Blackface Vibro Champ, low output

[mfreqmaster]

I have a Vibro Champ that worked & sounded great. One day I plugged in & the output was very low & thin sounding. I changed the tubes with known good ones from another amp & the problem persisted. I took voltage measurements on the 3 tubes:

v1
pin 1 248V
pin 3 2V
pin 6 238V
pin 8 2V

v2
pin 1 (vascillates between 98-240V, could not get a reading that lasted long enough for my DMM to be stable)
pin 3 2V
pin 6 395V
pin 8 (vascillates between 117-250V, same kind of thing as in pin 1)

v3
pin 3 391V
pin 4 393V
pin 8 20V

I have replaced bypass capacitors for V1 as well as the 6V6.
Checked the cathode resistors for the preamp tube as well as the 6V6, they appear to be good. Checked grounds from the board, the grounds are grounded.
I replaced the filter caps, retensioned the sockets to the best of my ability.
The sound is still thin & lacks power. Not at all what it was before. Also the speaker is a new Weber 4 ohm & works well.
I know this is a simple circuit but I am currently, (no pun intended), stumped.

[mfreqmaster]

OK, I've found the problem. It was the speaker. I have another tweed champ clone with a ceramic 8 inch speaker. I found the fact that the speaker is at fault hard to believe since the Weber speaker is less than a year old. I checked the measurements on the bad speaker. The speaker still measures 4 ohms. The wires don't appear to be detached from the voice coil. I used the same wiring harness for both speakers so I am pretty sure it's the speaker. Does anyone have any ideas on what would have caused this speaker to fail?

[The Dude]

Did the magnet shift? (my best guess). Carefully see if you can move the cone in and out with your fingers. My bet is that you will find it frozen because the glue has let loose on the magnet causing a shifted gap scenario.

[mfreqmaster]

I can push the dustcap but the cone is very stiff doesn't appear to move at all. If the magnet has shifted, is this something a layperson can fix? Thanks.

[Jazz P Bass]

Nope.

[mfreqmaster]

OK. Thanks for the replies Dude, and Jazz P Bass. Fortunately the speaker was only $45. It sounded great but I didn't get much playtime on it.

[Jazz P Bass]

The 'air gap' between the voice coil & the magnet pole piece is something like .003 (a piece of paper).

It certainly does not take much to seize the coil.

[mfreqmaster]

I should be fair to the company. I e-mailed & explained my situation. They offered to replace the speaker free of charge, one has been shipped today.