Building my first 18watt from the ground up.

[spin]

Greetings everyone, this is my first post here. Quick intro, my name is Tommy, I build pedals and sometimes I build amps. I've done some Champs, a Bassman, a 100w SLO, and a Fender stand alone reverb. All of which were verified projects before I started. A few months back I picked up a small headshell on another forum and decided to do something 18 watt, from scratch. I chose to try the TMB with single/parallel input. Any criticisms of my schematic below would be well received (note the written voltages have since been raised from PI forward). I've built a working prototype as well, but it's not quite where I want it to be.

62385958_594086901068314_6094121915109081088_n.jpg

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[JMPGuitars]

Welcome to the site!

I would recommend comparing your schematic to one of our verified schematics in the download section: viewtopic.php?f=25&t=24433

Find what's closest to yours, and then ask follow-up questions if you have any.

Thanks,
Josh

[geoff 1965]

hello,
looking forward to seeing this one! what transformers are you going to use? your el84 plate voltage is quite low,is there a reason for this?
good luck with your build.

[spin]

hello,
looking forward to seeing this one! what transformers are you going to use? your el84 plate voltage is quite low,is there a reason for this?
good luck with your build.

I'm using a set of Edcor transformers (xpwr221, cxpp21-mx-8.6k). When I did the math at the beginning, I calculated 250-0-250 would give me the 340V B+ I was going for, obviously there was an error in this calculation. I'm pondering ordering a 285-0-285 for the final build. As it sits right now, I have 318 at B+, 310 at plates. 295 at screens, 281 at PI, 273 at V2, and 268 at V1.
Thanks for the encouragement, it's been a learning experience.

What the chassis may look like:

57272206_259951784798068_1032227005124313088_n.jpg

57504476_572973899874750_4839009961570729984_n.jpg

[geoff 1965]

look's good!
if you are using diodes to rectify 285-0-285 will be a bit too high,275-0-275 will give you a B+ of around 355VDC give or take.have a look at the classic 18W voltage chart in the downloads also if you look through the schematics a few have voltages.there is quite a bit of variation i.e. the lite 2b's can have up to 350V on the plates whereas the latest superlite voltages are lower in comparison.it depends on what you are aiming for with tone & headroom.

[crgfrench]

Hi Spin, are you the guy who builds BMP PCBs?

[spin]

look's good!
if you are using diodes to rectify 285-0-285 will be a bit too high,275-0-275 will give you a B+ of around 355VDC give or take.have a look at the classic 18W voltage chart in the downloads also if you look through the schematics a few have voltages.there is quite a bit of variation i.e. the lite 2b's can have up to 350V on the plates whereas the latest superlite voltages are lower in comparison.it depends on what you are aiming for with tone & headroom.

I really appreciate the input, I'm looking into some options now. 275-0-275 seems more reasonable, I figured if I went high, I could use a dropping resistor to bring it down. Now that I have a working example, I'll have something to measure current draw on and get a better calculation. For the first go-around, the trial and error hasn't been too bad, just wish it wasn't on iron. Maybe I can come up with some cool SE one off to utilize the transformer.
I wish I knew what I was aiming for tone wise. I do like some gain, but I don't want to end up with a collection of high gain amps. As I said in my opening post, I make pedals, so realistically I should keep this kinda low gain to use a pedal platform. It's about the journey anyway, I'll be having fun regardless.

Hi Spin, are you the guy who builds BMP PCBs?

Yes, I do make a BMP and RAT project PCB that I was offering on the DIY Stompboxes Facebook page. I also have an assortment of other non-project boards.

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[JMPGuitars]

Yes, I do make a BMP and RAT project PCB that I was offering on the DIY Stompboxes Facebook page. I also have an assortment of other non-project boards.
64319954_1047106062151775_3436845118160633856_n.jpg

Nice looking boards, where do you have them made?

Thanks,
Josh

[spin]

Nice looking boards, where do you have them made?

Thanks,
Josh

The ones pictured are from JLCpcb.com out of China. I usually start with a small batch from OshPark before committing to a larger order. I'm not overly happy about using a Chinese supplier (Sorry to any Chinese folks here, I like to source locally, nothing personal), but the service from JLC has been great and the turnaround is fast. I've had no issues at all with the PCBs and the quality is higher than you'd expect for the price.
EagleCAD is my primary software, but I'm looking at moving over to KiCAD once I figure it out.

[JMPGuitars]

The ones pictured are from JLCpcb.com out of China. I usually start with a small batch from OshPark before committing to a larger order. I'm not overly happy about using a Chinese supplier (Sorry to any Chinese folks here, I like to source locally, nothing personal), but the service from JLC has been great and the turnaround is fast. I've had no issues at all with the PCBs and the quality is higher than you'd expect for the price.
EagleCAD is my primary software, but I'm looking at moving over to KiCAD once I figure it out.

Interesting. I'll have to check them out. I've been interested in trying out OSHPark, but I originally designed all my boards in Express PCB, and I've been too busy to redesign them in a different program. I'd try out JLC too, but do they do through-hole vias? I downloaded kicad, maybe I'll see how it goes when I get some free time.

Thanks,
Josh

[spin]

Interesting. I'll have to check them out. I've been interested in trying out OSHPark, but I originally designed all my boards in Express PCB, and I've been too busy to redesign them in a different program. I'd try out JLC too, but do they do through-hole vias? I downloaded kicad, maybe I'll see how it goes when I get some free time.

Thanks,
Josh

The strain relief on the wiring of the BMP board is just a large plated via. I actually think JLC is more capable than OSHPark (slots and whatnot). They also offer a lot more layers, though I don't even expect to use more than the standard 2 sided boards. Another draw of JLC is the solder mask color options at no extra charge. You will have to export Gerbers for JLC, OSH will natively read .brd EagleCAD files.

[JMPGuitars]

The strain relief on the wiring of the BMP board is just a large plated via. I actually think JLC is more capable than OSHPark (slots and whatnot). They also offer a lot more layers, though I don't even expect to use more than the standard 2 sided boards. Another draw of JLC is the solder mask color options at no extra charge. You will have to export Gerbers for JLC, OSH will natively read .brd EagleCAD files.

Yeah, I usually am only using 2 layers too. I definitely like free color options.

[crgfrench]

Huh ...similarities abound:
Caps BMP 13 & Fullerwell 14
Resistors BMP 23 & Fullerwell 24
Transistors BMP 4 & Fullerwell (tubes) 4 or 5
Diodes BMP 4 & Fullerwell 4
Pots BMP 3 & Fullerwell 4

I will order your PCB that looks like a fun project!

[spin]

Huh ...similarities abound:
Caps BMP 13 & Fullerwell 14
Resistors BMP 23 & Fullerwell 24
Transistors BMP 4 & Fullerwell (tubes) 4 or 5
Diodes BMP 4 & Fullerwell 4
Pots BMP 3 & Fullerwell 4

I will order your PCB that looks like a fun project!

I appreciate the support. The BMP is the better of the two projects, not to say the RAT isn't fun, just that the BMP has a lot more range, IMO. Shoot me a PM, we'll get one out your way. I have a BOM from my vintage ramshead and some button top transistors I can pass on, well worth a test run.

[spin]

Made some boards after I verified the layout. I think they turned out quite nice. 2mm FR-4 and 2oz copper.

JLC PCB (low).jpg

[JMPGuitars]

Looks nice!

BTW- I started using KiCad. So far it's not bad. I already made my schematic, when I have time I'll move on to the board.

[spin]

I used KiCad for these boards, but I did not use the schematic editor. I'm working on learning that part soon when I can put some time into it. I was able to draw these using just plated VIAs for the turrets and wirepads. I used eagle to do the base layout as I'm still faster using it and have my libraries built up. Looking forward to seeing what you come up with in it.

[spin]

Drilled the top of chassis today and did a test fit. Little tight, but I'm not seeing any problems yet.

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[JMPGuitars]

If you turn your tube sockets 45 degrees, they'd all fit better, and you could put them in a single row. Having them in a single row means the heater wires won't be traveling under or around the board. The heater wires can cause issues with noise and such, so keeping them shorter and together usually works out to your advantage.

I'd also suggest using taller standoffs. A little more room will give better airflow around the board.

Thanks,
Josh

[colossal]

Very creative!

So did you swage and then solder the turrets (on the bottom) to the vias?