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Positive Feedback ISSUE 68
july/august 2013


Hot Review: The NOS Philips 5R4GYS Rectifier Tube (Replaces GZ34/5AR4) - Bargain Priced! Awesome Sound!
by Robert H. Levi


This 1960's made tube developed for rugged video application has been found in quantity by Upscale Audio, in Upland, CA. Kevin Deal searches the world for new old stock tubes hidden in the wildest places, and he struck gold here! It may have been made for video, but it kicks ass for audio!!

From Upscale:

Product Description

The best buy and best made 5AR4/5U4G/GZ33/GZ37 that we have or ever had. Made in Holland, where the famous Amperex Bugle Boy tubes were made.  First-rate, absolutely stunning tubes. Available now at a crazy bargain. This is because I made a nice score on them, but take my word, they will go for $100 each eventually. 

NOTE: Like the 5u4g, these are a bit taller than a typical 5AR4. They require 5 inches of clearance from the tube socket base to the top of the tube. (At lease 2 inches taller than the 5AR4.)This is mostly for folks who may want to use these in an enclosed piece of gear that may have limited clearance... if your equipment keeps them out in the open, the ST-shaped glass will look stunning. They will fit the DiaLogue pieces quite well with cage on.

The Sound

I compared them to the holy grail of rectifiers, the Mullard GZ34/5AR4 which I bought used for $80. New is $250, if you can find them. In the ModWright PS9 Power supply and in a Dynaco Stereo 70, the Phillips worked wonders. I experienced more definition, more subtlety, more elegance, tighter imaging, fleshier, quicker, added depth, and just more realism. Vocals are better than ever, and alive with inner definition and nuance.

This is a ModWright alert for sure. If you use the PS9, get this tube, but forget the cage. It is two inches higher than the cage top. Amazing improvement will be on tap! You will be stunned by the overall improvement over the stock tube, or your NOS upgrade you paid dearly for. They should work well in any Cary application. Ask Upscale for advice on this.

The 5R4GYS is totally compatible with the GZ34/5AR4 so no worries. Plus, here's the good news! They cost only $55 new and tested in the box from Upscale Audio.

Since 5AR4's last 20-30,000 hours, do not wait until your tube dies to buy this, because Upscale will run out. Buy one or two now and take your precious Mullard and keep it as backup. The Philips is way beyond the GE, HT, Sovtek, JJ, and any others. I have tried them all I assure you. This is a cut above the PrimaLuna-made tube as well, and I really like the PrimaLuna rectifier a lot.

The 5R4GYS is a great looking tube, too. It has brought new life and authority to my ModWright Sony which I already considered reference grade. Kevin, keep up the great work and good hunting! The Philips 5R4GYS Rectifier Tube from Holland is the very best I have heard and tested to date! Highest recommendation!

5R4GYS Rectifier Tube, Upscale Audio MSRP: $55

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