powering a relay

[daz]

Where is the best place to tap some power for a relay without causing any amp noise or any other problems? I was thinking of tapping off the heaters and rectifying it to get about 6v DC for at least 1 if not 2 relays. I'll have to find my hammond PT specs, but i'm pretty sure the heater current is nowhere near maxed, and i'm only powering 2 EL34's and 2 ax7's. Or if theres a better way, please enlighten me.

[txstrat]

I don't see a problem in the way you wanna go for it. I usually had a separate tap in my transformers for the relays. But if I hadn't I would have done it the way you described. Make sure you use a separate wire for the relay ground to the star ground (are U using a star ground anyway?). I once didn't and it caused noise. Learned it the hard way. Thanks again to this forum.

[pdf64]

Problem with the heater supply is that neither wire is ground referenced but the cnetre tap is, so you can't ground the rectified negative output with a half wave rectifier(1 diode) or with a bridge rectifier (if memory serves me correctly). Plus it's goes back to the most sensitive parts of the amp, so there's the potential for switching transients etc to crossover from heaters to input grids.
When possible I prefer to take a separate diode/limiting resistor from the bias wire off the PT, and use 50V coil relays. Put a diode across the coil to kill the switch off spike. Peter.

[daz]

Wait...i just remembered i have a rectifier tap ! I had a tube rectifier when i first built the amp but went to diode rectification. So can anyone tell me how to do this in regards to ground? Should i use a bridge rectifier so i wouldn't have to use the chassis as ground? If i'm off base here, how exactly would you guys wire it?

[txstrat]

Depends if the 5v rectifier tap has a CT or not. If not you have to go for a bridge recto cause you need the bridge for ground (anodes). After the bridge the voltage should be around 7v. You can use an IC 7806 paralleled with two filter caps (1st=1000uF / 25v, 2nd 22uF/25v) to calm the ripple. Output of the 7806 should be exactly 6v. Don't forget the diode over the relay coil (anode to ground).

[daz]

I think it has a CT, but i'll check when i get around to it. Would it then be done exactly like the main power, IE: CT to star, diodes from the two sides to create a DC + point? Or is there a better way such as it's own ground which i imagine would mean doing it the same way but instead of chassis grounding the CT it would go right to the negitive side of the relay coil?

[NorCalTuna]

I've had good results with the method Mesa uses for the early mk amps- they rectify the last one or two pre tubes (depending on amp), so you have dc filaments and then just adjust your voltage with some lil' resistors for your relays, or be super sleazy and use 6v+ relays. good grounding and routing seems to leave me with no pops or oddness. The bridge on the 6.3v will about 9v, or a little more, so you'll have to use some resistors- I use 2w, just an ohm or two. You don't need to rectify anything push pull- power tubes or phase inv. Since I guess your second 12ax7 is the inv., you could use a pretty small bridge. I use a flat 4a, 600v one I buy from surplus for a buck on a surplus heatsink, never lost one. I use a 25v, 6800 uf+ cap to smooth it. Just makes sense to

you can do the same for the 5v tap. In fact, the 5v tap will yield about 7v dc with a bridge. this interests me, as most "champ" transformers have more 5v capacity than 6.3v... I have a taped up set of taps on my dumble pre clone i'm trying to think up a use for (current idea: el84 power section- 1.5 a, too much for the 6.3v side but just right over on the 5v team). any ideas?


so I digress... hope your supply comes together!

[txstrat]

That's what I did and it's dead quiet. I don't even hear the switching while I play. (actually after help from this forum with the grounding) The switch can even be in a footswitch. By switching the ground you don't have to lead the voltage over several feet long cables.

Hope this helps

Matt

[daz]

Well, i'm just going to do it the same way i always have because it's already done. Let me explain. I always use a very small rack that i built for my 1.2 rack boss effects, (which i send to a second amp, so no need for the efeects loop for effects) wireless, tuner, and all needed wall warts. In that rack i have a pot and relay for this very purpose. I'd simply take the loop out to some jacks in the back of the rack and the relay switches the pot in and out. the pot simply has one side grounded and the wiper is going to the hot of the jacks. So basically it would be a variable resistor to ground from the signal point. The footswitch i built already has a LED in it too. So it's already done. All i have to do is put a jack in the amp with the wiper of the master going to the jack's hot tab and i'm done.

the only reason i wanted to do it differently is because i always felt that way was probably not the most "correct" way of doing it. But i asked this at another forum too and someone said thats exactly how they do it, so i just figured what the heck....it's always worked fine and heres someone else saying that how they do it, so as they say, if it ain't broke, don't fix it.

[Vaughan]

Relay drive

Hi Guys,
As coincidence has it, I am just in the process of installing relay switching for the boost function of two small amps in our workshop. I've used the heater line (6.3VAC centre tapped) to supply a full wave rec. and a regulator chip.
I've only just finished wiring it up but all seems to be OK. The relay voltage also feeds a front panel LED.
This is the first time I've done this mod. but I checked the heaters and there is plenty enough current supplied from the Mains Tx so no problems expected.

[Vaughan]

Relay Driver

Sorry Folks
My attachment in the last post (sic.) doesn't seem to enlarge. Not quite sure what happened, but I'll re-attach to this post. Wish me luck!!

[hamfist]

Sorry Folks
My attachment in the last post (sic.) doesn't seem to enlarge. Not quite sure what happened, but I'll re-attach to this post. Wish me luck!!

I'm pretty new at fiddling with voltage regulators, but isn't this circuit doomed to failure because you would need a positive voltage regulator for it ? The LM79L05 is a negative voltage regulator.

[Vaughan]

I'm pretty new at fiddling with voltage regulators, but isn't this circuit doomed to failure because you would need a positive voltage regulator for it ? The LM79L05 is a negative voltage regulator.

Sorry Hamfist.
Gross typing error. should have been LM78M05 - must get my fingers retrained!!
All works fine with LM78M05

[Enzo]

As drawn it should be a 7805, yes.

You are rectifying 3.15VAC, which yields about 4.5vDC once filtered. If the 5v relays work at all I bet it has little to do with the regulator. it cannot be working within its regulating range. It certainly needs an input voltage higher than the output to function. Try replacing it with a wire and see if the relays work just as well.

[hamfist]

Sorry Hamfist.
Gross typing error. should have been LM78M05 - must get my fingers retrained!!
All works fine with LM78M05

I've been having great fun trying to get a LM79L05 to work in such a circuit over the last week or so !

It's certainly been a learning experience

I now have 5V positive voltage regulators on order !