Many of the so called NOS tubes are actually OUT (Old Used Trash). Be careful when you buy them.
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I'm trying to persuade Sophia Electric to make a 5AR4/GZ34 rectifier tube that would replace the Mullard NOS in my Modwright LS100. I am already using Sophia's 6SN7's and they are wonderful. So, anyone else interested please send them an email and let's see if we can encourage them to add to their product line.
Just to be on the safe side, don't try a 5AR4 in an amp that calls for a 5R4. The 5R4 can handle more voltage, so stay with the one the manufacturer of the amp recommends.
Some tubes in power supplies handle a lot of voltage relative to their maximum voltage. As such, they will wear out relatively quickly. If I were you, I would ask Jadis what voltage that tube is exposed to in the power supply. If it is close to the maximum voltage specified for that tube type, then you are going to have to replace the tube more frequently, unless there is a more sturdy version of that tube type available (for example, the "GTA" and "GTB" versions of the 6SN7 can handle 50% more voltage than standard 6SN7's), or an alternative tube available that will work in that application and that can handle more voltage. If you have a good, trustworthy tube vendor, another alternative would be to have him screen a large quantity of 5R4's in order to find the top two or three performers - there is often great variation in performance between tubes of the same type and brand (like dogs and people), and the better performing tubes stand a better chance of withstanding the stress of the application.
Whenever a tube is run near its maximum voltage level, it will die relatively quickly because of the extra heat.
I've only had a couple of tube rectified amps,most were old designs, like the old 1961 Bell.
What I have been using for the last year of trouble free listening is a DecWare Zen Select.
I came across a collection of old 5U4GB rectifier tubes from RCA and Sylvania to name a few.
I never thought a rectifier tube change from the stock one would make that great a difference, but it did.
Now here is the nice part,they measured 60 on a tube tester,so they were still good.
The even better news is that in the DecWare amp, they should last longer than I will.
I suppose it depends on the amplifier design,but I think the Op's rectifier tubes may not have been all they were cracked up to be.
I don't think rectifier tubes are as prone to wearing out as fasat or faster than the output tubes, at least not in any amps that I am familiar with.
Perhaps there is something wrong with the amp.
It may not be the tube's fault, and if it was me, I wouldn't spend any more money on tubes until I had a tech go over the amp.