New cab day - and a question re: reconing.

[coreyfyfe]

I recently purchased this 70s Ampeg B25B cab. I was looking for a smaller (than my 8x10) 4 ohm cab to run with my SVT for smaller gigs and settled on finding a B25. Circumstances were right and I picked this one up on ebay a few weeks ago. After a bit of a wait, it showed up on my door step this afternoon. I haven't had much chance to play around with it since I had rehearsal today, but the seller informed me that one of the speakers may be in need of a recone, which leads to my question - is there a recommended place that will service these speakers? I know Orange county speaker, but any others? Anyone ever use fliptops recone service?

My crappy cell phone pic -


some pics from the ebay listing -

[coreyfyfe]

More pics.......and more questions.

Speakers date the cab to 73:


Only had a little bit of time to play around with this using my Micro-VR but it definitely sounds like the bottom speaker is a little funky. Sounds like something is rattling around in there. I tried to check the impedance to make sure the switch was working properly before I went and hooked my SVT up to this but the meter was giving me funny readings. With the switch at 4 it seemed to settle around 12-14, and with the switch on 16 I wouldn't get a reading - this was on the lowest setting. Admittedly I gave up kind of quick. Anyone know if this wiring looks correct? The bottom right connection looks like it may have been re-done.





I remember seeing a written out version of this connection on here once or twice, but the search function is failing me at the moment. Any help would be appreciated.

[beans-on-toast]

Very nice pics Corey.

The wiring for the switch that you are looking for is on the B-25B schematic in the box at the top right. The switch selects either a serial (16 ohm) or parallel (4 ohm) wiring for the speakers. It is hard to tell from your pic but it looks like wires are going to the correct tabs on the switch.

I would measure the resistance of each speaker with the wires disconnected. You should read less than 8 ohms on each speaker. Then test all the connections of the wiring harness. It might be a good idea to clean the switch contacts with DeOxit. Also snip those stray strands on the green wire. It is probably just the camera angle but it looks like there could be a short to the terminal below with the black wire on it.

A copy is located here (http://www.el34world.com/charts/Sche...Ampeg_B25B.pdf)



David

[coreyfyfe]

Thanks David, I hadn't noticed the diagram on the B25 schematic, I actually have a copy but didn't see it there. The top right contact was slightly bent downward but I don't think it was contacting the lower, it could just the camera angle.

[beans-on-toast]

It might be a good idea to remove both speakers and inspect them. You might be able to see what the problem is and repair it without a re-cone. You can also confirm that both are original and have the same cones.

If you have to get the problem speaker re-coned, it would be best to try to get an original kit. That way, both speakers will sound as close to each other as possible. If dope is applied around the edge, get it applied so that it is consistent on both speakers (light, medium, or heavy).

Another option is to get both speakers re-coned so that they are the same. Then again, sometimes having two slightly different sounding speakers is a plus.

[coreyfyfe]

The plot thickens. I checked both speakers with a meter this morning before heading out to work. The supposedly troublesome bottom speaker gave me a reading of 8 ohms - on the dot, not slightly below as I expected? - while the top speaker wouldn't give any reading. This does explain why I couldn't get a reading from the 16 ohm setting since they'd be wired in series, but doesn't really explain why I was seeing 16 ohms in the parallel setting - though that may have been a mistake.

I'll pull them out tonight and give a closer inspection, with snowmageddon part 12 swooping in I'm sure I'll be looking for indoor activities.

Thanks again for your help.

[beans-on-toast]

Yes it is normally slightly less than 8 ohms but getting anything close is a good sign. Clean the terminals (sand them if necessary) on the speaker before taking your readings to make sure that you are getting a good contact.

When you say no reading on the other speaker, check if the reading was infinite (an open connection), or zero (a short). Check the wires on the speaker itself to see if one has come undone.
You could also try the battery test on each speaker. If that works, connect one speaker at a time to a low output source with a speaker out jack like a computer or radio to test it.

With the harness connected, if one speaker is shorted, you would expect 0 ohms in parallel and 8 ohms in series. If one speaker is open you would expect 8 ohms in parallel and 0 ohms in series.

You guys have really been hard hit in Boston this winter. Schools closings scrolling across the bottom of the TV screen seem to be the norm.

[coreyfyfe]

I'm assuming it's an open connection, I get the same reading with the probes not touching anything that I do when I touch that speaker and when I was checking the speaker on the 16 ohm setting. For now I put the Delta 15A I had into that spot and ordered another. The seller said he tested the amp (with his boogie 400+) which is when he thought the bottom speaker sounded like it needed a recone, could have been the overall sound was just funky. I did a 5 minute or so play test when I got it home and it sounded like there was a metallic rattling but I didn't play around much because the wife was telling me not to disturb the neighbors.

Anyways, the speaker I pulled seems to have some serious rubbing going on when I push down on the cone. The contacts appear to be solid - no broken connections, frayed wires.

[coreyfyfe]

With the new speaker in place the readings were still off with the switch so I believe there may be something off with the switch or wiring to, though it appeared to be correct. I wanted to keep all the wiring original simply for the sake of originality - I don't plan on buying a B25 or other 16 ohm head any time soon - but decided to heck with that and pulled the connections and just rewired the cab to 4 ohms. It's reading around 3.9 on the meter, which given that the new eminence was reading 6.7 and the stock speaker was reading 8.0 sounds about right. I'm going to pop the other eminence in when it comes in and just hang onto the original speakers for now.

David, thanks again for all the help with this.

[beans-on-toast]

Glad I could help Corey.

I think that it was a good idea to remove the selector switch. I wouldn't want to be pumping a lot of watts through such a frail pathway. Your signal is going to sound better connected directly from the speakers to the jack.

It's a nice vintage cab. I wish I had one.


David

[christw]

Edit: Nevermind, haha.

Not to pry, but how much did you drop on it?

[coreyfyfe]

Originally Posted by christw

Edit: Nevermind, haha.

Not to pry, but how much did you drop on it?

Originally $300 but I was refunded $75 for potential re-coning costs. I had a delta 15 laying around and ordered another ($90) so the refunded amount pretty much covers that.

[fu22ba55]

Originally Posted by beans-on-toast

I think that it was a good idea to remove the selector switch. I wouldn't want to be pumping a lot of watts through such a frail pathway.

+1

Killer cab corey. Enjoy.