Marcel's scratch build AC15 based clone

[Marcel]

Only the tone stack and the tremolo oscillator to go before the real testing starts...

[DrNomis_44]

I checked out that link you posted, it's a good read so I've bookmarked it, cheers Marcel.

[dave.king1]

That loom lacing looks very much like what I learned as a TiT more than half a lifetime ago, nice work

[Marcel]

It's wonderful how memory works Dave.

It took me a number minutes of tying a few weird random knots before it all suddenly fell into place and I was getting it done again like a pro. I first tried loom lacing when I first started high school and later in the RAAF spent quite a few hours making up huge test harnesses with hundreds of wires for gear that was in service back then, and there only a few rules to remember, and it is so easy.

It will be interesting to see in a few years if anyone can accurately date this amp build. Add a bit of dust build up here and there, a spot of rust... I think most will guess wrong...

Might re-visit my 2204 build and give it the loom lacing treatment too ...

[Marcel]

It's all done... well the basic build is done. All the components I want in on this first build run are fitted.

Connected mains power to it and the HT volts and filament volts appear okay as what I measured is what I expected considering there are nil tubes fitted. HT came in at 429VDC which is a it high but should sag once tube idle current load comes on. Self discharge to a moderately safe 50VDC of HT without the tubes fitted took nearly 10 minutes. This time should substantially decrease once the tubes are fitted.

Still need to double/triple check it all that everything is in the right places, and then fit a set of tubes, and then check that it actually works....

[dave.king1]

And then the mandatory sound clips ( please )

[Marcel]

That's something which is happening in the background Dave.... Got a new Behringer UMC204HD box to get those quality real life sounds of sweetness into this darn tarnation Internetty thingamy-bob... just gotta work out how to make the darn com-putter play back what I think I put in .....lol

Might start by plugging in my SM57 into it and see what I can get out of this new USB dongle. It certainly seems a lot better and easier to use than the modified iMic that I was using before.

[Marcel]

Yeah, I know...Where is the sound clip?.... It's coming, okay...

It seems I have a working AC15 clone ...... Yay!!

Plugged in a set of JJ tubes. Fired it up... All the right glowy bits started glowing, and no smoke from unexpected places was a relief. Hooked up some multi-meters and started measuring... HT now at 345VDC, Cathode of V5 & V6 at 11.66V, Anodes at 331V....Hmmm, That makes out to be 14.9W of plate dissipation. They don't look Red at all.... I'll finish all my readings of the other tubes and come back once it has truly warmed up.

Long story short, after a good 15 minutes all the reading had remained pretty static and the EL84's were showing no signs of Red plating... Interestingly the 4 ohm 160W speaker that I was using as a test load made all the correct noises as I probed around inside the amp with my volt meter which gave me an abundance of confidence to try a real signal from a guitar.

My confidence was rewarded.... 15W of audio out isn't a lot, but it is respectable. A hour later I had tried my LP-1SSP with P90's, a LP Studio, a SD rails loaded Strat and even a JB and all sounded the way I thought they should. Winding up the gain control brought on a decent amount of crunch, tone controls seem a little weak but do as they should, and opening the master volume to full was loud but not ear damaging.

Only thing that didn't work was the tremolo. Checked the circuit again. The foot switch that controls the tremolo simply shorts out a 47K resistor, and in the default state that I had the amp the resistor was not shorted out.... so I fitted a alligator lead to see what would happen. Bingo, I had a working tremolo. Switched off the amp and changed the rear footswitch socket so the default is to have the tremolo switched on and then when a footswitch is plugged in the tremolo can be switched off an on.

So it is complete and it works.... I will need to re-visit the EL84 bias issue and cool the tube down to less than 12W plate dissipation at idle by fitting a larger cathode resistor once replacements arrive from RS-online.... but there is no hurry....

And yep, I did my usual..... forgot the knob/socket labels on the front and rear panels.... You'd think one day I'd learn to at least remember that....

[dave.king1]

Great work Marcel, I guess building an amp you don't have to wait for the finish to dry & cure

[Dedman]

Bravo! it's been interesting and educational watching this come together.