Bottle size, does it matter in matched quads?
I just purchased a quad of Penta Labs KT88SC power tubes from a longtime online vendor who told me they would be a matched quad.
When I opened the boxes I found that the quad was physically two different pairs with one of the pairs having different size bottles than the other.
I called the vendor and he gave me some mumbo jumbo about glass blowing etc but these are two uniformly different pairs not some random quad of different sizes.
If anything they look like they might be from two different production runs etc.
Do I need to worry about varying specs / gain or sonic characteristics with these two different sized pairs rather than having a uniformly matched bottle length quad of power tubes?
Should I use an evenly sized pair together on each stereo side or stagger them, or, does it not matter?
My custom made hifi stereo amp is cathode biased so no adjustments needed or possible in the bias dept.
This vendor does his own matching on a tester. None of the tubes had close consecutive numbers on the sticker labels.
Is this size variation a common practice in the tube matching/selling business? Or did he just build my quad out of mismatched size pairs of last remaining stock hoping I'd go away quietly?
I'm tempted to return them as this amp is in full display as the centerpiece of my system. Am I being too picky?
I don't want to be petty but besides performance issues I fear resale value may be compromised and I'm somewhat irritated by this unwelcome suprise included with my expensive tube order.
I was assured I have a very long warranty on the tubes which while reassuring felt a little like bum's rush.
Any advice from the more experienced tube afficionados on this forum?
I just purchased a quad of Penta Labs KT88SC power tubes from a longtime online vendor who told me they would be a matched quad.
When I opened the boxes I found that the quad was physically two different pairs with one of the pairs having different size bottles than the other.
I called the vendor and he gave me some mumbo jumbo about glass blowing etc but these are two uniformly different pairs not some random quad of different sizes.
If anything they look like they might be from two different production runs etc.
Do I need to worry about varying specs / gain or sonic characteristics with these two different sized pairs rather than having a uniformly matched bottle length quad of power tubes?
Should I use an evenly sized pair together on each stereo side or stagger them, or, does it not matter?
My custom made hifi stereo amp is cathode biased so no adjustments needed or possible in the bias dept.
This vendor does his own matching on a tester. None of the tubes had close consecutive numbers on the sticker labels.
Is this size variation a common practice in the tube matching/selling business? Or did he just build my quad out of mismatched size pairs of last remaining stock hoping I'd go away quietly?
I'm tempted to return them as this amp is in full display as the centerpiece of my system. Am I being too picky?
I don't want to be petty but besides performance issues I fear resale value may be compromised and I'm somewhat irritated by this unwelcome suprise included with my expensive tube order.
I was assured I have a very long warranty on the tubes which while reassuring felt a little like bum's rush.
Any advice from the more experienced tube afficionados on this forum?
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Different production runs ?
I'm no expert, but from what I've read I gather that there has always been a fair bit of variation from tube to tube in the manufacturing process. It's not like a transistor where devices from the same batch are all likely to be very similar because they have been diced out of the same silicon wafer after the manufacturing process has been completed. The only thing I can think of where it would help if the tubes were all from the same production run is the knowledge that they likely have the same materials inside them i.e. the cathode coatings are from the same batch from the cathode coating material supplier.
I can't think of a good reason to be troubled by the different bottle shapes other than aesthetic reasons.
I'm no expert, but from what I've read I gather that there has always been a fair bit of variation from tube to tube in the manufacturing process. It's not like a transistor where devices from the same batch are all likely to be very similar because they have been diced out of the same silicon wafer after the manufacturing process has been completed. The only thing I can think of where it would help if the tubes were all from the same production run is the knowledge that they likely have the same materials inside them i.e. the cathode coatings are from the same batch from the cathode coating material supplier.
I can't think of a good reason to be troubled by the different bottle shapes other than aesthetic reasons.
If you don't like how they look, return them, and go buy what you want!
after all, it is YOUR money.
my .02c
after all, it is YOUR money.
my .02c
If they were made in the Shuguang factory, everything is possible...
(seems they take pride in producing ugly tubes)
But that doesn't mean that they don't work as they should and it says nothing about the matching.
I often use 6L6WGC from TAD, those are downright ugly potatoes (and not all potatoes are equally shaped), but matching is perfect and it takes great NOS alternatives to get a better sound...
(seems they take pride in producing ugly tubes)
But that doesn't mean that they don't work as they should and it says nothing about the matching.
I often use 6L6WGC from TAD, those are downright ugly potatoes (and not all potatoes are equally shaped), but matching is perfect and it takes great NOS alternatives to get a better sound...
Well, I looked them over and they appear to have the same internal structures and the specs from matching them are written on the boxes.
There are two taller and two smaller and one tube even has the label printed on the opposite side of the other three.
But after finding a mounting pattern that doesn't offend my sensibilities too much I'm not as concerned .
I did write the importer (Penta Labs) and, depending on what their take is, I might conclude I'll live with the tubes as they do sound good and I really can't be bothered with this.
Just a word of warning to other consumers............. confirm everything twice so as not to be suprised!
I said I wanted a matched quad, his website says matched quad listed for the price I paid, and apparently to this vendor that means that they're matched on a tester only.
Glass blowing yea, more like gas blowing. I didn't need to be patronized in that fashion.
There are two taller and two smaller and one tube even has the label printed on the opposite side of the other three.
But after finding a mounting pattern that doesn't offend my sensibilities too much I'm not as concerned .
I did write the importer (Penta Labs) and, depending on what their take is, I might conclude I'll live with the tubes as they do sound good and I really can't be bothered with this.
Just a word of warning to other consumers............. confirm everything twice so as not to be suprised!
I said I wanted a matched quad, his website says matched quad listed for the price I paid, and apparently to this vendor that means that they're matched on a tester only.
Glass blowing yea, more like gas blowing. I didn't need to be patronized in that fashion.
Greetings everyone,
I worked at Amperex in the mid 80's as the test department supervisor. Even between different runs of the same tube, I never saw any glass differences. Just my 2 cents.
I worked at Amperex in the mid 80's as the test department supervisor. Even between different runs of the same tube, I never saw any glass differences. Just my 2 cents.
I'm not the Amperex man, but in more than 30yrs of tinkering I have never seen a mesh plate 7591 or any other beam tube for that matter.
Sylvania, RCA, and possibly GE (RCA?) made these. Most other brands seem to have been one of these rebranded.
That's because Amperex was a superior company that adhered to the standards and practices of the day, when they meant something. Today all that is out the window with these schlock manufactures.
I too have never seen a mesh plate beam/power pentode from Amperex. Only small signal RF pentodes (9 pin) like 6EH7, 6EJ7 & 6689. There's probably a couple other industrial numbers that I can't think of at the moment.
Thanks for settling that, A guy I bought a organ amp from swears to me he was running some "special" grey mesh 7951's, and he had a set of mesh plate 6v6's, I'm not very knowledgeable about tubes yet, but I spent a week searching for mesh plate tubes, and they have NOTHING in common with the 7951's I've looked at.
I worked at the Amperex plant in Hicksville NY. We made small and large transmitting tubes, rectifiers, x-ray tubes, and magnetrons. Troubleshooting the test equipment was a trip, since all the manuals were in Dutch.
Please feel free to ask Amperex questions, if I can answer them, I will.
Ray
Please feel free to ask Amperex questions, if I can answer them, I will.
Ray
6EH7, 6EJ7 etc. do not have mesh plates. They have a mesh screen. You can't see the plates as they are hidden by the screen.
I took a good look with a magnifying glass and it seems that you are right, so I stand corrected. It's called an internal shield and comes out through it's own pin. I never really looked that close before. Same for the 6689.
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