Showing posts with label 6J7. Show all posts
Showing posts with label 6J7. Show all posts

Friday, April 30, 2021

Bronson Amplifier circa 1949, in the original box with the matching lap steel

 Today I got to see a stunning piece of history. This Bronson amp dated 1949, still with the original shipping box. It spent some of it's life in New Mexico at the Aloha Conservatory of Music. Apparently this school was affiliated with the Bronson brand. I would love to know more! American musical instrument manufacturing is a fascinating subject for me. Especially when it is tied to schools. 


Nothing to really write here, the amp isn't NOS, but it's as clean as one can be for a 72 year old amplifier. The customer wants to use it so sadly I needed to change every capacitor in the house. All of the wax caps were leaking badly (yes even with little use, they likely leaked right out of the Valco factory!). And I also replaced the electrolytic caps and the power cable at the customers request. Easy job. These are so well made. 


So the insides are all "before" pictures for your amusement. 


















How does it sound? We happen to have a lovely old Kalamazoo model A with a real Charlie Christian pickup. Lovely combo. I'm a fan of a good field coil speaker which this has. Nice low end.

The filter cans are as follows: 40uf (big for the time!) and a dual 10uf can for the preamp and screens. 

Tubes are 5Y3, 6V6 pair, 6SC7 phase inverter and 6J7 pentode for the preamp. I'm a big fan of this arrangement having built a few amps with a 6SJ7 preamp into a 12AX7 or 6SL7 phase inverter. Big, warm sound with nice low end. 

Valco knew how to build a good amp. This thing runs pretty quiet. And it's a nice thing to look at. Easy on the eyes. An amp should be able to double as furniture so it doesn't get stuck in the closet when not being used. Potted plants should go near it alone with your sofa. These manufacturers had style back then. Not an ugly rock box or just some industrial looking thing that belongs in the garage. This is something you want to relax with and play some sweet music through. 





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....

JB