Testing tube amp 5y3 rectifier without load

[JMicro]

Im building an amp and want to test the power supply. Is it safe to test a 5y3s output with no tube or other main circuit load. It would just be the transformer, the 5y3 thats connected to 3 450v caps with a 1.2k and 22k 1watt between the caps nothing else for a load and i want to check the 3 voltages. I saw something about transformer arcing with no loads
Thanks

 

[cademan]

Voltages may be a little high but your okay. Arcing would normally happen if there were a load and or a short in the transformer loaded.

It would be even better if you had a variac.

 

[JMicro]

Thanks
I was planning on bringing it up slow on my variac and dim bulb tester. I will monitor voltage to caps. I want to make sure its all good before I continue.

 

[knockbill]

Watch the voltage out as you ramp it up with no load,,, may get past the caps limit quickly... the voltages thru the stages won't change much without a load...

 

[JMicro]

I noticed that today. My volt supply should be 345, 330 and 225. I have 2 resistors one between each cap. I only got to 100v ac on the Variac and was at 400v dc all the legs were pretty close in volts even with the resistors. I wanted to make sure my transformers worked OK and they did. I put in an old working 5y3 didnt check my 5v heater voltage but the tube did work. I also run it though a dim bulb just to be safe and to lower the current.
Thanks for your input.
John

 

[kvflyer]

John, you probably already know but since you have no load on the B+, all voltages are correct being the same. And there should be no problem with the power transformer arcing with no load. Also, as was also mentioned, no load could possibly harm the filter capacitors. But I would not worry. If you need to run the power supply for any length of time, you could tack a resistor on the last filter.

 

[JMicro]

This thing was gutted when I got it. The 6.3v heater supply was hooked up on both 12au7s but not on the 6v6s and the 6au6. Wondering if It should be one big long daisy chain. If so I can finish my heater wires on the 6au6 then cross over to the 6v6. I would then have the higher current draw at the end. Not sure that would be good.
Here is the schematic

 

[JMicro]

John, you probably already know but since you have no load on the B+, all voltages are correct being the same. And there should be no problem with the power transformer arcing with no load. Also, as was also mentioned, no load could possibly harm the filter capacitors. But I would not worry. If you need to run the power supply for any length of time, you could tack a resistor on the last filter.

thanks

 

[gadget73]

its not quite enough for me to read, but I see that the heater supply appears to have 3 letters marked on it. You'd have to look at which connections are marked on the tubes and route your heater wiring to match. Looks like its marked X, Y, Z, and you'll find that marking just under each tube to tell you where it goes.

 

[JMicro]

its not quite enough for me to read, but I see that the heater supply appears to have 3 letters marked on it. You'd have to look at which connections are marked on the tubes and route your heater wiring to match. Looks like its marked X, Y, Z, and you'll find that marking just under each tube to tell you where it goes.

Thanks

 

[JMicro]

I take that back my 6v6s are ok on heaters I was going by memory before I just looked at the unit. the 6.3 goes to 6v6s first then crosses over to 12au7s and 6au6 last the 6au6 was needing the heater wires I run one from the last 12au7 (Z) then its gets that y leg. It looks like all the heater connections are similar except the last one the 6au6 that z and y. All else is x and z.

 

[trainbuftony]

Somewhere in a data sheet somewhere it says that if you are operating a 5y3 horizontally, that certain pins must be vertically aligned otherwise the heater may sag, contacting the plate and creating a lightning show within the rectifier as soon as the filament gets good and hot. That data sheet, while technically correct is not the reason that this info sticks in my head. Be careful with your testing, and always operate 5y3s 5u4s, and any directly heated rectifier in a vertical position, never horizontally.

 

[JMicro]

good to know thanks

 

[kvflyer]

And to support what was mentioned above, this link to 6 pages explains how to mount the tube horizontally if required. Vertical is always preferred but details below. “Everything you ever wanted to know about a 5Y3G/GT!”

https://frank.pocnet.net/sheets/049/5/5Y3G.pdf

 

[JMicro]

Thanks
I am big fan of the frank tube data scans