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Ground Switch Mods 4 A Tweed Bassman


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2/10/2000 12:47 PM
Deltablues Ground Switch Mods 4 A Tweed Bassman
Ordinarily I would be the first to speak up and tell someone not to screw with a vintage amp. ESPECIALLY something like a real tweed 59 Bassman.  
 
But everytime I turn mine on I look over at the disconnected ground switch and think "There's got to be SOMETHING non-invasive I could do with that switch to give me another tonal option..."  
 
Any suggestions ???  
 
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2/10/2000 1:14 PM
Carl Z

Yup;  
 
Leave it in there. Just replace the switch with the center off variety found on the newer versions. If you gig with it you'll begin to appreciate the switch if you remove it.  
 
Regards;  
Carl Z  
Summit Amps  
 
2/10/2000 7:58 PM
Deltablues
I don't quite understand your reply. Replace it with a "center off" switch? What exactly is that and what does it do?  
 
I do gig with the amp and the ground switch is currently disconnected anyway. (This was done when I installed the 3 prong cord). So it's actually doing nothing at the moment.  
 
I was just looking for an easy mod that would utilize the switch in my particular amp. Something that would give the amp another tonal option via 'a flick of the switch'...
 
2/17/2000 6:31 AM
Tom Miller
 
Torres can use that switch to "heat up" one  
channel. It really works! Ive had him do  
stuff like that to my bassman.
 
2/17/2000 11:59 PM
Bob

I think Carl is saying that the 3 position ground switches are found on later Fender amps that have a 3 prong AC cord. They are a on-off-on config. The'on' sides switch a cap from from the neutral leg to the hot leg of the AC. The off/middle position takes the cap out of the circuit. Normally, with a 3 prong cord, I like to leave my ground switch in the off position (out of the circuit) but that's assuming we all live in a perfect world. Sometimes, a ground lift adapter is called for and then you'll be happy that you have that ground switch because you will be able to make things quieter. But be careful; in this state you could be vulnerable to big-time shocks. I tell players that on gigs, if you don't use a mic and don't use any other AC powered item like a pedalboard or 2nd amp, then you'll be less susceptible but not totally out of the woods. I saw a well-known session player here in LA get the shock of his life recently. He was playing slide thru some old '50's so and so that had a 2 prong cord (he didn't want to un-vintage it!) and then he laid down his metal slide on the recording console. Ouch!!  
 
I think one thing that all the guys on this BBS have in common is a very, very, healthy respect for electricity and safety. I've seen too much weird shit to not be extra careful. I have 3 prong AC cords on all of my stuff and I also build in a ground lift switch but when I use it to quiet a noise problem, I am very careful. Having said that , the ground switch is worth having on the amp. You'll never know when you'll encounter some funky electricity problem in a club or anywhere.  
 
Now that I've pontificated, if you want to get rid of it, figure out what your amp isn't doing that you'd like it to do (in addition to what it's already doing well). With a big switch like that (or a big DPDT), you could implement one of these ideas: switchable fixed/cathode biasing, triode mode, tube/solid state rectifier, extra sag mode, fat switch, tone stack bypass, lift negative feedback ect., ect. There are lots of possibilities. In the 5F6-A Bassman, I'm fond of switching in a 25uf/25volt cap across the 820 ohm resistor at V2-Pin 3. Try to figure out if you want to make the amp cleaner/dirtier or louder/softer with the new switching option. And then its mugs away!  
 
Have fun, but be safe,  
 
Bob
 

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