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tube question

J

jimribs

Feb 4, 2009
21
0
www.rockriverradio.com
#1
so i got a mesa buster bass amp today...my first tube amp

one of the plastic tips on one of the tubes was broken. i could get the tube in, but it doesn't glow purple like the others, it still glows orange, but not blueish purple like the others. what is the problem and do i need to replace this tube?
 
#2
Hi Jim, I had a Buster 2-10 combo. It was one heavy old gal, but did a nice job. On louder gigs the 10's were not enough, and you need an extension cab. The sound of 10's at their limits is not pretty, and there's plenty of power for more drivers.

Do you have a combo? If so, be careful using the little luggage handle and wheels as you come to sidewalk cracks. The little wheels get stuck pretty easy. This is how you break the little plastic piece out of your 6L6 tubes.

The different color glow from the tube can be an indication of a bad tube. I doubt that the filiment voltage supply is bad to only one tube. There is a chance of having a bad screen resistor. Does the amp pop or crackle (or have odd background noise), and does it change when the humidity level changes? I once had a Fender Bassman 50 watt that did, and it was a cracked screen resistor.

If you go with new tubes I think the recommendation is to replace in pairs. My amp had all Mesa rebranded tubes, each pair a different color rating. My recommendation is to replace all 6 in a matched set. Some people like the Mesa branded tubes. Some like other brands. The Buster is a self biasing amp, and any good 6L6 or 5881 should work well for you. Look at reviews to see which has the kind of bass response you want.

Good luck. Post what happens next.

- Paul
 
#3
Mesas aren't self-biasing. They are fixed bias. Self-biasing implies you can use any set of tubes and it will figure out its own bias. You can use any tubes in it, but you would either have to solder in a resistor or two to change the fixed bias or install an adjustable bias pot, which a lot of Mesa owners do.
 
#4
pbagley said:
Hi Jim, I had a Buster 2-10 combo. It was one heavy old gal, but did a nice job. On louder gigs the 10's were not enough, and you need an extension cab. The sound of 10's at their limits is not pretty, and there's plenty of power for more drivers.

Do you have a combo? If so, be careful using the little luggage handle and wheels as you come to sidewalk cracks. The little wheels get stuck pretty easy. This is how you break the little plastic piece out of your 6L6 tubes.

The different color glow from the tube can be an indication of a bad tube. I doubt that the filiment voltage supply is bad to only one tube. There is a chance of having a bad screen resistor. Does the amp pop or crackle (or have odd background noise), and does it change when the humidity level changes? I once had a Fender Bassman 50 watt that did, and it was a cracked screen resistor.

If you go with new tubes I think the recommendation is to replace in pairs. My amp had all Mesa rebranded tubes, each pair a different color rating. My recommendation is to replace all 6 in a matched set. Some people like the Mesa branded tubes. Some like other brands. The Buster is a self biasing amp, and any good 6L6 or 5881 should work well for you. Look at reviews to see which has the kind of bass response you want.

Good luck. Post what happens next.

- Paul
Click to expand...

thanks paul...the amp still sounds good, but yeah the tube doesn't seem to glow the same as the others. i think i will get new tubes for it. there is no hiss or pop tho. kick ass amp. so how did you set up you additional cab? it seems like the more we gig the bigger the venue! so i may in time get a 15" cab myself, but i still want to use these badass EV 10"'s in here.
 
#6
By the plastic tips, do you mean the keyed part of the output tube's base??? If it is, this is how the tube is aligned correctly in its socket. Crazy glue the broken bit back in the correct place. If the heater is actually lighting then you have it in right. The blue glow is a tube operating normally. If the heater is lit but no blue glow put a different tube in that position. If it both lights and glows the position is good and you need a new tube. Else the amp needs service.

Another Paul
 
#11
BassmanPaul said:
But it is broke Jimmy. If the heater lights then that tube is aligned correctly. If there is no blue glow then it's not passing current and is adding nothing to the amps performance. The amp is working using two tubes on one side and one on the other. It needs a new tube.

Paul
Click to expand...
Well, in all fairness I haven't checked out any of those links in that thread about learning amp repair yet ;) I should just bow out till then...never mind.

:hiding:
:D
 
#12
BassmanPaul said:
But it is broke Jimmy. If the heater lights then that tube is aligned correctly. If there is no blue glow then it's not passing current and is adding nothing to the amps performance. The amp is working using two tubes on one side and one on the other. It needs a new tube.

Paul
Click to expand...

haha yeah, the people at mesa agreed with paul. i don't know if a new tube will do though, because a working tube didn't fire in that particular socket either. sucks cuz i just got the amp, and i'll more than likely have to wait a month to play it again.
 
#14
jimribs said:
haha yeah, the people at mesa agreed with paul. i don't know if a new tube will do though, because a working tube didn't fire in that particular socket either. sucks cuz i just got the amp, and i'll more than likely have to wait a month to play it again.
Click to expand...

If what you say is true, you have more problems than a single tube which could actually be good. If you put the "bad" tube in another position and it lights and then glows blue it's probably OK.

Paul
 
#15
jimribs said:
haha yeah, the people at mesa agreed with paul. i don't know if a new tube will do though, because a working tube didn't fire in that particular socket either. sucks cuz i just got the amp, and i'll more than likely have to wait a month to play it again.
Click to expand...

My recommendations:

1: Swap the tubes in pairs. See if the pair behave the same in a new position, of if the problem remains in the same socket with a new pair installed. It's a long shot that the other tube in the pair is causing the problem.

2: Have someone who knows what they are doing inside a tube amp check the amp out. It could be as simple as a bad tube socket, one pin not making contact. Sometimes a tube socket can be tightened, a cheap and easy repair. The fact the tube had a broken center pin indicates it was stretched a bit, so this is a possibility. You also may have a broken solder joint.

Otherwise the tech may need to replace a resister or cap (or three) to get the tube back into the game.

3: Once all the tubes are working together to give all 200 watts then get new tubes. Bias if needed.

A side note - someone mentioned installing a tube wrong. I did that. Fried the tube. But the amp was fine. Mesa makes their amps pretty tough. I know some will disagree, so consider this just one guy's opinion.

And I stand corrected on the self bias mis-info I gave. That was from memory when I bought my Buster about 5-6 years ago. I guess the old memory isn't as good as I thought it was.

Extension cab - I used a 1-15" home built cab with an Eminence 200 Watt driver (became a Beta 15 I think). It's a 101 dB driver, so really efficient. It sure helped on an outdoor wedding gig. Lifting that 100 lb. monster was not fun, but it sounded good.

Good luck,

- Paul
 
#16
If that tube locator was broken in the non working socket, there is the chance that the tube socket pins just need to be retentioned (one or more socket pins not making contact with the tube). Might be a simple fix for the amp. ;)

I'm supprized you didn't think of that BassmanPaul, no burnt fingers from wiggling tubes in their sockets?
 
#18
B-string said:
If that tube locator was broken in the non working socket, there is the chance that the tube socket pins just need to be retentioned (one or more socket pins not making contact with the tube). Might be a simple fix for the amp. ;)

I'm supprised you didn't think of that BassmanPaul, no burnt fingers from wiggling tubes in their sockets?
Click to expand...

I did, BUT I consider that beyond what I would recommend for someone not experienced in tube amp repair to do. The plate and screen pins are connected almost directly to the filter caps and therefore have potentially lethal voltages on them! Besides I have never had a tube socket go down in that way. Arcing yes, many times. Noise indeed but never so bad that the tube failed completely. Never having seen the Buster schematic I cannot opine on the cause of the problem. Most likely culprit. I would think, would be in the screen supply or cathode circuit of the bad position.

JimRibs, if the tube with the broken base turns out to be good you gan buy, from Antique Electronics, a little plastic device that will replace the key. Just slips over the tube pins and is held in place with a spot of glue.

I think you should get your amp to a tech. Trying to go further could be hazardous to your health.

Paul
 

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