Noticed a loud hum from My Maz 38 head

[guitarman2]

Just noticed tonight my Maz head has a very loud hum. When I look at the tubes It seems only the V3 tube has a glow as if its on. The other preamp tubes don't have any orange glow to them. Just wondering if anyone knows what the problem could be?
I have recently replaced Vi, V2, V4 and V5 with Tung Sol reissues. Every one of those would not light.I had a Jan Phillips in V3 and that one seems all right. I switch back to all the original Preamp tubes except the Jan Phillips which I left in. Of the originals V1, V2 and V4 worked but the original V5 didn't seem to light and the hum was still there. I switched V4 and V5 just to be sure it was the tube and not the socket. It was indeed the tube as when I switched the non working V6 in to V4 it still did not work and the tube that worked in V4 was now working in V5.I wonder if something is wrong with the amp that would blow all the Tong Sol reissues? As well one of the original Preamp tubes.
I bought the Tong Sol Reissue tubes from the tube store in Hamilton.

[Wild Bill]

Just noticed tonight my Maz head has a very loud hum. When I look at the tubes It seems only the V3 tube has a glow as if its on. The other preamp tubes don't have any orange glow to them. Just wondering if anyone knows what the problem could be?
I have recently replaced Vi, V2, V4 and V5 with Tung Sol reissues. Every one of those would not light.I had a Jan Phillips in V3 and that one seems all right. I switch back to all the original Preamp tubes except the Jan Phillips which I left in. Of the originals V1, V2 and V4 worked but the original V5 didn't seem to light and the hum was still there. I switched V4 and V5 just to be sure it was the tube and not the socket. It was indeed the tube as when I switched the non working V6 in to V4 it still did not work and the tube that worked in V4 was now working in V5.I wonder if something is wrong with the amp that would blow all the Tong Sol reissues? As well one of the original Preamp tubes.
I bought the Tong Sol Reissue tubes from the tube store in Hamilton.

If something blew new tubes it likely would also have blown the old ones. I wouldn't worry about being able to see a tube light up. Lots of 12AX7's are made in such a way that things wrap around the glowing filament and block your view. Even at best you only see the glow from the top and very bottom of the tube elements inside, right in the centre.

Even if you can't see the glow, understand this: If the tube works then it's lighting up, even if you can't see it. It CAN'T work if it's not lit up! Also, a tube can light up fine and still be very weak or dead. Lastly, how much it glows has NOTHING to do with how hard it's working! It glows or it doesn't. It works or it doesn't.

If signal is getting through then the TungSols are fine, period. If you can swap an old tube you know is good with a new tube in the same socket and the amp still works then forget about seeing any glow.

The signal passes through the 12AX7's in a chain. If one tube is dead then EVERYTHING goes quiet! There may be a couple of tubes in some amps that are wired to separate functions, like reverb or trem. These are not in the chain. If they go dead only the reverb or trem dies, the amp still wails.

V1 normally is the first amplifier and so it has to be working. Swap your tubes in this socket and you will quickly find which ones work and which don't.

Hope this helps...

:food-smiley-004:
If a new tube and an old tube don't work in a socket then there's something wrong in the amp circuitry inside around that socket.

[guitarman2]

If something blew new tubes it likely would also have blown the old ones. I wouldn't worry about being able to see a tube light up. Lots of 12AX7's are made in such a way that things wrap around the glowing filament and block your view. Even at best you only see the glow from the top and very bottom of the tube elements inside, right in the centre.

Even if you can't see the glow, understand this: If the tube works then it's lighting up, even if you can't see it. It CAN'T work if it's not lit up! Also, a tube can light up fine and still be very weak or dead. Lastly, how much it glows has NOTHING to do with how hard it's working! It glows or it doesn't. It works or it doesn't.

If signal is getting through then the TungSols are fine, period. If you can swap an old tube you know is good with a new tube in the same socket and the amp still works then forget about seeing any glow.

The signal passes through the 12AX7's in a chain. If one tube is dead then EVERYTHING goes quiet! There may be a couple of tubes in some amps that are wired to separate functions, like reverb or trem. These are not in the chain. If they go dead only the reverb or trem dies, the amp still wails.

V1 normally is the first amplifier and so it has to be working. Swap your tubes in this socket and you will quickly find which ones work and which don't.

Hope this helps...

:food-smiley-004:
If a new tube and an old tube don't work in a socket then there's something wrong in the amp circuitry inside around that socket.



When I put the old tubes in all of them light up bright. Except one. All sockets will light up if I put a tube in that lights. The Tung Sols and one of my old tubes do no light up whatsoever.

[Wild Bill]

When I put the old tubes in all of them light up bright. Except one. All sockets will light up if I put a tube in that lights. The Tung Sols and one of my old tubes do no light up whatsoever.

Terry, as I had said, some tubes are made a bit differently inside and it can be very hard to see the lit filaments. If you can, look at the metal part inside the glass. You might be able to see a glow at the very top and very bottom, right at the centre.

You still haven't told us if the amp works! If you can wail your guitar, the tubes have to be working! No tube will work if it's not actually lit up, even if you can't easily see it. You might as well have a brick plugged in to the socket. So if the guitar wails the tubes are working.

So let's back up here. Does the amp work? Then the new tubes work. If the amp is dead then the tubes might be bad.

Some brands have a bright, easily seen glow. Some don't. That's the way they're made. Stop caring. It doesn't mean anything.

I know for a fact that thetubestore tests ALL their tubes! The chances of getting a dead one are very, very low. The chances of getting a number of dead ones at the same time would be like winning the 649!

If the tubes are truly dead it's very possible that something in your amp is blowing them but you haven't told us the most important factors to know!

I ask again, does the amp appear to work with the new tubes, glow or not?

If the amp doesn't work, it's possible that your amp has the tubes wired in what's called a "series string". This is rare but some amps are done that way. The tubes are wired like old-fashioned Christmas lights, where if one bulb is bad then none of them will light. If that's the case then ALL tubes have to be good for the amp to work.

:food-smiley-004:

[guitarman2]

Terry, as I had said, some tubes are made a bit differently inside and it can be very hard to see the lit filaments. If you can, look at the metal part inside the glass. You might be able to see a glow at the very top and very bottom, right at the centre.

You still haven't told us if the amp works! If you can wail your guitar, the tubes have to be working! No tube will work if it's not actually lit up, even if you can't easily see it. You might as well have a brick plugged in to the socket. So if the guitar wails the tubes are working.

So let's back up here. Does the amp work? Then the new tubes work. If the amp is dead then the tubes might be bad.

Some brands have a bright, easily seen glow. Some don't. That's the way they're made. Stop caring. It doesn't mean anything.

I know for a fact that thetubestore tests ALL their tubes! The chances of getting a dead one are very, very low. The chances of getting a number of dead ones at the same time would be like winning the 649!

If the tubes are truly dead it's very possible that something in your amp is blowing them but you haven't told us the most important factors to know!

I ask again, does the amp appear to work with the new tubes, glow or not?

:food-smiley-004:


Ok I see what you mean. Yes the amp does work. And it is the only Tong Sols that don't glow as well as one of old tubes. I am pretty sure that all of the old tubes used to glow but not 100%. Of the new tubes I admit I don't know that they ever glowed.
So then regarding your post the only problem I have here is a hum that was not there before.

[guitarman2]

changed the guitar chord and the speaker cable but the hum is still there.

[Paul]

changed the guitar chord and the speaker cable but the hum is still there.

Does it hum/buzz without a guitar or cord connected???

[Wild Bill]

changed the guitar chord and the speaker cable but the hum is still there.

Ok, now we're getting somewhere. The tubes must be ok. You just can't get your head crammed into the amp at the right angle to see the glow!:smile:

Now, let's go step by step so we don't get confused. Did the hum appear immediately AFTER the new tubes had been installed?

If you had the hum with the old tubes then there may be a problem inside the amp. If the hum happened after you had replaced the tubes then it's quite possible one of the new ones is the problem.

I would take one of the old tubes that you know is still good and swap it with one of the new ones. Then swap it with another new one and so on until you've covered all the new tubes. If a new tube is causing the hum it should go away when you change it for the old working tube.

Do this to nail down a possible cause. If it doesn't work then we can see if we can try something else.

:food-smiley-004:

[LowWatt]

Tighten the screws on the top of the head.

I'll bet it goes away.

Seriously, if you haven't tried this, do it. The connection between the chassis and the headbox is a key part of the Maz Sr./Jr. grounding scheme. If it isn't tight, you get bad hum.

[guitarman2]

Does it hum/buzz without a guitar or cord connected???

yes it hums with no guitar chord attached.

[guitarman2]

Did the hum appear immediately AFTER the new tubes had been installed?

No. About a week after I installed the new tubes.


If you had the hum with the old tubes then there may be a problem inside the amp. If the hum happened after you had replaced the tubes then it's quite possible one of the new ones is the problem.

I would take one of the old tubes that you know is still good and swap it with one of the new ones. Then swap it with another new one and so on until you've covered all the new tubes. If a new tube is causing the hum it should go away when you change it for the old working tube.

Do this to nail down a possible cause. If it doesn't work then we can see if we can try something else.

:food-smiley-004:

I've done this and the hum is still there.

[guitarman2]

Did you tighten the top screws? I'm not kidding. Check the Dr. Z forums. There's some kind of sheilding that can become disconnected if the top screws aren't tight. It's standard maintenance on the good Dr.'s wares. It wouldn't explain the issues with the tubes, but 9 times out of 10, if a Z amp is humming, it's the top screws.


Actually the chassis mounting screws are on the bottom of the head. Checked them all and they are pretty tight.

[Wild Bill]

Actually the chassis mounting screws are on the bottom of the head. Checked them all and they are pretty tight.

Sorry Terry, I'm tapped out. If you've done the tube swapping then the problem must be elsewhere. This is when I'd put the amp on my bench, open it up and start checking with test equipment.

Good luck!

:food-smiley-004:

[guitarman2]

Sorry Terry, I'm tapped out. If you've done the tube swapping then the problem must be elsewhere. This is when I'd put the amp on my bench, open it up and start checking with test equipment.

Good luck!

:food-smiley-004:

Maybe I'm just going crazy. When I last brought my amp home I put my z best cab down horizontally and placed the head on it. Normally I always place the cab up vertically. The reason I mention this is last night after going through many steps of further troubleshooting including taking the amp to another room to plug it in, I returned it to the original room and placed it up vertically again. This is when I noticed that the hum almost disappeared. Now I know this amp has a slight buzz/hum due to the reverb location in the head. This is a bit of a design flaw and it is barely noticeable. Much quieter than a single coil hum. It just seemed that the hum was twice as loud when I laid the cabinet horizontally. Tonight I"m going to check and reseat the reverb cables but maybe there is nothing wrong. Does this sound crazy or what?

[Wild Bill]

Maybe I'm just going crazy. When I last brought my amp home I put my z best cab down horizontally and placed the head on it. Normally I always place the cab up vertically. The reason I mention this is last night after going through many steps of further troubleshooting including taking the amp to another room to plug it in, I returned it to the original room and placed it up vertically again. This is when I noticed that the hum almost disappeared. Now I know this amp has a slight buzz/hum due to the reverb location in the head. This is a bit of a design flaw and it is barely noticeable. Much quieter than a single coil hum. It just seemed that the hum was twice as loud when I laid the cabinet horizontally. Tonight I"m going to check and reseat the reverb cables but maybe there is nothing wrong. Does this sound crazy or what?

Not at all! Especially after what jroberts told you!

I think you misunderstood him. He wasn't talking about the chassis mounting screws at the bottom. He specifically said TOP! I've never worked on this amp but I believe he's referring to some kind of shielding plate or cover on the TOP of the amp chassis! You would have to take the chassis out of the cabinet and look for something like that on the top side. The weight of the chassis hanging in a different position might mean that the cover doesn't make good contact with loose screws in that position. Tightening them up means the cover will have a good ground to the chassis. If it's not grounded due to loose screws the cover will do nothing to shield out hum.

:food-smiley-004:

[Big White Tele]

The head and combos are upside down to each other (like a Marshall) I believe JR has 2 combo"s so his screws will be on top, On the head, its on the bottom. My Maz 38 reverb hummed like crazy. It was a reverb grounding issue. It also picked up Radio signals like crazy!!!

[guitarman2]

The head and combos are upside down to each other (like a Marshall) I believe JR has 2 combo"s so his screws will be on top, On the head, its on the bottom. My Maz 38 reverb hummed like crazy. It was a reverb grounding issue. It also picked up Radio signals like crazy!!!


Yeah its kind of weird. When I have the Z best cab in the vertical position the hum is pretty much non-existent. Its there but just faintly and is normal for the Dr Z heads with reverb. When I have the Z best cab in the horizontal position is when I could really notice it and it just didn't seem right. I don't understand this because it shouldn't matter which way I have the cabinet as the head is still in the same position.
Yes there are times when my Maz picks up radio stations quite loudly. I wonder if there is a fix for that.
Other than that I love the amp. I just practiced with a new band last night and the first thing they commented on was the great tone. Although as soon as my Dr Z Stangray comes in it may become my main gigging amp and I may sell the Maz and Z best cabinet for a smaller amp that will be just for a backup.

[guitarman2]

Well I've decided to get rid of my Maz. I think the hum problem is just the reverb unit which is just a symptom of design. The doc explained it to me once that the reverb unit being so close to everything in a small space will cause this hum. I guess I should have gotten the no reverb model. Since I got my Stangray to me the tone of that is much more desirable to me. When I picked up my stangray last week I just traded the Maz head in on it. The hum for some reason just seemed unreasonably loud when the Z best cab was in the horizontal position. Anyway the Stangray doesn't have reverb and I'll probably be getting either a 63 fender reverb or the Valvetrain. After I check out a couple of other cheaper options I'll decide.
I think for my second amp I'll be getting the Dr Z Carmen Ghia. No more built in reverbs though.

[Big White Tele]

The fix for the Reverb hum and radio signals, from DR Z is to istall Ferrite Chokes on the cables, Most people have had decent success with that. You can buy them at Radio Shack for a couple of bucks.. They just clamp on the cables and are supposed to reduce the interference. I'll try to find a link to them.

[Big White Tele]

http://www.radioshack.com/product/index.jsp?productId=3012599&cp=&sr=1&origkw=ferrite&kw=ferrite&parentPage=search

[Big White Tele]

http://drzamplifiers.proboards41.com/index.cgi?board=maz18&action=display&thread=1626