Altec 604D question. What sort of DCR readings are within spec?

I've had a single Altec 604D in a furniture style cabinet for years. It has always sort of disappointed me with its sound so last week I decided to burrow into it. I cracked open the N1600B crossover and measured the capacitor. It says 16mf, it measured 38mf so there's a problem right there. The only questions are; In the immediate, how much do I want to spend on a cap and long range, what will I have to sell in order to clone a Mastering Labs crossover.

Which leads me to my question about DCR readings. The LF section meters out to 8.6 ohms and the HF section weighs in at 8.0 ohms. Is this within spec? Also should I use these values plugged into a crossover calculator to determine the actual value of the new cap I plan to install? Using those actual values and a crossover point of 1600 hz suggests a cap value of 12.4 mf.

As always, thanks for your expertise.

Hi pete,

There's very little info on the 604D, most of the tech data available starts with 604E version as i have noted during my search to try to help you. The LF part of the 604E, closest one to 604D for which i've found data, has RE 7.0 Ohm according to T/S parameter table for Altec drivers. Plus noted as versions get more recent that number decreases a little down to 6.4 ohm, for those i found data.

Make sure your multimeter's residual resistance is measured before testing DCR on speakers. Many people forget to do this which often leads to a little too high DCR number. Depending on the quality of the multimeter used, i've seen meter residual resistance as high as 0.8 Ohm on lower cost ones...

You can easily assess residual ohm with meter in resistance mode then putting the two test leads together for a few seconds up until the number shown has stabilized. Then you need to SUBTRACT that residual meter number from the DCR readings the meter gives you when checking the Altec.

I'm including a pic with some 604D info. Finally, the attached 604 matrix is probably among the most recent info Altec provided for that series, outlining the differences between versions. You may still search the Great Plains Audio web site, as well as the Unofficial Altec Lansing web site in case there's more...

Hopefully the above will help you somehow. Regards,

Richard

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Originally Posted by RMC

Hopefully the above will help you somehow.



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Richard, Thanks! This helps a lot​. The literature notes that both the D and the E had a system impedance of 16 ohms and that leads me to believe the anticipated RE of the D and E components ought not be that far apart. Despite a fair amount of research, this is the first time I have seen the cut sheet on the 604D. Also thanks for the tip on proper metering.

"Transients are virtually eliminated" square waves come out as virtual sine waves?

"Guaranteed Frequency Response: 30 to 22,000 cycles" Hmmm... 90dB down, but both extremes are faithfully reproduced!


Sorry, just having fun with vintage marketing. :D


Widget

Hi pete,

RE "... that leads me to believe the anticipated RE of the D and E components ought not be that far apart."

That's what i thought too in giving you the 604E LF DCR. Here's why i got this impression. First, of the four 604 versions i had data for, the two older are at 7 Ohm LF section and the two more recent at 6.4-6.5 Ohm. Second, in Altec's 604 Matrix i posted Gary Jones has made some grouping of models, which i perceive (right or wrong) as being models from the same generation (though slightly different versions). This idea seems also supported by the fact that Jones mentions in the notes: "604 B,C,D,E = Only small differences in construction." So there you got my reasons for thinking that way.

Don't forget to re-check the LF DCR on 604D with the meter residual resistance removed. That might get you little closer to 7 Ohm i guess.

Thanks Widget, had a good laugh. Yup, marketing has always been King!

Richard

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Originally Posted by Mr. Widget

"Transients are virtually eliminated" :D


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But are they digital ready?

I spoke with Bill at Great Plains Audio. He said that any DCR readings of 8 ohms or above for each component are acceptable. He 's seen some that were in the high 7's that played fine.

I have caps coming from Madisound for the N1600B crossover and will see how much that increases my enjoyment of my 604D.