t=7405

Not being happy with any of the currently available D-type chassis, I decided to try to make a drawing from the #124 info. I think the attached file is pretty close now after a couple of days of nudging things around to agree with pictures and known part dimensions. Any comments?

MPM

You can see the choke picks up quite an erratic waveform when placed midway between the PT and OT but I'm reliably informed this is not a serious issue. Erring on the side of caution, it is probably better to place the choke slightly closer to the PT than to the OT which is what I ended up doing. Though looking at it now, you would be hard pressed to say it isn't centered.

That decided and the holes cut, it was time to prepare the remainder of the chassis.

[Stephen1966]

After placing the transformers it came down to a lot of nudging in the design of placement in the rest of the components. The chief concern was to pack all the tubes in at a sensible distance from each other but also, to ensure the PI tube is as much out of the area of the OT as possible. Following the traditional - tubes in a row - idea, it doesn't offer much leeway. It required thinking in 3D since the components shouldn't just fit in the plan but in the elevations as well and a note - you can't always trust datasheets, I took all the measurements from the components in hand and there were often discrepancies with the published data.

However, a long time later, it was possible to finish the work on the chassis.

SAM_7385.JPG

SAM_7396.JPG

By this stage I had already had my face plates cut and these needed to be fixed to the front and back before going any further. I used double-sided tape, but it was a real pain and in the future I will use something like silicon which allows for some adjustment before it sets in place. You get one-shot with double-sided tape and if you are even a few tenths of a millimeter out, you will know about it. Please don't ask me how I know about it

SAM_7392.JPG

SAM_7395.JPG

[bepone]

great ! with time, no need to plan anything, just random making holes by inspiration

[Stephen1966]

careful! "Random" was my mother's name!

bepone, my friend, we are talking about forming the caps. In your experience or in any of your studies did you find anything about waking the dielectric with a jolt to get the process started? I have some information - I'm not sure if it is privelaged or not so I'm hesitant to share it at the moment - but there is an idea that the process might start at about 50%-60% the final mains voltage.

What do you think?

Stephen

[bepone]

if you consider building amps like an art then also random holes on the cahassis are acceptable"!
about caps.. i dont know, idea is to slowly charge them to max voltage, then there is a formula about leakage current, so charging current neds to be below that ..the best is to put hundreads of Kohms before +terminal and see how it is going and slowly raising the voltage on variac.. inrush current would be limited to (Vmax/100.000 ohms)= couple of mA this should be acceptable. install that and go to drink several beers and return after one hour im often lazy to do that because i want to hear the sound, and have destroyed some caps in progress (JJ, several times)

after initial forming (several times) caps will be reformed more after in use and come to normal state.. so no need to worry after

[Stephen1966]

Install 100k resistor before the B+ terminal? I see how I could do that. I'll have a look at the datasheets to see if there is any information about leakage current.

I guess there is another way to limit the carnage using the light bulb limiter. Using a 40W bulb at maximum (240V) gives us 0.17A, but 40W at 50% of 240V (40/120=0.34A). I mean, is it possible that starting with a higher initial voltage is about limiting the available current? Have I understood it well?

It would appear safer to go with the 100k resistor between the rectifier and B+ terminal.

[bepone]

sorry i meant "inrush" current to the first capacitor , so if you apply in theory 450VDC and Cap is on 0 V, and between is 100k , then first "inrush" (charging) current is limited to mAmps only, this all without any protection bulb. so you can turn the variac slowly and cap is portected with 100k

[Stephen1966]

The intended leakage current of my reservoir caps is very small so I'm glad you clarified.

Let me see if I now have this straight. The 100k resistor limits the inrush current and using a DVM across it provides a sensing function of ESR as the forming takes place. The dielectric needs heat to form and the current produces this. I'm not too worried about starting with a higher initial voltage or with zero voltage but the process of increasing the voltage and charging the caps has to be slow, and repeated. I first estimated it would take a couple of hours to reach full voltage. I think RobRobinette considers his caps fully formed after a single cycle, but it seems for the optimum longevity of the caps it is a process that should be performed several times.

[Stephen1966]

So, we are going this way and that here but if anyone has any further ideas about cap forming I would like to hear them. I'm eager to get started but I've been building up to this point for over a year so I'm not in any rush to blow it at the last moments.

Here are some more build and testing ideas... In the #060 HAD separated the preamp from the reverb and PI boards and it produces a nice modular design that we were also looking for. Keeping the reverb board separate means it could be replaced with a different design without too much effort.. later perhaps.

In this photo you see the preparation of the boards before integration with the chassis.

SAM_7496.JPG

You will note the black marks on the orange drop caps. This is outer foil placement for a low SNR covered in a sticky in the Discussion pages 'Capacitor Outside Foil Placement Dumble' https://ampgarage.com/forum/viewtopic.p ... 17#p298917 you will notice also the silicone around the base of these caps. That's there for two reason: first, it provides a measure of mechanical stability but more importantly, it conceals the legs where they enter the epoxy body of the caps. There may be some slight thermal protection here as well but its main purpose is to keep moisture out of the caps. This silicone is sensor safe meaning it doesn't include acetic acid as a curing agent and it is safe to use with electrical components. We talked a lot about gunk in the last topic, but it has its uses, and it should handle the intense heat expected from the amp going full throttle. Sorry if white offends you

[Stephen1966]

Moving on, after the initial components were installed in the base up to the 'Switches and jack wiring' layer in the layout pdf it was possible to test the relay system. The relay filters and coils are entirely separate from the amp circuit apart from the common connections to ground and the mains power supply. Once this part of the build is complete and without any signal wires attached anywhere, you can jury rig the relay transformer to test.

The mains wires, hanging over the back here are attached to a plug and socket with a switch (in case of fireworks). The manual/pedal switches on the back have nothing to do with the signal but only open or close the circuit with the relay coils: keeping the circuit in the chassis (manual) or extending it out to the pedal, not connected here. Because the pedal is not connected, the circuit is open and so switching between manual/pedal effectively turns the relays on and off.

SAM_7514.JPG

The relay circuit design was experimental so it was a relief to see that it worked.

SAM_7519.JPG

A word about relays... Never having worked with them before it was something of a learning curve to understand how they work and I wouldn't call myself an expert in them now but here is what I learned. These kind of relays are non-latching which means they are only active or polarised when a current passes through the coil. This particular type, it doesn't seem to matter which side of the coil you feed in the DC but all mine take it in the same side and they work so... yay! Researching schematics for all the different ODS versions, Fender's you name it, you find a number of different ways they are represented in schematic form. And some of them look more forbidding than they are but with the relay in hand, you can attach a DVM probe to one of the COM legs and test for continuity by touching the other probe to first the normally closed leg, then the normally open leg. The datasheet told me that the relay is normally closed when it is unpolarised and this little experiment, without hooking them up in any other way, proved that: you get a closed circuit between COM and NC in the relay's idle state.

Of course when it fixed on its board and under test as in the photos above, you can then test for signal switching COM1/COM2, NC1/NC2, NO1/NO2 checking it for continuity against the schematic, checking that it behaves as expected. It takes a bit of time to go through this, but it's worth the effort because when it all works, you can move on with a little peace of mind that it is one more complicating factor off the list.