I recently started playing my old MM RD112 again, which I bought new in '81, and immediately noticed a "woofy" quality coming from the speaker in response to picked notes, particularly as I raise the volume, almost as if extra air was being driven into the speaker in advance of the sound itself.
This effect lessens when I just use the clean channel and a pedal overdrive, but it's still there The 6L6 tubes appear fine, visually (not running hot, as far as I can tell) and - other than some excess hissy noise from the reverb when set above 5 - the amp is loud as ever. Maybe too loud for these old ears.
Any idea what might be causing this? The tubes? The amp's preamp? The speaker?
Thanks in advance,
Gordon
Strange "woofy" quality coming from amp/speaker
Maybe a blown speaker? ...or just not responding well to being in storage.
Did you try disengaging the speaker and hooking it up to another 8ohm speaker or cabinet? The speaker is easy to disconnect re-connect with the 1/4-inch mono output jack on the back of the chassis.
Thanks, but, no - I think the
Thanks, but, no - I think the speaker is fine. I've been playing around with it more since I posted, and the sound, though still there, has lessened a bit, particularly when I reduce the gain. I'm wondering if too much power is hitting the tubes. When I put it on standby this morning, there was still some amplification coming out of the amp from the guitar and a kind of crackling sound.
I suppose it's time to bring it to an amp tech, but they're few and far between 'round here. Maybe just new power tubes?
ReCapped?
Has the amp ever been re-capped and/or given a thorough cleaning? They get dirty and tired like the knees of an old timer.
No - probably a good idea;
No - probably a good idea; thanks. While the amp was used for one or two gigs over the past few decades, I'd mostly used other amps and figured nothing had changed without this amp's use. Apparently, I was wrong! ;)
Contact Cleaner
If your are handy with screwdrivers and small socket wrenches, you could give it a good cleaning with contact cleaner like DeOxit. Spray a little into the backside of each pot and rotate the knob. After that, pull each IC (one at a time), spray the socket contacts and IC legs and re-install. Next pull each tube, clean the socket contacts and tube pins and reinstall. Lastly, use contact cleaner and Q-Tips to clean all of the 1/4 inch phone jacks on the amp. That takes care of the cleaning part. -mgriffin
Wow - thanks! Does the
Wow - thanks! Does the chassis need to be removed in order to do most of this work? I'm pretty good with basic tools/repairs and would like to give this a shot.
Remove the Chassis
Yes, You need to remove the chassis to perform the cleaning procedure. Mark the foot switch and reverb tank cables (RCA jacks and plugs) when you pull the chassis for easy re-connection. You can do this. -mgriffin
Sounds reasonably doable -
Sounds reasonably doable - thanks again!