My new toy - Ampeg B-18-N head

aborgman · #1 10-23-2010, 03:00 PM

Well, when I went to check it out I was expecting a '63 B-15-N... and it turns out to be (I think) a '65 B-18-N.

It's definitely a B-18-N, serial 001523 under the power cord - which from what I can tell makes it a 1965.

Missing the plexi and someone cut the original speaker cord off... but everything else is original, including all the tubes except the power tubes.

I finally got my B-series Ampeg... and for way less than the re-issue B-15 is going to go for

stiles72 · #2 10-23-2010, 03:26 PM

Good score! Match that up with a Vintage Blue cab and you'll be set!

JimmyM · #3 10-23-2010, 03:39 PM

very nice! +1 for vintage blue. mark's a real artist and makes great replica cabs even better than the originals.

craig.p · #4 10-23-2010, 04:07 PM

Wow, that takes me back. I had one of those in high school. It replaced my 2x15 Teneyck. Didn't get anywhere near as loud but it had a lot more character. And reliability.

Ric Vice · #5 10-23-2010, 04:36 PM

Quote:

Originally Posted by aborgman

Well, when I went to check it out I was expecting a '63 B-15-N... and it turns out to be (I think) a '65 B-18-N.

It's definitely a B-18-N, serial 001523 under the power cord - which from what I can tell makes it a 1965.

Missing the plexi and someone cut the original speaker cord off... but everything else is original, including all the tubes except the power tubes.

I finally got my B-series Ampeg... and for way less than the re-issue B-15 is going to go for

Nice,
It's got twice the power output of the B-15 and it was also used as a head for the shortlived B-15 ND. A lot of players cut that cord off because it had a four pin connector that put the amp in stand by mode when you disconnected it from the portaflex cabinet. Unfortunately, that connector was a little hard to find.

Ric

Ric

metalmariachi · #6 10-23-2010, 04:45 PM

Not too hard to find, it's a 4 pin female mic plug.

Nice find, great amp.

MM

JimmyM · #7 10-23-2010, 05:01 PM

that's actually a nice feature. when jess oliver restored my b-15n he reinstalled it and i think it's great. not very universal, no, but it works just like it's supposed to work. beats that wacky way of connecting the cab to the sb-12. ever see that? it connects through the fliptop latches.

not every idea can be a winner, i guess.

Jhtjon · #8 10-23-2010, 06:14 PM

Since no one asked....

.... What does she sound like. And would you take a gut shot for me?

**garmenteros** · #9 10-23-2010, 06:59 PM

can someone confirm the wattage on the b-18n and the b-15n?

JimmyM · #10 10-23-2010, 07:21 PM

b-15n: 25w before 1965, 30 after.

b-18n: 50w.

aborgman · #11 10-24-2010, 04:26 AM

Quote:

Originally Posted by Jhtjon

Since no one asked....

.... What does she sound like.

Wonderful - like angels singing about hot buttered *ss.

Quote:

Originally Posted by Jhtjon

And would you take a gut shot for me?

Definitely. As soon as I pull her apart to put in a power cord with a safety ground I'll get some pics up.

aborgman · #12 10-24-2010, 04:30 AM

Quote:

Originally Posted by JimmyM

that's actually a nice feature. when jess oliver restored my b-15n he reinstalled it and i think it's great. not very universal, no, but it works just like it's supposed to work. beats that wacky way of connecting the cab to the sb-12. ever see that? it connects through the fliptop latches.

not every idea can be a winner, i guess.

One nice thing about the B-18 is the way the extension speaker jack is wired. It expects a 16ohm speaker to parallel with the built-in 16ohm speaker - so when you plug into the extension jack it connects to the 8ohm tap... even if you've got the old cable cut off.

This means you can actually just wire an 8ohm cab to the extension jack and have it be connected to the correct OPT tap - as long as the actual cab isn't also connected.

aborgman · #13 10-24-2010, 04:35 AM

Quote:

Originally Posted by JimmyM

b-15n: 25w before 1965, 30 after.

b-18n: 50w.

From the same output tubes. A pair of 7027/6L6's. The plate voltages on the B-18 must be insane.

Although design specs for the tube do show a max signal output of 55W, you're definitely bumping up against the upper edge of the design window.

BassmanPaul · #14 10-24-2010, 11:23 AM

It looks to me that your amp does not have the slot required for the plexi Ampeg plate. What that means I'm not sure but my B15N does not have the slot either.

aborgman · #15 10-24-2010, 11:40 AM

Quote:

Originally Posted by BassmanPaul

It looks to me that your amp does not have the slot required for the plexi Ampeg plate. What that means I'm not sure but my B15N does not have the slot either.

It has the slot, but the tube cage covers it.

aborgman · #16 10-24-2010, 11:42 AM

Quote:

Originally Posted by Jhtjon

And would you take a gut shot for me?

Gut shots:

aborgman · #17 10-24-2010, 11:48 AM

So I got a new, safe, power cord put in - and got the ground switch of death disconnected.

It turns out the output jacks have been completely rewired - so it has the 16ohm tap to the extension speaker jack, and the 8ohm tap wired to the external amp jack.

So no preamp out, and the negative feedback loop is being fed off the 8ohm tap instead of the 16ohm tap (which appears to be wrong from the schematic)... but no big deal, it just means a little less negative feedback.

aborgman · #18 10-28-2010, 07:58 AM

So last night I rewired the output jacks and the NFB loop.

Connected the 8 ohm tap to the jack at the extension speaker hole (it's been replaced, no longer a shorting jack).

Connected the NFB loop feed to the 16ohm tap on the OPT (was attached to 8 ohm tap).

Connected the "ext. amp" jack back as it should be - to the connection point between the two 270k ohm mix resistors and pin 7 of the 7199 (control grid of pentode section).

Plugged a cabinet in - sounds great.

Hooked a power amp up to the ext. amp jack. Uh oh. Not so great. With the connection made there was a huge loss of volume from the cabinet (80%?) and the signal going to the power amp (Carvin DCM1000) was so low as to be barely able to drive the amp at all. Unplug the connection to the power amp and everything is back to normal.

Tried different cable between the B-18 and the power amp - no difference.

I'm pretty certain it's wired correctly - or at least, it is wired exactly as every schematic I've been able to find.

I'm going to open it back up and take another look when I get home this afternoon, and if I don't see anything I'll haul it into work and put it on a scope... but anyone have any ideas?

stiles72 · #19 10-28-2010, 08:26 AM

The Ext Amp jack is a little strange by todays standards and was designed to chain two Portaflexes together. Rather than working like a standard line out (preamp signal going one direction to a power amp for example), it almost works like a two way conduit - so that whatever you are connecting it to may also affect the originating amp.

aborgman · #20 10-28-2010, 09:01 AM

Quote:

Originally Posted by stiles72

The Ext Amp jack is a little strange by todays standards and was designed to chain two Portaflexes together. Rather than working like a standard line out (preamp signal going one direction to a power amp for example), it almost works like a two way conduit - so that whatever you are connecting it to may also affect the originating amp.

No doubt - it's basically more like an insert point than a traditional line out... but I still wouldn't expect a power amp with a 20k ohm input impedance would load it enough to have much effect.