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. 

J 

1939 Kalamazoo KEH amplifier built by Gibson

Such a cool amp. This came from a good friend of mine. He bought it at a local shop as-is and it was dead.

I love them when they are dead. It's easier to fix a dead amp than one that sort of works. Example is the Oahu amp I bought in Dallas last year at the guitar show for $100. The power switch was dis-connected. Simple fix. The rest is just change caps and resistors as needed.

This was no exception. Dis-connected wire got it going. I had to re-cap it, ground it and change a couple super microphonic 6C5 tubes but that's it.

These early Gibson amps are exceptionally well made. Easier to work on than what they produced from the 1940s on forward. Odd, cause the early ones are service friendly like a Fender. They got worse over time where Fender just kept getting better. I like how you can simply unplug the field coil speaker in these. You just pull the chassis after that and do your thing.

Plus the looks:









This is one beautiful piece of equipment!

Tubes are 3 6C5 preamp tubes, a single 6L6 and an 80 rectifier tube. They do run rather hot. This one showed evidence of the transformers getting hot. I replaced the cathode bias resistor with a bit higher value. Makes things sound a little 'looser' but you know, I'd hate to see the output transformer die in this 80 year old amp.









Tube sockets were labeled right on the socket itself. Classy!


Yup. From the glory days of American manufacturing. These were factory built. Not cheap! You need to pay a builder to get this kind of quality today. Not cheap but come on, you're worth it!

-J

Early 50's Magnatone A-646. Perfect tiny amp!

Just finished this one, a very rare Magnatone A-646 amp from about 1951. This one us a real gem and is visually striking as well.

I bought this amp by mistake on Reverb this winter. I put an offer on a Varsity that I wanted as a backup to my main one and the owner declined. It wasn't a bad price and I love those early Varsity amps and it was pretty enough that I was willing to pay his price anyway. This one came up in my feed and I was curious so I put an offer on it. The owner said he would think about it. First amp wound up coming through at my price so I bought it then.......so did this one!

This one arrived first. It was noisy, had some really poor tech work done to it so I got it going. I wasn't all that impressed with it though and even after re-capping the power supply it had a considerable amount of hum. I even added another filter stage. I knew there were other solutions, maybe filament, maybe ground loop but I shelved it. If it's mine I tend to just put it away and forget about it.

So today I did a better re-cap, with a nice expensive C.E. can, an additional filter stage and while it got better and was certainly tidier, still hummed at an unacceptable level. So I disconnected the center tap of the 6.3v filament and added a hum balance: 2x 100 ohm resistors, one on each side of the filament, the other sides both going to the cathode bias resistor on the 6V6 tube. Looks like this:

When I brought this up on my Variac I thought "dammit! I killed my amp! Time for more troubleshooting!" I just wanted to be done with it. But reality is, the amp is just so quiet now! Hum free with only a little bit of noise when it's turned all the way up.

This amp I believe is the precursor to the Varsity Deluxe I reviewed here. Similar circuit, 40's style box, single 6V6 and 5Y3 but driven by the darker more euphonic 6SL7 tube rather than the snappier 12Ax7. It has a single 8" Alnico 5 Jensen speaker.

More pics:

How does it sound? Like the early version of the Tweed Fender Princeton. It's a similar circuit, but this plays cleaner and more articulate. It has a big sound for such a small box, warm but not fuzzy. Ideal Wes Montgomery or Charlie Christian sound. I'm a big fan of the Magnatone amplifier, especially the early ones. They are a bargain. I may sell this one but not for cheap! I like it a little too much.

The only drawback is the 6SL7 tube can be microphonic. If you turn both the volume and tone all the way up it may sing a song. The 12AX7 is a better tube for guitar amps. You could simply use a 6SL7 to 12AX7 adapter available on EBay, or you can just roll a little bit of the tone control back and enjoy that big warm sound.

If you like something different, give one of these a try! They are lovely little amps!

JB


8/29. After tracking with a Les Paul all weekend I've decided this is my best sounding amp. Bigger tone than a tweed Champ, smoother top, goes to tape beautifully! It's a keeper! Do look out for one of these. I did some reading about the hum and one tech mentions he struggled with his as well. he resorted to installing a big ass choke and extra filter stage. That should do the trick but try the hum balance first along with adding one filter stage. Quite happy with the results here. JB