Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mikeg on September 01, 2018, 11:10:15 am

Title: Grounding scheme question.
Post by: mikeg on September 01, 2018, 11:10:15 am

Hi folks. I am new here and had some experience with amp repair and some builds 20 years ago and have a good lot of parts etc. So decided to get back at it now that I'm semi retired. I'm about 85% finished with a 5F4 build and have two questions I was hoping some of you might help with. One , I have checked out several sites regarding grounding schemes, and on Rob Robinette's site he shows two 5E3 examples. One has the power amp and preamp on a single ground buss and one  has the power amp and preamp ground busses  separated. Any thoughts on which is better, would be appreciated.

 I know the second is a very basic question that I probably should be able to figure out but I don't want to do it wrong and ruin an OT.  I am thinking, instead of having one speaker and one ext spk jack, I'd prefer to have one as 4 ohm and other as 8 ohm and possibly make two baffle boards for 2x10 and 1x15. If i do that, I assume I'd use the shunting type jack on both? Would I connect the green and yellow wires to the tips of each jack, then connect the black wire to the shunt(switch terminal) on one and then jump to the same tab on the other. Do the ground lugs get connected together and also to the chassis or connected or are the jack already grounded by the connection through the chassis. Sorry for such basic questions but I don't have enough confidence in my memory/understanding to assume anything.   Thanks for any guidance.

Title: Re: Grounding scheme question.
Post by: shooter on September 01, 2018, 11:22:23 am

start here;

https://el34world.com/Forum/index.php?topic=9267.msg84015#msg84015

once your head quits spinning you'll be ready to solder  :icon_biggrin:

Title: Re: Grounding scheme question.
Post by: sluckey on September 01, 2018, 11:35:37 am

Separate preamp and power amp grounds is superior to one single ground buss.

When using multiple OT impedances, each connected to it's own jack, don't use shunting jacks for any of them. And only use one jack at a time. A better arrangement might be to use an impedance selector switch and a single main jack with a shunt connected to ground. You could also use an external jack (no shunt) wired in parallel to the main speaker jack, like a typical old Fender.

Title: Re: Grounding scheme question.
Post by: Willabe on September 01, 2018, 01:16:43 pm

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

Title: Re: Grounding scheme question.
Post by: mikeg on September 01, 2018, 03:05:52 pm

OK. Thanks all. Will start with the links provided and do that in the future as well.