Post by wraparoundsrule on Dec 13, 2018 16:18:21 GMT -7
Thanks in advance for any help on this!
I have a MAZ-38SR 2x12 combo, S/N M.5381 that I bought used years ago. The reverb has never been very strong. It had a 9AB2C1B tank in it when I got it. Recently, I saw that the Doc recommended a MOD 8AB2A1B tank, so I got one and with the tank sitting on top of the amp (just to test it), it sounded MUCH better.
So, I finally decided to mount it and button the old girl up. I remembered playing around with the old tank in a tank bag in the past to find a location where it wouldn't hum or squeal. This time, I finally gave up on the bag as there was no way to find a location and keep it there (movement of 1/4 inch went from go to no-go), so I opted to mount it without the bag. Took me around 45 minutes to find a quiet spot on the floor of the cabinet. Had to move the connecting cables. Screws tightened only enough to keep the tank from bouncing around.
Played for about a half hour just to make sure it was okay (with reverb cranked all the way up). Then put on the lower back cover and thought I was done. Nope. No squeal with the lower back cover off. Put it in place (with or without screws) and it howled like a banshee. Spent another 45 minutes finding a location that worked with the $%^&@ lower cover in place. Anchored it to the floor of the cabinet as before and now it seems to be happy.
After all of that preamble - is this normal or does my amp have a problem? It plays well otherwise. Both cables show proper continuity with an ohm meter and no shorts.
Post by Jaguarguy (Mike) on Dec 13, 2018 16:38:24 GMT -7
Z amps do not usually howl from the reverb tank. I have a number of Zs with reverb and none of them howl. I would check to make sure your cables are shielded - sounds like they might not be. (Todd at PCNS has a great shielded cable that he sells). Also, if you haven't done so, I'd clean the inputs and the cable ends with deoxit.
I've also seen reverb tanks run vertically attached to one of the sides - not sure if that can be done with your amp.
Post by wraparoundsrule on Dec 13, 2018 22:12:56 GMT -7
I swapped the cables with some good quality ones and used Deoxit on the RCA connectors. That was a good thought, but same problem. I put the tank back in the magical place where it's happy and called it a day.
Disconnecting the internal speakers and hooking up to a speaker box helped a lot, but I can still find a place that makes it squeal.
There is room to mount the tank vertically, but it's designed to be used flat. I suspect that it would just wear out faster. I held it vertical on the side of the cab and it still sounded ok - and no squeal. Last resort, I guess.
Anyway, since I'm able to play it with the tank in its happy place, I'll leave well enough alone for now. Frustrating.
I was recently refurbing a vintage amp for a customer. Besides the normal stuff it needed (cleaning, tubes, caps, etc.) he said the reverb would start to howl when turned up around half. While testing the amp I used the tank I keep for that purpose and the reverb worked fine. I was going to suggest he replace his tank but when I plugged the old tank back in it did not howl. I looked and I had inadvertently placed it upside down. I told this to the customer and he decided to leave it that way. It has been about a year since and he is still happy with it that way.
I have also at times had luck with wrapping several layers of felt around tanks before putting them back in the bag and in the amp.
Post by wraparoundsrule on Dec 14, 2018 11:03:36 GMT -7
Rubber (or whatever cushioning material) is there. Squeal occurs whether screwed down or not. If not screwed down, just moving the tank 1/4" in the wrong direction will cause it to squeal. That's why it's now screwed down. It's ridiculously location dependent. Its "happy place" is mounted diagonally in the right rear corner (looking at the back of the amp), with one corner of the tank visible under the cut out in the cover. Strange. Still sounds good, though.
Didn't try laying it on its back as zpilot relates. If it starts squealing where it now is, I'll try putting it back in the bag, but upside down. Maybe it's possessed?
The reverb wasn't working well (had the old tank in it) when BW played it a few years ago. But with Buddy playing, it still sounded killer.
Post by premiumplus (Dave) on Dec 17, 2018 9:30:15 GMT -7
I know that the old Accutronics tanks had different holes for mounting the suspension springs inside them. Depending on whether it was to be mounted vertically or horizontally you could change the arrangement of the suspension. It's just something else you might try, but I'd try it on it's back first. The felt wrap is also a good idea.
"Tone, tone, tone, tone. Is there a substitute?" -Dr.Z
Post by wraparoundsrule on Dec 23, 2018 16:46:27 GMT -7
Thanks to everyone for the suggestions!
Haunted MAZ-38SR update:
Last post, I found a "happy place" on the floor of the cab that the reverb tank liked (no howl) and screwed it down. Buttoned it up and played for 30 minutes. No problems.
So 2 days ago, I decided to play through it again - figuring that since it played fine the last time with the reverb tank in its "happy place" (no howling) that it would be the same.
Wrong! The banshee came back. HOWL!!!
So took off the lower back panel, unscrewed the tank from the floor of the cab and tried something a friend here suggested (not overly different from some of your suggestions).
I cut a piece of cardboard to completely cover the open bottom of the tank so that nothing could touch the springs (cut out corners for the "mounting feet"), wrapped the tank in an old dishtowel and stuffed it into the reverb tank bag (snug fit). Found a place in the amp it seemed to like and used 2 screws to hold the bag in place. Buttoned it all back up. Played for an hour - no howl.
Today, I plugged back in and HOORAY! The banshee seems to have left. Good reverb and the amp is back to sounding like its normal self.
Post by wraparoundsrule on Jan 10, 2019 11:39:25 GMT -7
Final (I think) follow up to this thread.
Although wrapping the tank in a dishtowel and stuffing it into the bag made the howl go away, I kept thinking about this and being sort of OCD, I wanted to find the REAL cause. I think that I did (but I'm not taking the tank out of the bag to prove it).
Since the howl seemed to be affected by the stiffness of the case (removing/installing the lower back cover made the squeal come/go), I figured that the problem was likely caused by vibration. The speakers were mounted okay as was the chassis, so I decided to dismount the fan and set it on top of the amp (it was blowing just fine). Happened to rest my hand near the fan and could feel vibration. I disconnected it and cleaned the blades to ensure that there was no dust buildup causing blade balance issues. In the process, I noted that when spinning the blades slowly there was a slightly rough spot in the rotation. Vibration source found. Bad bearing.
Got on eBay and found a replacement 4" box fan that moves a little more air, but is a bit noisier for less than $20. Installed and hopefully banished the banshee forever. It plays better than ever and if anyone else runs into this issue, it's something you can try.
Post by Chilly Gibbons (Todd T.) on Jan 10, 2019 15:40:28 GMT -7
Awesome, thanks for sharing this update. Would never have thought of that, good to know.
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