Grounding a PT's primary without a center tap

[dehughes]

Hello all,

I'm working with a power section that is essentially a Brown Deluxe, and the PT only has the two hot wires with no ground on the primary. Need I be concerned as to what wire goes to the switch and fuse, being as I'm not going to be installing a ground switch? Or, should I install a ground switch? I will be using a 3-wire power cord, though... Most transformers I've worked with have a grounded primary as well as secondaries, so I'm a bit uncertain as to what to do.

Thanks.

[rfgordon]

I've never used a PT with a primary CT. The HT and sometimes filament windings are center tapped. So it's no issue if the Pri has no CT.

[dehughes]

I've never used a PT with a primary CT. The HT and sometimes filament windings are center tapped. So it's no issue if the Pri has no CT.

Cool. Thanks. That's what I thought. My reservation came when I looked back at all those Fender PT's (and others as well...) that had the two primary leads connected to a ground switch and "death cap", and it got me wondering if there was an inherent benefit to connecting one lead or the other to a particular point, being either the power switch or the fuse. It's been a while since I built my last amp, so I'm a bit rusty.

[dehughes]

*deleted double post...*

[titanicslim]

Hey, David

Do you know how to hook up a bridge rectifier?

[dehughes]

Hey, David

Do you know how to hook up a bridge rectifier?

Not off the top of my head...

[wallybob]

Well that's what you'll need if there's no center tap - a full wave bridge rectifier.

[titanicslim]

I've been looking for a straightforward, descriptive schematic and this is the best I've come up with so far. It's the Blues Jr. and I guess it'll do. the HV taps are the red leads. When there's no center tap you make this "diamond" with the diodes (in this case 1N5062s - 800v - are shown) and the tail goes to ground. You can see in this case it goes to the P.S. buss, which is normal.

This was new to me a short time ago. I had no idea how common it was, so it threw me for a loop until somebody here straightened me out. (Thanks again, by the way )

http://www.schematicheaven.com/fenderamps/blues_jr.pdf

Good Luck

[dehughes]

Ah yes, bridge rectifiers...thanks. However, those are on the secondary, and my question pertains to what one might do if there is no ground on the primary side of a PT. Perhaps nothing is required (I've seen many and amp without that...), but I'm just curious.

[titanicslim]

OK, yes, I see it. You have cleverly concealed it in the first sentence of your original note and just about every sentence after that.

[skyboltone]

Ah yes, bridge rectifiers...thanks. However, those are on the secondary, and my question pertains to what one might do if there is no ground on the primary side of a PT. Perhaps nothing is required (I've seen many and amp without that...), but I'm just curious.

Don't worry about it. Screw the PT to the chassis. The grounding conductor (green in AC systems) and the grounded conductor (white in AC systems) are tied together at you service. Do NOT tie the white and green together at the amp!!!!

Dan

[dehughes]

I shall not worry about it then. Many thanks.