Monitor 7As

kkritsilas

I just picked up a pair of Monitor 7As from a pawnshop. They were $13. As you can guess, they have some issues, but I do have a two week period in which I can return them, so it was worth the gamble.

On one speaker, the tweeter seems to be blown. I would guess that it needs to be replaced; probably end up replacing both of them. I think the correct replacement is the RO194 ( I will, of course, check the crossover network, first)? I think, because I live in Canada, that I would need to get the tweeters from Walter Moser.

I was also thinking of changing the resistors & capacitors in the crossover, just on the basis of the original parts being about 30 years old. Are Solen capacitors the way to go, or is there something better? Can somebody recommend resistors that would be better than just standard carbon composition acoustically? Is it necessary to change the inductors, or is there some sort of inductor that will improve the sound?

tonyp063

You'll want to post a picture of the tweeter. I believe the 7As used Peerless & the RDO-194 is *not* a drop in replacement for them.

Copying a post from Dave (westmassguy) in another thread where he says:

"Your Crossovers most likely have a mix of Mylar and Non-polarized Electrolytics, with Sandcast Resistors. You'll want to replace all of them.
You'll want Metalized Polypropylene Caps, and Mills or Mundorf MOX Resistors.
Entry Level, I.E. inexpensive, would be Dayton or Solen MP Caps, and Clarity PX would be a step above. The much better, and expensive Caps would be Sonicap Gen I, or Clarity ESAs."

kkritsilas

Sorry, I will get that soon. I haven't opened up the speakers yet.

Thanks for the information about the crossover components.

Nightfall

You can't drop in RDO-194's. You either need a used original:

http://www.ebay.com/itm/Sweet-Polk-Audio-Peerless-Pinhole-Tweeter-No-5-514-05-82-Free-Shipping-/252121415767?hash=item3ab39b8057

...or a new Midwest clone:

http://www.ebay.com/itm/8-ohm-Tweeter-for-Polk-Audio-HF1000-SL1000-for-Monitor-RTA-Speakers-MT-4115-8-/150791478865?hash=item231bdf5e51

pitdogg2

Might be a fuse issue as some were fused. Check binding cup got fuse holders

Cfidave

I used Sonicaps for the high freq. capacitor and Solens pollys for the low freq. Mills resistors. I have 7A's as well and that combination sounds great.

F1nut

Yep, check the fuse.

Don't use Solen in the high pass.

leftwinger57

When I got my M7s a few months ago I didn't know what generation they were.I'm guessing since the x-overs were from '78 they have to be 7A also w/ the out board 1a fuse. For my taste the Peerless tweeters are still smoother than the RDO-194-s but a boatload better than the SL-2000 silver
domes. If only tweeters are beat than replace them , I got mine for $60 w/ chewed up corners but the sound was great. Xx-overs are now out for Dave to do his magic and these will be keepers.

michaeljhsda2

More than likely the fuse is making poor contact with the fuse holder due to corrosion. Spray contact cleaner on it and rotate the fuse in the holder to distribute the cleaner. If you don't have contact cleaner, try rotating the fuse while music is playing and listen for sound trying to get through to the tweeter. A piece of wire can be used in place of the fuse to test for continuity in case the fuse is blown.

kkritsilas

I will try the fuse idea tonight or tomorrow. Thanks for the idea. It may be worth the time and effort to clean up the fuse holder with steel wool, and replace the fuses; they should be cheap enough.

pitdogg2

kkritsilas wrote: »

I will try the fuse idea tonight or tomorrow. Thanks for the idea. It may be worth the time and effort to clean up the fuse holder with steel wool, and replace the fuses; they should be cheap enough.

that a boy excellent idea

leftwinger57

If the cleaner doesn't do it and you see corrosion try a little emry cloth but be gentle ,you don't want to rip the crap out of the holder. Any car parts place has those fuses.

kkritsilas

Tweeters are the ones with the pinhole in the middle, so Peerless.

Tonight, I will be cleaning up the fuse holders; one of the speakers had a slow blow fuse, which will be going (I have new 1A fuses). We'll see if the tweeter works after I clean up the fuse holder. If not, I would like to check the resistor values, and the wiring of the crossovers, just to make sure that everything is wired up properly (looks like somebody got in there at some point in the past).

Regarding the tweeter that is blown, is there some way of doing a resistance test on it? I know with midranges and woofers, you can check DC resistance (an 8 ohm driver will have a DC resistance of 6-7.2 Ohms), so is there a value for the tweeter that I should be looking for? I figure if it is blown, it will be open, and if it is just damaged, it may (or may not) show up as an altered resistance value.

kkritsilas

Here is the tweeter picture. The tweeter is dusty, so the pinhole in the middle is not as obvious.

F1nut

Do NOT use steel wool on the fuse holder.

If you don't have a purpose made non-scratching metal cleaner product on hand, use a clean pencil eraser.

westmassguy

kkritsilas wrote: »

Tweeters are the ones with the pinhole in the middle, so Peerless.

Tonight, I will be cleaning up the fuse holders; one of the speakers had a slow blow fuse, which will be going (I have new 1A fuses). We'll see if the tweeter works after I clean up the fuse holder. If not, I would like to check the resistor values, and the wiring of the crossovers, just to make sure that everything is wired up properly (looks like somebody got in there at some point in the past).

Regarding the tweeter that is blown, is there some way of doing a resistance test on it? I know with midranges and woofers, you can check DC resistance (an 8 ohm driver will have a DC resistance of 6-7.2 Ohms), so is there a value for the tweeter that I should be looking for? I figure if it is blown, it will be open, and if it is just damaged, it may (or may not) show up as an altered resistance value.

The Peerless should read about 7.5 ohms if the coil is good.

kkritsilas

F1nut:

Would you care to elaborate? What is the issue with steel wool (0000 is what I had intended to use). Another poster suggested emery cloth, which is far more coarse than the 0000 steel wool. Alternatively, I have some 2000 grit wet/dry sandpaper. Is the concern with scraping off the plating on the fuse holder?

F1nut

It will leave fine scratches. Emery cloth and even 2000 grit W/D will too. Use a clean pencil eraser if you don't want to invest in DeOxit/ProGold.

dhart86

I have a couple of peerless tweeters sitting in reserve. If the tweeter is busted and needs to be replaced, shoot me a pm

kkritsilas

dhart86 wrote: »

I have a couple of peerless tweeters sitting in reserve. If the tweeter is busted and needs to be replaced, shoot me a pm

Sent what I thought was a private message last week. Did you get it? or did I not do it properly? It was regarding your Peerless tweeters.

dhart86

pm sent

kkritsilas

Hi,

Back with more questions, although I haven't located a Peerless tweeter yet. In regards to the crossover, I have read the part about using Clarity ESA capacitors, and maybe Solen being acceptable in the low pass section. My real question is the value of the low pass capacitor. The value, from the schematic in another posting, is 34 uF, yet none of the manufacturers make that value, they make 33 uF. Do I use a 33 uF capacitor, or do I use a 33uF capacitor and put a 1 uf capacitor in parallel with it? I am getting close to ordering the parts, and want to order them once, and correctly, as opposed to ordering them and then going back and ordering a second time (paying for shipping twice to Canada does not appeal to me).

Gus

westmassguy

33uf is fine for those. Best practice when combining two capacitors, is to match their values as closely as possible. Two 17ufs for example. No one makes those either, but you get the idea.

Mike53

What luck...I'm glad I found this thread.

Just last week I was given an pair of Monitor 7A's. They sound fine but I plan on upgrading the cross over...using the suggested components you guys have recommended.

One question I do have, is it possible to tell where these were made using the serial #?
I was told they were made here in Baltimore, at their original location.

Any thoughts are greatly appreciated.