How To Mod a SP TB1

S

Sonic Idiot

New member
I've got a SP TB1 that I'm not very fond of. But it wasn't very expensive and instead of e-baying it, I'm thinking of using it as a test dummy for me to break my mod cherry on. First up, replace the tube? Next step? I don't know. Any suggestions?
 
Okay, open 'er up and take out all the little things that look like miniature firecrackers. Put those on the left side of the table. Now put in some blue colored caps (look like firecrackers again). Now get a tube out of your Fender Vibroverb and replace the tube very carefully . There! that was easy now wasn't it. Now take the old caps and sell them to your friends, tell them they are "vintage"
 
I should know to be more specific. What tube, if any, might improve the mics substance...this is where I find it lacks: it lacks beef. It's thin. I can do research on the ins and outs of this process, but name some tubes. Thankers.
 
nice! thanks. Do you have a resource that discusses the characteristics of these tubes (I know, I know, this is sooo broad, but I'm looking for starting points, really). Does anyone have another resource for tube mic moding - a book or otherwise? I'm willing to take a leap based on recommendations. I'm starting from scratch here. Any advice on which tube to get from that list?
 
I just went through something like this with a Nady TCM-1100 I picked up for $119 on eBay. They said it came with a 6072A tube (a special 12AT7). Well, those at Nady are both idiots AND liars. For one thing, it was a 12AX7 tube! It said so right on the glass. Next off, a 6072A is a 12AY7, not a 12AT7.

With a 12AX7, the mic sounded bright and scooped. Lows and Highs were pronounced.

Added a 9 pin socket so I could change tubes easily and tried a 12AT7. It sounded a bit fuller, but all the 12AT7's I used created that "wind" noise after they warmed up. Nixed that!!!

Tried a 6072A (12AY7) and the sound really got full, round and smooth.

The areas that make the biggest changes in sound are the capsule, the tube, and the transformer. The capsules are made by 797, which are fine capsules, so no real need to upgrade those. If the tube you have IS a 6072A, try different NOS versions to get the timre you like.

Try different types.

The 12AX7 has a gain factor of 100
The 5751 has a gain factor of 70
The 12AT7 has a gain factor of 60
The 12AY7 has a gain factor of 45
The 12AV7 has a gain factor of 41
The 12AU7 has a gain factor of 19

The higher gains push the low and high end frequencies and saturate the transformer. A good transformer can handle this, but a poor trafo can sound bittle and muddy. The mid ground gain facters won't saturate the transformer as much, so the overall is smoother. The lower values smooth also, but increase floor noise as the preamp level is raised.

You could also replace the transformer ,with a special tranny that is produced by Cinemag. Great trafos.
 
Not sure whether SP uses the WIMA polypropylene caps in the cheaper B series line, but if they are using ceramics instead you might want to swap them out for polypropylene or polystyrene caps. There's probably a coupling cap that connects the capsule to the rest of the circuit, usually mounted off the PCB on little standoffs (again, I'm not familiar with that particular mic), this cap change will make the greatest difference. You can order polystyrene caps (1000pf) from mouser.com that sound great. I've done this mod in my MXL603's and Octava MK319, both with good results. If there are any electrolytics in the signal path, they could be bypassed (paralleled) with a polypropylene as well. Probably not as noticable as a tube upgrade, but it's a subtle but worthwhile reduction in "graininess."
 
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Thanks for the info. I'll crack the mic open in the next few days and bump this thread back up with some specifics.
 
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