My new-to-me 820s

**wws944** · October 25th, 2012, 11:24 AM

Update: I decided to bite the bullet and have both cabinets completely refinished. The fellow who is going to refinish them has been around pro-sound for a long time, and does a lot of custom speaker building. He is taking great personal interest in the project - which is making it a lot of fun.

He brought by some mahogany samples the other day. We determined that the 1955 cabinet has a 'Bombay mahogany' finish, whereas the 1957 cabinet has a 'red mahogany' finish. The Bombay mahogany appears a little more brown, and is also a bit darker than the red mahogany. I decided to have both cabinets done in the red mahogany finish. Then yesterday he brought by more samples comparing satin vs semi-gloss lacquer. The original cabinets definitely seem to be satin, so that is what I am going with. When finished, they will have 14 coats of lacquer on them!

He also applied one of the repro decals to one of the samples, and put a couple of coats of lacquer over it. It worked quite well, but he noted that the decals are very fragile. We are wondering if Radio Daze can print them on a little thicker stock. Panomaniac gave me his blessing to contact them about it. If they can do anything, I will share whatever I find with the group. I may adjust the color a little bit too.

**Earl K** · October 25th, 2012, 12:14 PM

Nice !!!

Looking forward to some pics of the finished product .

**wws944** · November 26th, 2012, 02:41 PM

Update: My cabinet guy is just about ready to pick up the cabinets for refinishing. Hopefully in the next day or two. We will be removing the drivers and crossovers before loading them up. While out of the box, is there anything I should do with these 55+ y/o components? For example, should I send them to GPA for checkout and possible Alnico magnet recharging?

In particular, I am wondering about re-capping the N800Ds. According to the schematic in TL-121, there are two 10.5 mf caps in each. Considering that the crossovers are fairly simple first-order crossovers, how noticable would it be to simply use commonly available 10.0 mf caps? Or should I get pairs of caps (say 10.0 and 11.0) and wire them to get 10.5?

Also what kind of caps are recommended? I am not terribly budget concious, but would find it real hard to pay hundreds of dollars per cap for fancy Mundorfs.

As far as the decals go, I have decided to use our "group buy" decal with its gold leaf lettering on my 1955 cabinet - rather than trying to get a little closer color match. Will give it a bit of "street cred" with this group, at least.

(The 1957 cabinet has the Little Conductor emblem on the grill cloth. So won't get a decal.)

**Alien_Shore** · November 30th, 2012, 10:03 PM

Originally Posted by wws944

Update: My cabinet guy is just about ready to pick up the cabinets for refinishing. Hopefully in the next day or two. We will be removing the drivers and crossovers before loading them up. While out of the box, is there anything I should do with these 55+ y/o components? For example, should I send them to GPA for checkout and possible Alnico magnet recharging?

In particular, I am wondering about re-capping the N800Ds. According to the schematic in TL-121, there are two 10.5 mf caps in each. Considering that the crossovers are fairly simple first-order crossovers, how noticable would it be to simply use commonly available 10.0 mf caps? Or should I get pairs of caps (say 10.0 and 11.0) and wire them to get 10.5?

Also what kind of caps are recommended? I am not terribly budget concious, but would find it real hard to pay hundreds of dollars per cap for fancy Mundorfs.

As far as the decals go, I have decided to use our "group buy" decal with its gold leaf lettering on my 1955 cabinet - rather than trying to get a little closer color match. Will give it a bit of "street cred" with this group, at least.

(The 1957 cabinet has the Little Conductor emblem on the grill cloth. So won't get a decal.)

Yeah, you definitely should re-work those tired old crossovers. The difference between a decent cap and the uber-fancy caps is....well, let's just say a matter of preference. My old ears certainly wouldn't tell the difference. Just go to parts express or erse audio and grab some decent poly caps and enjoy the improvement. Regarding the use of 10.0 vs 10.5 uF in a 2nd order XO for 16ohm drivers is <100 Hz. You'd probably be off that much by variances in the Re of the voice coils and other things. In other words, unless you measure all your drivers and adjust your XO to fit those values, you likely won't notice a 0.5 uF difference in your caps. Have you measured your drivers to see if the voice coils are healthy?

**wws944** · December 1st, 2012, 08:23 PM

Originally Posted by Alien_Shore

Yeah, you definitely should re-work those tired old crossovers. The difference between a decent cap and the uber-fancy caps is....well, let's just say a matter of preference. My old ears certainly wouldn't tell the difference. Just go to parts express or erse audio and grab some decent poly caps and enjoy the improvement. Regarding the use of 10.0 vs 10.5 uF in a 2nd order XO for 16ohm drivers is <100 Hz. You'd probably be off that much by variances in the Re of the voice coils and other things. In other words, unless you measure all your drivers and adjust your XO to fit those values, you likely won't notice a 0.5 uF difference in your caps. Have you measured your drivers to see if the voice coils are healthy?

Thanks Alien. He picked them up a few days ago, just ahead of the major storm we've been having here on the left coast. We were in a bit of a hurry, so he is removing the drivers at his shop. Will check them out there.

As I mentioned near the beginning of this thread, I have been feeling like the bass is a bit weaker than it should be. (Even with the systems properly connected in phase...) It is interesting that you mention the 16 ohm load. The twin woofers in the 1955 cabinet are marked 12 ohms, whereas the 1957 woofers are 16 ohms. So considering that they are wired in parallel, we are talking 6 ohm and 8 ohm loads at the respective crossovers. There aren't any capacitors in the bass circuit. Just a 3 mh inductor. So I am wondering if the magnets might need recharging? Alternatively, the treble horns are connected to the 0 db taps on the crossovers. So we could lower them a few db by using one of the other taps. Here of course, the capacitors come into play though. Would new caps avoid moving the taps?

**Alien_Shore** · December 1st, 2012, 11:28 PM

I'd need to see that schematic - I thought that those old 800 networks were series filters, right? Can you take pictures of the crossover and post it? I'd like to see that, too. Most of those multi-tap units just have more (shunt) resistance in series between taps. But I don't know how the coils are laid out.

**wws944** · December 2nd, 2012, 05:18 PM

Originally Posted by Alien_Shore

I'd need to see that schematic - I thought that those old 800 networks were series filters, right? Can you take pictures of the crossover and post it? I'd like to see that, too. Most of those multi-tap units just have more (shunt) resistance in series between taps. But I don't know how the coils are laid out.

The N800D schematic appears in Altec Technical Letter 121: http://alteclansingunofficial.nlenet...ers/TL_121.pdf (These Technical Letters really make for some fun reading. My thanks to whoever scanned them!)

Looking at the schematic again, I think my posting above is wrong. The capacitors do come into play in the LF portion of the circuit as well.

**wws944** · December 9th, 2012, 04:21 PM

Was talking with the owner of a local high end audio shop yesterday and got into a discussion of crossovers for the 820s. Besides the capacitors, the topic of the coils came up. According to the N800D schematic, the stock crossovers use iron core inductors. I was musing over whether air core would be better and he was fairly adamant that air cores are the way to go. OTOH, considering how efficient these horns are, would the stock inductors get to the point where they start to saturate?

If I bought some air core inductors along with the new caps, I may as well just build my own crossovers - rather than retrofitting the new parts into the N800Ds. I would simply follow the N800D schematic - unless someone knows a good reason not to.

**cradeldorf** · December 9th, 2012, 09:19 PM

I'm gonna do Iron cores on the LF side and Air core on the HF side. I didn't like how the air cores sounded on the LF side. And not real happy with how Iron cores sound on my HF side. I have iron core on both now but the air cores for the HF side will be here Tuesday.

**wws944** · December 10th, 2012, 10:23 AM

Originally Posted by cradeldorf

I'm gonna do Iron cores on the LF side and Air core on the HF side. I didn't like how the air cores sounded on the LF side. And not real happy with how Iron cores sound on my HF side. I have iron core on both now but the air cores for the HF side will be here Tuesday.

That is a useful observation. I guess I would have expected the opposite - since the high power, where saturation might be an issue, would be on the bass side.

Which air cores did you go with?