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Old 14th January 2006, 11:39 AM   #1
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Default Rectifier voltage difference, Why?

A week or so ago I experienced a 5AR4 failure in one of my Quicksilver 8417 mono block amplifiers so I was forced to replace it since it requires two 5AR4's for operation. A Sovtek 5AR4 failed for no reason so I pulled the remaining Sovtek and installed two Japanese Mullards (international Brand) in their place.

Something prompted me to take a voltage check just to be sure everything was ok and I ended up with higher voltage on the Mullard tubes than I did on the two remaining Sovtek tubes in the other mono block amplifier. I switched the tubes from one mono block to the other and the voltage difference followed. The results were 465 volts B+ at the 5AR4 with the Sovtek name and 480 volts with the Japanese Mullard 5AR4 tubes.

Why? Is this the reason people say Mullards sound better?
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Old 14th January 2006, 12:02 PM   #2
SY is offline SY  United States
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Quote:
Is this the reason people say Mullards sound better?
No; by that logic, people would say that the 1N4007 sounds even better. Why people say that is sociological, not technical. Why the voltage drop from tube A is lower than tube B is technical.
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Old 14th January 2006, 12:04 PM   #3
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Are the Mullards superior because there is less voltage drop?
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Old 14th January 2006, 12:23 PM   #4
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Superior in that they have less voltage drop. But that's not the only critereon. Reliability, noise, and warmup time are important.

But the most important of all is the ink.
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Old 14th January 2006, 12:34 PM   #5
Giaime is offline Giaime  Italy
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Have you tried other 5AR4? I say this because I've heard that Sovtek rectifiers are made after soviet tube types, that are a little different than european GZ34 or american 5AR4. I remember reading tests that showed the Sovtek 5Y3 as a far less voltage dropper than NOS 5Y3...
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Old 14th January 2006, 12:41 PM   #6
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Giaime

I have four NOS GE 5AR4 rectifiers in another pair of 8417 amplifiers and I will check the B+ just for ***** and grins. I am far from being happy with the Sovtek brand of 5AR4 rectumfiers. They seem to have a short life in anything I put them in. The GE 5AR4's have been running for years without problems. Some people say the 5AR4 Sovtek's are just relabeled 5Y3's.
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Old 14th January 2006, 12:47 PM   #7
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Quote:
Originally posted by burnedfingers
Some people say the 5AR4 Sovtek's are just relabeled 5Y3's.
That should explain something, and also the fact that my Amperex GZ34 (Philips marked) has worked for 20 years on a 100uF cap and still tests strong...

Btw I discovered that it was 100uf (a multisection cap, 50+50 but connected in parallel) only because the cap died before the tube
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Old 14th January 2006, 01:57 PM   #8
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This is strange, because I found the opposite. If any of you follow some of the other threads that I have written, you will know that because of bad experiences with Sovtek 300B's, and poor customer service, I swore never to buy them again. When I was building my 845SE, I called Ned at Triode to get some Chinese 845's. He said that he had Sovtek 5AR4's (newly released at the time). He offered to take them back if I didn't like them, so I got 4. I do all of my initial amp experimentation with "expendable" tubes.

The amp uses 2 5AR4's in a voltage doubler circuit with a 480 volt industrial transformer (very low winding resistance). The input caps are 50uF. B+ is around 1100 volts. I am using the 5AR4's as turn on delay. I have run the output tube bias as high as 110 mA per tube (220Ma total). This design should be tough on rectifier tubes.

After the amp was finished I tested several brands of 5AR4's both for sound, and output voltage. I did not try any of the high end brands. The Sovteks consistently put out the most voltage and provided the best musical dynamics. The difference in sound could have been caused by the difference in voltage. I tried Japanese International, Wegtinghouse (Chinese) RCA, and some JAN military surplus. There was a 40 volt difference between the best and the worst, but I can't find the paper with the test results on it. The Sovteks have been in the amp ever since, with no incidents.

Maybe the circuit accounts for the different results, or maybe I got a good set of Sovteks, and you didn't. I have seen wide lot to lot variations is Sovtek tubes. All (4) of the 300B's that I bought from a local tube vendor died within a year, but 4 that are older are still going strong after 4 years of continuous use.

Quote:
Some people say the 5AR4 Sovtek's are just relabeled 5Y3's.
Actually the Sovtek 5AR4's that I have look like a copy of the Mullard design. I have seen a Sovtek 5Y3 that looks like a relabled 5AR4. It has a cathode in it. This could be dangerous in a guitar amp that runs the output tubes hard. A 5AR4 will give you more voltage than a 5Y3.
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Old 14th January 2006, 02:10 PM   #9
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I appreciate your comments. I had one 5AR4 Sovtek that the heater went open and the other one recently delivers no DC anymore. This is from the second batch of 5AR4's Sovtek. I guess I am in error judging the Sovtek 5AR4's because I could have gotten some bad ones. I will recheck the DC voltage of the International (Mullards) and the GE's as well as the Sovteks to seeif I have made an error.


WoW! an 845 SE amplifier! Someday I hope to follow in your footsteps and build an animal like that. I have a nasty power supply that is capable of over 2000VDC @ 200mA. It has a voltage doubler in the circuit so I assume it would be capable of around 400mA at half the voltage if I run it without the doubler? It puts out 1180 vac with 118 ac in.
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Old 14th January 2006, 02:19 PM   #10
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Quote:
Originally posted by burnedfingers

WoW! an 845 SE amplifier! Someday I hope to follow in your footsteps and build an animal like that. I have a nasty power supply that is capable of over 2000VDC @ 200mA. It has a voltage doubler in the circuit so I assume it would be capable of around 400mA at half the voltage if I run it without the doubler? It puts out 1180 vac with 118 ac in.
That will be quite a beast. May I suggest a PP one?
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