ampeg b15 build, now trouble shooting

[nateflanigan]

My point was: report all 3 voltages on a triode

Ah, ok, fair enough.

Reversing the NFB phase did the trick.  I now have a working bass amp.  It's a little on the noisy side though, channel 1 isn't too bad but channel 2 is a bit much.  The grounding in my house is terrible, and my bass can be weird at times, the amp sounds considerably less noisy with my les paulish guitar.  I plan on taking it to a friends studio that has a mains isolation transformer and comparing it with some know amps using a known bass.  

I've never really had noise issues with an amp before, I'm familiar with some of the basic ideas but could use some help.  I imagine it's the kind of fix that involves doing lots of little things that add up to a significant improvement.  I'll take some detailed photos and label the ground points and what not.  

Aside from that, the amp sounds excellent, there should be more modern bass amps like these.
Thank you for the help everybody!

[Willabe]

I now have a working bass amp.

Nice Nate.      

Did you get the amp to work with either grid or cathode bias?

              Brad      

[nateflanigan]

Yes, both bias modes are working now.  I didn't spend much time going back and forth but on an initial listen I couldn't tell the difference.

[nateflanigan]

I would verify pin locations from the technical specs of the various tubes

Yeah, taking for granted that everything on the schematic was correct was a mistake.

I brought the amp over to my friends studio last night, it sounded great.  Tone wise it was very different from his matchless thunderman but just as good and more importantly a bit less noisy.

Turning the amp up about 3/4 of the way the effect of the bias switch was very noticeable.  In cathode bias mode it was pretty over driven, in fixed still quite clean.  Seeing how the intent of this amp is mainly for recording this could be a pretty useful feature.  Also I really enjoy the implementation of the two different channels.  The only difference is where the volume knob goes, but sonically it has a pretty big impact.  When I get home from work I'll do a little photo session and post back.

Again, thanks so much for the help everyone.

[GDSound]

Great, thanks for pointing that out! 

I just went through the "heritage" schematic comparing it to the "Joe Piazza"schematics in the library.  There's plenty of slightly different component values but the circuits appear to be the same. 

However, the "heritage" schematic also shows the wrong pins for the heater connections on the 6sl7's.  I noticed this while initially wiring the heaters.   Go figure.

Hi, you have got a PM.

[GDSound]

Hi guys,

I'd like to ask you about two resistors on Heritage B15 schematic. On schematic they are 1W carbon film (two 120K) but from inside pictures from Heritage B15 on that place they put the same values but 1/2W, carbon composite. My friend, who is serious tube amp builder says that it would be better with 1W, because of high voltages there (about 200V) or something other (that I can't remember :-) ). What do you think about it? Is there any difference in sound between the two (or some other)?

Thanks!

[John]

Did not look at the schematic, but if they are plate resistors 1/2 watt is fine. 1 watt is quieter (less hissy). From what I have read, anyway. :)

[GDSound]

Great, thanks!

Here is a position on the schematic (marked) so you could see:

[kagliostro]

Here the documentation for a clone, or better, a derived amp

as it is a complete documentation with layout, schematics, BOM, chassis measures, I hope it can be of some interest

http://ctgelectronics.weebly.com/custom-amplifier---fcbn-51b.html

K

[John]

Great, thanks!

Here is a position on the schematic (marked) so you could see:

Yes sir, plate R's they are. FWIW, my first project was replacing a bunch of stuff in an old Harmony, they were all 1/2 watt carbon comp except for a few power resistors that were a whopping 1 W.  The amp is nearly as old as I am and sounds great. Probably because of so much drift.

[GDSound]

Thanks so much guys!

[HotBluePlates]

I'd like to ask you about two resistors on Heritage B15 schematic. On schematic they are 1W carbon film (two 120K) but from inside pictures from Heritage B15 on that place they put the same values but 1/2W, carbon composite. My friend, who is serious tube amp builder says that it would be better with 1W, because of high voltages there (about 200V) or something other (that I can't remember :-) ). What do you think about it? Is there any difference in sound between the two (or some other)?

The resistors in the schematic section you posted would be fine as 1/2w.

Some folks feel 1w carbon comps will exhibit less noise than a similar 1/2w in the same position. Others worry about the voltage rating of resistors, which is typically higher in a 1w part than a 1/2w part.

On my latest build, I used 1/2w metal film resistors which have less noise than either 1/2w or 1w carbon comps, and a sufficient voltage rating. No issues with noise and no loss of "mojo".

[drew]

Here the documentation for a clone, or better, a derived amp

as it is a complete documentation with layout, schematics, BOM, chassis measures, I hope it can be of some interest

http://ctgelectronics.weebly.com/custom-amplifier---fcbn-51b.html

K

That's a very nice write-up.  Thanks for the link.