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In Reply to: RE: Anyone compare these? posted by Winston Smith on October 29, 2016 at 12:31:11
I just checked out the ad for those Phillips tube and I am surprised that he would have these listed as "5ar4/5u4g. It is rather loose tube cross referencing. Those tubes will all "work" in the socket that can use any of those tubes but the specs are different. The 5u4 requires 3A current, while the r4 and ar4 only need 2A for the heaters. The u4 and r4 have directly heated cathodes whereas the ar4 is indirectly heated hence the ar4 has a "slow warm up" while the other 2 rectifiers will have a huge voltage surge before the tube starts rectifying and the B+ settles down to normal. I would call it irresponsible for him to cross reference a 5r4 with a 5ar4 since a newbie would not know the difference and might blow up his capacitors if the amp is designed for a 5ar4 and the caps are only rated to 450 or even 500vdc.
Follow Ups:
The differences between the 5AR4/GZ34 and the 5R4 are very substantial. About the only things the 2 types have in common is the 2 A. filament current draw and a 250 mA. B+ capability.
Forward drop in a 5AR4 is comparatively small, while it is a whopping 67 V. @ 250 mA. in a 5R4.
The 5AR4 tolerates substantial capacitance, at the PSU filter's I/P. The 5R4 is not nearly as tolerant of I/P filter capacitance.
The direct, as opposed to indirect, heating has already been mentioned.
The PIV rating of the 5R4 is greater than that of the 5AR4.
Don't let greedy and/or non-knowledgeable sellers take your hard earned money.
Eli D.
Upscale tubes has been around almost from when i started collecting tubes which i will not count but suffice it to say, a good long time. As the saying goes "he should know better! , Kevin that is.
Now the greedy part, it goes without saying that he probably financed his move into his new building by selling those 5RGYA as 5AR4 to unsuspecting noobs.
Graph may help.
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