Is it possible....

[12AX7]

....that if a combo amp's OT is almost touching the speaker's frame and the tubes are right near the magnet it could cause the following? When i tweak this amp i have the chassis sitting atop the combo cab. Then when i put it back in it seems like the amp has more gain than it did before i stuck the chassis back and sounds almost like it's on the verge of blocking distortion. It's fairly subtle but thats what it sound like. I built it from a old SS marshall 1x12 combo thats quite small so not a lot of room for trannys and tubes. I had to shoehorn the thing in.

[shooter]

It's fairly subtle but thats what it sound like

Do you have something to measure AC signal, scope, good meter?  measure the signal @ speaker out of combo, install, repeat.  Gremlins are pesky little things

[hesamadman]

If you determine that this is causing you trouble, you can try making a new baffle and offsetting the speaker. Instead of center of cabinet, offset to lower corner away from transformers if possible. I will generally place mine offset for this reason. Its not an incredibly difficult undertaking.

[12AX7]

If you determine that this is causing you trouble, you can try making a new baffle and offsetting the speaker. Instead of center of cabinet, offset to lower corner away from transformers if possible. I will generally place mine offset for this reason. Its not an incredibly difficult undertaking.

I already did that when i first built it because it wouldn't fit even tho it WAS offset in the corner. I made a new baffle to offset it even more. I was only able to move it less than an inch because that already left me with the speaker hole only about 1/2"from the edge of the baffle. Look at the old JCM lead 30 solid state combo.....thats what i gutted and built it into. The speaker is offset.... http://www.amparchives.com/Amp%20Archives/Marshall/Solid%20State%20Amps/5203%20Lead%20Master%20Volume%20Reverb%2030%201x12%20Combo/88%205203%20Master%20Reverb%2030%201x12%20Combo%20SN%20W29767/DSCN3874.jpg

  I was able to fit the chassis in with the original baffle but i had to jam it in with the OT pressing hard against the speaker frame then ram the 2 chassis screws in on an angle ! I made the new baffle partially to gain about 1/2" so the OT wouldn't be pressing against it, but also to make one from plywood instead of that crappy particle board. I also gained a bit of space by using thinner ply than the particle board was by 50%.