Just need Verification

[turbo chicken]

My Peavey Combo 300 cuts out after playing it a little while. At first i thought it was the amp but I don't see anything loose bad solder points etc ...

i took my speaker apart ... and found a burnt spot on the voice coil. Please look at the attachment and tell me if you think this would cause the coil to rub the driver or would it cause the speaker to cut in and out. I can give the thing a nice "technical tap" when it's doing this and it will work again... im assuming this is because im "unsticking" the voice coil.

also there is damage to the cone as well.. the speaker has this damage when i purchased it a few weeks ago it seems to be "repaired" with some silicone... im thinking this had something to do with the original damage to the coil.

i also get a 3.5 ohm reading across the positive and negative post where the wire goes. it would seem to me that if some of the wires coils are shorted together than it would be less resistance since there is a shorter path. It should read 4ohm right?

just want to double check before i drop 75 bucks on a cone for my 1502-dt black widow

but that's 75 bucks out of my fEarful savings as well

 

[JimmyM]

3.5 ohms is typical reading for a 4 ohm speaker. Don't know if that's causing the problem, but it possibly could. Have you tried the head with another cab?

 

[1n3]

i took my speaker apart ... and found a burnt spot on the voice coil. Please look at the attachment and tell me if you think this would cause the coil to rub the driver or would it cause the speaker to cut in and out. I can give the thing a nice "technical tap" when it's doing this and it will work again... im assuming this is because im "unsticking" the voice coil.

The shot's a little out of focus, but it looks like you have two rub marks. It's possible that the VC is sticking; more likely, you've got an intermittent short or open.

As Jimmy says, 3.5 ohms is a normal DC resistance for a 4 ohm speaker. If you can make that number go up or down by manipulating the cone/coil, that would indicate for a short (down) or open (up) in the coil.

One long-shot possibility - BWs of a certain era have a known problem where the foam dust filter (rear center of the magnet structure) disintegrates into kind of a sticky dust, which will migrate to the VC aperture, and mess things up. If those discolored spots are a little sticky to the touch, that could be your problem. A cleaning would fix that.

But since there is also cone damage, this speaker has probably been abused, and the VC has gotten too hot.

 

[turbo chicken]

that mark on the left is just marker... the other mark is definitely burn marks.

when i move the cone... resistance goes up... so an open?

that foam dust filter is still there...

Unfortunately the only other amp i own is a small acoustic b20... if i had an extension cab i'd hook it up and give the head another "technical tap" and see if the sound cut out on the extension. if it cuts out then i know there is something funky going on with the head.

Is there any way to check the output at the speaker to see if it's the signal that cuts in and out?

 

[1n3]

when i move the cone... resistance goes up... so an open?

If resistance goes up a lot, that would indicate an open; maybe a break in the coil that connects intermittently.

... if i had an extension cab i'd hook it up and give the head another "technical tap" and see if the sound cut out on the extension. if it cuts out then i know there is something funky going on with the head.

Is there any way to check the output at the speaker to see if it's the signal that cuts in and out?

Short of stuff like a scope or meter with a dummy load, no. Can you borrow a speaker? Doesn't have to be a bass cab for testing.

 

[turbo chicken]

none of my buddies has a speaker or cab i can use to test... all they have is their guitar combos

or I could take out the 12" speaker out of the practice amp?

either way im getting a new basket for the speaker... guess i could wait till i get that to test the amplifier out again

 

[B-string]

Are you "tapping" on the speaker or the amp head?

 

[turbo chicken]

amp head... i put the speaker back together... hooked it back but didn't put it back in this time.

Wacked the head and sound cut off... wacked it again and it starts to work...

Since i had the speaker out of the cabinet ... looks like my head unit needs to be repaired.

thanks for the help... just not sure if i want to get something else or repair this one

what to do ... what to do??

 

[B-string]

If it has an effects loop, use a spare cable to run from effects send to effects return. If the trouble is gone the effects return jack needs to be cleaned.

 

[turbo chicken]

Okay since this amp has ...
-Patch in/out which is pre-equalization
-Preamp out/Power amp in are post-EQ

I need to do what you suggested to both seperately.

It would probably be a good idea to go ahead and use some type of cleaner to clean out all of the pots and jacks. After I do the test first of course. After searching it looks like many intermittent issues have been fixed doing this. After looking at the head again and inspecting for weak solder points (found none) poking around with a wood dowel to try and move individual components I have nothing to loose may as well clean the controls and jacks.

I'll search for some suggestions on what cleaner to get. There's an electronics store right down the road... i'll go on my lunch and get something

Looks like i need to get some DeoxIT ... radio shack here i come http://www.radioshack.com/product/index.jsp?productId=2104746

 

[B-string]

Yes to DeoxIT. Not the Radio Shack brand. The patch connection will probably the one that interupts the signal inside the amp head.