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6EM7 Unit 1
6EM7 Unit 1
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Old 4th March 2011, 05:32 PM   #11
smoking-amp is offline smoking-amp  United States
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"The 6EM7 and 6EA7 are not identical according to this:"

I agree, I didn't say they were. Thats why I posted the real equivalents.
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Old 4th March 2011, 08:33 PM   #12
Ardee is offline Ardee  England
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Sorry, I misunderstood what you were saying. Thanks for the links, but the 6EA7 and 6FM7 don't look the same to me either.
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Old 4th March 2011, 10:36 PM   #13
smoking-amp is offline smoking-amp  United States
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Oh, see what you mean. The GE handbook has the data identical for them.

The 6EA7 datasheet is evaluated at different operating currents than the handbook 6EA7 data or the 6FM7 datasheet & handbook data.

Only way to tell if they are the same would be to put them on a curve tracer,
or see if the 6FM7 curves evaluate to the same data as the 6EA7 data at those different rating currents.

Could also be that later issue tubes were made identical.
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Old 4th March 2011, 11:15 PM   #14
smoking-amp is offline smoking-amp  United States
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The 6EA7 datasheet data looks very similar to the RCA 6GL7 datasheet data. Interestingly, for triode #1, the 6GL7 datasheet also lists a second set of data for triode #1 equal to the 6FM7 data. Triode #2 6GL7 data is at 46 mA versus 48 mA for the 6EA7 datasheet and is very similar too. Kind of odd for two tubes on the same base to be identical though.

Then there are 6DR7, 6FY7

Last edited by smoking-amp; 4th March 2011 at 11:29 PM.
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Old 5th March 2011, 01:08 AM   #15
Tubelab_com is online now Tubelab_com  United States
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As I stated earlier I have seen a large tube to tube variation with these tubes. Looking at my collection some are marked 6EA7 some are 6EM7 and most are 6EA7/6EM7. Maybe it didn't make much difference in a TV set, but there seems to be two or more different tubes being sold as 6EA7/6EM7. There are three different constructions of the tubes marked with both numbers. The ones with the wide flat plates for the big section seem to have more bass, but they red plate easier than the other flavors when pushed hard.
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Old 5th March 2011, 08:07 AM   #16
Yvesm is offline Yvesm  France
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Ahem . . .

Being optimistic, + or - 10% dispersion is probably the best you can assume even for the same batch from the same factory !
You must keep that in mind when designing and don't forget ageing . . .

Yves.
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Old 5th March 2011, 03:58 PM   #17
smoking-amp is offline smoking-amp  United States
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I tried a couple of Sylvania 13GF7 and 13FM7 in the curve tracer, and they are definately the same tube. They both look the same, all black plates, the big flat plate on section #2. Only difference is that the 13GF7 has a little cooler fin atop g1 of section #1.

Then I looked thru some other brands, and after only 12 tubes out, I see 3 different constructions of each type too. All the others had no cooler fin on section #1 g1 (but small or large cooler fins on section #2 g1 on all). The GE and RCA usually have grey plates, but one RCA has black plates (Sylvania black plated). Section #2 is sometimes a big flat plate (Sylvania, RCA, Zenith) and sometimes a rectangle at 90 degrees in the middle (GE). Section #1 is usually a rectangular box, but some have flat fins out the narrow ends.

The most significant difference I see is that section #1 sometimes has a round cathode (Zenith, GE) and others have a flat cathode (Sylvania, RCA). Usually this means different curves, but I put one of each on the curve tracer and the same curves still, but a DC bias difference. With only 12 tubes out so far, looks like construction was a free for all with these tubes. But the curves were remarkably similar on the few I have tried (only tried 4 on the tracer).

I bought a box of 156 of the 13FM7 type when VT.net had the box sale, something like $0.35 each. Probably got every brand possible here. Lets see, Dumont, Tung-Sol, Philco, Raytheon, International, PhilipsECG, Zenith, RCA, GE, Sylvania, Lindal, Westinghouse, Amperex, El Menco, Canadian Marconi, Admiral, Sears, Silvertone. Am I missing any? And that was just the 13FM7 box.

Last edited by smoking-amp; 5th March 2011 at 04:03 PM.
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Old 5th March 2011, 07:48 PM   #18
Ardee is offline Ardee  England
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Thanks for doing that investigation s-a. It looks as if a curve tracer is a useful thing to have when using this family of tubes.
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Old 1st November 2011, 11:13 AM   #19
mhouston is offline mhouston  Australia
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Quote:
Originally Posted by Ardee View Post
Thanks for doing that investigation s-a. It looks as if a curve tracer is a useful thing to have when using this family of tubes.
I'm part way through a 6EM7 build with a pair of Salvania tubes (NOS I'm sure). But "tracer" not heard of this before.
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Old 1st November 2011, 03:35 PM   #20
smoking-amp is offline smoking-amp  United States
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"But "tracer" not heard of this before."

A Tektronix Type 576 Curve Tracer modified for tube tracing.
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File Type: jpg curve_tracer.jpg (36.9 KB, 319 views)
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