604g impedance

[petero]

Hi,
This is my first post on this forum. I live in Sydney, Australia and I've just purchased some Altec 604g's in Stonehenge 3 cabinets which I'm in the midst of refurbishing.
My question relates to the impedance of the drivers which I've just measured across the terminals with my multimeter. Both the Woofers measure 7 ohms which I think, correct me if I'm wrong, OK but there is a 3 ohm difference on the high frequency drivers. One measures 6.5 and the other 9.5 ohms. Is this anything to be concerned about ?.

Thanks, Saturn V.

[selmerdave]

I think so, sounds like one of the HF VC's is 16 ohm and the other is 8 ohm. You may be able to compensate with a crossover tailor made for each driver but it would probably be much simpler to get the 16-ohm one changed to 8 ohms. Although from Australia that could be a PITA.

I'll defer to others.

Dave

[Fran604g]

I am also very curious what the DCR of 604-8G's was originally designed to be, I've never found any specs for this measurement anywhere, and have looked many times.

I have 2 old diaphrams (newer version connectors) and they measure 6.8 ohms.

1 of them has a hole in it due to me using the wrong crossover a couple of decades ago when I didn't realise it wasn't the correct one for the speakers (it was given to me by an "expert" to use in the 620B cabinets I bought from him in 1986). The 2nd one is unmolested.

[GM]

FWIW my 1st generation ultralights are 6.9, 7.1 ohms, but they've been periodically pushed hard over the decades, so probably a bit higher than when new.

GM

[Fran604g]

Thanks, GM!

[selmerdave]

My 16-ohm E's are 9.2 ohms on the HF.

Dave

[GM]

Interesting, you'd think they would be ~2x an 8 ohm unit and my very dim memory of the '60s era 16 ohm drivers were all around 12.8 ohms, making the 8 ohm units ~6.4 ohms.

Anyway, the main thing is that they match up well to maintain a good tonal balance between channels.

GM

[selmerdave]

Yes, I've inquired about that before, and not come to a solid conclusion. I think E's were maybe more like 12 ohm impedance to make them more compatible with the then new transistor amps? They are generally considered 16-ohm it seems although I think the label says something like "Impedance 8 to 16 ohms". Another possibility that I've understood is that they changed during the production run.

I remember some others reporting DCR's of around 12 for E's, although I do recall yet others with measurements close to mine.

Both my HF's are 9.2, both my LF's are 10.0.

Dave

<font color="#FFFFFF" size="1">[ September 29, 2008 01:47 AM: Message edited by: selmerdave ]</font>

[petero]

Hi,

Thanks everyone for their replies. It seems likely that I have a 16 ohm HF driver in one of my 604g's. Does anyone know if there is a way of visually identifying the difference ?. If not where could I source an 8 ohm unit ?. GPA maybe ?.

Thanks Again
Saturn V.

[petero]

Hi,
Just a follow-up to my previous message. I have visually inspected both the diaphragms of the HF units and yes they are distinctly different. The one with the lower DCR reading ( 8 ohms ? ) is circled by one tan coloured flat plastic inner ring then a flat metallic outer ring. The one with the higher DCR reading ( 16 ohms ? ) is circled by just one raised metallic spiral. So I guess the evidence is definitly pointing to units of diferent impedance.

Saturn V