Ampeg polarity switch?

[flamesfan011]

What does the polarity switch on older Ampeg's do? (1975 Ampeg B25B)

[crentest]

it dose the same thing as unpluging the power cord and fliping it and pluging it back in.
sometimes the chassis would be "hot" and you could get shocked.

[flamesfan011]

Mine is broken. Should I be worried?
The switch is busted. I haven't gotten a look inside.
It plays fine though.

[JimmyM]

if you have a 3 prong power cord on it, no problem. with the 3 prong power cord, a polatiry switch is unnecessary.

[crentest]

you would most likely notice a problem when singing....lol

[flamesfan011]

Thanks guys

[ampegfuzz]

Yeah if I'm playing my SVT and I'm singing and getting shocked ill flip the switch. No more mouth shock

[billfitzmaurice]

Originally Posted by crentest

it dose the same thing as unpluging the power cord and fliping it and pluging it back in.
sometimes the chassis would be "hot" and you could get shocked.

Not quite. A capacitor connects the chassis to the A/C ground wire, to filter noise. But with a two wire system there's no way of determining which wire is hot and which is ground, so the switch is used via trial and error to get the right connection. If it's switched to the hot wire a shock hazard does exist. It's not a direct connection to the A/C line, the capacitor filters out most of the voltage, but not all.
OP, go to a qualified repair shop and have the cord replaced with a 3 wire. While he's in there have one if these installed, along with MOVs, and you've got the equivalent of a $100 power conditioner.
http://www.excesssolutions.com/cgi-bin/category/11700

[raytsmith]

So if you install a 3 prong, should the cap be removed as some suggest, or should it be left in place to help filter noise ?

I recently picked up an early 70's theil B15 that still has a 2 prong.

No shocks yet, but I'm not looking forward to one, either.

[raytsmith]

And by the way, I picked up a 4-pin to 1/4 inch speaker cord from fliptops while ordering tubes -

A B15 sounds really sweet and loud through 2 BFM Jack 12's. Not quite the same vibe as the the theil cabinet, but it has a very nice tone of its own.

Doubt if I'll gig that configuration until the B15 has proven to be reliable, but it is an interesting combination. The tube distortion is still there if you want it, but it gives a lot a lot more usable volume.

[beans-on-toast]

Originally Posted by raytsmith

So if you install a 3 prong, should the cap be removed as some suggest, or should it be left in place to help filter noise ?

I find it safer to operate the amp with the cap removed. The problem with these old caps is that they can leak. The more that they leak, the more dangerous they are.

Now to complicate things even more, the Ampeg VR, as an example, has both a three prong power cord AND a three position polarity switch. The middle position is the same as having no switch. So if you have a good cap, you can have both a ground reverse switch and a three prong power cord.

[billfitzmaurice]

Originally Posted by raytsmith

So if you install a 3 prong, should the cap be removed as some suggest, or should it be left in place to help filter noise ?

I recently picked up an early 70's theil B15 that still has a 2 prong.

No shocks yet, but I'm not looking forward to one, either.

A cap is normally placed across the incoming A/C for filtering. The cap isn't the source of the problem, the lack of a direct ground connection to the chassis is.

[Jonyak]

my question about that switch is why didn't they put it on the back where the standby switch is and the standby where the polarity switch is.

it would be so much more convienient.

[KramerBassFan]

They call those "Death caps", right Bill?

My V4 still has one... to my enjoyment.

[MAMMOTHvolume]

Originally Posted by KramerBassFan

They call those "Death caps", right Bill?

My V4 still has one... to my enjoyment.

aye, there quite good at storing a charge.

[KramerBassFan]

Originally Posted by MAMMOTHvolume

aye, there quite good at storing a charge.

Oh i know, and so do my hands.

I keep tally on the amp now with a white crayon now... but the death cap is on its way out.

[beans-on-toast]

Originally Posted by Jonyak

my question about that switch is why didn't they put it on the back where the standby switch is and the standby where the polarity switch is. it would be so much more convienient.

I think that it was a cost saving decision. With a little extra wire and maybe a terminal strip they could have done it. Probably saved $1.

In the current SVT's they have the standby switch on the front panel. To implement it, they separated the mains AC in and standby wires from the others and added an extra molex connector. Slightly higher cost.

[billfitzmaurice]

Originally Posted by KramerBassFan

They call those "Death caps", right Bill?

:

Only those who don't understand how they function. The arrangement was half-assed for sure, but with two wire AC and high impedance pickups they did what they had to do. If only the original Code had gone with 3 wire balanced AC all the way to the outlet, instead of just as far as the street entrance, we'd never experience any noise or interference. But they chose the cheap way rather than the right way...

[KramerBassFan]

Cheap vs. right in the Amp business?

Is that even a concept?

[billfitzmaurice]

Originally Posted by KramerBassFan

Cheap vs. right in the Amp business?

No, in the AC supply that we use. Two wire single phase unbalanced AC is the worst possible configuration. But it's the cheapest, so that's what was made the standard circa 1920.