Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: JB on September 23, 2017, 12:23:33 pm

Title: 5E3 grounding
Post by: JB on September 23, 2017, 12:23:33 pm

First Fender style build for me.

So I was going to group the grounds into 3:

1/ Centre taps, PA cathode resistor, first filter cap - bolt to chassis near the PT.

2/ The other two filter caps, PI cathode resistor, PA 220K resistors - bolt to chassis near PI stage

3/ Pots, jacks, cathode resistors for first two stages - bolt to chassis near the jacks??

I'm not using the brass plate, or a bus wire on the back of the pots.  But, unlike a Marshall build where the input jacks are floating, the sleeve of the jacks will act as ground number 3.  So should I avoid also bolting a ground wire to the chassis, or should I do that and get the shoulder washers for the switchcraft jacks?



 

Title: Re: 5E3 grounding
Post by: PRR on September 23, 2017, 03:52:24 pm

There are many ways to do it.

> bolt to chassis near the jacks??

Then if you have more than one jack, why not just let the jack shell be your input section chassis bond? (More than one because jacks can get loose, which is not-good.)

Title: Re: 5E3 grounding
Post by: JB on September 23, 2017, 04:22:21 pm

Yes, I guess 4 jacks all down to chassis should be pretty good.  I can start with that and see what the noise floor is like.

Title: Re: 5E3 grounding
Post by: Ed_Chambley on September 24, 2017, 07:06:34 am

Take ten to read this


http://www.valvewizard.co.uk/Grounding.html (http://www.valvewizard.co.uk/Grounding.html)


In a low gain all is certainly not needed, but the understanding of this will enable you to actually know where to look if you get noise.


For instance , forr fender designs I have never used isolated jacks and it is stilll very quiet. I am an extreme advocate of building with blue loctite on input jacks and all ground connection threads, well actuallly everywhere really.

Title: Re: 5E3 grounding
Post by: bnwitt on September 24, 2017, 08:19:48 am

This is the layout I've used to build some 30+ Hoffman 5E3 amplifiers.  It is dead quiet on idle.  just a preamp ground on the side of the chassis and a power section ground near the PT

Title: Re: 5E3 grounding
Post by: JB on September 24, 2017, 01:02:45 pm

Merlins' ground info is very good.  Makes sense.

With the Hoffman layout are you isolating the input jacks from the chassis? 

My board is the laid out Fender style.  I think i'll start with just the jacks acting as the pre-amp ground and then a power amp ground on a bolt with the B+ centre tap.  If it's noisy I can float the jacks, use a pre-amp ground point and maybe ground the PI stage separate from the PA. Loctite is a good idea.

Should know in a couple of weeks when the final parts come in and I get it powered up.

Thanks for the replies.
 

Title: Re: 5E3 grounding
Post by: bnwitt on September 24, 2017, 02:44:26 pm

Quote from: JB on September 24, 2017, 01:02:45 pm

With the Hoffman layout are you isolating the input jacks from the chassis? 

No.  No isolation of jacks or pots