Trainwreck - Amp Development Platform

[JazzGuitarGimp]

Hey RJ! Looking great! What a cool testbed. I've got to wonder if those ITT caps had their polarity marked backwards at the factory?

[xtian]

That's Mad Scientists cool, and very good looking, to boot. Reminds me of a Cornell box.

http://mehtapozer.blogspot.com/2013/09/ ... boxes.html

[njwrecks]

Great work RJ, congratulations on your daughters wedding!!!

[RJ Guitars]

yeah, I am puzzled by the ITT cap problem. The vendor i was using to get the old Mallory 10uF 100v couldn't provide them any more and and sent me these as a replacement. they have been sad performers for sure. I was able to find some CDE brand that I'll keep in stock once I verify a few of them in my own builds. This had me really scratching my head wondering how I messed up the PS board design.

I had another 10 minutes with the amp today and it still sounds like a good Express. it is odd to look at it on the bench and hear that attitude aned volume from something that looks like a science experiment... "back to the future sorta" thing.

I broke a lot of Express rules in the layout but tried to follow good practices in lead dress and layout in those deviations. It really doesn't seem any especially unruly but you can tell it's on the edge... probably the best I could ask for. gonna take some more measurements then start swapping OT's.

[JPGraphX]

Good job RJ! Nice work. I think you/we are going to learn a lot from that test platform!

[RCGPNY1]

Great stuff,RJ...and congrats on your daughter's wedding

[RJ Guitars]

With this amp system, I can move between the Express and Rocket power supplies with just the flip of a switch. I can also look at the B+ voltages with the analog voltmeter on the front panel. I can also follow the voltages all the way down the rail using a rotary switch. It's very cool to watch the voltages on the front panel as I play through the amp. On the Express PS I get almost exactly 400 volts going to the OT and I can see a very small dip (less than 10 volts - it's hard to get precise with the analog gauge) and quick recovery in voltage when I hit a hard power chord. With the flip of a switch I get around 340 volts on the Rocket side of the PS and see a much bigger voltage dip (~15-20 volts) and slower recovery doing that same routine. I initially had an old 5U4B rectifier tube and got a huge voltage drop and very slow recovery. If I kept driving it hard with power chords I saw the voltage drop way down to around 250v and just sorta warble up and down but never recover.

In case you were wondering... the Express sounds like crap at the lower voltage, even when playing clean gentle strums and not seeing much voltage sag. The volume gets noticeably less and much of the bottom end goes away... just sorta sounds thin and lifeless. I'm going to put a SS plug into the rectifier socket and listen to how it sounds to test if the Express really isn't happy at that lower voltage or just with the tube rectifier.

[angelodp]

Nothing like seeing the electrons actually move in analogue real time. Wish we could se a demo of what you described - vid.

Always an inspiration…. you da man.

[RJ Guitars]

Thanks Ange.... good to see you among us here.

I received the prototype Mercury Magnetics Stancor A-3801 clone late last week and had a chance to swap it into the test platform yesterday... very sweet tranny for sure.

After I played through that a couple hours I swapped in the A-3801 that they rebuilt after they cloned it... it sounded cool but not as good as the MM clone??

The quick swap feature on the OT's is just delightful... less than 2 minutes to swap a tranny out. This could be quite handy...

[rp]

This is one the the best thought out things I've ever seen. Terrific stuff RJ.

[M Fowler]

Cool testing rj, man those Mercury transformers look sweet.