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Thread: Newb needs help with tubes.

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    Question Newb needs help with tubes.

    So i have a used Randall RD45 that i bought which i need to buy tubes for. I'm a complete newb to tube amps and any information about replacing tubes regarding that fact would be greatly appreciated. I need to know what type of tubes to buy and where they go in the slots on the amp, and if i need to do any biasing.

    https://imgur.com/a/vrdLZtk

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    Last edited by Joshua M; 11-26-2019 at 11:30 PM.

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    Supporting Member TomCarlos's Avatar
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    If I am not mistaken, your amp uses dual 6L6 power tubes and 12AX7 preamp tubes. Are you sure you need to replace the tubes?

    A copy of the schematic can be found here - https://el34world.com/Forum/index.php?topic=20389.0

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    I might not actually have to replace those two power tubes now that you mention it, but from what i've read replacing those definitely improves the tone according to people who have used this amp and swapped out the tubes. As for the preamp tubes that you mentioned they are, there aren't any so those i have to buy for sure. Do i have to do a bias adjustment if only replacing preamp tubes? or is it just for power tubes or changing any tube in general? Thanks for the help.

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    Supporting Member TomCarlos's Avatar
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    You do not set bias for preamp tubes.

    As for the Power Tubes, do not assume the bias was set correctly. You might want to check that. The schematic has a recommended setting. You should see the bias pots near the tubes (on the chassis) - VR4B25K and VR5B25K. Do you know how to SAFELY use a voltmeter to measure voltages in a tube amp? If not, let someone else do it. The amp has HIGH VOLTAGE points and you could injure yourself if you are not familiar with this process.

    Check a datasheet for the 6L6 - https://www.tubesandmore.com/product...jj-electronics

    You might also read this thread for additional info - https://www.robchapman.tv/forum/thre...l-rd45h.35893/

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    Supporting Member The Dude's Avatar
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    Your amp uses two 6L6's and four 12AX7's. Generally, you only need to bias when changing output tubes, but it wouldn't hurt to check it even if you leave the existing tubes to verify they are working correctly.

    Edit: Another good link for calculating bias:

    http://www.tedweber.com/webervst/tubes1/calcbias.htm

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    All good questions, and welcome to the forum!
    Preamp tubes generally are used in a circuit that makes them self-biasing, so that they do not need to be biased by the user.

    edit: I see other, more detailed, posts were made while I was composing. Carry on!

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    Thanks for the replies everyone! I got all the answers i needed AND more, i appreciate it. I just have a question or two more. I was reading there is enough voltage in an amp to kill you? so IF i was to learn how to bias myself would i be encountering that risk?

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    Lifetime Member Enzo's Avatar
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    ANy time you expose the insides while it is powered up, that voltage is also exposed. You need to respect it. I mean the burners on your stove can incinerate your hand, so you need to respect that too, and not touch teh burners. It is a matter of paying attention to what you re touching. Nothing looks different just from having 500 volts on it.

    There are amps with EXTERNAL test points for bias, and EXTERNAL controls for that bias. In those cases, you generally are not exposed to danger.

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    That makes sense Enzo. So as long as you're knowledgeable in what you're doing and practice safety you'll be okay. I have no idea if my amp has external test points or controls. My other question was about the tubes. Do the tubes have to be the same model as are specified for the amp, or can you use other model tubes?

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    Supporting Member The Dude's Avatar
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    You need only be concerned about tube type (6L6 and 12AX7). Any brand will work.

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    Also know that 12AX7, 7025, & ECC83 are all the same tube type and will work the same in your amp.

    I would also stick with 6L6GC to start. There are other 6L6 types that are not the same spec as the GC version.

    Justin

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    Lifetime Member Enzo's Avatar
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    Agree^^^

    But any new tube sold these days with 6L6 on it or 12AX7 on it will work. You can learn for later about alternatives like 5881 for 6L6, or the 12AX7 types Justin mentioned.

    Tubes are like guitar strings. You may prefer Fenders or D'Addarios, but ANY brand will work in your guitar.

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    Awesome! Thanks a lot guys. I'll just stick with the 6L6GC then. Are the power tubes the only ones that change the sound of the amp? or do preamp tubes affect it also?

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    Supporting Member TomCarlos's Avatar
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    Any time you change anything in the signal path or even in the power supply, it "could" (and probably does) affect the sound of the amp. But will you hear it? That is another question and highly debated. And the same can be said for speakers. I had a friend try to demo this for me with his amp and power tubes. He swore he could hear a difference. All I could hear was a guitar that was out of tune and horrific playing skills!!

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    I think the person playing the guitar has the upper hand hearing the difference or rather feeling it. 😋

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    People get fixated about tube brands, which era they're from, whether they're NOS (new old stock) or whatever mojo they want to attribute to them. There's a load of rubbish talked about tubes and tone on the internet that I don't subscribe to. The main thing is that in general unless they go microphonic or otherwise faulty, preamp tubes last for many years. My '61 Ampeg still has its original preamp tubes and it sounds fine just like it is. I don't replace preamp tubes for the sake of it, in search of some imaginary goal - I replace them when they're faulty. Maybe the gain is down due to low emission, maybe a tube has become microphonic. Otherwise they last pretty well. The concern with tube amps is the power tubes. They get a beating in modern amps and are often pushed to the limit of their specs. An old tube is like old strings and an amp can sound refreshed just for having a new set of correctly biased tubes. An old power tube can fail dramatically and cause damage, whereas a failed preamp tube is often just a nuisance.

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    Joshua....

    Maybe these videos will answer some of your questions.

    Tube Amp Survival Guide #1

    Tube Amp Survival Guide #2

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Joshua M View Post
    So i have a used Randall RD45 that i bought which i need to buy tubes for.
    Do you know that it works? If so, how, if there are no preamp tubes in it?

    Quote Originally Posted by Joshua M View Post
    I might not actually have to replace those two power tubes now that you mention it, but from what i've read replacing those definitely improves the tone according to people who have used this amp and swapped out the tubes.
    Pay no attention to internet hype about changing tubes for tone. It's absolutely never a night and day difference between brands. Assuming the tubes are working correctly of course. Especially WRT an amp like that, where the preamp tubes will be doing virtually all of the clipping. The thing to remember is that few players are ever 100% satisfied with their tone and changing things gives them a security blanket that they've done what they can short of buying a different amp, which probably also wouldn't help. And, of course, many will spend the equivalent of another amp changing parts in their existing amp trying to find a tone that makes them happy. So they're ALWAYS super duper stoked about whatever they bought or did to their amp and ALWAYS hear a positive change whether it's there or not. Sometimes there's change, but it's so small as to be ignorable. And sometimes the change is only change, and not necessarily an improvement in every players subjective opinion. Soooo...

    Don't fall into this trap. Make sure the tubes you have are working properly and biased correctly and then play your guitar. That's the very best way to improve your tone. Most players on a quest to change up their gear are really looking for the magic tone that makes them sound like they PLAY better as apposed to sound better. JM2C on that. And...

    If you're going to do the work yourself then please search and read here and elsewhere about safety when working inside amplifiers. There aren't that many things you need to know though some of it may seem over your head before the first time you do it. Learn it anyway and be careful. You shouldn't feel threatened though. People work in amplifiers all the time. Just consider that flying in a plane has a relatively safe record, but you wouldn't want to suddenly find yourself at the yolk a mile high without having ever read the instructions

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    Last edited by Chuck H; 11-27-2019 at 04:06 PM.
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    Member HaroldBrooks's Avatar
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    Quote Originally Posted by Chuck H View Post
    Do you know that it works? If so, how, if there are no preamp tubes in it?



    Pay no attention to internet hype about changing tubes for tone. It's absolutely never a night and day difference between brands. Assuming the tubes are working correctly of course. Especially WRT an amp like that, where the preamp tubes will be doing virtually all of the clipping. The thing to remember is that few players are ever 100% satisfied with their tone and changing things gives them a security blanket that they've done what they can short of buying a different amp, which probably also wouldn't help. And, of course, many will spend the equivalent of another amp changing parts in their existing amp trying to find a tone that makes them happy. So they're ALWAYS super duper stoked about whatever they bought or did to their amp and ALWAYS hear a positive change whether it's there or not. Sometimes there's change, but it's so small as to be ignorable. And sometimes the change is only change, and not necessarily an improvement in every players subjective opinion. Soooo...

    Don't fall into this trap. Make sure the tubes you have are working properly and biased correctly and then play your guitar. That's the very best way to improve your tone. Most players on a quest to change up their gear are really looking for the magic tone that makes them sound like they PLAY better as apposed to sound better. JM2C on that. And...

    If you're going to do the work yourself then please search and read here and elsewhere about safety when working inside amplifiers. There aren't that many things you need to know though some of it may seem over hour head before the first time you do it. Learn it anyway and be careful. You shouldn't feel threatened though. People work in amplifiers all the time. Just consider that flying in a plane has a relatively safe record, but you wouldn't want to suddenly find yourself at the yolk a mile high without having ever read the instructions
    This ! All of it !

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    Quote Originally Posted by Chuck H View Post
    Do you know that it works? If so, how, if there are no preamp tubes in it?



    Pay no attention to internet hype about changing tubes for tone. It's absolutely never a night and day difference between brands. Assuming the tubes are working correctly of course. Especially WRT an amp like that, where the preamp tubes will be doing virtually all of the clipping. The thing to remember is that few players are ever 100% satisfied with their tone and changing things gives them a security blanket that they've done what they can short of buying a different amp, which probably also wouldn't help. And, of course, many will spend the equivalent of another amp changing parts in their existing amp trying to find a tone that makes them happy. So they're ALWAYS super duper stoked about whatever they bought or did to their amp and ALWAYS hear a positive change whether it's there or not. Sometimes there's change, but it's so small as to be ignorable. And sometimes the change is only change, and not necessarily an improvement in every players subjective opinion. Soooo...

    Don't fall into this trap. Make sure the tubes you have are working properly and biased correctly and then play your guitar. That's the very best way to improve your tone. Most players on a quest to change up their gear are really looking for the magic tone that makes them sound like they PLAY better as apposed to sound better. JM2C on that. And...

    If you're going to do the work yourself then please search and read here and elsewhere about safety when working inside amplifiers. There aren't that many things you need to know though some of it may seem over your head before the first time you do it. Learn it anyway and be careful. You shouldn't feel threatened though. People work in amplifiers all the time. Just consider that flying in a plane has a relatively safe record, but you wouldn't want to suddenly find yourself at the yolk a mile high without having ever read the instructions

    I'll trust everyone's wisdom here and treat amp tubes like guitar strings and only replace them if they're broken or really old and i actually have not turned the amp on yet due to not having a speaker to connect it to which i'm currently working on(i've made my own 1x12 speaker box) so i don't actually know if the tubes are working properly AND i also was assuming that it didn't have preamp tubes because the metal caps over them until yesterday that i took them off and revealed what i did not know

    Quote Originally Posted by TomCarlos View Post
    Joshua....

    Maybe these videos will answer some of your questions.

    Tube Amp Survival Guide #1

    Tube Amp Survival Guide #2
    These videos were helpful, thanks! it was what prompted me to take off the caps from the preamp tubes and find them hiding lol.

    ---I have a question regarding the 1/4" speaker cable plug which i hope i can get answered here instead of have to make another thread?? The positive and negative sides that connect to the speaker i have attached a pair of disconnects--as for the other end, do i have to solder them onto the plug terminals? i've noticed that i could also just use a pair of disconnects on the terminals of the plug. And which wire goes onto which terminal(one is shorter than the other)?

    https://imgur.com/a/VnR4dtl

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    Last edited by Joshua M; 11-28-2019 at 07:30 AM.

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    Lifetime Member Enzo's Avatar
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    Nothing wrong with crimp connectors, I use them all the time.

    That said, I generally prefer to solder wires to my jacks in cabs simply because any vibration will not knock them loose.

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    Member HaroldBrooks's Avatar
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    Quote Originally Posted by Enzo View Post
    Nothing wrong with crimp connectors, I use them all the time.

    That said, I generally prefer to solder wires to my jacks in cabs simply because any vibration will not knock them loose.
    Enzo, I have used crimp connectors for many years, until... The other guitarist in my band had a poor connector that eventually failed at a gig, and the single speaker in his amp became disconnected right in the middle of a roaring rock song. Fortunately, no damage was done to the output transformer because he stopped playing fairly quickly, but I realized at that point that an good, and I underscore the word "good" and correctly executed solder connection would minimize such a connection failure.

    Since then I only solder all my speaker leads. Cheap insurance, and if you solder correctly, an extra 5 minutes at most for a single speaker. Not trying to disparage the use of crimp connectors, just saying there is a slight chance of a type of failure that is less apt to happen with a properly wire wrapped and soldered connection.

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    Last edited by HaroldBrooks; 11-28-2019 at 09:27 AM.

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    On your speaker jack, the shorter lug would be (-) and go to the negative speaker terminal.

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    Lifetime Member Enzo's Avatar
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    Harold, your point is taken, but there is no connection of any kind that cannot fail. Threads here are endless with failed solder connections. But literally millions of speakers have push on crimped connectors in our speaker cabs and combos, and they work reliably and well. Certainly nothing wrong with solder, I prefer it, but crimps are not something to mistrust, at least in my opinion.

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    Member HaroldBrooks's Avatar
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    Quote Originally Posted by Enzo View Post
    Harold, your point is taken, but there is no connection of any kind that cannot fail. Threads here are endless with failed solder connections. But literally millions of speakers have push on crimped connectors in our speaker cabs and combos, and they work reliably and well. Certainly nothing wrong with solder, I prefer it, but crimps are not something to mistrust, at least in my opinion.
    Ok, I see your point. I believe it also has to do with the way you dress the crimp connection, if at all, and if corrosion on the metal to metal surfaces gets hold of it because of touching the surfaces of the connection, and exposure to the air and oxidation directly over time.

    I realize solder joints can fail, but I have a feeling (based on some observation) if you wrap the wire around a cleaned post with a few turns tightly, and cover the whole affair with solder at the right temperature, the connection becomes a high surface area contact that is encased after a fashion, and only the outside of the "Blob" is exposed direclty to the air, hence the potential for longevity. That's why I've see a fair amount of connections from the 1940's amps that are still solid, because they were done right.

    But you have to go with the actual stats as you know them, and if you see very little issues with crimp connections, then I will defer to your larger experience and judgment. Nothing like seeing a lot of amps to determine the reality of what fails and does not, and for that I might still be lacking.

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    Lifetime Member Enzo's Avatar
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    For what it is worth, and just my opinion, but I think most solder joints fail from vibration or thermal expansion, rather than oxidation on the surface.

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    Aside from the reliability factor, it drives me nuts when a manufacturer of a combo amp has the amp end of the speaker lead hardwired and also soldered to the speaker. This is when I want to see spade connectors at the speaker end. I don't want to have to unsolder at the speaker just to pull a chassis.
    If you have a connector at the amp end, then I agree with soldering at the speaker end.

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    Lifetime Member Enzo's Avatar
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    yes, I like that better than the way I tried to say it.

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