peavey 5150 / marshll 1987x

[dazzlindino]

Have a Peavey 5150 60w combo, going into a weber mass attenuator, then line out to effects return on a Marshall 1987X, then into a 4 x 12 cab.
Delema = with weber line out volume almost off the volume is at about 95db, which is fine, however as the amps are being played the volume starts increasing and about 10 min later it is up to 100db.
What would / could be causing this volume increase to occur?
weber set to 16 ohm / peavey combo speakers checked out to be 13.8 ohm
4 x 12 cab checked out at 14.4 ohm, however the speakers on the combo are disconnected and running that amp output into the weber.
Thanks, Dazzlindino

[Chuck H]

Resistors have a derate curve that is affected by heat. The attenuator has resistors in it, and it gets hot. I'm just guessing, but I think this could be the issue. If so then you could open up the attenuator and measure the R values. Then play through it awhile and as soon as it changes and while it's still hot, retest. The resistors will return to the original tested values if allowed to cool off much. So it must be done very quickly. If you find resistors that seems to be drifting much you could replace them with resistors that have a better derate curve.

As long as the output doesn't continue to change after the initial shift, another other option would be to simply turn it down a tad after it has shifted. You could probably modify the line out for a lower output to give it more adjustability in the lower ranges.

Chuck

[dazzlindino]

Thanks for the reply. Have tried a thd hot plate with the same result, so the resistors in both are possibly overloaded for their rating?
Have run these antennuators on some other amps and not had this problem,
but I'm guessing that this amp puts out a hotter signal?
Guess turning down the post volume ( master ) might help in this but the tone
is not the same ( running on 8 now ) .
Also the volume control on the antennuators is virtually off, and this is still producing 95 dbs at the start of use, cant turn them down, but it will turn them off.
Thanks again.