New Bass Amp Build Ampeg B-18-N/B-15-ND

[jon]

Finished my B-18/B-15-ND yesterday. The amp is bone stock with the exception to the following changes.

Screen Resistor is 500ohm (I damaged my 1K)
Chanel 2 has a 1nF cap feeding the treble pot originals have a 500pF, this bumped the midrange slightly (TSC file included).

The amp sounds amazing, tight and thumpy like a fliptop should be.

[IMG:600:800]http://i82.photobucket.com/albums/j250/ ... G_0301.jpg[/img]

[IMG:800:600]http://i82.photobucket.com/albums/j250/ ... G_0304.jpg[/img]

[Structo]

Nice looking build.

Did you build this as a bass amp?

What are the green caps on the board?

[Cliff Schecht]

Those green caps are made by Cornell Dubilier. I have very few but they are fantastic sounding caps IME. Where did you get them?!?

[jon]

our leader Allynmey had a few

[jon]

Nice looking build.

Did you build this as a bass amp?

What are the green caps on the board?

Yes it was built as a bass amp

[dartanion]

Looks great Jon!

I would change only one thing, and thats the ceramic sockets.

[rp]

Nice, very Ampeg looking! I bet it sounds great with a full compliment of original greenies. Looks like Hammond iron? If so which models did you choose?

What are you using for a speaker?

[sliberty]

The green caps are not very well aligned. SOme sit further to one side of the board than the others. This will probably kill the Mojo, man.

All kidding aside, really nice build Jon. I can't wait to hear her rip.

[Structo]

Looks great Jon!

I would change only one thing, and thats the ceramic sockets.

Is that because they tend to be microphonic?

[jon]

I got a chance to really open up the amp tonight and I found a small problem. When you strike certain notes ie: an ope "A" string I get a brief amount of farty distortion. I tried swapping power tubes, preamp tubes, I chop-sticked the entire amp. I even swapped to a solid state "Slug" rectifier and re-biased. It is present on all my speaker cabinets. Any thoughts.

[rp]

There are better people than me here to help but I'll hazard a guess from my own experience:

Cold solder joint, or a forgotten solder joint somewhere, maybe PS end. Chopstick poking is rarely useful IME, but I wrap pretty tight around terminals.

Loose socket, try to retention the pins.

Leaky coupling cap maybe? Rare to find so many NOS and have them all be good. Any scratchy pots? Any off voltages? If you can determine the problem stage that would be easiest, otherwise just start swapping with good modern caps from one end to the other. I'd start at the power stage side just cause it sounds like it might be around the PI.

[jon]

i'll give that a try. thanks

[jon]

All fixed. I found a slight mis-wiring on the Bass controls of the tone circuits. Additionally I moved the negative feedback from the 16 ohm tap to the 8 ohm tap.

[azatplayer]

I did a B15N last year for my brother, single channel style and added a bias vary tremolo, just for kicks
Used Hammond iron and running 6L6's fixed bias into a 2x12 cab with warehouse ET65's. Sounds freakin! I did it becuz he has a penchant for baritone's and what he does is pretty great. The B15N is a great circuit for Bari's. The trem is a cool option too.