[Markwatkiss]

4 your consideration one pair of NOS RCA 5R4GY Rectifier tubes branded Westinghouse.Manufactured in the USA 1950.Black plates,square getter.The 5R4GY is a variant of the 5AR4.Comes complete with original factory boxes.
A highly regarded rare tube that will complement any sophisticated tube based amp.Offered at $175 for the pair or $95 each.Shipping within 24 hours of payment and I would invite you to check my audiogon feedback under my AudioCircle user name.

[sfox7076]

I am not trying to derail your sale, but I think we need some clarity.  I  will start by saying that I love 5R4GYs.  They are great tubes and I prefer them to 5AR4s in most applications (I really like directly heated tubes).  All that said, the 5R4GY is in no way a variant of the 5AR4 (unless you just mean they are 5v rectifiers).  They certainly are not interchangeable in all uses, though they are in some. 

First, the 5R4 is directly heated (cathode is the filament).  5AR4 is indirectly heated.  That means that when you power it up, the 5R4 does not bring the B+ up slowly, it just goes on.  5AR4 has a longer warm up time because the filament heats the cathode up, so B+ comes up slowly. 

The 5R4 also has a much greater voltage drop.  At average rating power, it's about I think about 65 volts vs. a 15 volt drop for the 5AR4. The B+ from the 5AR4 will be higher than the 5R4 (assuming the circuit is otherwise unchanged). 

The RCA 5R4GY spec sheet suggests that in the power supply a 4uf capacitor should be used as the input filter.  The 5AR4 suggests that there be a 60uf capacitor as the input filter. 

There is also a 10% difference in heater current draw (5r4 takes more).  That would, I hope, not overtax the 5v winding, but you should check the current capability of the 5v winding of your transformer.

Shawn

[hibuckhobby]

Accurate information.  Worth mentioning though that OP did not say they were equivalents,
but rather a variant.  He also made no allusions to the interchangeability of the two.
Hibuck....

[Markwatkiss]

Thank you for your input Shawn,it is not my intent to mislead anyone.Hibuck is correct I did not say equivalent,although I have inter changed 5R4GY's and 5AR4's in my amp with favorable results.