Can't work this out myself

wayneh

Joined Sep 9, 2010
17,498
We need a little more context about what you're doing, especially since these are dangerous voltages.

What load are you powering and what is the power supply?
 

Thread Starter

Colin Chandler

Joined Oct 2, 2018
38
This is all new to me, I'm powering a tape echo machineView attachment 162277
I've put a meter between the supply and load with everything on and it draws 9.98ma 358vdc
The supply is a transformer from a guitar amp with an EZ81 rectifier valve,
Should I use a bridge diode instead?
Thanks for your time
Colin
 

wayneh

Joined Sep 9, 2010
17,498
This is all new to me, I'm powering a tape echo machineView attachment 162277
OK, let's dig into the details a bit more and see if we can't sort it out.

This machine must have a recommended power supply, perhaps written on the label? What is it supposed to plug into normally and why aren't you just using whatever that is? In the schematic, where are you applying power?
I've put a meter between the supply and load with everything on and it draws 9.98ma 358vdc
There are a lot of ways to get measurements that are confusing at best, and it's possible to short out equipment when trying to measure current if you put the meter in parallel (as you do when measuring voltage) instead of in series. Are you using the AC or DC scale? Most meters will measure only DC current in mA, not AC. Where and how are you making your measurements?
The supply is a transformer from a guitar amp with an EZ81 rectifier valve,
Should I use a bridge diode instead?
It's impossible to comment on the supply until we understand what the load requires. A diode-based rectifier bridge will likely be more efficient than a tube rectifier but let's solve the rest first.
 

Thread Starter

Colin Chandler

Joined Oct 2, 2018
38
OK, let's dig into the details a bit more and see if we can't sort it out.

This machine must have a recommended power supply, perhaps written on the label? What is it supposed to plug into normally and why aren't you just using whatever that is? In the schematic, where are you applying power?
There are a lot of ways to get measurements that are confusing at best, and it's possible to short out equipment when trying to measure current if you put the meter in parallel (as you do when measuring voltage) instead of in series. Are you using the AC or DC scale? Most meters will measure only DC current in mA, not AC. Where and how are you making your measurements?
It's impossible to comment on the supply until we understand what the load requires. A diode-based rectifier bridge will likely be more efficient than a tube rectifier but let's solve the rest first.
I've built it from the schematic, I don't have the same transformer, the one I have is connected to the ez81 and the dc out put from the ez81 is 358.5vdc with nothing connected, i.e. The wire from the valve is not in circuit just the end of it to my multimeter, should I check the voltage with it connected under load?
Colin
 

wayneh

Joined Sep 9, 2010
17,498
I've built it from the schematic, I don't have the same transformer, the one I have is connected to the ez81 and the dc out put from the ez81 is 358.5vdc with nothing connected, i.e. The wire from the valve is not in circuit just the end of it to my multimeter, should I check the voltage with it connected under load?
Colin
Ah, OK, I'm beginning to understand. Do you already have a solution for V2, which I suppose is for the tube heaters?

Assuming you have that worked out, it looks like you need just 10mA at 280 VDC. I'd be tempted to set up a resistive divider using maybe 50mA total. That might look like two, 4.7KΩ resistors (20W rated) in series across the transformer output. You'd tap off the center of those two and see what voltage appears on the first cap after your bridge rectifier. This may take some fiddling with the values to get it to the target.

The problem with this approach, in addition to the big hot resistors, is that the voltage will vary depending on the power usage by the machine. If that varies, so will the voltage. But if the variation is really within 0-10mA, the voltage won't vary all that much. I'm sure there are more elegant approaches (such as voltage regulators) but the high voltages are unfamiliar to me. Maybe someone with the right chops can show us the way.
 

Thread Starter

Colin Chandler

Joined Oct 2, 2018
38
Ah, OK, I'm beginning to understand. Do you already have a solution for V2, which I suppose is for the tube heaters?

Assuming you have that worked out, it looks like you need just 10mA at 280 VDC. I'd be tempted to set up a resistive divider using maybe 50mA total. That might look like two, 4.7KΩ resistors (20W rated) in series across the transformer output. You'd tap off the center of those two and see what voltage appears on the first cap after your bridge rectifier. This may take some fiddling with the values to get it to the target.

The problem with this approach, in addition to the big hot resistors, is that the voltage will vary depending on the power usage by the machine. If that varies, so will the voltage. But if the variation is really within 0-10mA, the voltage won't vary all that much. I'm sure there are more elegant approaches (such as voltage regulators) but the high voltages are unfamiliar to me. Maybe someone with the right chops can show us the way.
Yes the tube heaters are sorted,Thankyou for your help, regards colin
 
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