Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: rubyfocus on July 26, 2024, 01:46:08 am
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Hi all- Perhaps someone out there might know what's going on here... I'm trying to use a 5V DC relay to alternately ground out my two preamp tubes, so I'm using the filament voltage (6.3VAC) to power it. I'm rectifying this voltage with a series diode on both wires, then combining them to one wire. It's a center-tapped PT, so shouldn't I be getting at least 6 volts DC between ground and my rectified filament lines? Well, I'm not. It's barely 3 volts, not enough to trip my relay. What am I missing here? :dontknow:
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I think it's easier for people to chime in if you show a schematic/wiring drawing.
/Max
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You need to use full bridge rectifier
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If you want to ground the negative output of the FWB, the heater winding CT will need disconnecting from ground.
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It's a center-tapped PT, so shouldn't I be getting at least 6 volts DC between ground and my rectified filament lines?
You basically have a 3.15V - CT - 3.15V transformer, so no, you won't get 6V that way.
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Hoffman has a very nice small 5V power supply board made for this purpose. On the website, look around for "Channel Switching" and it's on that page. Not expensive. Works great, I've used these a number times.
:icon_biggrin: The 5V regulator makes all the difference.
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Hoffman has a very nice small 5V power supply board made for this purpose. On the website, look around for "Channel Switching" and it's on that page. Not expensive. Works great, I've used these a number times.
:icon_biggrin: The 5V regulator makes all the difference.
+1. I just added relay switching to an amp by adding the Hoffman boards. Works great. The power supply board is 1.5"x2". It is a good way to go if you can make it fit.
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You need to use full bridge rectifier
If I use a bridge, will that mess with the chassis ground that I'm switching the tubes with? Attached is the schematic. I'm no longer using the voltage regulator that I originally was going to use because I am getting around 5V with this circuit. But I'm wondering if I'm going to have a problem hooking the negative DC lead from the bridge to chassis ground.
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After thinking about this a bit, I figured that I can simply switch the amp chassis ground in isolation of the rest of the circuit. Yes, I know that Doug offers a handy-dandy PCB arrangement that probably works real well, but I like to make my own stuff wherever possible. I'm just funny that way, I guess. That being said, here's what I got: The "ground" from the bridge is only utilized for the benefit of the footswitch, which energizes the relay, and the two alternating LED indicators, which also utilize the fake ground. The chassis ground which alternately kills the tube I'm NOT using, is simply one of the two things that the relay switches. Piece of cake! Now let's hope that I don't burn anything up!
But as always, feel free to comment, 'cuz I'm no expert. I just love to dick around with this stuff...
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You need to use full bridge rectifier
If I use a bridge, will that mess with the chassis ground that I'm switching the tubes with? Attached is the schematic. I'm no longer using the voltage regulator that I originally was going to use because I am getting around 5V with this circuit. But I'm wondering if I'm going to have a problem hooking the negative DC lead from the bridge to chassis ground.
Bridge rectifier with a filter cap should work .
It do no need and will not mess the ground. Look at my screen shot , there are no ground
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Bridge rectifier with a filter cap should work .
It do no need and will not mess the ground. Look at my screen shot , there are no ground
Yes as long as your relay and control switch are floating it will work.
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Bridge rectifier with a filter cap should work .
It do no need and will not mess the ground. Look at my screen shot , there are no ground
Yes as long as your relay and control switch are floating it will work.
How can you make them no floating ? Easier to built them floating
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How can you make them no floating ? Easier to built them floating
Many people use a footswitch jack that is grounded to the chassis
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How can you make them no floating ? Easier to built them floating
Many people use a footswitch jack that is grounded to the chassis
Many use isolated jack too.
I just say it is very easy ( more easy) to built that floatinf
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Wrong post
Delete
Franco
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Many use isolated jack too.
I just say it is very easy ( more easy) to built that floatinf
If you do use a footswitch, don't let the cable shield touch the chassis or you'll blow a diode!
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Many use isolated jack too.
I just say it is very easy ( more easy) to built that floatinf
If you do use a footswitch, don't let the cable shield touch the chassis or you'll blow a diode!
With plastic isolated jack, it can't happen
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With plastic isolated jack, it can't happen
I was thinking of a situation like this