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The Fender Super Bassman 300 thread

#901
Hey Frank. you probably did already, but try swapping the tube in question with one that has a green light associated with it. If the previously green one now shows orange or red in the new position, and the orange light one is now green where it was moved, then you might have a bad auto bias module. That's what happened to me. If the tube gets the same color in a new position, then you just have to deal with tubes. I am also wondering out loud if one can replace just the problem tube, since the auto bias should balance them out? Anyone know?
 
#903
tombowlus said:
Someone had asked about KT88's and/or KT66's in the SB300, and I'm having a hard time finding the original post. I did ask Dave Lewis from Fender about this, though, and here is his response:

Hi Tom-

Definitely not KT66’s, the plate voltage (+740V) in the SB is too high.

KT88’s electrically are just fine, however, when we designed the mechanical chassis layout we packed everything as tightly as we could, and it was overlooked that the diameter of the KT88 bottle is slightly larger than the 6550. You can physically fit KT88’s in there (I’ve tried), but the tubes are extremely close to each other (front to rear) as to not recommend their use based on that.

Regards,

-Dave​
Click to expand...

Very interesting. I'm happy I read this. I was looking into getting a backup set based on increased gigging and I was going to get KT88s as my new primaries and push the 6550s to backup status. So due to their close proximity, is the concern around physical contact during schlepping, or is it more of a heat concern? Heat is usually pretty easy... replace the fan with a better one (the PC market has much better fans than we get OEM in amps). Physical contact though... not sure... rubber baby buggy bumpers?
 
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#904
mntngrown said:
Hey Frank. you probably did already, but try swapping the tube in question with one that has a green light associated with it. If the previously green one now shows orange or red in the new position, and the orange light one is now green where it was moved, then you might have a bad auto bias module. That's what happened to me. If the tube gets the same color in a new position, then you just have to deal with tubes. I am also wondering out loud if one can replace just the problem tube, since the auto bias should balance them out? Anyone know?
Click to expand...

If the replacement tube has the same specs (ie. matched) as the good tube you're pairing it with, you are fine. The general recommendation from vendors is that you replace them in pairs though. :/ Give the tube stores a call and ask them if they'll match a tube to yours if you send it in or have the ability to measure it yourself.

Unrelated question: Can I remove a pair or two of tubes from the SB300 to choke it down to 200/100w? Do I need to make any adjustments to the cab impedance?
 
#905
tombowlus said:
Someone had asked about KT88's and/or KT66's in the SB300, and I'm having a hard time finding the original post. I did ask Dave Lewis from Fender about this, though, and here is his response:

Hi Tom-

Definitely not KT66’s, the plate voltage (+740V) in the SB is too high.

KT88’s electrically are just fine, however, when we designed the mechanical chassis layout we packed everything as tightly as we could, and it was overlooked that the diameter of the KT88 bottle is slightly larger than the 6550. You can physically fit KT88’s in there (I’ve tried), but the tubes are extremely close to each other (front to rear) as to not recommend their use based on that.

Regards,

-Dave​
Click to expand...
HI Tom,
that's for taking the time to suss that out for us.
 
#908
eyeballkid said:
Sheer awesomeness.
Click to expand...
what cab(s) did you end up using? Did you notice or feel like the SB300 was getting stressed out? Only reason I ask is that when I wuz a youngster and used tube amps, nothing ran at 2 ohms. Now I realize we've come a long way in electrical design since those halcyon days, but I am curious and hestant at the same time to run the SB300 at 2 ohms until i get some +ive feedback from the forum.
 
#909
I tried mine into the neo 610 /Berg NV215 combo which was 2 ohms. The amp seemed happy and sound was awesome if way over the top for that particular gig :D . Unfortunately my band mates insisted that sanity ruled and I reverted back to a single cab after one set. Didn't seemed to stress the head at all, not particularly hot and a nice clean tone. The amp is designed to be used with a two ohm load so I see no reason not to do so.
 
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#910
The 2b light is still orange. I used it at a show on Wed night and the SBM has never sounded better. Go figure. I actually haven't tried to change the tubes around. This is my first tube head so Im hesitant to open it up and start poking around. My friend is coming over sunday morning and we are gonna try that out. Thanks for the suggestion.
I wasn't considering the KT88's but thats still good to know. I will most likely go with JJ 6550C's. They are less expensive that the Groove tubes and from what I hear, in the same range quality and sound wise.
Not sure if I'm ready to get into the tube rolling game.
 
#911
Really easy. you grab the base of the tube, not the glass, (when everything is unplugged and cool), and wiggle a little back and forth while pulling up. You can even wear some latex or nitrile gloves if you really want to be careful. Swap with any green indicator tube. If it turns out the position, is the problem, not the tube, Fender will replace the module under the 5 yr warranty, at an authorized repair facility. They are quite aware they had some bad ones.
 
#912
azwhofan said:
what cab(s) did you end up using? Did you notice or feel like the SB300 was getting stressed out? Only reason I ask is that when I wuz a youngster and used tube amps, nothing ran at 2 ohms. Now I realize we've come a long way in electrical design since those halcyon days, but I am curious and hestant at the same time to run the SB300 at 2 ohms until i get some +ive feedback from the forum.
Click to expand...
2 berg NV412 s... actually, the amp runs easier because with the extra speaker surface area I can turn down and have the same volume.
 
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#914
ImageUploadedByTalkBass1400348965.500732.jpg

I'm running the SB300 at 2 ohms and it sounds killer. Handles it no problem. Even with the $#!+ power in our rehearsal space.
 
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#918
Havent tried em, but if they are anything close to being as reported its got to be an improvement.
< not a fan of groove tubes!
But dont expect it to be drastic changes. I put winged c's in mine and it opened up the sound a little more in a 3D kind of way, and the tone balance is more pleasing, but it still sounds like the same amp to me. Just the same amp performing a little nicer.
 
#919
mntngrown said:
Hey Frank. you probably did already, but try swapping the tube in question with one that has a green light associated with it. If the previously green one now shows orange or red in the new position, and the orange light one is now green where it was moved, then you might have a bad auto bias module. That's what happened to me. If the tube gets the same color in a new position, then you just have to deal with tubes. I am also wondering out loud if one can replace just the problem tube, since the auto bias should balance them out? Anyone know?
Click to expand...

So I switched the tube positions. As I took the problem tube out, I noticed the top was filled with white swirls, not silver like the rest. So its pretty obvious that it burnt out. I know this is the nature of tubes. But this amp is not even six months old and I bought it brand new. That said, I also just decided that I don't like groove tubes.
I'm gonna replace the one for now and look into buying a matched set of tung sol, possibly JJ's. I'm gonna continue to do some research. The winged C's sound like they would be great. But it would cost me $600 for all six. I would do it if I was sure that they wouldn't burn out. But, as I'm learning, there is no way you could know. So a mid priced tube seems to be my best bet.
 

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