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Post subject: Howdy--re-tubing my Fender Super Bassman
Posted: Wed May 15, 2013 12:59 pm
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Hobbyist
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Howdy...new to the forums, so just wanted to say HI first

I have a question about re-tubing my Super Bassman (obviously, 300 watts)....here goes

i want to re-tube using Tung Sol KT 120's (cryo treated) instead of the 6550 Groove Tubes that came with the amp.

my question is: can the filament transformers take it? or for any other reason would this be a bad idea.

if it is a bad idea, how about regular KT 88's....would that also be too much for the amp to take?

any thoughts appreciated

Dave


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Post subject: Re: Howdy--re-tubing my Fender Super Bassman
Posted: Wed May 15, 2013 4:19 pm
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Aspiring Musician
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Joined: Wed Jan 14, 2009 10:54 am
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Location: Alabama, Michigan, Florida, Wisconsin, Mississippi and Tennessee seasonally
I'm sure BrotherDave has info for you and we'll await his next visit - in the mean time, do some research as to the shock mounting of the filaments in any tubes that you will be considering for a bass head. Some tubes have the same electrical specifications, but if the tubes are subjected to several hundred watts of bass audio from a speaker system close by shaking the tubes in the amp head, the filaments may not survive the vibration. I haven't used a tube type amp in over 40 years, but I ran into this issue once and then went with the original equipment type that were equipped with a heavy duty filament system. That was an expensive lesson.


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Post subject: Re: Howdy--re-tubing my Fender Super Bassman
Posted: Fri May 17, 2013 9:47 am
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I would never put KT120's in a Super Bassman because KT120's draw up to 3 amps more per tube than a 5550/KT88 and I've got a feeling that is way out of spec for the power available. 5x 3 = 15 more amps....WOWSER! That also would make that like a 500 watt amp and pretty sure

I've not seen the schematic or transformer specs so I can't say for certain, but I would suspect if it would push KT120's they would have used KT120's in the first place.

I am sort of surprised Fender went with 6550's instead of KT88's in the Super B. While not identical twins they are usually interchangeable. The KT88's have the benefit of lower distortion for a cleaner tone. Clean tone is usually a desirable thing for electric bass amps more than in electric Spanish guitar amps. Groove Tubes makes a KT88, so it isn't a supply issue and they wanted them to have more crunch by design.

I'm 99.5% sure the KT88's will work fine, but I'm 100% positive they will also void your warranty. In fact if I had one I'd probably try the KT88 quintuplet myself, but after the warranty was done of course.


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