Speaker for B-15 clone

[BassmanPaul]

Nice work Matt. The only problem I see is the big caps on the turret board. From experience I know that, especially in a bass amp, vibration is going to make those break their leads. I feel that they need to be anchored to the board for longevity.

 

[thebassbuilder]

That looks amazing! I would have an anxiety attack with that wirring. This is by far the smoothest and sweetest sounding amp ever made. I would love to have this. Keep us posted.

 

[Matt B]

Thanks for the comments guys...

Nice work Matt. The only problem I see is the big caps on the turret board. From experience I know that, especially in a bass amp, vibration is going to make those break their leads. I feel that they need to be anchored to the board for longevity.

Thanks for the advice i will look for a suitable way to restrain them better. the filter caps at the far end will be easy enough with hot glue but I will need to think of a different solution for some of the others.

What do you mean by "laser shop"? I question because I have six blank chassis that need cutting.

Edit: I would also like to see an example of your work. How other folk put stuff together interests me greatly.

I just re read this Paul, I would have been happy to help out with your six blank chassis but I am in New Zealand... freight might be a killer.

On this one i built the tone stack directly onto the pots which has some benefits but next time I will use a different layout and put it on the turret board I think. Paul, do you have any thought on the 'best' place to build the tone stack? (i made 2 chassis so still have an empty one...)

Matt

 

[beans-on-toast]

Matt, we have a section in the TB portaflex wiki for related models. If you have time to put together some images and a description of what you did, I think that people would find this very useful. There isn't anything in there on chassis building. That is about the only B-15 part that you can't buy off the shelf today.

Let me know if you have time to put something together.

You mentioned that you have some hum issues. I looked at your image of the circuit and couldn't see if you are using shielded wires, grounded at one end, between the input jacks and the tubes and from the tone stages. Not doing so could be a source of noise and hum. If you can't resolve your issue, it might help to consider this.

As for the tone on the controls or the board, I don't think that it matters. From a production and repair standpoint, it is easier to put them on the board. It might even be quieter on the turret board.

 

[Matt B]

Matt, we have a section in the TB portaflex wiki for related models. If you have time to put together some images and a description of what you did, I think that people would find this very useful. There isn't anything in there on chassis building. That is about the only B-15 part that you can't buy off the shelf today.

Let me know if you have time to put something together.

You mentioned that you have some hum issues. I looked at your image of the circuit and couldn't see if you are using shielded wires, grounded at one end, between the input jacks and the tubes and from the tone stages. Not doing so could be a source of noise and hum. If you can't resolve your issue, it might help to consider this.

As for the tone on the controls or the board, I don't think that it matters. From a production and repair standpoint, it is easier to put them on the board. It might even be quieter on the turret board.

Thanks, once I have finished the cabs too I will take the time to put more info and pics together. the CTG electronics website is where i got my info from so that is well worth looking at.

I have shielded cable grounded at the input for the first gain stage of both channels but not the second gain stage. I will change that this weekend with more shielded cable along with moving a couple of other things i noticed.

I think it will be on the turret board next time...

 

[beans-on-toast]

With very low level signals, not using unshielded wires can leave the amp open to induced hum. If you look at an image of an early B-15, all the gray wires are shielded. Moving the ones connected to the tone stage can lead to hum so layout (what they call lead dress) is important. In the early amps, the cables ran along the inside face of the chassis, then along the bottom. I'm not saying that you needed to do this, just to be aware of noise related issues. Wires carrying higher level signals that are near by and especially the twisted pairs carrying AC have to be separated from the low level signal wires.

There are details in the technical amp section on adding a grid stopper resistor to the input of the second channel. Something to consider if you haven't already added one. This resistor will reduce radio frequencies from being picked up by the amp.

Such a simple looking amp but always a lot of things to consider that can complicate things.

 

[Matt B]

With very low level signals, not using unshielded wires can leave the amp open to induced hum. If you look at an image of an early B-15, all the gray wires are shielded. Moving the ones connected to the tone stage can lead to hum so layout (what they call lead dress) is important. In the early amps, the cables ran along the inside face of the chassis, then along the bottom. I'm not saying that you needed to do this, just to be aware of noise related issues. Wires carrying higher level signals that are near by and especially the twisted pairs carrying AC have to be separated from the low level signal wires.

There are details in the technical amp section on adding a grid stopper resistor to the input of the second channel. Something to consider if you haven't already added one. This resistor will reduce radio frequencies from being picked up by the amp.

Such a simple looking amp but always a lot of things to consider that can complicate things.

That wiki has some great info!! some good easter reading. Yes I have a 68k grid stopper on the input of the second channel.

I think the fact it is not mounted on a proper shielded base yet could be part of the problem too.

Yeah, there is a lot to consider in a simple amp, ... grounding is the dark art of amp building in my mind.

 

[rodl2005]

Beautiful work Matt B. Congrats.
I sure it sounds great. Keep us posted and the pics coming.