Bronson Melody King

[Pedro Vecino]

Hello everyone. I have to restore a Bronson Melody King combo from the early 50's. With 6SC7, 6SN7, and new 5AR4 rectifier and new 6L6GC pair. The speaker is an old Jensen P12R. I'm not sure if originally uses this rectifier and these power tubes. At the top, faced with the voltage indications, it says "54 watts". I imagine it refers to electric consumption. I have read that the origin of the amplifier is probably Magnatone.
Does anyone have information about this amp? Or a scheme?
Thanks to all.

[Enzo]

This is a super simple amplifier, you should be sable to draw a schematic from the circuit without a lot of effort.

Yes, 54 watts is power consumption from the mains.

[J M Fahey]

Are you sure it uses 2 x 6L6? Not 2 x 6V6?
Reason is that P12R stands no more than 12W RMS.

Very reasonable for a pair 6V6 á la Gibsonette, definitely unable to stand a couple 6V6, in any configuration:





notice one version is self inverting push pull and does NOT use a cathode cap at the 6V6, while the other is parallel single ended and does, think a "doubled Champ power section".

[Chuck H]

Kewell amp! Love the brown enamel with white script, faux alligator and wood handle. I'd do as Enzo said and just trace out a schematic. Looks like someone already installed a grounded AC cord at some time. And I think Juan must be right about it likely being a pair of 6V6's intended, though there's probably no danger using 6L6's because it wouldn't change the actual power output much without other changes.

A pair of 6V6's in a simple circuit played into a p12r is probably going to be as much a hoot to play as that amp is to look at

[Pedro Vecino]

Thank you all. I also think that it is more possible that have a pair of 6V6 and a 5Y3. The only tube that gives me confidence as original is the 6SC7 having a common cathode. 6SN7 could be 6SL7 (same pinout).
If there is no other solution I will have to draw the schematic. It´s a messy construction and it will take me work. What worries me the most is knowing the exact models of tubes. Archeology is not my thing.

[Chuck H]

Tracing and drawing out the circuit in schematic form shouldn't be that bad if you've ever drawn any schematics at all. Just take it pin for pin, lug for lug and keep basic circuit design in mind. It'll be a breeze. And it'll be a lot easier to speculate about tube types once the circuit is known.

[Enzo]

You already know what a push pull output circuit looks like, they are all the same. And the rectifier tube circuit. That leaves only the two preamp tubes to draw. The dual triode is likely to be a phase inverter, or at least half of it.

The way I do it is I look up the tube, and draw an image for the tube with pin numbers, then I draw in the parts connected to it. You should be able to tell pretty quick if the B+ resistor goes to a pin that doesn;t make sense (As would happen if the wrong tube type were in the socket).

[Randall]

I don't know if this will help, but I have a Bronson amp in my shop. It has 5Y3,
6V6, 6SC7 and 6J7 tubes. And a little field transformer Rola speaker.

[Pedro Vecino]

Thanks again. This is the scheme that I have drawn. I have not desoldered any component and only lack the value of potentiometers and voltages.

[g1]

What worries me the most is knowing the exact models of tubes. Archeology is not my thing.

For collector or value purposes it would be nice to know if the tubes are the historically correct type. Here is one for sale. Perhaps they would tell you which tube complement it has installed.

https://reverb.com/item/802056-brons...tube-amp-brown

[Pedro Vecino]

Thanks, g1. Fortunately I have found an image of one with original tubes: a pair of metallic 6L6 and a 5Y3. I have discovered that there are at least two different models in the same cabinet. One of them has a speaker with self inductor and a different circuit from mine.
I put a safe grounding and removed the capacitor between a phase and ground. After that I've tried it. Direct to a reference cabinet sounds wide and deep (the tone circuit, as was predictable is somehow strange), but at max volume I find its power limited. A 5C3 Deluxe sounds louder and with more overdrive in high settings. More alive too
With the Jensen P12R it loses a lot of depth and distorts prematurely. Develops relatively little volume. I will have to try another model with more power and greater sensitivity (P12N or similar).
Tubes are fine, with good readings. Except the 6SC7, which as usual has a lot of microphony.
Does anyone see any way to generate more gain in the preamp in a discreet but appreciable way?
Thanks again.

[nickb]

Does anyone see any way to generate more gain in the preamp in a discreet but appreciable way?
Thanks again.

That 100K resistor between the plates of the 6SC7, if it is really like that, will lower the gain a lot. Double check that area.

If it is as drawn lift then one end of it.

[Pedro Vecino]

Thank you. It's the first (and only) thing I've tried and there appears oscillations (torn paper sound) even at very low volume. It gives the feeling that its function is to "fix" that same problem.

[nickb]

Thank you. It's the first (and only) thing I've tried and there appears oscillations (torn paper sound) even at very low volume. It gives the feeling that its function is to "fix" that same problem.

If it's steady then that sounds like thermal noise to me. It's what I'd expect from big jump in gain. The primary reason for that noise is the numberof high value of the resistors at the input to the amp. If it's more crackly and or popping then I suspect a bad component around the first stage.

[Pedro Vecino]

Yes. Value of these resistors is very high. All of them are carbon composition.
I will try three things:
- I will reduce the value of the input resistor using another different type.
- I will raise the value of the cross resistor. I understand that withdrawing it is a very drastic step.
- Installing previously a new 6SC7. If with limited gain it is already microphonic, with high gain it can create all kinds of noises.

Thanks