Altec 604 question

[vendo81]

I recently got out my old Altec 604 speakers from storage as I now have a place to use them.

I notice that one has slight less overall volume than the other. Not a lot, but enough that I have to move the balance knob on both amplifiers I tried about one number off. This problem wasn't there when last used. I did a DC resistance check on both drivers in each cabinet and they are all the same.
A friend had suggested that maybe the original sealed crossovers have changed? Any ideas?

 

[mhardy6647]

Could be XOs or it could be that the AlNiCo magnets need to be recharged.

The former is certainly straightforward to evaluate; the latter means shippin' 'em off to GPA or someone else with the not insubstantial hardware required to recharge big magnets.

PS The 604B is a truly classic loudspeaker (last Duplex model with a true multicell treble horn) and well worthy of rehabilitation.

 

[vendo81]

Thank you for the response. I sure hope it's not the magnet as I'd hate to have to ship one of these. I'd be worried that the original cone could get damaged.

What is the best way to check the XO, swap the two? I do have a schematic and wiring diagram around here somewhere.

 

[elitopus]

Yes swap the xovers and see if the problem follows, or stays with the same driver.

Also it could just be the diaphragm in the one speaker. You didn't mention if it was total volume or just bass/treble. You could hook the xover up just to the woofer section and see if they are the same. Then do the same for the tweeter

If it turns out to just be one of the diaphragms going bad, you can buy a new pair through GPA and not have to mail out your drivers.

 

[gdmoore28]

Yes to all the excellent advice proffered so far. I would only add that, since these have been stored for a while, you need to check every connection in the speaker. From the inputs on the back to the connections to and from the crossover, to the connections to the speaker itself, the introduction of corrosion of any sort can present extra impedance. A simple check with a multi meter, as you've done, can read fine, but once power is applied the resistance will show up.

This has never happened to me, but I've run across several service threads where the introduction of current causes the problem to manifest itself. This one is a long shot, but it never hurts to make sure.

GeeDeeEmm

 

[vendo81]

Thanks to all for the help.
Yes it's the overall volume. On the weak speaker I still keep the pot for the horn tweeter at the same level and it sounds very balanced. It can still play at very loud levels without distortion.
I'll check all connections and then swap crossovers. The diaphragms are all original and have a DC resistance of 9.3 to 9.4 ohms which I've read is correct for the B's.

 

[gdmoore28]

How about some pictures of those speakers, Vendo? It won't make a spit's worth of difference as to the technical questions, but we still love seeing the real thing. Makes the connection more personal - or something.

GeeDeeEmm

 

[vendo81]

How about some pictures of those speakers, Vendo? It won't make a spit's worth of difference as to the technical questions, but we still love seeing the real thing. Makes the connection more personal - or something.

GeeDeeEmm

Sure.... I'll do that.

 

[vendo81]

Probably loose connections in the crossovers.

 

[Goldjazz]

Not sure if this was mentioned yet or not, but be sure to try to clean the pots with deoxit and work them back and forth. It's the eaiest thing to try first. Also deoxit and clean all connections (on the driver and crossover). Great speakers, I'm listening to my 604e's right now. The other thing to try, of course, is take the crossover from the louder speaker and hook it up to the quieter one and see if that changes things. A way to rule in or out the driver as the issue. Best of luck.

 

[gdmoore28]

Seeing those pics just reminds me how prevalent was building your own speakers back in the early days of hifi. Altec and other companies spent LOTS of money and research on teaching the general public how to be directly involved in DIY projects. Popular Mechanics, remember, was one of the most popular magazines of the day because most men assumed that if they wanted something they would need to build it themselves.

GeeDeeEmm

 

[vendo81]

Yes Goldjazz, I do need to go through and clean these first and definitely swap the crossovers out.

 

[turnitdown]

That may be the most elite garage system ever. Nice

 

[vendo81]

That may be the most elite garage system ever. Nice

Thanks.
I do find it a bit odd to use these in my garage but until I get them in nice cabinets they won't be going inside the house. I work on my tube
items several nights a week at a bench the speakers face so they are getting well used and enjoyed.