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Post subject: 65 DRRI rectifier tubes
Posted: Wed Nov 20, 2013 4:37 am
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Ran a search about these and came up with no results.
Does it matter all that much if one tube measures higher than another given the same output tubes?Lets say tube A reads at 431v and tube B reads 419v,does this matter at all to the output tubes/amp if the bias setting on the output tubes is set to yield the same idle plate wattage(lets say 10 watts). If I understand this correctly and do some math,.024 x 431 = 10.34 and .025 x 419 = 10.47.Does one way sound better than the other and is it better to run the lower voltage rectifier?Just curious/thinking about different things with the new amp,didn't come up with much info on my own.


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Post subject: Re: 65 DRRI rectifier tubes
Posted: Wed Nov 20, 2013 6:04 am
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Hi rhythmism,

It is best to use the correct rectifier tube, which is a 5AR4, and with the correct output voltage. There is more to a rectifier tube than just output voltage, such as heater current draw.

But, yes, you have the right idea as far as biasing to the desired wattage. If a rectifier tube is weak, low output voltage, then it could be a bad sign for that tube.

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Post subject: Re: 65 DRRI rectifier tubes
Posted: Thu Nov 21, 2013 7:16 am
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Hi Shimmilou
What I was up to was changing the power tubes as a set,(5ar4 and the 2 6v6s)stock vs new.Thought there might have been some sonic or longevity benefit from running the set with the lower voltage.
Thanks for your reply


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Post subject: Re: 65 DRRI rectifier tubes
Posted: Fri Nov 22, 2013 6:47 am
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rhythmism, sorry to but in... but... :D

Plate voltage is not the only factor in tone and tube life. Really, the idle watts of dissipation is more important factor. Watts takes into account plate voltage and idle bias current, where:

Watts = *(plate volts) times (idle bias current, in amps)

* not taking into account the small dissipation between cathode and signal grid.

So you can have higher voltage if you compensate with lower idle current to get the same watts of dissipation, at idle.

One thing about power supplies. Higher plate volts can cause issues, if the power supply is under-engineered and/or the bias power supply is also weak. Steady, consistent power and idle bias are two of the big factors in tube life.


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Post subject: Re: 65 DRRI rectifier tubes
Posted: Fri Nov 22, 2013 9:02 am
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BMW2002Ti wrote:
Steady, consistent power and idle bias are two of the big factors in tube life.


+1000

That, plus the number of times a tube is cycled (heated up and cooled down). Tubes seldom fail during actual use -- they're actually quite similar to an incandescent light bulb.

Arjay

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Post subject: Re: 65 DRRI rectifier tubes
Posted: Sat Nov 23, 2013 12:53 am
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Thats ok BMW2002Ti "but" right in there.It has taken me quite some time to acquire this amp(new) and I need to take care of it and to make sure it'll last.I thought some of the folks here who have had this amp for awhile might have found a sweet spot or pitfall as to what voltages are recommended and or prefered,being passed through the rectifier.I'm sure it has a range of acceptable voltages and would like to stay within that range.The output tubes will probably react differently to the voltages supplied from the rectifier,some 6v6s might prefer voltages in the high range while others might not like to be driven as hard.
Thanks for your comments and was able to track down some affordable 6201s.


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Post subject: Re: 65 DRRI rectifier tubes
Posted: Sat Nov 23, 2013 5:47 am
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In my experience, the old 1950-60 6V6GT and GZ34/5AR4 were some of the toughest tubes made. And it's reflected in the liberties that amp makers of those days used in applying these tubes. Both tube type were pushed pretty hard.

No one realized how tought these tubes were, until they tried new issued tubes in their old amps --- and started popping resistors and fuses. As far as I know only the JJ 6V6S can handle those amps that placed close to 450VDC onto the anode plates. And there is yet to be a new issue GZ34/5AR4 to compare to the original Mullard GZ34, Sylvania or GE 5AR4 --- in both steady high voltage and current ouput, over a long period of time. For hi-fi amps that really asked a lot from the GZ34 (like the Dynaco ST-70, pushing four EL34's) --- prolly best to go to a solid-state replacement.


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Post subject: Re: 65 DRRI rectifier tubes
Posted: Sat Nov 23, 2013 10:24 am
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BMW2002Ti wrote:
In my experience, the old 1950-60 6V6GT and GZ34/5AR4 were some of the toughest tubes made. And it's reflected in the liberties that amp makers of those days used in applying these tubes. Both tube type were pushed pretty hard.

No one realized how tought these tubes were, until they tried new issued tubes in their old amps --- and started popping resistors and fuses. As far as I know only the JJ 6V6S can handle those amps that placed close to 450VDC onto the anode plates. And there is yet to be a new issue GZ34/5AR4 to compare to the original Mullard GZ34, Sylvania or GE 5AR4 --- in both steady high voltage and current ouput, over a long period of time. For hi-fi amps that really asked a lot from the GZ34 (like the Dynaco ST-70, pushing four EL34's) --- prolly best to go to a solid-state replacement.


The DRRI only pushes 410VDC to the plates -- well within the parameters for most quality-built GZ34/5AR4 re-issues. As for the power tubes, longevity will be extended by keeping the idle bias at a reasonable level and religious use of the standby switch during the power-up and power-down procedure.

Arjay

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Post subject: Re: 65 DRRI rectifier tubes
Posted: Sun Nov 24, 2013 12:50 am
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Took a look at those tubes you mentioned BMW2002Ti,some of them are close to $200 apiece,deep pockets for sure.NOS has really jumped off limits.Real glad I picked up a bias tester to keep what I can afford in check.Good to know and Thanks for the info,again.
Ya Retroverbial I have no choice but to stick with the current reissues.I hope to get lucky and have a few last 3-5 years maybe.I do use the stand-by switch upon powering on but refrain from using it to shut down.When I throw that switch after the amp is on I get a rather loud "thwap" after doing that,I figured that can't be good so I don't shut down that way.Audio equipment is like that to sometimes,pre amp on first and pre amp off last,again resulting in a thwap through the speakers if I don't shut down in that order.What the hell is that noise,I was told many many moons ago it was the voice coils bottoming in their cavities?,not sure on that but I didn't like the sound so I always shut down and avoided the noise.


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Post subject: Re: 65 DRRI rectifier tubes
Posted: Sun Nov 24, 2013 1:49 am
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I believe the noise that sometimes accompanies the shut-down procedure is a "fly-back" effect caused when the filter caps discharge through the rectifier circuit as the high voltage is removed. IIRC there is a mod to tame that which consists of adding a diode and a cap somewhere within the power supply. The issue seems to be more prevalent with the re-issue amps than with the vintage editions. BMW2002ti is more familiar with the phenomenon and the fix -- let's see if he can further expound upon it.

Arjay

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Post subject: Re: 65 DRRI rectifier tubes
Posted: Sun Nov 24, 2013 2:13 am
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rhythmism,

There are no modern made GZ34/5AR4 that matches the steady voltage and current output of the original Mullard GZ34, Sylvania, or GE 5AR4. That is why NOS GZ34/5AR4 are so expensive. Now, if your amp can handle the heater current draw of the 5U4GB, you can find good NOS for good price. US made 5U4GB are very good rectifiers. With any rectifier change (any change --- type, brand, manufacturing date, etc), you need to re-bias the output tubes.

If you check EBay every now-&-then, you can find good GZ34/5AR4 for sale at around $60-75 apiece. You should only need one, for a long, long time. As long as the amp is working ok. Maybe the life of many Russian or Chinese rectifiers. With better tone and less stress on other components. YMMV, of course.

Some 5U4GB prices:

http://www.ebay.com/sch/i.html?_odkw=%2 ... B&_sacat=0

Good hunting!


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Post subject: Re: 65 DRRI rectifier tubes
Posted: Mon Nov 25, 2013 5:41 pm
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That does seem to make sense Retroverbial,I do notice that if I shut down the amp while the stand by is off(meaning the amp is ready to play)and my meter hooked up,the voltage drops down below 10v rather quickly.I'm guessing the stand by switch is acting almost in the same fashion.
I will certainly keep my eyes peeled BMW2002Ti.I understand what you mean about cost effectiveness,by 1 tube that'll last 10 years or 5 that might last for 10 years.The 5U4 is an interesting substitute but I have no way of knowing if my amp can handle the extra heat or not,last thing I need is to slide one in there an have "cook" things down stream!Thanks for the help gents.


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Post subject: Re: 65 DRRI rectifier tubes
Posted: Sat Nov 30, 2013 12:09 am
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Just a follow up,installed a Sovtek 5AR4 and I get 420v with bias meter,seems ok so far and will check it in a week or so.I will still keep the 5U4 option in mind but only when I learn how to check for correct heater current draw,not ready to mingle inside chassis just yet.Also installed a pair of 6201s from Tung-Sol,they are lower in noise and no feedback or howling(great!).You guys were helpful. :)


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Post subject: Re: 65 DRRI rectifier tubes
Posted: Sat Nov 30, 2013 12:37 am
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Sovtek builds a pretty sturdy bottle so I'd bet that new 5AR4 gives you several years of reliable service. You may find some "current creep" when you check the idle bias again in a week or so (as likely with any new rectifier or power tubes) but once the "cook down" is complete it should remain steady from that point forward.

Rawk on!

8)

Arjay

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Post subject: Re: 65 DRRI rectifier tubes
Posted: Fri Dec 13, 2013 5:12 am
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I came across some info on the rectifier tubes,I found this interesting.
http://acruhl.freeshell.org/mga/main/rectifiers.html
Hope that works,quick easy read.


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