Friday, January 17, 2014

1971 Vibrochamp

Okay, sorry for the crap photo:

This came in for some TLC. It was cutting out and sounding weak when it was working. Simple solutions on this one. Power switch was dying and replaced the 2 12AX7 preamp tubes as they were weak. Also replaced the cathode caps which helped the background noise. On the 6V6 470 ohm cathode resistor someone had replaced it with a Sprague Atom 25@25V. I've had those pop in the past in that position so I replaced that with a 25@50V cap.

The back panels were missing:

Had a new set made by Mojo Musical Supply. They do great work:

Added some "tube teeth" to prevent the 5Y3 and 6V6 tube from falling out:

It's not uncommon for these tubes to fall out during a performance no matter how much you re-tension the sockets. This was no exception. Amp has a heavy glass JJ 6V6. Gravity dig?

Here's some shots of the inside of the amp:

The infamous "brick drop" 70's CBS caps. These tend to be leaky but not in this case. I prefer to leave signal caps alone in an amp unless they are leaking or dead. Better to maintain the integrity of the amp.
And in this case, this is easily the best sounding VibroChamp I've had the pleasure of working on. Big and warm, full bodied tone. These can sound really scooped in the mids but this one is just majic.


Friday, January 10, 2014

RCA BA-2C rebuild.

This walked in the other day from a fellow who met me in Los Angeles. I sold him a preamp I built so I could make that months rent. Small world, found me here in Brooklyn through Linkedin.

In it's original form you can really see the folks at RCA were genius. Such beautiful wiring.

What amazes me is there is an absence of shielded cable in this, the inputs and outputs are right by the 120V ac in. How did they build these to be hum free?

First thing, the filter caps are DEAD:

You can see the now dried up interiors making their way outside. I'll also change the old power supply resistors, the main signal cap and the load resistor. One of the 1620 (super quiet 6J7 tube) tubes was dead too, I'm replacing both with NOS ones. The rectifier has years to go so I'll leave that.

My customer opted for the "spare no cost" correct filter cap way to go:

This job could be done much cheaper by wiring individual caps inside but ya know, this is really the way to go all out on such a beautiful piece of vintage studio gear. I did have to wire a couple caps inside only because I couldn't get the correct cans.

But the best part of course is the sound.......

And the last difficult to find part, these lovely tube grid shields:

Thank goodness for Ebay!

Voice sample:

And one of my trusty old Epiphone Spartan:

And some fingerpicking. Just a good old Yamaha FG-150:

Yeah, I want to build one of these now. Easy to fall for a great sounding piece of studio gear. Amazingly enough this baby is quiet, virtually hum free. Warm as can be but not fuzzy. That's what I like. Damn, I want one....