Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Jennings on March 29, 2025, 01:15:53 am

Title: Relay switching grounding
Post by: Jennings on March 29, 2025, 01:15:53 am

I’m toying with some relay-driven channel switching for the first time. Where/how do I best ground the relay circuit? Well away from circuit ground points, I presume?

Title: Re: Relay switching grounding
Post by: TIMBO on March 29, 2025, 02:24:36 am

Yes

Title: Re: Relay switching grounding
Post by: glass54 on March 29, 2025, 06:16:58 am

+1 with Timbo  :laugh:
DO NOT earth your relays if using heater generated PS!!
See Doug's very useful pages:
https://el34world.com/projects/relay_switch.htm (https://el34world.com/projects/relay_switch.htm)
Regards
Mirek

Title: Re: Relay switching grounding
Post by: tubenit on March 30, 2025, 05:00:37 am

There is a lengthy thread loaded with great information about relays in ARCHIVES!


Relay circuit & layout board & ft switch (https://el34world.com/Forum/index.php?topic=14348.0)


With respect, Tubenit

Title: Re: Relay switching grounding
Post by: Jennings on April 05, 2025, 04:04:52 am

Thanks folks...great info on those pages.  I was planning on using the heater supply for the relay power supply also.  The transformer I'm using has a centre tap available on the 6.3V winding.  So if I'm understanding correctly the relay circuit "common" points just tie together as in the attached schematic?

Title: Re: Relay switching grounding
Post by: Merlin on April 05, 2025, 06:04:44 am

You can't have a ground on both sides of the rectifier or it will be shorted out.
So either you ground the transformer centre tap and let the relay circuit float (in which case you need an insulated footswitch jack, and don't connect the footswitch enclosure to the anything), which is what your diagram seems to show so that's good.
Or you ground your footswitch circuit and disconnect the transformer centre tap, which might not be great for heater hum.

Btw you don't really need a regulator, a simple resistor before the 4700uF cap will do.

Title: Re: Relay switching grounding
Post by: Jennings on April 05, 2025, 02:10:49 pm

Thanks Merlin for the info and confirmation I’m on the right track. I didn’t think to use a resistor! I haven’t wired this up yet (although the relay tagboard is already made up), but as there’s a centre tap on the heater secondary I’ll use that and keep the relay power supply floating as per the diagram. I was planning on using isolated Cliff style jacks for the footswitch. Although I’m half tempted to add LEDs…in which case I might need a DIN / multi pin style instead.