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
In my experience they rarely need replacing unless they fail.I would keep a spare on hand though because when they go bad they usually just stop working with very little drama (although the other tubes are not going to light up either).
If it makes you feel better you can remove it from the socket whenever you change the output tubes and shake it next to your ear to make sure that none of the internals have worked loose. I had one rectifier tube that was sketchy and had a piece loose inside- sometimes the amp would work but after moving or transporting it it wouldn't work at all...until I moved it again.
I would not check the voltage on the rectifier tube filament, if that is what your speaking of. The voltage there is several hundred volts, and *deadly*. Even if you could measure it, it wouldn't tell you the condition of the rectifier. The high voltage will be on all the pins. That tube changes the high voltage AC, to high voltage DC. Way to risky unless you no what your doing, and have a good high quality meter capable of handling the high voltage there. Plus you would need a schematic for, and understand it.
Pardon the grammar, I just got worried about losing a new member.
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
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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]
Btw, is it possible to receive e-mail notifications when my thread is answered?

Not that I am aware of....

If you look at the Agon Home page on the lower right hind side you will see

"MyPage Login"..... Click on.

Enter your username and password.

select, "Forum Threads".... Click on.

Your threads along with posts will be shown.

Also when you are logged in you can edit your posts. That is if no one has posted after your post.
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.
06-21-11: Meisterfloh

If you look at the data sheet for the 5V4 you will see pin 8 of the tube is common to one side of the filament and the cathode. Lethal full wave DC voltage from pin 8 on the tube socket to the metal chassis (B-).

Yes you will measure 5 volts AC across #2 & #8 of the tube socket but if the meter probe was to slip and short 8 to chassis (B-) sparks are going to fly big time.....
I guess you guys are right (and I was wrong), the actual potential on the filament is quite high. Of course, it is still not a big deal to measure, but one shall be careful and not get fooled by the 5V specs :)

Anyways, I guess I have no reason to worry as long as everything sounds as perfect as it does, thanks for your answers!
Yes you will measure 5 volts AC across #2 & #8 of the tube socket but if the meter probe was to slip and short 8 to chassis (B-) sparks are going to fly big time.....

Jea48 (Threads | Answers | This Thread)

That's what I was missing. When I type, I loose my train of thought. And I'm lousy at typing.
If you look at the Agon Home page on the lower right hind side you will see
06-21-11: Jea48
Should read,
lower right hand side
.
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