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Thread: i need help retubing a Marshall TSL602 combo

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    i need help retubing a Marshall TSL602 combo

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    Does anyone have experience tun=bing one of these or a similar amp?
    Right now I'm only changing pre amp tubes. There are three preamp tubes in a row on a metal strip, and the last one (furthest from the power tubes) has some kind of metal tube over it and I can't figure out how to take it off! Why is this tube covered? Also, wondering if this may be the phase inverter, or if the phase inverter is the preamp tube right next to the power tubes.
    Thanks for the help.
    werewolf

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    Hi!

    I don't have that amp but I can take a couple educated guesses for you.

    Either you push in and twist on the cover and it will come off, OR it's not a tube at all, but a capacitor and it should not be removed. Sometimes these look the same, and on some amos they're right next to each other. If I had a schematic of that amp I'd tell you, but I don't. If you twist on the cover ever so gently and it doesnt move, it probably isnt a tube cover.

    Hopefully someone else may own that amp and be able to tell you.

    H2H

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    I was able to take it off. Pushed in and twisted it off and there was a tube in there. This cover had a little spring inside of it. It wouldn't have anything to do with reverb would it? I'd still like to know what this cover is for.

    I'm just going to assume that this covered tube is not the phase inverter since it's furthest from the power tubes.

    Thanks for the reply H2H.

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    Another question, same topic.

    I know it's best to have an amp rebiased when changing power tubes. BUT, is there any danger in taking out the old power tubes to clean the pins with contact cleaner and then put them back in? I noticed the preamp pins were absolutely filthy. I imagine the power tubes are just as bad.

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    On some amps all the pre amp tubes have those covers. The only purpose for the spring it to hold the cover on well for the "push and twist" thing and so it doesn't rattle. The covers themselves act as heat shields mostly. Though I have ran amps without them at all and not hurt a thing. I'm kind of suprised that there was only one cover, usually they're all covered, or none covered.

    As far as which is the phase inverter, it's hard to tell without a tube schematic. Maybe they have those on their site? I dunno.

    H2H

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    there is no danger in pulling out the power tubes. You won't mess up the bias.

    Just make sure it's unplugged and turned off.

    H2H

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    Quote Originally Posted by werewolf831
    This cover had a little spring inside of it. It wouldn't have anything to do with reverb would it? I'd still like to know what this cover is for.

    I'm just going to assume that this covered tube is not the phase inverter since it's furthest from the power tubes.
    The metal cover's purpose is SCREENING that tube.This is the main issue (because the first tube is the most critical regarding external influences) but such a cover helps as well on reducing microphonics and cooling the tube in question.
    If your amp has that "bayonet" shield on the first tube only,that's it....the engineers thought that there's no need to put shields on the others.Still,I'd look at the shape of each small tube's socket:including the first one,do they have the same metal collar around the base?In this case,the amp was initially provided with shields on all smaller tubes,but someone got them off and forget the shields somewhere,except the first tube!
    Yes,your assumption is correct:the farthest tube from the outputs is in most cases the input tube (gain).The PI tube is the closest to the outputs,due to a logical signal path.
    About the pin cleaning,please DO NOT,for any reason,use something like you said you'd use (contact cleaner) for cleaning!
    The point is that this kind of stuff goes for pots,switches or whatever what's supposed to work at ambient temperature.Tube's pins are,thermally,another story....they heat together with the tube and,even if they don't reach the bulb temperature,any of those chemicals used for cleaning will caramelize there.This means a poor contact and more trouble in the future.
    You can clean the pins with isopropyl alcohol (the one wich is evaporate fast and doesn't leave any traces of water),the same alcohol we used two decades ago for cleaning the magnetic heads on our beloved reel-tracks.
    About bias,yes,it's safe to get the amp to a tech for that operation (it's a must if you changed the output tubes and it should take only a few minutes).
    Regards,

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    Quote Originally Posted by Hard2Hear
    Though I have ran amps without them at all and not hurt a thing. H2H
    You forget to mention WHAT amps you ran without those shield cans.
    I wouldn't try that on a medium-gain (Mesa,Acoustic) or hi-gain (Soldano,Peavey 5150),especially if the amp in question is cranked!

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    I hate mesas and I TOTALLY HATE Soldanos. But I did run my Soldano without the shields while I was experimenting with different pre amp tubes in it. I didn't notice any extra noise or added microphonics when I did it. Mostly I have removed the covers from Fenders, cause I have owned about 15 Fender tube amps. I do it when changing around pre amp tubes all the time. Its a PITA to put them back on when swapping in and out. I always put them back on when I'm done, mostly because I'd lose them if I didn't.


    But don't you find it interesting that there was only a cover on ONE of the pre amp tubes? I would think they all had covers at one time.


    H2H

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    Wow, good info.

    FYI, I bought this amp about 4 yrs ago from Musicians Friend "scratch and dent" section. Never had any problems, and yes only one tube cover. Mind you, I only use this amp at home and the Master volume rarely gets cranked past 3. Although I do crank up the channel volume.

    As for the contact cleaner, it's too late. I already used it. I got the idea from the Eurotube websites FAQ. Here's a quote.

    "It's also a good idea to clean the tube sockets before installing new tubes. This can easily be done by spraying contact cleaner on the pins of one of your old tubes and working the tube in and out of each socket a few times. Do this for both preamp and power tubes."

    After reading some posts here, I've seen several people recommend Isopropyl alcohol as well. Think I'll go this route next time.

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