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Differences between Polk 7A and 7B

Tim D

Tim D

Super Member
I won an auction for a set of 7A's and brought them home. Sitting them next to my 7B's, I couldn't tell the difference other than the model. They both have peerless tweets, they both have the same surface mounted drivers and they both have a single tweeter fuse in the cup on the back. They both have the walnut vinyl veneer and they both have the same grills. I know that 7B's went through some serious changes throughout their manufacturing lifecycle, but these appear to be identical to the 7A's I just picked up.

Any ideas as to what makes them different?

I'll get some picks and upload them soon.
 
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I found a difference. The passive radiator has a deeper cone on the 7A's. The weighted center is smaller on the 7A's too. I'll know more when I open them up to see if the crossovers are the same.
 
Here are some pics of the 7A and 7B passive radiators.

Side-by-side (7A is on the right):
IMG_2335.JPG

7A:
IMG_2336.JPG
7B:
IMG_2337.JPG
 
One of my tweeters on my 7b starts to distort when I turned up the volume could it be the caps the wires look fine. I'll try switching the tweeters and see if that makes a difference later
 
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bgymnastics said:
One of my tweeters on my 7b starts to distort when I turned up the volume could it be the caps the wires look fine. I'll try switching the tweeters and see if that makes a difference later
Click to expand...

Right. Try swapping the tweeters to see if the problem moves with the tweeter. That will tell you if the problem is with the tweeter.
 
I listened a little closer and it wasn't just the Twitter that was cutting out the whole speaker. Or maybe starting with just the tweeter other day and now it's the whole right speaker. It cuts in and out.what do you all think about that.
 
bgymnastics said:
I listened a little closer and it wasn't just the Twitter that was cutting out the whole speaker. Or maybe starting with just the tweeter other day and now it's the whole right speaker. It cuts in and out.what do you all think about that.
Click to expand...
That's not good.:no:
 
bgymnastics said:
I listened a little closer and it wasn't just the Twitter that was cutting out the whole speaker. Or maybe starting with just the tweeter other day and now it's the whole right speaker. It cuts in and out.what do you all think about that.
Click to expand...

If you swap them left to right, does the cutting out follow the speaker or stay in the same channel?
 
Tim, you were very specific about them having walnut vinyl veneers. Possibly another difference w/ them would be that the older 7s had faux rosewood veneers. I had original older '78 7s again w/ all you said w/ the covering being the only difference. I'm not sure if the rosewood finish was an added extra or just a pick and choose situation because theIMG_3804.JPG y were both vinyl.
 
I had a set of original 5B's back in the 80's that had the rosewood. I regret selling them. The 7A's and B's I have are much less red and have that brown walnut color to them. As far as vinyl goes it's not a bad look though and it has held up well - maybe better than real veneer. I think my 7A's are older than the 5B's I had with rosewood, so I don't know that it has much to do with the vintage during the 70's and 80s. It must have been an option or something. The Polkies over at the Polk website would know I'm sure.
 
The 7A uses a MW6502 mid-driver while the 7B uses a MW6500 as well as a different PR, which you already noted. Therefore, the circuits use different components. The 7B is considered the best of the series.
 
F1nut said:
The 7A uses a MW6502 mid-driver while the 7B uses a MW6500 as well as a different PR, which you already noted. Therefore, the circuits use different components. The 7B is considered the best of the series.
Click to expand...

Thanks F1nut. I've got to open up the 7A's to dynamat the baskets. I'll check the model number on the mid-woofer. I'm thinking my 7A's are late run units. They look nearly identical to my 7B's from the outside except for the PR being slightly different. I found the cross-over caps were the same size in both. (Already had them open for recapping.)
 
The cap values are the same in all the 7 series, it's the resistor and inductor values that change.

This is the schematic for the 7B. M7Crossover.jpg
 
Mine had the tweeter cutting in and out. It was the fuse holder that was kind of dirty.
Sanded it a little to make it clean again and everything was alright.

Now.

For a whole speaker cutting out, it has to be wiring from your amp to the speaker OR
wiring inside, that is, the stretch from the binding post to the crossover printed board circuit.

Check that fuse holder for shure
 
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Do not sand the fuse or holder as that will damage the plating. If you don't have Deoxit and Pro Gold around, use a pencil eraser.
 
traded for a pair of 7A's today.These were purchased in Japan I was told.
They do appear slightly different from the US version with the scotchlok grill mounting setup and brown fascia-
 

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There's nothing different about them having been purchased in Japan, they are what the early 7A's looked like. Yours are not the very first though, they had a plain paper passive radiator verses the doped paper in yours.
 
I think the guy said it was around 1983 while stationed in Alaska his wife hopped on a P3 and flew to Japan and purchased them.
 
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