powering 5v relays with the filament supply.

[phsyconoodler]

Is there a way to wire up the filament supply to operate my existing 5v relays?
I realize that i'd have to rectify it,but how would I wire up a voltage regualtor?I don't have a 5v winding on the transformer I'm using.
Thanks in advance!

[gilgalad101]

Just follow the 124 schematic, but pretend the separate 6.3V transformer is the filament supply.

http://ampgarage.com/forum/files/124_schematic_182.pdf

[paulster]

And don't tie the DC ground to the chassis at all, since it is referenced to ground via the heaters.

Your bridge rectifier won't last long if you do, and they smell nasty when they blow!

[wjdunham]

I use a PT with the a center tap for the heaters, so I can reference the relays to ground. I don't use a voltage regulator, just two diodes and cap. The voltage on the relays is very marginal, down to 3.7V when on one relay when the other is engaged, but the Omron 5V relays switch just fine. Simple and cheap way to do it IMHO. I probably wouldn't do this in a "commercial" amp, but my home-brews they work fine. I built one without a center tap on the heaters, it worked fine but I was always afraid that I'd forget and ground the footswitch or relay and blow something up.
Bill

[paulster]

I use a PT with the a center tap for the heaters, so I can reference the relays to ground. I don't use a voltage regulator, just two diodes and cap. The voltage on the relays is very marginal, down to 3.7V when on one relay when the other is engaged, but the Omron 5V relays switch just fine. Simple and cheap way to do it IMHO. I probably wouldn't do this in a "commercial" amp, but my home-brews they work fine. I built one without a center tap on the heaters, it worked fine but I was always afraid that I'd forget and ground the footswitch or relay and blow something up.
Bill

You're only getting 3.7V because you're using full-wave rectification of a 3.15-0-3.15V supply effectively, rather than a 6.3V supply if you'd used a bridge rectifier, so you've rectified 3.15Vac.

Using a bridge rectifier is fine, so long as you don't connect anything on the DC 0V side to ground, and there's no reason why you need to anyway.

The DC supply still has a ground reference via the AC side of the circuit, so it won't introduce noise and it'll work just fine.

I do exactly the same thing in my amps, using AC heaters, DC heaters and DC switching supplies all from the same filament winding.

[David Root]

Relays take very little current and operate intermittently, sooooo...

Why does HAD use a separate transformer instead of taking it off the 6V3 heater winding???

[FUCHSAUDIO]

it's guieter.

[talbany]

The relays really need to see a separate ground potential like Bill says.... If the relays don't have that potential they will buzz..Weber tried to make a relay board several years ago that ran off the filaments..No ground potential on the relays buzzed like nuts..Been there.. Good idea bad design....Go with the transformer
Henry had one he claimed worked well.. Maybe he'll repost it
Tony

[paulster]

The relays really need to see a separate ground potential like Bill says.... If the relays don't have that potential they will buzz..Weber tried to make a relay board several years ago that ran off the filaments..No ground potential on the relays buzzed like nuts..Been there.. Good idea bad design....Go with the transformer

That's not been my experience but then I prefer to do my ground reference on the DC rather than the AC side as a matter of course since my preamps all run on DC and they're the most sensitive part of the amp.

One thing you do need to be careful of, and this is where the isolated tap or transformer can really help, is that you are effectively extending the filament supply outside the amp and this is where noise can get in, depending on how well filtered your relay supply is and how much noise rejection you'll have as a consequence. My relay supply has a bridge rectifier and filtering completely independent of the rectification and filtering for the preamp heaters although they are both sourced from the same winding.

I have no hum, buzz or issues whatsoever with this setup.

[David Root]

Thank you Gents, that all makes good sense.

In my current build (#13, 50W, no reverb) in a BFPR chassis, I have a separate transformer/PS for the relay, but I'm using AC on the preamp heaters because I now have no room for a DC PS for the preamp tubes.

I guess I could have done it the other way around, used a transformer for the DC heater supply and taken the relay supply off the 6V3 winding and used a voltage doubler a la Dumble (12V relay), but it would be very difficult to fit the doubler circuit with those two caps in.

I also have an extended main board with serial buffered loop built in, had to put the main board caps in a doghouse on top of the chassis, power tubes plate/screen caps are in a can in the rectifier tube slot, space is tight!

[talbany]

The relays really need to see a separate ground potential like Bill says.... If the relays don't have that potential they will buzz..Weber tried to make a relay board several years ago that ran off the filaments..No ground potential on the relays buzzed like nuts..Been there.. Good idea bad design....Go with the transformer

That's not been my experience but then I prefer to do my ground reference on the DC rather than the AC side as a matter of course since my preamps all run on DC and they're the most sensitive part of the amp.

One thing you do need to be careful of, and this is where the isolated tap or transformer can really help, is that you are effectively extending the filament supply outside the amp and this is where noise can get in, depending on how well filtered your relay supply is and how much noise rejection you'll have as a consequence. My relay supply has a bridge rectifier and filtering completely independent of the rectification and filtering for the preamp heaters although they are both sourced from the same winding.

I have no hum, buzz or issues whatsoever with this setup.

Paulster
Great info... Thanks for sharing

Tony

[markusw]

My relay supply has a bridge rectifier and filtering completely independent of the rectification and filtering for the preamp heaters although they are both sourced from the same winding.

I have no hum, buzz or issues whatsoever with this setup.

Sorry if this is a dumb question, just trying to learn
you run den power tubes with 6,3V AC (not referenced to gnd), then you have two bridge rectifiers (each with its own filter caps) both connected to the same 6,3V AC winding as the power tubes, one is used for the preamp tube heaters, one for relay supply. Both bridge rectifiers are referenced to gnd.

Peace,

Markus

[paulster]

Sorry if this is a dumb question, just trying to learn
you run den power tubes with 6,3V AC (not referenced to gnd), then you have two bridge rectifiers (each with its own filter caps) both connected to the same 6,3V AC winding as the power tubes, one is used for the preamp tube heaters, one for relay supply. Both bridge rectifiers are referenced to gnd.

The only dumb questions are the ones that aren't asked.

Yes, that's exactly how I do it. You really only need one of the DC sides referenced to ground, but I find it's quietest when both are in really high gain circuits.

The key thing is that you can't have the DC side and the AC side referenced to ground, as the DC ground is effectively alternating between + and -3.15V 50 or 60 times a second, so you'd short out your rectifiers if you did this.

[FUCHSAUDIO]

The way Dumble does (or did) it, is clean. If you have a balanced filament line (whether via center tap or resistors) and you build and float a relay supply, you are asking for noise trouble. If someone grounds the foot switch somehow (pedal board or whatever) things can blow out or hum can be created.

When we do mods, I use standalone transformers we buy surplus for less then ten bucks, and build a regulated DC supply which we use for our solid state reverb as well as the relays. No noise issues. We used to share the filament lines, but it took too much fudging around to make or keep things quiet. When using transformers with 5-V windings for rectifier tube filaments the 5-V winding can be voltage doubled, then regulated down to relay voltage easily (Assuming you don't have a rectifier tube of course).

[markusw]

The only dumb questions are the ones that aren't asked.

Yes, that's exactly how I do it. You really only need one of the DC sides referenced to ground, but I find it's quietest when both are in really high gain circuits.

The key thing is that you can't have the DC side and the AC side referenced to ground, as the DC ground is effectively alternating between + and -3.15V 50 or 60 times a second, so you'd short out your rectifiers if you did this.

Thanks a lot for your explanation!
If the heater winding has a center tap you simply leave it unconnected?
Edit: do you use Schottky diodes for the DC heater bridge or just normal ones?