Shopping for EL84's: What do these specs tell me?

Discussion in 'Amp Tech Center' started by boneyguy, Mar 8, 2013.

  1. boneyguy

    boneyguy Doctor of Teleocity

    Age:
    61
    Posts:
    11,857
    Joined:
    Mar 31, 2007
    Location:
    victoria b.c. CANADA
    What do these specs tell me about these two pairs of EL84's. Is there a prediction we can make about their performance, clean headroom, tonal character, loudness etc, in comparison to each other, from these specs?

    TESTED & MATCHED PAIR #1

    ----------Ia------ S
    ----------mA----mA/V
    EL84-----44.0----9.3
    EL84-----44.0----9.2


    TESTED & MATCHED PAIR #2

    ----------Ia------ S
    ----------mA----mA/V
    EL84-----38.0----8.8
    EL84-----39.0----8.8
     
  2. uriah1

    uriah1 Telefied Gold Supporter

    Posts:
    20,682
    Joined:
    Feb 12, 2011
    Location:
    Around
    -Nope (it could be chinese or a thick US or German bottle)...

    that is my take...

    imho
     
  3. BiggerJohn

    BiggerJohn Friend of Leo's

    Posts:
    3,311
    Joined:
    Jun 1, 2009
    Location:
    California
    I would be more concerned about who/where they were made. The match on the pairs is close enough.
     
  4. boneyguy

    boneyguy Doctor of Teleocity

    Age:
    61
    Posts:
    11,857
    Joined:
    Mar 31, 2007
    Location:
    victoria b.c. CANADA
    I'm sorry but what the heck does this even have to do with my question? ::lol: Are you assuming I don't know who the manufacturer of the tubes is? :confused


    Okay let's assume I've done my homework (I have) and the tubes are good quality without any doubt, so...

    ....what do those specs tell us about the performance of the tubes (each pair compared to the other) in terms of headroom, output etc?

    Thanks.
     
  5. Telenut62

    Telenut62 Poster Extraordinaire

    Age:
    59
    Posts:
    5,590
    Joined:
    Oct 29, 2008
    Location:
    Eugowra, Australia
    Nope, those figures won't tell zip about tone or performance. Ia is plate current and S being mA/V is transconductance, I'm assuming. They are just showing that the tubes are a match like two motors running at the same revs putting out the same specs....

    ie. ...At idle, both valves will draw a small amount of current - say 38mA. If both valves are drawing the same current, and have the same amount of gain, they will do a good job of cancelling any mains hum and other noise on the HT (B+) rail. However, if those valves are not balanced, more hum will be present.

    Also, if there is a mismatch in the current draw, one valve will get hotter than the other(s). This may be severe enough to cause the valve to glow red which is not good for reliability.

    A third consideration is the sonic one! On half of the signal will be amplified more that the other half leading to increased 2nd harmonic distortion. This may or may not be desirable!
     
  6. boneyguy

    boneyguy Doctor of Teleocity

    Age:
    61
    Posts:
    11,857
    Joined:
    Mar 31, 2007
    Location:
    victoria b.c. CANADA
    I don't understand a lot of what you are saying but thank you. :lol: This is the kind of info I was looking for.
     
  7. TheSmokingMan

    TheSmokingMan Banned

    Posts:
    610
    Joined:
    Jan 7, 2011
    Location:
    Belle Plaine, KS
    Depending on amp design, those tubes don't need to be matched. There are some serious sonic differences between brands though.
     
  8. boneyguy

    boneyguy Doctor of Teleocity

    Age:
    61
    Posts:
    11,857
    Joined:
    Mar 31, 2007
    Location:
    victoria b.c. CANADA
    It's for a Blues Jr. and the tubes in question are Polam brand. I just read about them at thetubestore.com. They are NOS produced I believe in the 1960's in a Philips plant in Poland. Apparently very good quality so I was considering a pair.
     
  9. Telenut62

    Telenut62 Poster Extraordinaire

    Age:
    59
    Posts:
    5,590
    Joined:
    Oct 29, 2008
    Location:
    Eugowra, Australia
  10. boneyguy

    boneyguy Doctor of Teleocity

    Age:
    61
    Posts:
    11,857
    Joined:
    Mar 31, 2007
    Location:
    victoria b.c. CANADA
  11. BiggerJohn

    BiggerJohn Friend of Leo's

    Posts:
    3,311
    Joined:
    Jun 1, 2009
    Location:
    California
    OK, now that we know the tubes are for a BJ, that helps us. Unlike the Vox and many other EL84 amps, the BJ is fixed bias. And the factory bias is a bit on the hot side, that is unless they have made some changes since I last was inside a BJ. BillM would know for sure.

    Since the BJ does run the tubes hot, I would definitely consider the heavy duty russian EL84M that they sell as a special. I would also consider a russian 12AX7LPS for the V1 position.
     
  12. boneyguy

    boneyguy Doctor of Teleocity

    Age:
    61
    Posts:
    11,857
    Joined:
    Mar 31, 2007
    Location:
    victoria b.c. CANADA
    Got a pair of NOS Polam-Philips off Ebay coming from Bulgaria. Should be interesting.

    From thetubestore.com:

    Telam and Polam EL84 - Two wild and crazy tubes! I think for single coil guitars they are the best sounding tubes available. Fender amps love them. Pro Junior, Blues Junior two thumbs up. Mesa Boogie, VOX, Dr Z another two thumbs up. The midrange is very rich in harmonic content. JJ’s sound flat and one dimensional by comparison. The great mids transition into a smooth clear treble and the bass frequencies are solid with no flabbiness. I had a couple of players testing them and they had no problem in picking these tubes as their favorites. Numerous tube swaps were done and the boys would always be able to tell if Polam or Telam were installed.

    From a construction standpoint there is more good news. They seem to have stayed very close to the original bottle specification. A lesson that a lot of tube makers have not learned. I’m convinced that the Telam and Polam tubes are out of the same factory. The bottles are the same, the spacers, pins and internal connections all look the same. The only difference is in the stamping of the plate. Telam has a ribbed plate that is spot welded while Polam has a smooth plate that is crimped. The coating on both looks identical. Microphonics or mechanical noise doesn’t seem to care about the construction methods as both are excellent. Picking one over the other is difficult because they sound so much alike. Both tubes sound great clean and both have a beautiful natural overdrive sound with bite and a good aggressive sound.
     

    Attached Files:

  13. gionnio

    gionnio Tele-Meister

    Posts:
    298
    Joined:
    Oct 27, 2007
    Location:
    baja rockridge
    Thanks for posting that. I'm thinking of getting a set to replace JJs in a Badger 18. Maybe I'll give them a try.
     
  14. boneyguy

    boneyguy Doctor of Teleocity

    Age:
    61
    Posts:
    11,857
    Joined:
    Mar 31, 2007
    Location:
    victoria b.c. CANADA
    The Polams will be replacing a pair of JJ's in my BJr.
     
  15. uriah1

    uriah1 Telefied Gold Supporter

    Posts:
    20,682
    Joined:
    Feb 12, 2011
    Location:
    Around
    Neat...always cool seeing new NOS types.
     
  16. Dave1234

    Dave1234 Tele-Afflicted

    Age:
    56
    Posts:
    1,348
    Joined:
    Mar 4, 2012
    Location:
    Leicestershire
    I put the Russian Mil spec EL84's (Sovtek 1970's) in my Laney LC30, Love 'em to bits, but that is cathode biased.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.