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    Output tube life?

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    xlr8

    Posts : 68
    Join date : 2010-02-09

    Output tube life?

    Post by xlr8 on Mon Nov 01, 2010 9:17 am

    I was wondering if someone could tell me in order from least influence to greatest, what factors would cause tubes to wear out quick? Leaving the amp on too long, pushing it hard, bias too high, etc.? Reason I ask is because I decided to see where my kt66's were on the meter yesterday, and they are ALL just barely on the strong side of "weak" and are not that old. I'm trying to narrow down what I could be doing to wear them out this fast!

    Thanks folks!

    dynacophil

    Posts : 33
    Join date : 2010-10-26
    Age : 59
    Location : Berlin/Germany

    Re: Output tube life?

    Post by dynacophil on Mon Nov 01, 2010 9:45 am

    did you test them when they were new? have you got a new reference-tube to compare them to? is your tester calibrated? you test emission only anyway, don't you?
    probably your tester isn't restored to new and shows just something...

    xlr8

    Posts : 68
    Join date : 2010-02-09

    Re: Output tube life?

    Post by xlr8 on Mon Nov 01, 2010 11:14 am

    Well, I'm using a Mercury Model 1100 tester. I have no idea whether it has ever been calibrated or not. I have tested some small signal tubes from another piece that all test good except for 1 and I tested the El34's that I replaced and they are all strong. I tested one of my really old Mullard 5AR4s with it and it was still very strong. I did not test the kt66's when I bought them. Beggining to think I should have...

    dynacophil

    Posts : 33
    Join date : 2010-10-26
    Age : 59
    Location : Berlin/Germany

    Re: Output tube life?

    Post by dynacophil on Mon Nov 01, 2010 11:25 am

    how many hours did your kt66 run..? I have several sets el34 of all kinds and NONE of them had a significant difference in emission after a year of normal moderate use. Ok, I don't let the amps rund 24h/d...
    but... emission may differ.. I have a set of used brownbase DD-Getter Philipps that beat any new tube by 20% on the simple bad-good-scale of my cheesy old tester Smile

    xlr8

    Posts : 68
    Join date : 2010-02-09

    Re: Output tube life?

    Post by xlr8 on Tue Nov 02, 2010 8:45 am

    Well, I would guess they have been running about 1500-2000 hrs. That is about half of the entire time I've owned them. I hear ya' on the "cheesy" tester. Mine reminds me of the "Good Egg Bad Egg" scale in the Willy Wonka and the Chocolate factory movie lol! It does seem to work though, and all 8 tubes read the same on the scale.

    I should state for the record that the bias has been set at around 49ma for most of the time they've been running. I cut it back to around 45ma after testing the tubes.


    Last edited by xlr8 on Tue Nov 02, 2010 8:53 am; edited 1 time in total (Reason for editing : Included recent bias settings.)

    xlr8

    Posts : 68
    Join date : 2010-02-09

    Re: Output tube life?

    Post by xlr8 on Thu Nov 11, 2010 8:16 am

    Ok, I feel much better about things now. My good friend and fellow tube head was in town and dropped by my place last night with his huge Hickok (don't think I'm spelling that right) 533 tube tester. This guy has a lot more experience with tubes than I do and knows what he's doing. We tested every single tube I own, even the known bad ones. We got some very interesting results.

    First of all, all 8 of my GL kt66 tubes test brand new after at least 1500 hrs. He told me transconductance was the paramater that was most important? All of the kt66's were in the 5600-5900 range and all 8 of my EH EL34's were around 6000. Shocked

    The interesting part came when we tested the input tubes. Both sides of each tube failed when tested as a 12AT7, but when tested as a 12AX7, the machine said they were fine??? My friend seems to think that JJ made some 12AX7 tubes that came out with specs a little closer to 12AT7 and they just re-badged and sold them as 12AT7's. One of the middle tubes was bad either way and my friend politely left me with a National branded 12AX7 from russia in it's place. So I have basically been running 12AX7's this whole time???

    kevco

    Posts : 70
    Join date : 2009-07-16
    Location : Aldan, PA, USA

    Re: Output tube life?

    Post by kevco on Thu Nov 11, 2010 9:07 am

    JJ's IMHO are the worst tubes out there. If you want to go cheap, use Chinese. I've never had a silver plate Chinese 12AX7 fail and I use them in all the non signal path sockets in my Fisher receiver.

    xlr8

    Posts : 68
    Join date : 2010-02-09

    Re: Output tube life?

    Post by xlr8 on Thu Nov 11, 2010 9:22 am

    Well, could running 12AX7 tubes in the high gain VTA board do any damage? They sound fine, but when the local shop opens this morning, I'll be at the door to pick up some cheap JAN's and be done with it for now. Been using the same JAN tubes in my preamp for 4 years now...

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