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Old 4th May 2008, 11:54 PM   #1
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Default Different 5AR4's have different voltages and warm up time.

Recently I ordered two JJ 5AR4 rectifier tubes to try because I haven't had the best luck with the Sovtek brand. I noticed that the bias was lower and so was the b+ voltage.

I tried a Sylvania 5AR4 and got 472 VDC at the rectifier tube and the warm up time was about 7 seconds.

I tried a JJ and got 469VDC with a warm up time exceeding 15 seconds.

I then tried a International and got 475VDC with a warm up time of 13 seconds.

A SS rectifier was then tried and gave 491 VDC.

Last I tried a 5U4 and it gave 442VDC with a fast warm up time.

Question is why is there a difference among the different 5AR4 tubes?
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Old 5th May 2008, 01:01 AM   #2
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Default Re: Different 5AR4's have different voltages and warm up time.

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Originally posted by burnedfingers

Question is why is there a difference among the different 5AR4 tubes?
Hah! I'll answer that. It's because standards and specifications mean very little to the foreign tube manufacturers of today. Specifically China and Russia. I remember when Chinese imports first began to come into the U.S. in the early nineties. They were deplorable. Sure they looked good, but wouldn't test worth a damn. They were very good at copying the look, but dismal failures at copying the preformance. Yea, they've gotten better at it over the years, but they still can't hold a candle to the old American made tubes of yesteryear where quality control meant something. And the Ruskies are only a little bit better themselves.

I say this because, being self employed in the business, I spent years at a friends testing operation in New Jersey. JFF Research was a tube testing facillty that did work for all the well known surplus tube dealers of the time. Unity, Calvert, Jaro, Aero, Lowell, Jolida, Penta, even Richardson to name a few that I remember. They even ran some 6550s for Audio Research at one time. Although most testing was for industrial tubes, receiving types were also done. I watched the meters and saw the results. I also learned a lot about testing. Most of the instruments used were custom built by the owner. When he finally retired and closed the doors in the late nineties, I acquired two of the testing racks. These now reside in my basement and are still functional.

Victor
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Old 5th May 2008, 03:05 AM   #3
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Default Re: Different 5AR4's have different voltages and warm up time.

Quote:
Originally posted by burnedfingers
I tried a Sylvania 5AR4 and got 472 VDC

I tried a JJ and got 469VDC

I then tried a International and got 475VDC
Taking the Sylvania's voltage as the standard, the others deviate by less than 1%. I'd imagine a batch of all Sylvanias could deviate by more. I think you need more data points.
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Old 5th May 2008, 03:11 AM   #4
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Default Re: Re: Different 5AR4's have different voltages and warm up time.

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Originally posted by dsavitsk


Taking the Sylvania's voltage as the standard, the others deviate by less than 1%. I'd imagine a batch of all Sylvanias could deviate by more. I think you need more data points.
I totally agree, and other than with early Chinese 5AR4 which seem to have slightly higher forward drop my experience has been similar with the Mullards I tend to favor as well.

I have had problems with the thinner glass particularly in Shuguang made samples where overly rough (read relatively gentle) insertion resulted in failure. (White death syndrome, or how'd the air get in there? ) I had some problems with arcing, but have seen this with genuine Mullard and Telefunken 5AR4 in ST-70 amongst others.
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