When does a 5V4G/GZ32 have to be replaced?

I'll to try to give you a little idea, why you wouldn't measure the 5 volts on the filament. There would be the full B+ plus high voltage on it *also*. That is why it is dangerous. Pin 8(rectifier tube) on this Dynaco amp (link below), has the output from pin 8 (high voltage DC ) coming out of it (rectifier tube) to feed the filter caps, and choke for the B+ high voltage. I don't know your amp, but on this one, that it basically where the high voltage for the B+ originates. With the schematic, it would tell the proper voltage that should be there. This amp shows 480 volts after the choke. Risky high voltage. That's why you need to know what is happening, and I don't recommend trying to measure it. Dynaco Mk3 link [http://www.triodeel.com/dynamk3.gif]

Retry Dynaco link above[http://www.triodeel.com/dynamk3.gif]

Meisterfloh,

Get it tested or just buy a new one....

It would seem to me if the tube were to short you could burn out the 5 volt filament winding or possibly the high voltage winding of the power transformer.
The tube is by far the cheaper of the two.

http://www.r-type.org/pdfs/5v4g.pdf

http://www.r-type.org/exhib/aaa0597.htm
.

Hi Guys,

Thanks a lot! Btw, is it possible to receive e-mail notifications when my thread is answered?

I do have schematics of my amp. In particular, unlike the Dynaco, in my case 5V4G has its own secondary that is used just for its filament, so there is no high potential there. The reason I was asking was that I had no idea (neither did the guy who had designed and built this outstanding piece of art for me) how exactly a tube rectifier starts to behave when the tube's emission becomes too low. As the 5V4G is only used to get the plate voltages for the triodes, I would expect that when it starts to die those voltages go down, but that's just my guess; besides, the plate voltages are high indeed, and somewhat inconvenient to measure...

I have access to a (friend's) tube tester, I use that when I buy new tubes, but it would be nice if I could check the condition of a working 5V4G once in a while without a tube tester. And measuring the cathode current allows me sometimes to do things without a tube tester: for example, I match the voltage on cathode resistors of 417A-s in order to find matching pairs. Right now I do not have any issue with 5V4G, I am asking to have this information in future when I need it (the rectifier is the only tube in my amp that I do not know how to watch "locally").

Btw, what is the life expectancy of a new 5V4G?

Thanks for your hospitality here at forum.audiogon, and for your worries not to lose a new member! :)

This is part of my concern. When you look at the diagram for the 5V4, the cathode and heater are tied together. That will put the voltage of your filament to from what I learned. Actually, they refer to pin 8 as both the heater, and cathode.

With this in mind, I believe you'll have the high voltage in your filament transformer too, and reason for the risk. I'll post the link below. If it doesn't work, just copy and paste. Might be to small, or something their system doesn't like about some small, and real large links.

I don't now if there are any common rules for the way the tube would act. They seem to lose voltage, and current when they get weaker. Sort of like a tired car battery acts. The lights get dim (low voltage) and it doesn't have the current to spin the starter fast enough. All amp designs would probably act different as the tube rectifier tube weakens. So the B+ high voltage should stay in the range the amp designer wants it to be.

The one tube link is from Jea48's post(Sylvania) , the other is from a RCA manual. You'll see they both agree with the pins being tied together, like I mentioned, that will put the high voltage on the filament supply in any amp they are in, including yours. [http://www.r-type.org/pdfs/5v4g.pdf] [http://www.tubezone.net/pdf/5v4.pdf]