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

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]

Meisterfloh, I forgot about this. I don't know of any email notification from them. You can put a link at the top of your search page to click on, and see what changed as far as other people posting on your thread, and any threads you may have posted an answer on.

Even if it was a 5U4, there will be dangerous voltage everywhere. Maybe read some tube theory books. It's to hard for me to explain. A long time since I learned this. Some are directly heated, others are indirectly heated. The risk is still there with both. 5U4 link. Plus RCA tube manual links that have some theory about tubes. [http://www.tubezone.net/pdf/5u4.pdf] [http://www.tubebooks.org/tubedata/RC20.pdf] [http://www.tubebooks.org/tube_data.htm]