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5AR4 or something else??

6/8/1999 3:39 PM
5AR4 or something else??
I just purchased a 5AR4/GZ34 for my Princeton Reverb and it's very strange. It was sold to me as NOS and is branded National Electronics 5AR4/GZ34 made in the USA. It is different than my Mullard; it has a base like a 5Y3, yet the bottle looks like a 5AR4 and it has all 8 pins rather than 5 like my Mullard. The strange thing is what happened when I plugged it in. When I first plugged it in, I was getting 385vdc on the plate of the 6V6's and about 25ma's of current each. After playing guitar through it for about 10min, I get 339vdc on the plate and 23ma's of current! I then plugged my "known good" Mullard in there and get 428vdc and 27ma's of current (more reasonable for a 5AR4. Do you think I have a fake 5AR4?? The tube sounded decent, yet it wasn't as clear in the low-end as the Mullard. BTW, I have modded my PR to cathode-biased. Oh, I put the questionable 5AR4 on my emission tester and it tests in the bad range. I contacted the seller and he tested it on his Hickok before it was sent and says it's NOS. I know that emission testers can be inaccurate.  
Thanks for any help!  
6/8/1999 4:51 PM
Troy, try this test: A 5AR4 has a cathode where a 5Y3 doesn't. Measure the warmup time of the tube. A 5AR4 will take several seconds for the output to ramp up to full voltage because the cathode is heating up. A 5Y3 will obtain full voltage in a couple of seconds.  
You could also have a mislabelled or a defective tube that starts breaking down after it runs for awhile. Another,heated cathode tube, which resembles a 5Y3 is a 5V4, but has a lower current rating than a 5AR4.  
6/8/1999 7:49 PM

Thanks Bob! If my memory serves me correctly. That questionable 5AR4 took little time to warm up. And it didn't glow like the Mullard either. I'm inclined to send it back (it is guaranteed), yet it gave such a huge voltage drop, that I'm curious to try it in other amps to see if it "browns" the sound a little more. I don't want to keep it though if it's defective and ready to short out!  
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