• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

DB750 replacing tubes every 2 months.

S

Stride000

Mar 15, 2006
128
0
#1
Hi there,

I own a DB750 since march. I totally love this amp, it's got my sound and it made me stop looking at any other amps. I seem to have a problem though and I'm not sure what the souce is exactly.

I had to change the tubes 3 times since I got it and it made me wonder if I've been unlucky with the tubes I bought or if this might have something to do with the amp itself?

Forward thanks!
 
#3
Well, the first time I had to change them, there was a buzz in the sound and shortly after one of the tubes became microphonic.

The second time, two of the tubes had became microphonic.

This time around, I had more grit in the sound and less bass. It also as if the sound was dying really fast and was over compressed.

Yes the amp is moved around alot and in the trunk of the car. THis time I put some foam underneath the amp to prevent from vibrations.
 
#4
Before you go spending any more money on tubes....

All tubes are microphonic to some degree, whether we like it or not, and this attribute can vary between examples of the same type, so this is not necessarily a sign of a failing tube.

The buzzing you heard might have been caused by failing cathode/heater insulation inside a tube, but it seems very odd for this to occur after only two months of use, unless the tube in question was very old or faulty to begin with. Equally, though, the buzzing could have a number of other (more likely) causes unrelated to the tubes.

If the amp gets shoved around a lot, I would strongly recommend opening up the case before each gig or practice session (and before plugging it in, obviously) and checking that all your tubes are firmly and squarely seated in their sockets. This will only take 5 minutes and could save you a lot of trouble. If it appears that the tubes are getting knocked off their proper seating rather frequently, I would think about getting a good tube tech to fit them with spring-clip retainers (like they use in Ampeg SVTs).

And while you're getting that done, ask him/her to check that the tubes' voltage/current measurements are within the manufacturer's tolerance. If you really do need a new set of tubes every 2 months, something is seriously awry in there!
 
#5
The sockets are really tight so I know it's not a problem of tubes getting knocked out. Plus there's a cap for one of them to hold it in place.

As for the buzzing, I tried cleaning the jacks at first which did no good and the buzz went away when I changed the tubes the first time but now it's back with the new set.

I suspect tubes at music store to be dodgy a bit. The only good set of tubes I got was when Aguilar sent me one themselves.
 
#6
Stride000 said:
The sockets are really tight so I know it's not a problem of tubes getting knocked out.
Click to expand...

It's not a matter of being knocked out. Tubes that are barely in their sockets can have arcs on the socket which will damage the amp. Besides that, if the tube is not snug and sceure in its socket it can get moved and banged around FAR more.

Microphony is generally not a symptom of amp trouble, but a tube overheating from plate current can overheat its support structure and loosen its internals. This is common in Svetlana/Winged C power tubes.

Plus there's a cap for one of them to hold it in place.
Click to expand...

That cap is NOT a holder. It's an RF sheild. If the top of the tube is coming in contact with it, then the tube is NOT securely in its socket.

As for the buzzing, I tried cleaning the jacks at first which did no good and the buzz went away when I changed the tubes the first time but now it's back with the new set.
Click to expand...

I'm not convinced the tubes are properly seated, and that may be your only problem.

I suspect tubes at music store to be dodgy a bit. The only good set of tubes I got was when Aguilar sent me one themselves.
Click to expand...

That is also a possiblility.
 
#7
Well... I opened it up again and checked to make sure every tube was properly seated and they were.

Then, I unplugged to switch bass and the buzz became a bit stronger, there was a bit of crackle and then it disappeared. So guess it's a dirty input problem.

So that's solved. I still change my tubes too often though and it makes me wonder... What the hell happens when you tour with a big production and your gear is shoved on and off the stage and into touring trucks and everything??? Do you change tubes every evening????
 
#8
Stride000 said:
So that's solved. I still change my tubes too often though and it makes me wonder... What the hell happens when you tour with a big production and your gear is shoved on and off the stage and into touring trucks and everything??? Do you change tubes every evening????
Click to expand...

No. Not at all. Don't perpetuate "tubes are unreliable" myths, especially with preamp tubes. Everyone already "knows" that tube power amps are "ungiggable," because they are "fragile." The last thing we need are preamp tubes going the way of the dinosaur, especially just because someone has a problem with his amp, and whether or not it has anything to do with the preamp tubes, suspects the preamp tubes and changes them every 3 months.
 
#9
Stride000 said:
Well... I opened it up again and checked to make sure every tube was properly seated and they were.

Then, I unplugged to switch bass and the buzz became a bit stronger, there was a bit of crackle and then it disappeared. So guess it's a dirty input problem.

So that's solved. I still change my tubes too often though and it makes me wonder... What the hell happens when you tour with a big production and your gear is shoved on and off the stage and into touring trucks and everything??? Do you change tubes every evening????
Click to expand...

Not at all, there are hundreds if not thousands of bassists and (especially) guitarists that tour with tube amps all the time.

They're a time tested design for instrument amplification, that IMO, is impossible to be tonaly replicated by another means of amplifier design.

I believe how the amp is designed has much more to do with amp reliability than the actual tubes themselves. Especially with amp with just preamp tubes.
 
#10
Two months? Tubes have 3 month warranties so you should get them changed for free.

Anybody with a tube amp carries spares, and unfortunately the warranty times out just carrying the spares around. Test the spares good.

Get some Mesa/Boogie's - look what they do to squeeze out three extra months of warranty:
http://www.mesaboogie.com/Product_Info/Accessories/Tubes/Robotube/robotube.html

I understand Aguilar has good service, so I wonder what they say about your problem?
 
#11
seamonkey said:
Get some Mesa/Boogie's - look what they do to squeeze out three extra months of warranty:
http://www.mesaboogie.com/Product_Info/Accessories/Tubes/Robotube/robotube.html
Click to expand...

This is bull cocka. Mesa Boogie's tubes are rebranded, just like every other tube. Mesa likes to make their customers think that they need "specially matched and paired" tubes to get the most out of their amp. Mesa does many things very nicely, but marketing and selling tubes is not one of them.
 
#14
I have had a handful of bizarre early preamp tube deaths. one time was a defective or damaged tube ... a good sounding, used old stock 12au7 that gave up the ghost a couple of months after installation. another couple of times it was from a crappy (possibly incorrectly repaired) amp.

it was my my first amp, bought used. it had been the house amp at a club called "down time." 'nuff said.
 

Latest posts

Top Bottom
Back