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

Hi all, this is my first post here, and I would appreciate some help! :)

I have a custom made pre+amp built on 4 triodes and a 5V4G rectifier. The triodes are relatively easy to keep an eye on (I am measuring the cathode current), but what about the rectifier? How do I test whether it is still in a good shape (preferably, without removing it from the socket)? Would measuring the actual filament voltage (that is directly fed from a secondary winding) tell me whether the tube is still alive?

Thanks!
meisterfloh
hifihvn
943 posts
 
Pardon the grammar, I just got worried about losing a new member.
hifihvn
943 posts
 
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]
hifihvn
943 posts
 
Retry Dynaco link above[http://www.triodeel.com/dynamk3.gif]
jea48
4,446 posts
 
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
.
meisterfloh OP
15 posts
 
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! :)
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