Building a TC-15, this amp design comes from a local amp company Trinity Amps. The amp is basically a 15W Matchless DC-30 with some very small changes. The amp has two channels, a tube recto (5UG4) and 15W output (two EL84s). It’s a Voxy type amp, kinda bright with lots of balls and really rockin break up.

Channel 1 uses a single pentode tube, the EF86. This channel has a Volume control and a six position Rotary Tone control.
Channel 2 uses two 12AX7 dual triodes and has Volume, Treble and Bass controls.

There is a master Cut control and also a Master Volume control that is common to both channels. It should be noted the Master Volume control is a push-pull pot so it can be taken in and out of the circuit as desired.

- Choke/Resistor switch. This three way switch functions as a switch that selects either a choke or resistor with the middle position being the standby function for the amp. A resistor is often subbed for a choke in power supplies in the amp. Both have their own unique tone and feel on the amp.
- Reverb! Going to add one tube reverb circuit to channel two (non-EF86 channel, TB channel). Single mix control to control reverb level/strength. Medium decay reverb tank mounted in the head cabinet. Reverb will be foot-switchable.
- Cascaded/Parallel switch. On Channel 2 the first tube parallels the two triodes. I am using a 3PDT switch to either select the two paralleled triodes or cascade the two triodes for a bunch for gain and sustain. When the triodes are cascaded there is a 70% increase in gain. In cascade the sound should be pretty smooth and rich sounding.
- Phase Inverter limiter mod. This is a trim pot in series with the “tail resistor”. This trim pot controls how clean or dirty the signal is after exiting the phase inverter and is passed on to the output tubes. Ken Fischer of Trainwreck Circuits often did a similar mod to this.
- May mod Channel 1 (EF86) to tame the highs and also add a Compression control.

Using a mix of JJ, Tung Sol, NOS Aprex and Chinese (recto) tubes.

I have a few holes to drill in the chassis and a couple of eyelets to add to the eyelet board. Once that is done I will start building. Hoping to have the amp completed by the end of the week or so. I have built a few TC-15 for Trinity before so I am not new to the amp. Going to be getting a head cabinet in the next few weeks, all black with white piping.

Here are the parts. Belton sockets, Cliff jacks, Mountain switches, Alpha pots, black Chickenhead knobs. Not pictured are the passive electronic parts. Resistors are a mix of metal cement, metal oxide, 1W carbon film and carbon composition. Capacitors are Orange Drop 6PS and Silver Mica.

Last edited by kurtlives91 at Jul 4, 2010,
Another amp build?...

Looking forward to this.
Just call me Bobby
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just seeing that pile of stuff is enough to make me happy.
I'll be very excited to see this.
will someone carry me across ten thousand miles under the silence
Can't have enough ampstruments.

Did the chassis work today. It was actually quite easy on this chassis, the aluminum isn't super thick so the drill press can easily handle it. Got a deburring tool for my other amp build that is going on so all the holes drilled are very smooth and clean. Also added two eyelets to the board for the PI mod.

Forgot to get a fuseholder that fits and a 6.2 1W Zener diode. Will get those this week.


What is that little black thing between the Transformers? And did you buy a transformer from them just for this amp? Lastly, how many amps do you have, it must be getting ridiculous now.

And I'm really looking forward to see how the cascaded vs parallel triodes will sound.


Monkey, that's a cap can. It is basically a large capacitor with multiple capacitors inside sharing a cathode, which is what you attach to ground. Most old school amps use one. Modern amps use separate capacitors rather than a can, which can even be cheaper as well as offering some advantages. But it's always nice to add some mojo.

Chris, I like it, another though is instead of a trim for the PI mod, you could make it an external pot and use an opto-isolator to control the resistance without the DC on the pot scratching noises. Might be too much effort for little more control.
THe cap can has a common negative terminal, never heard it called cathode. The TC-15 uses the cap can for B+ and screen filtering. There are five other HV electrolytic caps for filtering different supply nodes. Tons of modern production amps use them, and they aren't mojo despite what xgamer84 says.

Jared the PI mod is a set and forget type control that may be tweaked periodically for different tones. Never seen them external and I can't warrant a external one. The Phier trim pot is quite nice (I use them a lot with no issues) it can take the 70 or so odd volts.

EDIT: current own 10 amps with two incomplete ones (This TC-15 build and that own design/build of mine).
Last edited by kurtlives91 at Jul 4, 2010,
Did a bit of work on the PSU last night, wired heaters and other little odd ball off board stuff today. Here is where I am at now.

I removed the reverb footswitch and 3PDT, parallel/cascade switch for better visibility. The wiring is a bit sloppy in places, will fix up later.

This is looking really great so far! Very neat, as usual.
Can't wait!
will someone carry me across ten thousand miles under the silence
After I took those pics I decided to wire the input jacks. Usually I do those towards the end of a build because they are a real pain and annoying to wire. With being so early in the build (less other wires and more space now) they were way easier to wire and came out looking cleaner. I even got the co-ax cable to the ideal length, looks sharp.
I know you'be mentioned it before, but what kind of wire do you use? Cloth covered, 20 gauge?

Love Matchless style amps, this is going to be good.
I use PVC wire, I use both 20AWG and 22AWG.

The 20AWG has a thick jacket, is rated for 600V, a bit of a pain to work with as it is so big. I use it for the heaters, B+ runs and HV grounds.

The 20AWG is thin, super easy to work with but rated for 300V. I really like the stuff and use it as much as I can.

Both I get locally in small 100ft rolls.
Finished wiring the amp up tonight. All that I left off was two or three reverb connections. I am going to make sure the amp is working all right before adding the reverb.

Installed tubes but didn't test, that will be another night.

Last edited by kurtlives91 at Jul 12, 2010,

It makes me want to build my own amp. I will someday, but I gotta learn more first.




That was incredibly fast.
Can't wait for the tests!
will someone carry me across ten thousand miles under the silence

Going to do a quick look over tonight then go through my start up procedure.

Btw that trimpot floating near the pots... That is a 50K pot, it is a Mid control. Wired it in as a last minute decision.
Fired the amp up tonight, went through my usual start up procedure and everything went fine. The amp is working!

Besides a bad Volume pot on the EF86 (Channel 1) the amp is great.

The Cascade mode was initially howling like a scared piggie. I figured that was just the ridiculous amount of gain. I dropped some gain with a voltage divider and everything was good. No extra noise or oscillations.

Played the amp for a good hour or two and it sounds amazing, more on that tomorrow.

When I came back in tonight I wired the reverb in with alligator clips. Happy to say that is working too, though there are a few tweaks and idea's I would like to try on it.

Gotta run more on it another time...
Wow, this amp build has just flown by, (9 days) any sound clips? Or will you get to them later after you fully install the Reverb?


Last edited by MonkeyLink07 at Jul 14, 2010,
And here we go all done. Got the scratchy pot all fixed. Just playing it now and doing a bit of tweaking as I see fit.

The tones are great. Lots of versatility with the Parallel/Cascade switch. Parallel is much cleaner than cascade and a bit fuller and thicker. The Cascade mode it basically an overdrive mode, so sweet with lots of bite and gain.

The Choke/Resistor switch. The resistor mode has a bit more girth and underlying grind to it. Choke mode the sound is a bit tighter and focused, a bit cleaner. The choke runs all the voltages higher.

Reverb sounds amazing, I was stunned at how well the single tube reverb worked out. I did have to change a PSU dropping resistor to get the voltage up (290V) on the driver/tube but that was the only tweak from my original plan. The reverb is nice and full not spanky and in your face like BF reverb. When the reverb control is dimed you have a nice full sounding reverb which I like. I am not a fan of the BF Fender dimed reverb, it's much to intense for my tastes.

Still haven't fiddled much with the PI or Mid trimpots so I can't comment much there.

The Crunch/Munch switch which selects different primary windings on the OT provides two unique tones. In my prior experiences with the TC-15 I thought one mode was just brighter than the other. Not the case. Both the highs, clarity and gain differ between the two modes. I have no favorite as of now, they are both really unique and fun to play on.

Great harmonics, sustain and feel to both channels. Have already cranked the amp up and let it go into harmonic feedback while holding a note, sounds great.

More to come as I play more and the amp/speakers burn in...
Last edited by kurtlives91 at Sep 7, 2010,
Amp looks good, hopefully it sounds as good as it looks.

Out of curiosity, have you had any experience with the Triwatt? I played a Hiwatt once and somewhat liked it, and have wanted something like it but haven't wanted to shell out the money for a full blown Hiwatt.

Also as a side note, i don't know if you burn your speakers in before you use them, but I tend to use a variac and a 12.6V filament transformer to burn them in for a few hours when I get them. I use 1/3 to 1/2 the power of the speaker for 4 hour intervals. I've heard that Celestion speakers are quite a pain to break in though. Just an idea in case you were interested in doing that from now on.
Last edited by XgamerGt04 at Jul 15, 2010,
I use a 12V AC transformer for burning in. Go to school/work and leave it running. I also sometimes run my iPod through cabs to give the speakers a different kind of workout. Don't know if the difference helps or what not.

I have played a Triwatt. It definitely does the Hiwatt thing at 22W. That style of amp is not my thing though. Its too loud and clean, it just shows how bad my playing really is. It's got a huge sound though, very bold.
Here is the finished amp in it's cab, a very compact amp. The reverb tank barely fit, you can see how tight it is around the OT. It fit by mili meters.

Did some small tweaking on the EF86 channel. That channel seemed a bit too "hard" (stiff) for my single coil tastes. I recently got a Tone Tubby and that helped soften it up but it needed something more. At first I thought it had too many highs and needed bass but after lots of playing I decided that wasn't the case.

Experimented with increasing the screen voltage on the EF86. The layout calls for 2M2 but most are using 2M (I did anyways). I played around with resistors in parallel. Increasing the screen voltage increases the compression and touch of the stage. I went as low as 600K for the screen resistor, at that point it sounded like I was playing with my Dyna Comp plugged in front, lots of compression.

In the end I went for 2M in parallel for a combined resistance of 1M. The compression increased and I find it softer and more lively with my strats. Just seems easier to play through, but that's me.

2M screen resistor:
Supply node - 348V
Screen - 85V

1M screen resistor:
Supply node - 341V
Screen - 119V
Last edited by kurtlives91 at Sep 7, 2010,
Thing looks great man! One of these days when i get some money I definitively want to get a amp from you. Stuff is always top notch.
Just call me Bobby
Member of the official GB&C "Who to Listen to" list
Quote by mikeyElite
you build guitars worthy of sexual favors

Quote by Invader Jim
if this party gets any livelier a funeral is gonna break out.