Early Model Six - what am I getting into?

[Robthomp]

Hi everyone,

I just bought a pair of early model sixes this morning from a retired audio guy on CL.  I've read a lot about these speakers in the last week.  I had a lengthy discussion with the seller and I read up on the challenges of working on the early sealed versions before taking the plunge.   I'm still fairly new at this hobby, but I like challenges and problem solving.

The high range is not really present in the sound, and the seller and I both bet that a recap is needed to get the tweeters working.   The bass sounds good, and the cabs are in great shape.  My plan is to go in through the back plate, which seems to be the preferred method.  I am wondering:

1)  For initial  diagnostic purposes, what would be the best way to test the tweeters, to determine if a recap is going to work, or if the tweeters themselves are bad?

2) Is there a detailed write up of this job, with pictures?  Are all the capacitors near the switch and the back plate, or is there one buried further inside?   I imagine reaching in with my arm and grabbing it, but how the heck would you actually replace it?

3)  Is it possible they would benefit from resealing the woofer surround, and if so what's the best way to determine that - by listening?  If they would benefit from that is it even possible to do it?  I understand that the grills don't come off  - in fact I read somewhere that there really is no grill, the speaker cloth is just wrapped around the baffle board, and epoxied, so the only way to access the drivers from the front involves destroying the cloth.  Can you reseal woofer surrounds from the back? 

Thanks,

Rob

[dxho]

I don't know of any way to test if a recap will work, except to replace the old caps and
see what difference they make.

This is a pretty detailed account of restoration. All components should be fairly easy
to reach.

Chances are high the woofers need a coat or two of sealant. It would probably require
cutting the back open to seal them from the rear.

[lARrybody]

On 6/2/2017 at 2:33 PM, Robthomp said:

The high range is not really present in the sound, and the seller and I both bet that a recap is needed to get the tweeters working.   The bass sounds good, and the cabs are in great shape.  My plan is to go in through the back plate, which seems to be the preferred method.  I am wondering:

I have done two sets of 6's. Both had no tweeter output till I replaced the caps. It is a common thing since the caps KLH originally used are known low quality. Also you will want to replace the three resistors because they a also low quality, 5 watt I think. Here is a thread with pictures covering my first pair.

http://audiokarma.org/forums/index.php?threads/klh-model-six-restoration.632555/
 

It was bad enough working from the 3X3 hole in the back, I never considered resealing the woofer surrounds from the back. I took GD70's advise and found a pair of  replacement grills and cut the cloth from the front. Yes it did make a big difference. Use only the stuff from Vintage AR, for it is correct. That grill cloth is impossible to find and I was lucky to find a pair. Some people use linen cloth like AR used. You never get tired listening to 6's, they are so right.

[Robthomp]

Thank you for the links. These two threads really make it clear how to replace the crossover in these.   Thanks for the suggestion about the resistors too. Now I just have to decide on a strategy for resealing the woofers.  Based on what you are all saying, and what I've read in other threads, it sounds like the odds are very good that they will benefit from a resealing. My takeaway is that the original sealant degrades and just doesn't last 55 years.  It also sounds like no one has attempted to reseal the woofers from the back through the small hole, so that may be impossible.

Since the grills are in excellent condition, my initial impulse was not to touch them, for the sake of preservation and authenticity.  On the other hand, having them sound as good as they are capable of sounding may be the higher priority (they are speakers after all, so that is their ultimate reason for existing).   So maybe I will cut them out to reseal the woofers. I got sealant from Roy C for this pair of AR-4x's I'm finishing up, and it should be plenty for the KHL's.    If I can't find replacement  model 6 grills right away, maybe I'll make something out of the Wichelt linen ( which is such a close match to the original AR cloth!) and then keep looking for model 6 grills.

The serial numbers on these are 64,996 and 65,531.

 

[Robthomp]

Or cut a large hole in the back, as dxho suggested.