18Watt.com

Haven't been around for a bit and now ready to build an amp. Is the GDS kits still the "more" "preferred" kit at this time? Thanks.

Yes, GDS is still a great source for a kit.

Most important is to avoid bad sources like mojotone or tubedepot (and those that resell them). They're both good for some things, just not their 18W amp kits.

Alternatively, you could pick a specific circuit you want from the downloads section and build without a kit.

Thanks for the response. I have built only three pedals all from kits and they have been successful so I feel that I might be ready to build an amp from a kit. Not sure about just downloading the circuit and sourcing the parts. I took a glance and do see layouts, drawings and BOM so that is intriguing. On the cost side how much mark up on the kit versus buying all the parts? reason I ask is that it would be nice to buy as you build instead of shelling out the whole cost of the kit at once.

If you're referring to the Tremolo TMB with the full docs and BOM, that's not a beginner build. With some time practicing soldering (see videos linked in my signature), and taking your time with the build, you could do it. Though I would suggest building something else successfully first.

I'd suggest GDS' single channel kit, or the Lite 2b(ish) as your first build. It's a simpler build with less components, and it's a great sounding amp. You can use the BOM from the Tremolo TMB as a starting point for sourcing components.

JMPGuitars wrote: ↑

Wed 02/04/26 11:06 am

I'd suggest GDS' single channel kit, or the Lite 2b(ish) as your first build. It's a simpler build with less components, and it's a great sounding amp.

I did that amp as my first ever tube amp build - turned out great!

I didn't buy the Mojo kit, but I used their chassis and "small parts kit" as a starting point (the front facing combo cabinet from them is 1st rate) and got my transformers from Pacific Audio Magnetics (great OPT but cant understand why they have only 8 ohm tap - no 4-8-16). I radically changed my build to essentially Josh's Modern Classic, and i'm thrilled at first try today through a Vox/Celestion Blue (more in-depth later). So I used Mojo's turret board and modified the layout to the Mod. Classic schem.

I do have a few remarks about the parts kit from Mojo:
The chassis is very good, but has alot of sharp edges. Recommend filing it a bit before beginning to minimize cuts. It has everything punched or drilled you might need and some extras as well. I shock mounted the EF86 in the first position with Wel-nuts do had to drill one tiny hold for the external ground to of the socket.

The documentation online did not match the turret board i received so i emailed them and found that it was an old version turret board and they sent me the current layout (which I changed significantly anyway to match the Mod. Class. circuit).

I was unimpressed with the quality of some (but not all) of the Mojo parts. I changed most of the coupling caps to Mallory 150s since I was changing values anyway, but suspect the Mojo Dijon caps would've been ok had i used them, and the carbon film resistors seem fine. But in the end I replaced ALL the jacks with real UK made Rean and the switches with Carling, and ALL the pots with CTS (including a couple which have switches pull/push to control the bright/fat and additional brightness functions). I left the tube sockets as Mojo, but they seem to easily melt and have weaker pins with smaller holes than the Beltons or Mil-spec ones I typically use.

There were several things about the Mojo circuit I don't understand. They sent a 130 ohm cathode bias resistor (with a 25uF cap), which in my amp with my line (119VAC) over ran the output tubes. I replaced this with a 180 ohm and 1600 uF cap and now get 12VDC on the cathodes. With plate voltage of 338 Robinette's calculator says i'm doing about 10.6 watts or 88% which I believe is safe and sounds great.

Mojo also sent 100ohm resistors for the screen grid stoppers (I replaced with 2W 1K), and they used 5100ohm for the grids (I replaced with the 8.2K as per Modern Classic circuit).

But maybe the biggest problem was that MOJOTONE shows the screen grid and control grid resistors wired to pins 2 & 6 and 1 & 9 respectively. While this may seem to be ok as these are often shown as "not connected" or "unused" on tube charts, when I fired it up the first time to test, one of my (MULLARD) EL84s glowed bright red. Turned down the variac and started testing voltages finding an inexplicable high voltage on the control grid. After running out of explanations, i pulled out one of this pair of Mullard tubes & discovered pins 1& 2 were actually INTERNALLY CONNECTED! - But only one of them! So I went back, installed lug strips and tied the grid resistors to it removing them from the sockets. ANYONE using a MOJOTONE kit or schematic need to be aware of this issue - it may be that using modern tubes or certian brands might have been fine - but who wouln't want to use Mullard EL84s in a British type Marshall type amp? I've built dozens of EL84 amps over the years but never knew about this issue until now. Never tried to use the N/C pins for components before though.

MOJO also uses a ground scheme I don't think ideal - buss soldered to the rear of the pots and preamp supply caps tied to the buss, etc.

As I said the MOJO cabinet is first rate. When i finish some minor cleanup and full test I'll send pics & voltages, etc. I'm SURE Josh will have a few pointers on my wiring/soldering technique so looking forward to that! This is a GREAT forum and thanks to all who contribute!

whboyd wrote: ↑

Thu 02/05/26 5:01 pm

When i finish some minor cleanup and full test I'll send pics & voltages, etc. I'm SURE Josh will have a few pointers on my wiring/soldering technique so looking forward to that! This is a GREAT forum and thanks to all who contribute!

Looking forward to seeing your build!

Thanks for the rest as well- very good comments and feedback on the quality of the stuff you got from them.

I also agree on the comments about grounds and not using the unused pins.

Thanks,
Josh

thanks Josh, I did send my comments to Mojotone so they can think about improving some of these items. Why do you think so many seem to be using 130 ohm cathode bias caps when it seems they'll mostly over-run the EL84s?

And I am picking up a little radio signal on the TMB channel so wondering if you think the "R34" you suggested to another poster relative to his Trinity plexi noise might be a fix or would you suggest something else? Apologies if this should be posted in a different thread!

whboyd wrote: ↑

Sat 02/07/26 4:35 am

thanks Josh, I did send my comments to Mojotone so they can think about improving some of these items. Why do you think so many seem to be using 130 ohm cathode bias caps when it seems they'll mostly over-run the EL84s?

Because, like many of the components chosen in kits, they base them on historical nonsense instead of what's the best or most appropriate option now.

And I am picking up a little radio signal on the TMB channel so wondering if you think the "R34" you suggested to another poster relative to his Trinity plexi noise might be a fix or would you suggest something else? Apologies if this should be posted in a different thread!

Start your own thread.