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Help with tube type for bassman please

Discussion in 'Ampage Area' started by cowmoo, Jun 24, 2018.

  1. cowmoo

    cowmoo Country Gent

    Aug 19, 2011
    North Wales
    I’ve got a Marshamps 6G6 replica, bought second hand from its original owner.
    Has been making a sound like thunder and buzzing occasionally. It usually settles after a while or a good tap on top. I’ve tried swapping out pre amp tubes but my spares are pretty useless by the resulting sound.
    Anyhow, we were in the studio and it started playing up. Got so bad we had to call off recording until it is cured. The amp seemed hotter than it should be. Tubes looked fine though. A little microphonic.
    What I need to know is, can I use small bottle 6l6 without anything but a rebias and
    will they lower the overall output volume and what’s the best pre amp tube to compliment them.
    Failing that. Same question regarding regular 6l6.
    Also, is there a way to tell from the transformer code what impedance it needs from the speakers? I was told it was fine at 4ohm so that’s what i’ve been using. They are Heyboers. (sp)
    Thanks.
     
  2. loudnlousy

    loudnlousy Friend of Fred

    Age:
    52
    Oct 18, 2015
    Hildesheim, Germany
    The first culprit that would come to my mind would be the preamp tubes. These were the ones I would check first. Poweramp-tubes are quite long-lasting beasts.
    4 Ohms seem to be quite a unusual speaker-load, imho.
    It is always safer to use higher resistance-speaker if you are not sure.
     
    mrfixitmi likes this.
  3. vyndance

    vyndance Gretschie

    Age:
    63
    261
    Dec 12, 2014
    Bear Valley Springs, CA
    The 6G6 used 5881's and was a 4 ohm load if they stayed true to the original. 5881's are lower wattage. Short 6l6 will work but you probably won't like the tone. Doesn't sound like a power tube problem. Have you ruled out dirty sockets and cables?
     
  4. cowmoo

    cowmoo Country Gent

    Aug 19, 2011
    North Wales
    Thanks,
    4ohm was the 6G6b load and this is a clone.

    I did remove all tubes and clean the contacts and sockets. There is noise from the pre amps when tapped but the intensity and volume of the interference doesn’t change when they are swapped around so I’m not able to pin point the culprit.

    I’m ordering a new set but hope it’s not something more ominous.
     
  5. swivel

    swivel Electromatic

    60
    May 13, 2018
    PNW
    The 5881's or the small bottle 6L6WGB are fine in that amp. You may not even notice any volume difference..... unless you are playing real loud.
    There are so many things noise could be... but pre amp tubes is a place to start. A better description of the noise would help... and if it goes away when you turn the volume off, or unplug the cable etc.
    Pull the first pre tube... does the noise go away? That tube is for the Bass channel only.
    The 2nd tube is for the other channel only.
    As far as new Pre tubes/12AX7's I like the Mullard RI a lot. Have only them in amps for a few years now and not one problem. Probably 20-30 tubes now. I have a ton of old tubes and NOS old tubes but got tired of dealing with hiss, crackle or microphonics.
    You should be able to find the transformer impedance by checking the Heybauer number on line. I wouldnt assume it's 4 ohm as people build clones for single speaker combo cabs....
     
    Last edited: Jun 24, 2018
  6. cowmoo

    cowmoo Country Gent

    Aug 19, 2011
    North Wales
    The noise is there whether the volume is up or off. Sounds like a rustling thunder with the occasional sound like one of those big switches in a Frankenstein movie would make!!!
    I was reluctant to pull the tubes when on in case of damage.
     
  7. cowmoo

    cowmoo Country Gent

    Aug 19, 2011
    North Wales
    Well i’ve tried the only test I can do, tapping the tubes swapping around etc. Found that there is something bad in the pre amp section and one of the power tubes is either microphonic or boosting the pre amp problem. Only one tube though. There are sounds like rumbling, arcing and microphonic. Like a mig welder in a thunderstorm through a bad pa with cheap mics.
     
  8. vyndance

    vyndance Gretschie

    Age:
    63
    261
    Dec 12, 2014
    Bear Valley Springs, CA
    cowmoo likes this.
  9. drrohle

    drrohle Synchromatic

    675
    Jan 3, 2014
    Hays, KS
    May well have a cold solder joint somewhere too. If you are comfortable with pulling the chassis you could take a plastic or non-conductive screw driver type tool and drag it over the internal components and wires to see if you can locate anything wrong. If it is a cold solder joint you'll know it when you hit it.
     
    cowmoo likes this.
  10. slickfaster

    slickfaster Electromatic

    38
    Dec 29, 2009
    Redondo bch.
    Get chop stick n tap round inside circuits for cold solder connect.
    If cloned to go spec 4ohm is correct. Earlier blondes meant to run on one speaker were 8ohm. I have one. Small bottle 5881s drop amp to 35wts or so and head room. Combined with 12ax7 pre and phase you'll get an earlier break up if biased properly and especially whend using a preamp pedle and speakers like a celestiin v30...
    My guess..loose solder connect.
    Enjoy the Journey. And keep on runnin!
     
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  11. cowmoo

    cowmoo Country Gent

    Aug 19, 2011
    North Wales
    Thanks for the replies,
    I’m going to take it to a very reputable tech He’s going to give it a health check and find the bugs.

    Will the sound be much different with small bottle 6l6s? I’m not after replicating anyone’s tone, but do have the pedal and V30s
     
  12. slickfaster

    slickfaster Electromatic

    38
    Dec 29, 2009
    Redondo bch.
    I don't think so...Just a bit sooner break up. Output transformer and speaker choice would effect tone more.
    I installed 5881s.
     
    cowmoo likes this.
  13. cowmoo

    cowmoo Country Gent

    Aug 19, 2011
    North Wales
    2A3BADAB-5189-4D19-905D-06AB40701666.jpeg 8DDE29D5-9BAB-4251-B26F-51C1BA9521A3.jpeg I’ve got some NOS 6l6 tubes from a local amp repair fella. Also a new jj 12ax7. This seems to have quietened things down regarding the popping and thunder...but, there is still a faint hint of this and if I tap the amp cab above the cap tray I’m sure I can hear this as microphonics.
    The new power tubes have very short end caps. I’m reassured they are old military stock.
    I need to use this on Saturdays gig.
    Will it be ok!?!!
     
  14. Gretschtim1

    Gretschtim1 Country Gent

    Dec 4, 2012
    Dundalk, Md
    Chances are that amp repair fella just wanted to unload those crappy tubes.
    Those Russian power tubes with the low profile base have been known to crack easy and fail some times taking out other stuff in the process. I personally wouldn't use them. The newer Russian tubes stopped using those bases because of the high failure rate.
    I had a few amps come in with those low profiles bases - they shorted out and caused all kinds of damage to the amp.
    Check out Tubedepot.com. They have lots of information about tubes there and you can find a good set of 5881 tubes that will work well in your amp.
    Again I wouldn't use those tubes you bought.
    Get yourself a good set of tubes and let a decent tech check out the amp, set the bias properly and the amp will sound great.
    Good Luck.
     
    Last edited: Jul 15, 2018
    cowmoo likes this.
  15. cowmoo

    cowmoo Country Gent

    Aug 19, 2011
    North Wales
    I had to use them Saturday night. The amp actually sounded great. Really clear and was loud enough at 2 on the dial to compete with the drums and fill the room. But I agree that I’m dubious about the seemingly lack of substantial base on these. I did run the numbers through google and there were some positive things said., these being NOS 1980’s Russian military stock, but maybe that was as far as I read! Thanks for the advice. I shall source some modern replacements ASAP.
     
  16. Uncle Daddy

    Uncle Daddy Country Gent

    Jan 19, 2012
    Maldon UK
    Those beartrap retainers look like they're pressing on the glass; normally they would be gripping the base of the valve.
     
  17. cowmoo

    cowmoo Country Gent

    Aug 19, 2011
    North Wales
    They are, he assured me it was ok?
    He’s been a repair man since the 60’s so I sort of take his word for it. Is this a tad foolish of me!!
     
  18. Gretschtim1

    Gretschtim1 Country Gent

    Dec 4, 2012
    Dundalk, Md
    The problem with those tubes was not bad sound. They actually sound pretty good but the failure rate in those tubes was the problem. When companies in the US started getting involved with companies in Russia to make tubes one of the first things that happened was the Americans showed them how to make better tubes. Replacing those crappy bases with the more traditional style was one of the first things that happened. No doubt Russian made tubes have gotten much better since the 1980s. I can't believe the tech told you it was okay for those tube claws to be grabbing the glass. That's not what they were designed for. I would find myself a different tech. The small base tubes were designed to run in chassis with the glass pointing up like in a Marshall amp not upside down like in Fender style amps. It's not a pretty thing when a tube fails and arches across the base pins. Transformers can short out and cost a lot of money to fix.
     
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  19. cowmoo

    cowmoo Country Gent

    Aug 19, 2011
    North Wales
    Thanks again, I think the good stuff I’ve read is from hifi applications now I think about it. On ‘Jeffs place’ page. It came up in the first few on my search.
    I’ll swap him for some regular 6l6 tubes.
    Will I need a rebias if I put in a matched pair? ((I’m thinking the amp is getting hot even before these Russian tubes but there is no sign of anything untoward going on in the tubes when on)
     
  20. 6124Bassman

    6124Bassman Gretschie

    172
    May 20, 2018
    Tempe, Arizona
    Yes you will need a rebias. Chances are it’ll be close to how the tubes in it now are biased - but every set of tubes are different so I’d have it biased
     
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