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Altec 605A vs 604C

ochastan

ochastan

New Member
Hello -

I own a recording studio (professional facility). I have two Altec speaker systems. A single 604C NOS and a pair of 605A in great shape which I acquired recently. All three are installed in 612 cabinets with original crossover. I'm driving all three with Fisher 70-A amp.

For some reason, the 604C has perfect headroom but the 605A which are supposed to have more headroom and range are totally distorting and crapping out at high SPL. I'm a little baffled (no pun intended). I'm trying to think of various reasons:
1. Needs reconing but speaker sounds totally clear at low to mid volume so I doubt it.
2. The voice coil is rubbing at high SPL (I need to check manually but have not done though yet).
3. There is an issue with the crossover (original or they should be upgraded).

Anyone has any other ideas?

Thanks!
 
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To begin with, 605 is 3db less sensitive. For any given SPL level you will need twice the amplifier power as the 604 needs to produce the same SPL. Depending on how the 605's have been played in the past, the magnets could be weakened and need re-charging.
 
Good to know. I knew it was less sensitive but did not know by what measure. I wonder how Abbey Road powered theirs since that was the main system for a decade there. I doubt they would have been satisfied monitoring at low level. It seems impossible.
 
Abbey Road used a 25 watt EMI/Leak RS141 tube monitor amplifier. I wonder what the issue is then. I need to check the voice coil. It makes no sense. All the indicators and mentions online is that these were LOUD!

The Leak amplifier was a high-quality tube amplifier, one of the finest in England. EMI bought them in quantity for specific use at Abbey Road studios. Upon arrival, they were modified and repackaged (as you see here today) to become the model RS141 amplifier. The RS141 was used in almost every room at Abbey Road studios, as the main amplifier for any speaker system, large or small. Most visible is their use in Studio Two Control Room - where they powered the main monitors for all Beatles sessions. Although only 25 watts at output, they coupled with the efficient Altec 605A speakers to produce a surprisingly loud monitor system.

From "Recording The Beatles".
 
I don't know the problem with the OP's speakers but I owned 605As for several years and they could get pretty damned loud with no distress. I usually drove them with low to mid powered tube amps---ASL, Jolida, old Fisher SA-100, 80-AZ and 500B. They had nice tone and could do the image and soundstage trick marvelously.
 
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