my A7s are up and running- and 416a magnet questions

history: all original 1966 416A (16 Ohm), 802D (16 Ohm), 511B, N500-E component sets have been installed in my 828 MDF cabinets after repairing 500Hz XOs that had failed caps. Installed Russian MBGO PIO surplus caps for shunt and HF positions- other XO parts original in tar (see picture). I also improved and recessed the flimsy XO/binding post panel area (see picture). Running with 8 watt monoblock amps with Psvane 300B tubes. I'm very impressed by the sound of the horns (bug screens removed)- I think the Russian caps are opening my eyes to capacitor upgrade possibilities. The 416As are weak and one has a scuffing voice coil. I removed the gobs of surround glue at bottom per forum advice (thanks!) Accidently made small holes while removing. The HF attenuators are turned almost all the way down and woofs still lagging. Obviously something has to be done here.

Woofer options:
1) send 416As to GPA for stock rebuild and regauss
2) send to GPA for install of 8 Ohm cone/voice coil assy rebuild and regauss. And convert 802D to 8 Ohms diaphram myself to make an 8 Ohm set if this is not expensive. My initial thought is that there is more info, parts, and knowledge about 8 Ohm setups because they are the majority- and this might be an advantage. Downside: will no longer be "original".
3) replace a cone/voice coil assy myself and have Alnico regaussed locally- unfortunately, shipping is a pain and major cost for all of us. The magnet (see picture) is pretty small- and even looks like it could be taken apart to be gaussed (?).

Magnet question:
I took the back cover off the 416A woofs and when I placed a screw on the side of the magnet (see picture), it barely could hang on- and when touched, it would fall off. Very little magnetic force on back of magnets also. I seem to remember that the Ferrirte magnets on my 604-8Ks could pull the fillings out of my teeth if they had iron in them. I then placed the same screw on the side of my just reconed and regaussed Altec 604-8Hs (work by GPA), and to my suprise, there was also very little magnetic force on the side of the magnet. Do Alnico and ferrites exihibit different characteristics like this? I don't know what's going on here.

My impressions:
1) I think it's true that using these in a small room (see picture) is NOT a problem at all from sound quality point of view.
2) As mentioned above, horns sound great- some of the best treble I've heard ever I think. Chet Baker's "Almost Like Falling in Love": wow!
3) Despite reasons given for superiority of MDF, my gut says plywood is better. The previous owner had put a rough piece of 3/4" ply panel on the ports to get a 3 1/2" port opening. I decided to "clean things up" and make a more original look with a 5/8" MDF panel with T-nut mounting. When thumping on the panel with my fist, the MDF cab was buzzy- when thumping with the 3/4" ply panel in place, the resonant frequency of the cabinet structure itself went up (tighter), and the buzzing was way less. This removable port panel can contribute to the overall rigity of the cab significantly I think- and I will be making new better looking panels of different sizes out of 3/4" ply.
4) I am excited about moving foreward and hearing these guys with proper woofers and different crossovers. Consensus is that I should go to 800 Hz XOs, and I have diagrams from Bill for stock Altec 800 Hz XOs. Or, at some point, I will probably build XOs based on design advice I get in these forums. I'm gonna stay at 500 Hz for now (I think) so I can hear what these sound like at 500 Hz with properly running woofers before I move foreward. Needs bracing- If/when I get ambitious, I will make a a front-to-rear brace attaching top of front panel and bottom of motor board to rear cabinet panel, 3/4" plywood. Really difficult to go around drilling holes in these original boxes though- have to figure out least invasive way.

Links to Dropbox pictures:

Dropbox - repaired XO 2988-Edit.jpg
Dropbox - modified XO mounting 2990.jpg
Dropbox - weak Alnico magnet 3010.jpg
Dropbox - A7s in my home 3016.jpg

Congrats, nicely done!

If one woofer must be reconed, then I would do the other one as well since new GPA cones are probably different enough from those made 50 yrs ago, for there to be a mismatch in the frequency response (not saying that the older cones are necessarily better - just different). Better yet, in order to preserve the good 416, try to find a single defective 416 on epay and have that one along with your existing driver reconed and remaged by GPA.

I would stay with 16 Ohm drivers for two reasons: a) they're a better/easier load for SET amps. b) capacitor values are halved over those for the 8 Ohm version of the cross-over, which means that you'll either save money, or get better quality caps for the same amount. Capacitors are usually the most expensive components in a crossover. Speaking of crossovers, you must at some point try the Jean Hiraga crossover for the A5. A good write-up on the A7 is the one linked bellow by Pete Riggle. His A7's use the same components as your speakers. You could duplicate his crossovers using russian caps such as MBGO's and KBG-MN's for not that much money.

Good luck and keep us posted.

Altec A7 Voice Of Theatre Speakers

Just takled to Bill at GPA. If I want to replace the entire speaker, GPA 416-8B or 416-16B (Alnico Classics) are available at $360 ea. (416-8C ferrite magnet is no longer available apparently- think I prefer Alnicos anyway) Wondered if anyone had some feedback the GPA 416-8B/16B? Seems like a good option to me. Saw some posts from around 2010 about some issues with them.

**Just as I went to post this earlier, the board went off line for maintenance and it didn't take, so here's my second attempt.**


Congrats, nicely done!

If one woofer must be reconed, then I would do the other one as well since new GPA cones are probably different enough from those made 50 yrs ago, for there to be a mismatch in the frequency response and T/S parameters between the two (not saying that the older cones are necessarily better - just different). Better yet, in order to preserve the good 416 driver, try to find a single defective 416 on epay and have that one along with your existing driver reconed and remaged by GPA. You could thus recoup some of your money by selling the original driver.

I would stay with 16 Ohm drivers for two reasons: a) they're a better/easier load for SET amps. b) capacitor values are halved over those for the 8 Ohm version of the cross-over, which means that you'll either save money, or get better quality caps for the same amount. Capacitors are usually the most expensive components in a crossover.

Speaking of crossovers, you must at some point try the Jean Hiraga crossover for the A5. A good implementation of the Hiraga XO for the A7 was done by Pete Riggle as seen in the link bellow. His A7's use the same drivers and horn as your speakers. You could duplicate his crossovers using Russian caps such as MBGO's and KBG-MN's for not that much money.

Good luck and keep us posted.

Altec A7 Voice Of Theatre Speakers

For the sake of completeness and for future reference, the A7-500-8's in question use 416-8B Alnico woofers, 511B horns, and model 802-8D alnico magnet drivers.

Here's the crossover schematic.

great day!! new 416 8Bs alnicos for 360 $ each? screw the recones that's a good deal. especially considering two way shipping.

AlNiCo magnets are basically the original ?shielded? magnets. A screw won?t stick to the outside of them like a ferrite magnet. As I understand it, this is because of the magnetic return inside redirects all the force to the gap.

That is a good deal on the GPA woofers. I would seriously consider those.

As far as 8 versus 16 ohm, I would use whichever is easier for you. For instance, if you are running passive xovers, and like expensive caps, the 16 ohm versions are cheaper to build.
If you are like me, and use cheap caps, the bigger coils on the 16 ohm xovers make them more expensive to build, and I would go with 8 ohms.

Regardless of magnet material, for that entry fee, for woofers that likely don't sound exactly like an original 416B.................. i'll gladly run with TD15M's and not look back.

Acoustic Elegance TD15M high efficiency bass/midbass driver

Just my .02 y'all understand....................

Wow those look interesting. Do they have any of the ?Altec? sound?

Quote:

---

Originally Posted by Elitopus1

Wow those look interesting. Do they have any of the ?Altec? sound?

---

IMO, they have much of it, and retain it at SPL's beyond what the Altecs are capable of. They're kind of like "Altec meets TAD" at an affordable entry fee.

Expect to wait if you order. They're hand built in small lots here in the USA.