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What started as a repair project that was botched by a couple of techs, has now become a new amplifier project. I was hoping to find parts to try and salvage an old amplifier of mine but after doing some research and speaking to Stephen, I decided it would be best to just start from scratch with a new amplifier. I have something very specific in mind for this build so it will require a few modifications to do what I want but that should just make the project more interesting.

Although this is my first amp build, I have been inside guitar amps for many, many years doing minor things like altering tone stacks, re-caps, gain mods, etc. so I am not a total rookie. I thought I would share my progress with everyone here so that I could learn from others' experiences and hopefully add some of my own to the existing knowledge base.

So here is my chassis with transformers and VRM kit as it arrived:



It was very securely packed and very compact. I expected something larger. The manual was very detailed. I liked the background information on tube theory and the logic behind all of the component values. For the tinkerers out there, this was some great info.

My first step is to make some modifications to the chassis:





Now that I have the chassis right, it's time to start with the build. I will post more details later as time allows. Thanks.

What chassis mods are you planning?

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I just needed to angle the control face to match up with the angle of the head shell I am placing the chassis in. After checking all of the clearances, everything fits perfectly now.

Tonight I started test fitting all of the components to the board. I thought this would be a good idea before soldering to see how best to make the board look neat, verify my layout and verify all components are present. Unfortunately, I am missing the 2M resistor but, I have several local places to pick up whatever is missing.

The next step will be to solder each point from left to right, triple-checking layout and components as I go. I will add the flying leads and under-board jumpers at each point as needed so I only have to hit each point once with the iron.

Interesting Chasssis Mod. New one for me!!

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Built the tone selector switch tonight. I couldn't find the .0012uF and .0047uF caps so, I assumed the .0015uF and a .005uF were close enough. This looked like the most difficult wiring to task to complete and make neat looking. It wasn't too hard to assemble and although it didn't come out as neat as I would have liked, I think it turned out OK. I do need to get better lighting for my desk though.

Yes, .0015uF and a .005uF are to be used. Layout updated.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Great to see the forums back up!

I made some progress with the kit this weekend. I bolted up the chassis components, wired up the heaters and wired up the circuit board.





I do have a few questions though:

1) The polarity for the EF86 heater is shown opposite the EL84s on the layout sheet. Is this correct?
2) I assume the correct diagram to use for the VRM is Trinity Amps VRM II Installation Layout which intercepts the main B+ feed. Is this correct?
3) Are there any pictures detailing a VRM installation? With the pot and MOSFET being aligned at right angles on the circuit board and the MOSFET requiring a heatsink, I am having a hard time finding a good location to mount the pot.
4) Regarding the B+ supply for the VRM, aside from VRM being on when power is applied, is there any reason why I couldn't feed the VRM with the B+ before it hits the standby switch? I think the wiring would be much neater using that strategy. Thanks!

Now that the boards are back up, I found the answers to my VRM questions. I think I am going to hold off on the VRM install. I want to finish the amp as designed, listen to it and then decide if it needs any tweaks. Once that process is done, I will decide then if it really needs the VRM. Once I am done with all that, I will have my custom face plates made.

Next up, wiring of the jacks and controls.

Wuld be OK, but the layout has been changed to reflect the schematic correctly.



Yes, use the Trinity Amps VRM II Installation.



Havent seen that. There should be lots of options including immediately below the power switch hole, if you replaced that switch with the VRM control. Or in the centre of the chassis, between the transformer & board, and even on the chassis end/side. These last tow would require remote location of the control.



It would work, but would think it better if it was after the switch and not on when on stand-by.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

It works!

My real job kept me away from the project for a few weeks so this Saturday afternoon, I sat down and went to town. Once everything was wired up, I checked all of my ground points and looked for any obvious errors. I then encountered a few minor glitches:

1) When I popped in the rectifier and took it off standby, I noticed the 22K resistors off of the filter caps getting very hot. I found a jumper under the board had come undone and I noticed I had a wrong value in place of one of the 22Ks. Of course, this being Sunday, my chances of finding a 2W 22K resistor were next to impossible so it waited until today.

2) With the correct value in place, I had the same result with one of the resistors now. It turns out that using the center lug on those 3-way binding posts is a bad idea because they go straight to ground.

3) After fixing that faux pas, my voltage measurements were way off and I wasn't about to put any of my Mullards into any sockets until I could explain why I was reading 300V where I should have been reading 150V. I went through the BB postings and found a post that explained the voltages in the table are with tubes in, not out.

4) Confident that everything was now where it should be, I popped in my NOS Russian EL84s and some random EH and Groove Tube 12AX7s into the chassis, plugged in a rattling EV speaker that I didn't care about and turned it on. (I only have a Mullard EF86 and I wasn't about to toast that testing the amp. ) THe amp was so quiet, I was afraid it was dead but, a Strat plugged into the normal input worked perfectly and sounded beautiful!

5) Feeling my oats, I decided to plug in the EF86 and give that channel a whirl. Unfortunately, that was not too good. The volume pot was scratchy and the contour switch was not working. I found a shorted cap on the switch and replaced that but, that didn't solve my problem. So I removed the switch from the circuit and after poking around a bit, I discovered that the lead marked C on the switch does not stand for COMMON. . After reconnecting everything the right way this time and plugging into one of my 4X12s, now it all works and sounds great!

Here is what it looks like now:



It didn't quite come out as neat as I hoped, but it is the quietest EL84 amp I have ever heard and I have had a lot.

Next step is for the custom front and back panels to be made and then fit it into my head shell. Once it is all together, I can really put it through its paces and see where I want to take it.

Finally done!

Here is a brief history of this project. I am a Vox nut. I think the JMI era Vox amps were some of the best sounding guitar amplifiers ever made. I have one of those rare 64 AC30s with candy red control panel and built-in top boost. Not only does it sound great, but that control panel looks cool as hell. A short while after I aquired that amplifier and the Vox bug bit, I found this rare 65 AC10 head/2x10 cab combo at a vintage shop that was closing. It was a little ragged and didn't sound right but aside from some changed components, was all original and was offered very cheap. Here is a picture of the two back then:



After I got it home and had time to go through it, I found a lot wrong. The reverb pan was broken and used old phono cartridges that haven't been made in years as the transducers. (It turns out that Tom Jennings had a hard-on for Hammond since he thought they were trying to rob him on reverb tanks so he had Dick Denney and the boys come up with their own reverb.) I also found that the tube rectifier had been replaced by a few diodes and then learned that this was the only AC10 that was produced without the awesome EF86 front end.

I decided to try and restore it anyway and sent it off to one of the best-known Vox techs in the US. Almost 3 months later, the amp returned but produced more smoke than sound. I had a long discussion with the tech and he then apologized and refunded my money telling me that he tried his best with the amp. That was several years ago and the amp sat in pieces as I tinkered with it in my spare time.

I finally decided that the only way the amp was ever going to work was if I replaced the guts and started from scratch so, a kit became the logical choice. I looked EVERYWHERE for a kit that had the following pre-requisites:

1) It had to have an EF86 front end
2) It had to fit in the existing amp
3) It had to sound great

After I heard the clips of the TC15, I knew that was the amp I wanted but would it fit? I emailed Stephen a few times about how I could make his circuit board fit in my existing chassis and retain the same look as the original amp. After reviewing all of the work and modifications that would be required to do this, I did not have the heart to hack up a vintage amplifier chassis with a modified circuit. Fortunately, the specs for the TC15 chassis just so happen to barely fit in the old Vox head shell and so I had a plan to insert a TC15 chassis into the old Vox head shell.

Of course, there were a couple challenges:

1) The TC15 chassis is a tube up design. The Vox is tube down. This would require careful wiring to make the transition and some new control plates. Thanks to Jeanne at BNP lasers, she had an aluminum material that was close enough to the JMI candy red panels that I liked and she was able to take my drawings and make me new front and back control panels.

2) The TC15 chassis BARELY and I mean BARELY fit into the head shell with no cutting of the shell required. I did have to modify the chassis to match the shell face angle and I had to drill new holes and add speed nuts to the chassis to make it line up with the original Vox holes but, all worked out and everything fits perfectly.

I first tried the amp in one of my 4X12s and although it had the Vox vibe, it needed an opened back cab with old AlNiCos. The AC10 cab has the original, unreconed AlNiCo 10s from 65 still in it. They sound fine, but I never used that cabinet with any of my other amps as it lacked bass and just sounded thin. However, with the TC15 plugged in, it sounded fantastic! I tried several different guitars in it today and they all sounded killer, whether clean or cranked. This head and this cab are the perfect match. It is not too boomy but not too thin and you can get great, ripping tones from this combo at a reasonable level.

I am quite happy with how my project came out and can't thank Stephen enough for all of his assistance. I finally have a great sounding amp with a vintage vibe that didn't require hacking an antique.





Thanks for looking!