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Biasing the 1987X

Discussion in 'Amp Input - Normal or Bright' started by Electgumbo, May 12, 2018.

  1. Electgumbo

    Electgumbo Lost Planet Airman Strat-Talk Supporter

    Dec 26, 2010
    Scott La.
    A few weeks ago I purchased a tube bias probe from Amazon... the probe is actually from Eurotube. Anyway yesterday I cleaned off my work bench enough to crack open the head and got down to see what I could see

    I found one tube to be reading 34 to 35 milliamps and the other to be reading 22 to 23 milliamps. Ok so I know a 12 milliamp spread between the 2 EL34s wasn’t good. The tube seemed to be original and were dated 2008. I bought the amp used in 2015 and never changed anything.

    I remembered I had a new never been opened set of EL34s that’s been setting around for 20 years or more. I figured I’d put those in and see what happens. The milliamp readings on the new set was less then 2 milliamp difference. Yeah Dawg I was on to some thing!

    So with the new matched set I performed the following calculations.

    1 EL34 = 25 Watts
    Plate Voltage = 460Volts
    RMS = .7

    25/460 = 0.05434

    0.5434 X .7 = 0.03805 or 38milliamps

    So the correct bias setting for the amp is 38 milliamps. Yay! If I did it correctly. I set the reading as close as I felt I could get with one tube reading 38.5 and the other reading 37. And this is where I left it.

    I played for a while last night at all volume setting. I honestly can’t say if I can hear any difference... but it felt different. It felt more responsive and more articulate... but it could all be in my head.

    I PM’d forum member @Robins to see what he thought of my work and setting. He seems to think I did good! So I’m leaving it alone.

    I sprayed the pots and jacks with cleaner. Tighten up the bolts on the trannies. Cleaned the muck off the Plexi front and back. I think I’m done!


    265B018C-5198-4F79-A565-AC2A73798758.jpeg
     
    simoncroft, rudos1, Textele and 7 others like this.

  2. RJ Squirrel

    RJ Squirrel Strat-Talker

    Age:
    64
    404
    Jan 28, 2018
    Frostbite Falls
    What brand tubes did you put in?
     
    abnormaltoy likes this.

  3. Electgumbo

    Electgumbo Lost Planet Airman Strat-Talk Supporter

    Dec 26, 2010
    Scott La.
    @RJ Squirrel

    Mesa ... from the early 90’s. I was going to put them in my ancient Music Man HD 130. But I put the amp in storage instead and the 2 sets of 2 sat on a shelf. They were gifted to my as a birthday gift by a guy that want me to play that old amp again... but that never happened.
     
    Robins and abnormaltoy like this.

  4. rocknrollrich

    rocknrollrich Senior Stratmaster

    Age:
    47
    Jan 8, 2016
    philadelphia
    You did it right. Good job.
    Pretty easy right?
    I would recommend checking it again after you have a few hours on the new tubes.
     
    Robins, RJ Squirrel and Electgumbo like this.

  5. RJ Squirrel

    RJ Squirrel Strat-Talker

    Age:
    64
    404
    Jan 28, 2018
    Frostbite Falls
    Mesa purchased tubes from manufacturers, tested them, matched them, and then rebranded the tubes with their own logo. Your tubes appear to have been manufactured by SED "Winged C". Nice tubes.:thumb:
     
    carver, Robins and Electgumbo like this.

  6. carver

    carver The East Coast Strangler Strat-Talk Supporter

    I just kinda wanted to jump in here to nod to your excellent choice in amplifiers

    these little suckers sing when you get them cooking. volume too loud? dont worry. the X stands for effects loop. slap a volume pedal in there and get back to playing.
     
    Electgumbo likes this.

  7. Textele

    Textele Senior Stratmaster Strat-Talk Supporter

    Oct 10, 2009
    Texas
    So Mesa does match their tubes close. Doesn't surprise me, they are top notch through and through.

    Glad you got the Plexi up and kicking!
     
    Electgumbo likes this.

  8. Electgumbo

    Electgumbo Lost Planet Airman Strat-Talk Supporter

    Dec 26, 2010
    Scott La.
    @Textele

    These are old. I don’t know what they are like now a days. I went thru a few of their GZ34 Rectifier Tubes ... one about every 6 months in my Bluesbreaker RI. I can find them local but I finally ordered a Sovtech off line and it’s been in the BB quite a few years now. I didn’t care for their 12AX7’s in the late 90’s either. Thanks it is a great amp!!!
     
    Last edited: May 15, 2018
    Textele likes this.

  9. Electgumbo

    Electgumbo Lost Planet Airman Strat-Talk Supporter

    Dec 26, 2010
    Scott La.
    @carver

    A buddy saw it on the local CL in 2015. Things was rolling along pretty good back then so I bought it for $800. Yes it is loud. I removed the treble Bleed cap last year I think. Yes it’s 50 Watts of Whoop Ass dat’s fa sho’! I’ll have to try the volume pedal trick..
     
    carver likes this.

  10. Electgumbo

    Electgumbo Lost Planet Airman Strat-Talk Supporter

    Dec 26, 2010
    Scott La.
    @carver
    I tried the volume pedal in the effects loop. I didn’t see the advantage of it. I’ll just keep using my attenuator if I want to open it up.
     

  11. carver

    carver The East Coast Strangler Strat-Talk Supporter

    damn thats too bad.

    it works really well on my 5150. I can bring that amp down to a decent level and keep it sounding huge.

    different amps :)

    I know you know your stuff, so this could very well just be a useless thing to type.. but.. are you sure you had the effects loop turned on and not bypassed :) hahhaa
     
    Electgumbo likes this.

  12. Electgumbo

    Electgumbo Lost Planet Airman Strat-Talk Supporter

    Dec 26, 2010
    Scott La.
    @carver
    Would the volume pedal work if the effects loop was off? Com’ on Dawg! When using the attenuator with the amp driving I use the loop for Reverb and Delay pedals.

    Your 5150 has a modern gain stage my vintage style Marshall doesn’t. Your amp has more in common with my Soldano with preamp gain, volume, master volume and stuff like that. My Marshall just has a volume. It’s like a piss’d off Fender Bassman.... sorta.
     
    CigBurn likes this.

  13. carver

    carver The East Coast Strangler Strat-Talk Supporter

    hahahah yeah, I knew I was walking backwards into a hornets nest with that one. considering who I was talking too. :) I know you know your stuff better than most.

    pissed off bassmans are the best kind of bassmans
     
    Electgumbo likes this.

  14. Electgumbo

    Electgumbo Lost Planet Airman Strat-Talk Supporter

    Dec 26, 2010
    Scott La.
    @carver
    No harm no foul! I happen to have Volume pedals around so it’s not like it cost me money or anything. Heck I wanted to try it.
     
    carver likes this.

  15. RPKennedy

    RPKennedy Senior Stratmaster

    Age:
    61
    Apr 27, 2013
    Oconomowoc, WI
    @Electgumbo
    What attenuator are you using?
    Happy with it?
     
    Electgumbo likes this.

  16. heltershelton

    heltershelton ASKED TO LEAVE THE STAGE Strat-Talk Supporter

    Jun 5, 2013
    Not Florida
    pissed off bassman.....made me laugh.
     
    Electgumbo likes this.

  17. Electgumbo

    Electgumbo Lost Planet Airman Strat-Talk Supporter

    Dec 26, 2010
    Scott La.
    4CF053F6-0623-4B20-9C43-04003FD32C66.jpeg D6F24541-1A04-4DDC-90FF-9EF5BE5B2896.jpeg
    @RPKennedy
    I bought the Jettenator on clearance for $125... it works at 4,8,16 Ohms up to 100watts. For the price I Love It! I can use it on any amp I own! I think it sounds great!

    The OX Amp Top Box is getting all the love these days ... but it’s $1,200! Heck I didn’t pay that much for either of my Marshalls!!! But they supposed to be the stuff!
     
    Robins and RPKennedy like this.

  18. RJ Squirrel

    RJ Squirrel Strat-Talker

    Age:
    64
    404
    Jan 28, 2018
    Frostbite Falls
    She needs some tremoleaux, no? She needs some tremoleaux, yes!:D
     
    Electgumbo likes this.