New to me Audio Research VT130, tubes were old so I just got two matched quads 6550's Sovteks.
The quads have matched plate current and similar gains, on nice labels at the base of each tube.
Just getting back into tubes. From a long time ago, I had a Hickock 800 that never worked, an Eico 667 that I had forgotten about, and a BK 60X. The BK says all tubes are about the same good, but the Eico seems to work well and definitely gives different %cts for different tubes.
Checking the quads that I am sure were analyzed on something better than a 50 year old Eico, I did find different percentages for tubes within a quad. Yes, I know that I don't have a Hickock or something newer or better, and that the Eico likely tests at reduced voltage levels
Should I:
A) Install the quad with the closer matching (by Eico) in "parallel"?
B) Install the closer matching pair on diagonals?
C) Ignore my old cheap Eico and don't worry about it?
Want to fire up the amp tonight, so some quick advice would be appreciated, Thanks!
PS, my Eico did indicate that a new matched quad of 6CA7s for another amp were very close.
The quads have matched plate current and similar gains, on nice labels at the base of each tube.
Just getting back into tubes. From a long time ago, I had a Hickock 800 that never worked, an Eico 667 that I had forgotten about, and a BK 60X. The BK says all tubes are about the same good, but the Eico seems to work well and definitely gives different %cts for different tubes.
Checking the quads that I am sure were analyzed on something better than a 50 year old Eico, I did find different percentages for tubes within a quad. Yes, I know that I don't have a Hickock or something newer or better, and that the Eico likely tests at reduced voltage levels
Should I:
A) Install the quad with the closer matching (by Eico) in "parallel"?
B) Install the closer matching pair on diagonals?
C) Ignore my old cheap Eico and don't worry about it?
Want to fire up the amp tonight, so some quick advice would be appreciated, Thanks!
PS, my Eico did indicate that a new matched quad of 6CA7s for another amp were very close.
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Meaningful matching of tubes should be done at high voltage and load, something a
typical "tubetester" does not.
If the tubes comes from a reputable dealer he has matched them in a maximatcher or similar device, plug them into you AR.
You will find out when biasadjusting the AR, if they are matched you should have adjustment pots alike. I guess you also have a AC balance, but if you don't have
equip for distortion measurment, just leave it centered.
typical "tubetester" does not.
If the tubes comes from a reputable dealer he has matched them in a maximatcher or similar device, plug them into you AR.
You will find out when biasadjusting the AR, if they are matched you should have adjustment pots alike. I guess you also have a AC balance, but if you don't have
equip for distortion measurment, just leave it centered.
Those old EICOs are almost comic in their ability to "test" tubes. I have a 666, the devil's own tube tester, and I like to say it won't tell you how good a tube is but it will tell you how bad it is. OK for picking out shorts and gas but as far as putting a value on "goodness", highly suspect.
I think ARC are supplying Sovtek 6550s now that there are no more Winged C 6550s being made.
Cheers, Steve
I think ARC are supplying Sovtek 6550s now that there are no more Winged C 6550s being made.
Cheers, Steve
EICO 667 is an *emission* tester. It ties all loose electrodes together at lowish voltage and reads the total current.
The emission of a tube can be a little or a lot more than required, and it does not matter in a normal circuit.
It is mildly useful if a 10mA tube can only pass 1mA. But I bet all your 6550s are passing >400mA (not that the 667 has real numbers or voltages) which means they are plenty healthy.
A 667 once saved my butt. I had a 7027 which was fine when cold but shorted when heater got hot. This explained the smoke out of the power transformer, and told me which tube to trash.
The emission of a tube can be a little or a lot more than required, and it does not matter in a normal circuit.
It is mildly useful if a 10mA tube can only pass 1mA. But I bet all your 6550s are passing >400mA (not that the 667 has real numbers or voltages) which means they are plenty healthy.
A 667 once saved my butt. I had a 7027 which was fine when cold but shorted when heater got hot. This explained the smoke out of the power transformer, and told me which tube to trash.
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