Re: TEK514 needs new 5V4G tube


greenboxmaven
 

First, you need to do research on which one the AudioPhools go bonkers over! Then search for the one they reject. I have actually seen technicians and customers try a dozen different brands and types of 5V4s, trying to find the one that sounded best to them. I have seen them claim they can tell the difference between silicon rectifiers made by General Electric or Motorola. Some of the old metal 5V4s were of very unique construction. The envelope was a perforated metal screen. Inside were two metal cylinders- the plates, with seals at each end of the cylinders where the filament connections went in and out, and of course to seal the vacuum. So far, all of the Tektronix scopes I have seen will accept all three types. For testing, use a 5R4. They tend to be far more plentiful. They are probably not good to leave in the scope, they do have a higher forward drop than a 5V4 and are directly heated. On the other hand, they are far less likely to be fatally damaged if you have not yet found the short or cause of the overload. When working on any device using an indirectly heated rectifier, check the power switch, fuse holder, wiring, and any power connectors or cords for intermittent connections. A serious abuse of a 5V4 is to interrupt the power for a few seconds and then restore it if you have a condenser input filter. It is fully heated, the filter condenser is discharged, and the inrush current to recharge the condensers is brutal. If it is a choke input filter, there is usually no problem.

Bruce Gentry, KA2IVY

On 1/28/20 12:56 PM, Chuck Harris wrote:
Back in the olden days, if you saw:

5V4, you were talking of the metal envelope tube.
5V4G, you were talking of the coke bottle glass tube.
5V4GT, you were talking of the straight sided glass tube.

Metal tubes largely fell by the wayside, as they were
expensive to make, and caused problems with capacitance...

5V4GA, is typically an outlier, as it should be marked as
5V4GTA, but the "T" envelope was standard by the time any
of the letter revisions came out, so the nomenclature
revised it to simply "GA".

-Chuck Harris



Steve Hendrix wrote:
At 2020-01-28 12:11 PM, Tom Phillips wrote:

Note that, per the RCA tube manual, the 5V4G and the 5V4GA have the same
electrical specs but he 5V4G is packaged in a larger old style bottle. If
you fine one, you will need to determine if it will physically fit your
scope.
Thank you for that clarification. I was puzzled by the fact that two adjacent 5V4G tubes were in different bottles. So if I'm reading your comment correctly, the straight-sided, smaller one is newer (possibly replaced at some past time) and the bad one in the larger "coke bottle" glass is older, possibly the original.

Also thanks for the tips on a good source.

Steve Hendrix



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