Shout out to Earl K! Altec 802D question...

[jamesbythebay]

Hi Earl K!

I hope you don't mind a new guy reaching out to you directly...but I'm trying to sort out an Altec 802D driver and diaphragm that I just acquired. An earlier post of yours regarding the 802C was quoted, and in it you indicate that the DCR of the original diaphragms should be between 7-9 Ohms. Were you measuring the DCR of an 8 Ohm driver/diaphragm? Or a 16 Ohm diaphragm? Unfortunately the quoted sections did not include any pictures of the diaphragms you were measuring, or make it clear which impedance the models were supposed to be spec'd at.

My confusion is this: For an 8 Ohm driver, using a DVM I would have expected the DCR to read somewhere around 6.5 Ohm. For a 16 ohm speaker, I would have expected DCR to measure 11.5-12.5 Ohms. Of course, the real world is what it is. Am I missing something here? I have to admit I've only seen a dozen or so diaphragms from 806/802s.

The new (to me) 802D arrived a couple of days ago. It has a diaphragm marked on the underside 500818. It measures 8.46 Ohms DCR. I can't make out the marking on the top. It looks like a sloppily applied Altec marking. Although mostly, if not completely illegible, the silver ink looks identical to original Altec diaphragms I have. The typography/style of individual numbers looks the same as the typography used on original diaphragms.



Any thoughts you might have what will set me straight would be most appreciated.

Oh. I'm having another issue with the same driver. One of the mounting studs is bent. Can I just turn it counter-clockwise, and remove it? It appears to be a standard 1/4-20 threaded stud. Or do I need a special part?

Cheers,
~james

[Earl K]

Hi James,

That printed number is a new one on me ( although I'm not convinced it actually relates to the diaphragm model number ) .
- Mant times the older generation diaphragms ( when marked with a model number ) were written in pen on the inside of the coil former ( bobbin ) .

The DCR you measure is correct for an older Altec 16 ohm diaphragm ( pre mid-70's ) / after that the DCR increased for the 16 ohm diaphragm .

Altec noted ( & then designated ) a diaphragms AC impedance at the 4000hz ( ie; I bet if you made an impedance sweep of that fram and then looked at 4Khz mark, you'd see it's @ 16 ohms > assuming it's an Altec diaphragm > sure looks like one > I'd bet pre introduction of the 8-ohm series > so, before 1960 > just a guess ) .

Yes the mounting studs are 1/4-20 .

[jamesbythebay]

Earl!

I appreciate your detailed response, and the time you took to provide it.

I'm pretty sure I didn't see any hand written numbers anywhere on the diaphragm. But now you've piqued my interest. I'm pretty sure I'm going to have to take it apart again and look at it. Yeah, when I compare it to the other original Altec diaphragms, it does virtually identical.

Well, I've got one 802d with an original diaphragm. And one with a recent vintage GPA diaphragm. What to do? Listen to them, I guess!

Cheers,
James