Battle Of The B-15Ns!

PolkaHero · #1 06-17-2011, 08:46 AM

Just received both of these from my relative, I'm trying to decide which one I want to use. The left model is a late 70s model, the right one is from 1966:

The 1966 actually gave me a shock when I touched the chassis until I lifted the ground switch. Not a fan of its two-prong power cord. Some of the pots are noisy, I can probably fix those with some DeOxit. Here's a picture of the inside of the cabinet:

Does that extra insulation look stock? I'm wondering if my relative's father added that to add more bottom end?

The only issue with the 1977 model is that channel two doesn't produce any sound output. Not really a big deal unless I bring two basses to a gig which doesn't happen much.

I've been experimenting hooking up different heads to different cabinets and the combination I like best is the 1977 head with the 1966 cabinet! The 1977 head produces more output, is safer with its three-prong power cord, and it's a lot cleaner. I think the 1966 cabinet has a warmer sound, maybe not quite as much low end but not as harsh-sounding as the 1977 model. Do you guys think a hybrid is in order?! This is a good problem to have right now!

Here's some close up pics of the heads:

Too bad on the '66 head, looks like it was stored in a basement. The tolex on the cabinet is good though as it was always covered. Looks just like my B100R!

These things rock!

coreyfyfe · #2 06-17-2011, 09:06 AM

Those head cases aren't stock for sure. Looks like someone built in some extra large chasis trays. If channel 2 is completely out on the 70s amp you could try swapping the preamp tubes to see if it follows. Check under the lid of the 66 for a schematic, that should tell you which variant you have (NC or NF) and thus whether it is the 25 watt cathode biased version or the 30 watt fixed-bias version and could explain why the two sound different through the same cab. I think the change was in early 66, but it might have been late 65.

As far as the padding in the 66, no definitely not stock. It should only have the yellow pad against the back wall. I'd definitely get these looked over by a competent tech ASAP. No sense in playing gear that isn't up to spec. The good news is that these amps are pretty easy to service and a cap job shouldn't cost you more than $80-90. Definitely get that two prong cord changed over!

Congrats on the amps. That's quite the gift.

PolkaHero · #3 06-17-2011, 09:33 AM

Quote:

Originally Posted by coreyfyfe

Those head cases aren't stock for sure. Looks like someone built in some extra large chasis trays. If channel 2 is completely out on the 70s amp you could try swapping the preamp tubes to see if it follows. Check under the lid of the 66 for a schematic, that should tell you which variant you have (NC or NF) and thus whether it is the 25 watt cathode biased version or the 30 watt fixed-bias version and could explain why the two sound different through the same cab. I think the change was in early 66, but it might have been late 65.

As far as the padding in the 66, no definitely not stock. It should only have the yellow pad against the back wall. I'd definitely get these looked over by a competent tech ASAP. No sense in playing gear that isn't up to spec. The good news is that these amps are pretty easy to service and a cap job shouldn't cost you more than $80-90. Definitely get that two prong cord changed over!

Congrats on the amps. That's quite the gift.

Thanks for that info. His father built those cabinets for the heads to make them easier to lug around. He also modified the speaker cable on the '66 to a 1/4" connector. Do you think I should remove the extra padding in the '66 cabinet? The '77 is also producing a little static at the start of certain notes.

Oh, and it's not a gift yet. He'll probably want to sell one of them down the road. I just have to decide which one I want to keep!

beans-on-toast · #4 06-17-2011, 09:37 AM

You can have the best of both worlds by stacking the two cabinets (the older one on the top) and using the 70's head. The stack will be louder than each separately and will allow better monitoring.

The ext speaker jack on the back of the chassis was designed to accept an 8 ohm cab so you wouldn't have any impedance matching issues. Worth a try while you have both.

PolkaHero · #5 06-17-2011, 09:39 AM

Quote:

Originally Posted by beans-on-toast

You can have the best of both worlds by stacking the two cabinets (the older one on the top) and using the 70's head. The stack will be louder than each separately and will allow better monitoring.

The ext speaker jack on the back of the chassis was designed to accept an 8 ohm cab so you wouldn't have any impedance matching issues.

I was actually thinking of running one of these with my Bergantino NV610 this weekend. How do you think that would sound?

staindbass · #6 06-17-2011, 09:48 AM

what is the best vintage (years) for these ? the early ones?

BassmanPaul · #7 06-17-2011, 09:50 AM

Depends on the impedance of the NV610.

jimbilly · #8 06-17-2011, 09:52 AM

I don't know, I have a '66 and a '72/'73, - I'd keep them both if I were you. ;

beans-on-toast · #9 06-17-2011, 10:02 AM

I think that it would sound great with the NV610.

My only concern is running a 4 ohm load on an amp that may not be up to spec. Having an older amp looked at before putting it into service is always a good idea.

The lower load normally isn't a problem with the B-15's. Because of the impedance mismatch, the operating point of the power tubes changes and the tubes will be strained. Also the current through the output transformer will increase. If the capacitors are in borderline condition because of their age or the transformer is in rough shape, they could be pushed too hard and fail.

The only way that you'll know is to try it in advance and see how it performs. Since you're evaluating which amp you might want to keep, you have no choice to test it out under the conditions that you want to use it. It wouldn't hurt to have a backup available just in case.

PolkaHero · #10 06-17-2011, 10:17 AM

Quote:

Originally Posted by BassmanPaul

Depends on the impedance of the NV610.

4 ohms.

PolkaHero · #11 06-17-2011, 10:17 AM

Quote:

Originally Posted by beans-on-toast

I think that it would sound great with the NV610.

My only concern is running a 4 ohm load on an amp that may not be up to spec. Having an older amp looked at before putting it into service is always a good idea.

The lower load normally isn't a problem with the B-15's. Because of the impedance mismatch, the operating point of the power tubes changes and the tubes will be strained. Also the current through the output transformer will increase. If the capacitors are in borderline condition because of their age or the transformer is in rough shape, they could be pushed too hard and fail.

The only way that you'll know is to try it in advance and see how it performs. Since you're evaluating which amp you might want to keep, you have no choice to test it out under the conditions that you want to use it. It wouldn't hurt to have a backup available just in case.

My "backup" is my SVT-VR.

PolkaHero · #12 06-17-2011, 10:19 AM

Quote:

Originally Posted by jimbilly

I don't know, I have a '66 and a '72/'73, - I'd keep them both if I were you. ;

Don't think I'll be able to do that. I'm still thinking hybrid. . .

PolkaHero · #13 06-17-2011, 01:25 PM

Well, I've created a hybrid for tomorrow night. I'm using the head from the '77 with the cabinet from the '66 (I removed the extra insulation from the cabinet). I also replaced the dolly from the '66 cabinet with the one from the '77 (easier to take on and off and has better wheels). I'm going to try running a line out from the head or miking the cabinet before I experiment connecting the head to my NV610. Should be interesting!

Oh, and the schematic for the '66 says it's a B-15NF. I guess that means it's the 30-watt version. I think the preamp tubes (Sylvania vs. Maganox) make a difference in the gain stage. Either that or the volume taper is different between the two.

John D · #14 06-17-2011, 01:37 PM

The '66 would pair up nicely with that Hammond sitting behind it. Throw in an old Telecaster and some drums, and you've got blues heaven.

Dark Horse · #15 06-17-2011, 01:45 PM

Honestly, it is impossible to tell which is better without getting both serviced and back up to spec. The ones "second channel" being out is probably an indication of a needed tube change...and old tubes affect output, low end, etc. Also, the filter caps would need changed, pots cleaned, caps and resistors toleranced.

Then you could tell which was really better.

Of course if I HAD to choose one "as they sit", I'd go for the 66 personally.

But yeah, servicing is required on either one to tell the true tone.

Very cool relative you have ...congrats !

ButtUglyJeff · #16 06-17-2011, 01:49 PM

Looks like someone didn't want to fliptop them, but instead put the heads in wooden cases. Wonder why?

If I had to choose, it'd be the 66', only because is better know for old school rock, but the early 70's would be fun either way. Congrats!!

PolkaHero · #17 06-17-2011, 01:55 PM

I'm just curious why you guys think the '66 head is better. Is it because of the cool lucite logo?

Is it because it's pre-Magnavox? Better components inside?

Caca de Kick · #18 06-17-2011, 02:12 PM

Quote:

Originally Posted by ButtUglyJeff

Looks like someone didn't want to fliptop them, but instead put the heads in wooden cases. Wonder why?

My guess is because it's easier (and lighter) to carry them separately. Have you ever tried loading one in the back of a car or tall pickup truck by yourself?
I see the 'trays' have latches, so the ungle must have made lids for those head trays.

jumbodbassman · #19 06-17-2011, 02:21 PM

sweet gifts.... the 66, when up to snuff, is more valuable but you have to like which one you keep. I have 2 70's era B15S's so i like the 70's ampeg stuff alot and used to have V-4b and svt from that same era.

JimmyM · #20 06-17-2011, 02:51 PM

All B-15's are great, and there is no such thing as a bad one. The older they are, the more they're worth to collectors, but it's all a matter of personal preference. Me personally, I had a 77 and sold it because the 64 I already had was a little more full range and had more high end response than the 77. However, had I put an Altec in the 77, that might have changed, as the speakers they used in them back then were kind of on the dark side. But then you talk to someone like Justin MJ and he loves the dark speakers in the 70's cabs.

So really, there's no such thing as the best B-15 or the best years for B-15's...it's all about personal preferences.