Mark V reverb howl

[JamGuy]

Greetings all...

I just received my 2012 Mark V yesterday and all I can say is WOW! :shock: It's amazing, and I'm finding some incredible clean and on the fringes of breaking up juicy tones. Every effort to explore the options has proven more incredible sounds... all three channels are yielding fantastic sounds.

But, I'm having some issues with howling reverb... it gets progressively worse from ch 1, to 2, to 3. I can play for about ten seconds or so and then it sounds like an air conditioning unit firing up... slowly it builds and then heads towards what sounds like it's going to be ear splitting feedback but levels off to continue in a loud, deep toned whir.

The amp is sitting on a closed back TRM pine cab with 2, 12" Eminence Commonwealth speakers... they have ginormous magnets in them and can handle incredible amounts of volume and low end. I have the bass set pretty low across the board and it's not flabby or washed out so I don't think my mix is bass heavy. Could. I looked at all the wiring and that looks good, I removed the tube cage thinking maybe that vibration was causing it. The tank screws are tight and the tank is not vibrating. Could it be the reverb tube or just the fact that it's sitting on the cab. I placed a towel between the amp and the cab which was just high enough so the tank exerted some pressure on it but that didn't work. I also tried the cab sitting right on the floor and sitting on the low table that it usually rests on... again, no help. I'm stumped. Anyone else had a similar issue? It's not close to a radio or computer, and the amp is plugged into a high quality power strip.

As much as I'd love to make use of the amp's reverb, I decided to just go ahead and order a TC Electronics HOF reverb (the full features one, not the mini) which solves the problem for the time being. In the end, it'll have more flexibility than the amp's reverb but I guess it'd be nice to get the 'verb on the amp fixed or at least figure out what's going on with it.

 

[OldTelecasterMan]

Ok... try this. Read every word, first take off your watch, rings anything that conducts electricity. With the amp on you will notice that there are 5 big tubes. One of them is not lit as brightly as the others. The tube that is not lit as bright works with your reverb. Turn off the amp then Unplug the amp. Let it cool for a bit. Remove the tube guard (the black tube protector). Look at each side and you can see the white keepers on either side. It snaps right out.

The amp can bite, it can kill so with one hand (using one had insures you don't unload a capicitor through your heart) Remove the dust covers on the tubes by turning about 1/4 turn. Insure each of the tubes are seated all the way. Pushed all the way in. You can get more room if you remove the big tubes first. If you remove the big tubes in front be sure to put them back exactly where they came from.

On the right hand side directly under where you plug in the foot switch you will see a big black transformer. Behind that transformer you will see a silver round tube cover. On page 62 of your manual it is "V1". don't miss that one it's hidden.

The deal is mine made an odd noise and "V1" was loose. Your problem may be in...back to page 62 in the manual, Tube "5U4G". Back to the 5 big tubes. the 4 power tubes on the right are 6L6 Power tubes. The left most tube "5U4G" is for the reverb, make sure it is all the way in and seated. You might pull it out a little and push it in.

When I had an odd sound issue with mine I removed all the covers and insured all the tubes were seated. Not an odd sound since.

Be sure to put everything back, covers and tube guards.

Let me know it that fixes it...

 

[crane]

Try swapping a new 12AX7 in the V4 and V5 position (V4A is the reverb send, and V5B reverb return stage).
The rectifier tube (5U4G) has nothing to do with the reverb, it rectifies the alternate current into continuous current (like the diodes do if you select "diode" in 45W mode)

 

[JamGuy]

I do have some spare 12ax7s lying around, nothing fancy... just some GrooveTubes that i replaced from my Champ SCX2 so at least I know they're working.

 

[JamGuy]

I thought that I had some "regular" 12AX7's but a lot of them have some suffix... I think I'm going to hold off for a spell and order a pair sometime... I did check that they were snug and a few seemed a little loose. I was optimistic that that was the problem but alas, it's still howling. Oh well... the HOF will be here soon and then I can swim in some lush reverb.

 

[bandit2013]

You may want to check reverb wires, should be same on Head as it is on Combo.

They are connected to the chassis on RCA type jacks next to the output transformer on the right hand side of the chassis (looking at back of amp). The white wire should be closest to you and the black wire towards the front end of the amp. If the cables are backwards, the amp will squeal like a banshee after it powers up and the bypass switch is turned on. If you turn off the reverb with the footswitch control, does it make this noise? No the speaker magnets will not cause anything remotely what you are hearing. My 412 Cab has EVM12 and those magnets are big too. Also My Mark IV has a Fane, no skimping on magnet on that speaker either and the reverb tank sits less than an inch or so from the end of the magnet.

V4 is the reverb send (driver tube) and is shared with CH3 gain stage. V5 is the reverb return also shares part with CH3 gain stages.

You can run the amp with either V4 or V5 removed to listen if the noise is still there or does it go away. Don't pull both or you may be removing the one that is having the issue. Try v4 first, then put the tube back and try v5. If the noise disappears when pulling V4, it may be the tube or one that is prior like V3. You can replace the suspect tube with a good one if you prefer. Any 12AX7, 12AT7, 5751, and even 12AU7 could be used as a substitute if that is all you have. The lower gain tubes will effect tone of CH3. I would check reverb cables first.

 

[JamGuy]

I checked the cables and they're snug and correctly plugged in. No, when you switch the reverb off it's whisper quiet. In fact, this is the quietest tube amp I've ever owned!

I'll probably go the tube route one of these days. Honestly, I wouldn't mind a lower gain AX7 given that I play mostly clean... taming channel 3 would be fine by me... although I do have a great tone with it right now.

 

[JamGuy]

just tried some new tubes in those slots and no dice... still howling. Oh well, the HOF'll be here soon :roll:

 

[bandit2013]

Hmm, what about the connections on the reverb tank? The ports are marked in and out.

If it is not the reverb tank itself, it may be connections on the inside of the amp. Much harder to diagnose.

 

[Authorized Boogie]

Do you have anything in the effects loop? Where is the effects loop level control set? Does it happen with the effects loop bypassed? Have you inspected the inside of the tank to be sure its not a broken spring hanging down, making the reverb unit overly sensitive? Thanks!

 

[JamGuy]

Do you have anything in the effects loop? Where is the effects loop level control set? Does it happen with the effects loop bypassed? Have you inspected the inside of the tank to be sure its not a broken spring hanging down, making the reverb unit overly sensitive? Thanks!

Nope, nothing in the effects loop... all the effects are coming in from the front of the amp but the loop is not hard bypassed so I can use the master volume. I haven't opened the tank to check the springs but that seems a logical next step, though I haven't heard any rattling from in there. The effects level knob was at 12 o'clock... would turning it down to zero affect the master volume?

Thanks everyone for the suggestions... I'm optimistic we can get this figured out! I'll poke around in there and report back soon...
____________

Well... I experimented with by passing the effects loop and that made the problem worse BUT I did notice that the screws that hold the reverb tank down were looser than I thought they were. I was able to tighten them up slightly but there's one I couldn't reach. I need a right angle screw driver to get at the last one. The good news is that tightening the screws down did seem to help, at least with the effects loop engaged.

Another thing that's slightly related but maybe it offers some insight into the problem... I have used a Fender Twin for years. I got very used to the very lush reverb. On my last Twin I used to park the reverb at 3 1/2 or 4 and that was LOTS of reverb. The Mark V does not seem to be dishing up the same level, and maybe that's normal, I don't know. With the amount of reverb I'd like to be getting, I'm having to turn the reverb past 3 o'clock or more. Is this usual? Am I just expecting something that's not going to happen? The howl really begins when the reverb is at least at 12 o'clock but I'm not getting much reverb effect at that level. Anyway... I'll try to get my hands on a screw driver to reach the one screw I couldn't get at with the regular driver I used. Maybe that will seal the deal!

 

[JamGuy]

!!!PROBLEM SOLVED!!!

So... I decided to take the tank out and have a look inside. The springs were fine but there are two little black posts and two rubber donuts that should have been surrounding the donuts (there are probably more technical terms for these parts :lol: ). Well, one of the posts ended up on the outside of the donut... it probably bounced too much during shipping and slipped over the top. In any event, it's sorted... I have the reverb pegged and no more howling. After all this, I have to laugh, the reverb itself is nothing to write home about (IMO) The quality of the sound is fantastic but I wish that there was more of the effect. I'm glad I got it fixed but I'm still looking forward to the arrival of the TC Electronic reverb for my pedal board.

Thanks to all those who chimed in to help... I'm happy to be putting this thread to bed! 8)