ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

previous: Carl Z Yup;Leave it in the... -- 2/10/2000 1:14 PM

Re: Ground Switch Mods 4 A Tweed Bassman

2/17/2000 11:59 PM
Bob	Re: Ground Switch Mods 4 A Tweed Bassman 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

2/17/2000 11:59 PM

Bob

Re: Ground Switch Mods 4 A Tweed Bassman

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