Relay circuit supply voltage question

[NSB_Chris]

Hello All!  I just joined this forum.  I am building a JMP 2204 clone with channel switching using the Hoffman relay circuits.  The 5 VDC relay circuit power supply is designed to be powered by the 6.3 VAC heater supply.  Since I am using a solid state rectifier, I am not using the 5 VAC tap on the power transformer I purchased.  Can I use the 5 VAC leads on the power transformer to power the relay power supply?

Using the 5 VAC  tap just makes the wiring easier and if the relay power supply does not care, I will just use it instead of running another chained set off of the heater wire circuit.

Thanks for any advice you have! 

[PRR]

Yeah, probably.

[NSB_Chris]

Has anyone ever tried it?

I will probably test it with the 5 VAC transformer supply early in the build to see if it looks like it will work.  Really hoping someone has already done it.

[sluckey]

5 volt winding can theoretically produce 7VDC. But that 7805 regulator needs 2 volts headroom to stay in regulation. So, it's right on the edge. It may be constantly dropping in and out of regulation. That may cause some noise. That's probably why no one has offered a definitive answer. But try and see. You can always switch over to the 6.3v winding later. Back to the 5v winding... You don't need to regulate the voltage to the relays. You can run them very easily from 7VDC unreg. Just put a dropping resistor in series with each relay coil.

[TheKT88KilledJFK]

After filtering low forward voltage rectifiers, then loading it with 3 relays, you'll end up with about 5.9V.  That's not enough for the LM7805, but it's enough for the relays.  The LM7805 is a bit of a hungry component.

You'll only be using about 100ma for 3 relays but the forward voltage on the LM7805 is still above a volt even at low current draw. 

To be honest though, the regulator isn't really needed for a couple of relays.  I use it when I need to accurately drive a bunch of relays and bias a bunch of transistors for logic of switching LEDs for channel status.     

 

[NSB_Chris]

Thank you all for the feedback.  My plan now uses 3 relays and a couple sets of LED's for channel status.  I am just just finishing the faceplates on the chassis and then I will start loading components.  I plan on wiring up and testing the simple relay circuit I have first in case I need to make changes.

[TheKT88KilledJFK]

Thank you all for the feedback.  My plan now uses 3 relays and a couple sets of LED's for channel status.  I am just just finishing the faceplates on the chassis and then I will start loading components.  I plan on wiring up and testing the simple relay circuit I have first in case I need to make changes.

If you're going to treat the output of the rectifier as gnd then make sure not to ground the ct of the heater winding of the transformer.  You've probably already heard that or figured it out, but it's worth repeating.  Alternatively you can ground the CT but not the rectifier.  Just make sure the relay power and LEDs never reference gnd. 

I hate it when I blowing a pcb trace because I shorted a heater tap when probing so I tend to just leave the CT of the heater Tx floating. 

[SnickSound]

Hello All!  I just joined this forum.  I am building a JMP 2204 clone with channel switching using the Hoffman relay circuits.  The 5 VDC relay circuit power supply is designed to be powered by the 6.3 VAC heater supply.  Since I am using a solid state rectifier, I am not using the 5 VAC tap on the power transformer I purchased.  Can I use the 5 VAC leads on the power transformer to power the relay power supply?

Using the 5 VAC  tap just makes the wiring easier and if the relay power supply does not care, I will just use it instead of running another chained set off of the heater wire circuit.

Thanks for any advice you have!

It might not have enough voltage for regulation, but what I did in my case is use a Delon voltage doubling rectifier setup, which gave me around 12VDC after rectification. It runs 2 relays and a 2 LEDs without breaking a sweat.

The Delon voltage doubler is just 2 diodes and 2 caps, really simple. And using the 5VAC tap (assuming nothing else is using it) allows you to reference your relay supply to ground which can eliminate sources of noise and means there's no need to isolate the jack or foot switch.

I got the idea from the "AFD 35" amp

More info: http://el34world.com/Forum/index.php?topic=24186.0

[NSB_Chris]

If you're going to treat the output of the rectifier as gnd then make sure not to ground the ct of the heater winding of the transformer.

I have insulated jacks so the 5v power supply ground is not connected to the chassis ground. 

It might not have enough voltage for regulation, but what I did in my case is use a Delon voltage doubling rectifier setup, which gave me around 12VDC after rectification. It runs 2 relays and a 2 LEDs without breaking a sweat.

The Delon voltage doubler is just 2 diodes and 2 caps, really simple. And using the 5VAC tap (assuming nothing else is using it) allows you to reference your relay supply to ground which can eliminate sources of noise and means there's no need to isolate the jack or foot switch.

Thanks!  I will probably stick with the power supply for this build but will check that out for the next!

[NSB_Chris]

I got the idea from the "AFD 35" amp

More info: http://el34world.com/Forum/index.php?topic=24186.0

Holy smokes!  That amp has so many gain adjustments you could get speed wobbles.  A Master Volume and a PPIMV! The dirty channel has two preamp gain pots a MV and a PPIMV and the clean channel has just one less preamp gain.

[SnickSound]

I got the idea from the "AFD 35" amp

More info: http://el34world.com/Forum/index.php?topic=24186.0

Holy smokes!  That amp has so many gain adjustments you could get speed wobbles.  A Master Volume and a PPIMV! The dirty channel has two preamp gain pots a MV and a PPIMV and the clean channel has just one less preamp gain.

That's what happens when people want to build a clone of an amp that was modded through experimentation. Lots of things about this amp make little sense, but can't argue with the results.

But I didn't build an AFD clone, I just stole the relay supply idea. Works like a charm!

[jloewenheim]

The AFD supply uses a voltage doubler in combination with the 5v supply.  This yields plenty of VDC to power the LM7805, hope this helps.

-Jake