My Trinity OSD Kit Build

[Matt J]

Hey Everyone!

I recently picked up a kit from Trinity Amps of their new OSD kit. I thought I would share pics of it as I put it together. I haven't been able to do much amp building in the past years due to having to finish up grad school, but now that that is thankfully done I finally have the time to pick up my soldering iron and DMM again!

Some more info on the amp:
100K plates and based off of #124.
Switchable OT for either 6V6s or 6L6s.
FET has been removed.
Circuit board is one piece instead of separate sections for the PS, rectifier, and preamp.
Trim pot for the OD entrance is on the back.
Volume pot is push/pull for the bright switch

I'm not using all of the components that were included with the kit. Some of what you see are things I had left over from my Small Special build from a year ago, such as the 6PS coupling caps, pilot light holder, and much of the wire. I'm also running the pilot light off of the 120v supply instead of the heaters.

Feel free to chime in with any thoughts or suggestions! I haven't really seen any info on this kit on here yet so I thought I would go ahead and start putting stuff up. Also, I'm really enjoying pompeiisneaks' live build of #124 on YouTube. It's been nice to see its progress as I've worked on mine!

- Matt J.

[Matt J]

I still need to clean up some of the solder points on the board.
I noticed that the eyelets they use are a little different than what I'm normally used to working with. They had more of a brass appearance to them and solder flux left more residue on them than I've seen in the past, so I'm going to resolder some points before I finish things up and attach the flying leads.

[Matt J]

These last pictures were taken a few days ago, and since then I've hooked up and tested the PT with my current limiter. Bulb dimmed just fine on first fire up and the PT's secondaries all checked out to specs. I also installed and tested the relay board. You can spot two LEDs on the relay board itself that light up as well when the OD or PAB is engaged.

The kit comes with a Marshall style two button footswitch with red LEDs you disassemble then reassemble with a new layout and 5-connector cable for the XLR. I may end up building a new footswitch board though. The included one feels a little flimsy and one of the LED holders actually broke as I was repositioning the switch. Plus, as-is, both footswitch LEDs are red and I would personally like to have a different color light for the OD and PAB.

I'm taking a "Start on the outside, then work your way inward." approach with this build, so up next I'll finish the back panel components, then start working on the tube sockets.

- Matt J.

[M Fowler]

Nice I was just looking at that kit last week.

[norburybrook]

that's a sweet little build lovely kit.

M

[Matt J]

Thanks M Fowler and Norburybrook!

It has certainly been an interesting project to work on. Considering how much information I have learned over the years from this forum I thought it was the least I could do to just put up some pics as I go along in case anyone else wants to try this kit.

I would offer some suggestions:
- Rework some of the chassis mounting holes. Some were not drilled the proper size and I had to enlarge them, notably the holes to mount the bias probe jacks. The output and FX jacks were a little too large too, so I had to use extra washers to install to ensure they stayed securely bolted in place
- The chassis is designed so that the mounting bolts for most things screw directly into the chassis, such as to install the tube sockets, circuit board stand offs, and ground points. Because of this, the kit doesn't come with locking keps nuts for all of the #4 and #6 bolts. I picked up some extra washers and bolts due to this and installed them to be on the safe side. I don't want speaker vibrations to eventually weaken how well the bolts are held in place.
- The layout of the circuit board could be tweaked a little with some more access holes for the wires that need to run under the chassis, much as you see HAD do. I drilled a few extra holes so the flying leads would be a little more stable.

Anyways, I've made some more progress on it. Most this inside the chassis are in place and tested now. Tomorrow after work I'll start attaching the leads to the circuit boards and prepping it to be installed.

[Matt J]

I'm curious to see how the use of the 500r dropping resistor instead of a choke between B+1 and B+2 compares tonally. I'm guessing this should produce more sag in the power amp, but if I am wrong please correct me!

- Matt J.

[M Fowler]

Probably based more on the Dlite since it uses the 500R resistor instead of choke.

For the mounting screws/machine bolts you could have used paint or fingernail polish to lock them in.

Nice project though.

Mark

[Guy77]

Nice looking build. Good old Trinity amps from Ontario, Canada ! Nice and compact head , will be easy to transport.
I built a d'lite based build a while back and ended up switching the 500r resistor for a choke, the cleans sounded a little smoother with the choke but either way I am sure it will be a great sounding amp!

Cheers

Guy

[Matt J]

Update:

Finished wiring everything up. Checked all connections and made sure there were no shorts. Gave it a test run with the current limiter. Everything came out ok with. Switched on the Standby and checked the B+. The power supply voltages came out ok, within the specified ranges from the layout. I set the bias for the 6V6s and checked plugged in a guitar. The amp did work when I plugged in a guitar, but the volume started dropping pretty soon and eventually cut off. I doubled checked the plate voltages and found an issue with V1B. There, the plate voltage was well over ~310DVC, when it should be about ~210VDC.

I've checked over the plate resistor, it measured out to the correct 100k, same with the 1.5k/10uf cathode setup. I switched out tubes in case one was faulty and got the same results. This is the section where the LNFB is located, so I'm curious if that could be affecting the voltage. Any suggestions or feedback would be greatly appreciated!

- Matt J.

[Matt J]

Some close ups of the area in question.

[pompeiisneaks]

The ground solder point of what looks like v1b is looking like it could be a bit better, you could also just get the guitar plugged in on a stand, strum it and touch all the solder connections and components with a wooden chopstick, to see if one area makes it either come back or die and that's likely where you may need to reflow the joints etc. That kind of thing seems to hint of a solder connection getting more 'resistive' as the joints heat up with use. Reflowing those that don't look bright and shiny may solve it.

~Phil

[erwin_ve]

Can you measure the voltage on v1b grid and at the cathode of v1b? It usually is a symptom of bad ground when having these high voltages. Out of curiosity: what kind of resistors did you use on the Lnfb?

[Matt J]

Resoldered the ground point and double checked the cathode voltage. Something is definitely up with that!
V1A reads 209 VDC on the plate and 1.7 VDC on the cathode.
V1B reads 310 VDC on the plate and .0025 VDC on the cathode!

After reflowing the cathode solder, I'm still getting the same results. Looks like I may try to completely replace that grounding wire and try a new strip, see if that makes any difference.

As for the 22m resistors, they are the ones Trinity shipped with the kit - Dale CMF 55.

[Matt J]

Update:

IT'S ALIVE!

I replaced the ground wire for V1B and fired it up. Voltages were much better this time, right at ~200 VDC for V1A and V1B. Gave it a go with the guitar and everything checks out ok: channel switching and panel switches. The presence control really doesn't seem to have that much impact between zero and full, but that might just be from the stock design. There are, of course, LOTS more to do with tweaking the bias, setting the PI balance, OD trim, plus some good old fashioned burn-in time! I want to try it with the normal 6L6s as well. I'll post more pics once the cabinet arrives and start finalizing everything with it.

Right now I'm testing it with my Stratocaster. I picked up a 1990 Gibson Les Paul Studio last week and as soon as I put some new pickups in it and properly set it up I'll give it a go too. I'm really looking forward to seeing how a humbucker equipped guitar functions with the amp.

Thanks again for your suggestions! I took the ground wire I removed and tested it with the DMM, the continuity seemed to jump in and out with some slight flexing, so something must have shorted out within it.

Happy Easter everyone!
- Matt J.