I think I broke my Ampeg B-15N

[coreyfyfe]

That Schematic seems to be the closest to what I have. This one shows a 7199 tube in the V3 position, where mine is another 6SL7, but the rest of it seems right.

It also has 7027 power tubes and different transformers

The 1B5N(D)/B18N schematic is for the higher power models. Based on the pot dating and the look of the back panel there you'd have a 63 B-15N which with the tube rec would be an NC model and thus cathode biased. That would mean you can just pop in tubes and it will be all set (as long as the bias resistor/cap are good).

 

[Landy67]

Is this one accurate?
Ampeg B-15-NC

 

[coreyfyfe]

Assuming my dating based on pot code was right it should be.

 

[Vintage-Blue]

Is this one accurate?
Ampeg B-15-NC

I'm not sure how accurate the Piazza schematics are but I also have redrawn copies of several B15NC schematic versions available Link Removed.

 

[beans-on-toast]

An NC is a really nice revision to have. I think that it is the best one of them all.

It would help if you took a picture(s) of the guts inside the chassis showing the components.

Also, look on the silver metal capacitor can at the end of the line of the tubes. What capacitor values are written there? It might indicate 40-40-20-20 @ 500V or 40-40-40-40 @500V. Look for anything that looks like a date, 63-44 (44th week of 1963) for example, like on the pot that you took an image of.

 

[Landy67]

It looks like the can says:
SYNCR0 ME51809
40-40-40-40 all at 500 DC
10816340 85° C
It's hard to read with that big metal cube in front of it.

This is the underside

 

[coreyfyfe]

If my eyes are working properly it appears the blue electrolytic cap and the resistor next to it are tied to the cathodes of your power tubes which would mean it's indeed a cathode biased B-15NC.

Is that a replacement transformer inside there? Or maybe a choke?

 

[Landy67]

Is that a replacement transformer inside there? Or maybe a choke?

What, you mean this isn't original equipement?!?

I have to have that thing removed. It blocks the mounting screw hole on that side. I can't moun it on the chassis tray.

 

[JimmyM]

Does whoever installed it realize that they had to make the Heritage B-15 head slightly bigger for the choke? Sounds to me like they heard Jess Oliver use the world "choke," and decided they had to have one.

 

[Passinwind]

Is that a replacement transformer inside there? Or maybe a choke?

It's a filament transformer.

 

[coreyfyfe]

I believe it was because it can tighten up bass response by adding more AC filtering without causing a loss of low end, good for getting the most out of a low wattage tube rectified bass amp.

 

[JimmyM]

Well you know way more about it than me, Charlie, but it sure looks like chokes I saw on a Google search, Jess mentioned many times that he should have put a choke on them, and a filament tranny isn't needed for 6 tubes in a 25w amp.

But of course, this would be just another in a long line of screwups I made when it came to tech stuff if it IS a filament tranny, so hey...

 

[Passinwind]

Well you know way more about it than me, Charlie, but it sure looks like chokes I saw on a Google search,

Chokes are spec'ed by inductance (xx H or xx mH) and current, not voltage and current as that one is. Here's a direct link to that transformer's spec sheet.

If you couldn't read the label you might reasonably think it was either one though...

 

[coreyfyfe]

It's a filament transformer.

Ah well that makes it more interesting. Why the filament transformer in there? Can you use something like this to replace a PT with a shorted filament line? Or is it possible this was this originally a B-15NB and converted to a tube rectifier setup?

 

[Passinwind]

Ah well that makes it more interesting. Why the filament transformer in there? Can you use something like this to replace a PT with a shorted filament line? Or is it possible this was this originally a B-15NB and converted to a tube rectifier setup?

Both of those possibilities came to mind, but I'm not really up on all the different B15 iterations.

 

[coreyfyfe]

Both of those possibilities came to mind, but I'm not really up on all the different B15 iterations.

The B15NB was SS rectified and only made in around 62-63. The NC brought back a tube rec with a 5AR4 in 63-64.

Not much difference in the schematics:

NB

NC

I may only be seeing it now because of the curious nature of the this amp, but is the hole for the rectifier a little larger/less uniform than the mounting holes for the rest of the tubes?

Actually yes, looking back up above, there is no listing on the back of the head for a rectifier tube and the tube mounting rings look soldered on instead of riveted in.

This is a neat little amp you have here my friend.

 

[B-string]

I don't see a resistor of sufficient wattage to be a cathode resistor.

 

[coreyfyfe]

The white wire wound in the center? The wattage rating from the schematics should be 10 W. i had the same one in my 65 NC

 

[B-string]

I guess the pic is not clear enough for me to tell if that is a polarity band or bell end?

 

[Landy67]

I may only be seeing it now because of the curious nature of the this amp, but is the hole for the rectifier a little larger/less uniform than the mounting holes for the rest of the tubes?

Actually yes, looking back up above, there is no listing on the back of the head for a rectifier tube and the tube mounting rings look soldered on instead of riveted in.

The socket for the 5AR4 tube is bolted in, and the rest are riveted.