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tube amp... and a tube warehouse.

Discussion in 'Amps and Cabs [BG]' started by elgranluis, Mar 20, 2005.


  1. elgranluis

    elgranluis

    Feb 14, 2003
    El paso, TX
    hello everyone. Ok, i've gotten sick of searching for info on tube amps. Here is my dilemma: I recently purchased a tube amp from an old man. Said amp is basically a chassis from an unknown brand, which was modified (it contains some solid state components, sort of a mic preamp) by someone. There is a sticker inside that says omething like "serviced by *&^^ in "80. Ok, making the story short, ive looked all over the net for some deep info on tube amps, because i have the following questions:

    1.- The output transformer has two leads taped off. not in use. What are those? There is no impedance switch or evidence that there ever was one.
    2.- There are 3 12axt and two 12at7 tubes, plus a reverb tank. I am guessing that the 12at7s control the reverb. Can i just remove them?
    3.- i connected a speaker to the "ext speaker" output, without connecting one to the "speaker" output. Common sense told me that they would be connected in parallel and it would be the same if i used either one, but i got a very weak signal; very little volume. What is the reasoning behind this?
    4.- i can't find the exact filter capacitor values. What should i use ar replacements?

    Anyway, i have several of those questions, i was hoping to find an answer or maybe someone could point in the right direction....


    About the tube warehouse, well, it turns out i was searching for some caps, and just to make conversation with the guys at the electronics store, i asked them if by any chance they had some kt66 tubes, or 6l6. Well, the owner tells me "well, actually I do, I have a small warehouse full of old tubes :hyper: , but it just aint worth the hassle to go there and search around for a single tube. They are leftovers from the tube era. I haven't had a chance to throw them away." Of course, I wasn't gonna tell the man that those tubes may be worth some money :D . I talked the guy into letting me drive one of his employees to the warehouse and checking out the tubes to see if i can use some of them. I didnt want to look too excited so i told the guys i'd be back next week. So, bottomline is, i'm gonna offer the guy 100 bucks or so to "clean" his warehouse. What king of tubes should I be on the lookout for? Please include brands and , if available, pics.
     
  2. Kelly Lee

    Kelly Lee Yeah, I'm a guy! Supporting Member

    Feb 17, 2004
    Marana, AZ, USA
    Here are a few I have found since I'm a tube noob. Hope they help:

    Ask Jan First® Go to the infozone header and click. There are some links there.
    LONDON POWER Scroll to the bottom to the Help & Reference section.
    Tube Index ?'s
    Tube Amp FAQ
    Tube Amplifier Links
    Answers & Info

    Edit:BTW, if you can score me some vintage 6550 tubes I'd be your friend forever! ;) Seriously, tubes to be looking for that I know of are...
    KT-88
    6550
    EL84
    EL34
    6V6
    6L6GC
    12AX7 (ECC83)
    12AU7 (ECC82)
    I'm sure there are some more but those are the more common ones. As far as brands, I'm not real up on all of them so someone else will have to chime in on that.
     
  3. elgranluis

    elgranluis

    Feb 14, 2003
    El paso, TX
    thanks a lot, i'll start reading. I'll be on the lookout for your tubes ;) and the ones on the list, thanks a lot!
     
  4. the dude

    the dude Supporting Member

    Sep 19, 2004
    Indy
    Woah! Sounds like a possible find!

    I'd also be all over a half dozen or dozen vintage 6550's as well...if such a stock exists.
     
  5. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY
    Tube brands can be confusing, since tube makers cross branded their tubes....but if you found some old 6L6's I'd be your friend forever. ;)

    Look for RCA blackplates. For 12ax7's, RCA, Sylvania, Telefunken, Mullard...the list goes on and on...yet I've forgotten much of what I once knew about brands...

    Really, I wouldn't be surprised if you could do well with all you find, and there are collectors out there for most NOS tubes. A bunch of the online tube sellers will buy too. I'd try Eurotubes first, since that guy is super nice.
     
  6. jdombrow

    jdombrow Supporting Member

    Jan 16, 2002
    Colorado Springs, CO
    Here's another place to post your questions:

    http://www.audioasylum.com/forums/pro/bbs.html

    Do not turn this amp on without speakers connected. Tube amps must have a load, or you will damage the amp. If the 2nd speaker output is not connected directly in parallel, you may have damaged something already.
     
  7. elgranluis

    elgranluis

    Feb 14, 2003
    El paso, TX

    I was thinking that if they did have the 6l6, which the owner said they did, then they would certainly have the 12ax7's. I don't want to get too excited (moneywise); the tubes might as well be from some unknown brand name or manufacturer.
     
  8. elgranluis

    elgranluis

    Feb 14, 2003
    El paso, TX

    There was a load, since i could hear the amp though the speaker, but with very low gain. I opened it up and yes, the lead from the transformer is connected to the speaker jack and bridged to the ext speaker. I'm guessing it just went bad.
     
  9. Passinwind

    Passinwind I Know Nothing Supporting Member

    Try the Ampage guitar amp forum at www.firebottle.com . There are a lot of knowledgable, helpful people there.

    1.- The output transformer has two leads taped off. not in use. What are those? There is no impedance switch or evidence that there ever was one.

    Could still be alternate impedance taps, and that amp wasn't ever intended to drive those impedances. Could be ultralinear screen grid taps too. Unused taps are pretty common, actually, since one transformer may be used in many amp designs.

    2.- There are 3 12axt and two 12at7 tubes, plus a reverb tank. I am guessing that the 12at7s control the reverb. Can i just remove them?

    You can often safely remove preamp level tubes for long enough to figure out what their function is, but you should be able to trace connections to the reverb tank or reverb driver transformer pretty easily. If you leave them out, the other tubes will see a bit higher B+ voltage, you should check filter cap ratings to be sure you're not going past their ratings. You need to check voltages with a meter, don't just guess it's OK. Usually, there's enough margin, and for bass you might see some extra headroom. 12AT7 is used as a driver tube for power amps a lot though, so you might find you get no sound at all if you remove both of those.

    3.- i connected a speaker to the "ext speaker" output, without connecting one to the "speaker" output. Common sense told me that they would be connected in parallel and it would be the same if i used either one, but i got a very weak signal; very little volume. What is the reasoning behind this?

    On many amps (Fender comes to mind) you must first use the "speaker" output, and you can only then use the external speaker tap. Look for a switching jack on one or both of the outputs. That shorts an output tap to provide some load so you don't cook your OPT and/or tubes or tube sockets. Look at a schematic on the Fender Field Guide site to see how the two jacks usually are in some sort of series arrangement, not in parallel. What you heard is completely consistent with that wiring arrangement, BTW.

    4.- I can't find the exact filter capacitor values. What should I use as replacements?

    Go higher by 10-20%, not a big deal as long as the voltage ratings are sufficient and the replacement will physically fit.

    Oh, yeah: the usual warnings about life threatening voltages apply here. Make sure you're up to speed on safety issues, or don't poke around inside tube amps.

    luck,

    _________Charlie
     
  10. elgranluis

    elgranluis

    Feb 14, 2003
    El paso, TX
    You can often safely remove preamp level tubes for long enough to figure out what their function is, but you should be able to trace connections to the reverb tank or reverb driver transformer pretty easily.

    -----yep, i found the trace. There is a reverb transformer hooked to the 12at7. there is also another identical transformer hooked to what seems to be a rectifier section. Any info on that?


    12AT7 is used as a driver tube for power amps a lot though, so you might find you get no sound at all if you remove both of those.
    -------actually, i forgot to mention there are 6 power tube sockets, sporting general electric's kt66.


    On many amps (Fender comes to mind) you must first use the "speaker" output, and you can only then use the external speaker tap. Look for a switching jack on one or both of the outputs. That shorts an output tap to provide some load so you don't cook your OPT and/or tubes or tube sockets. Look at a schematic on the Fender Field Guide site to see how the two jacks usually are in some sort of series arrangement, not in parallel. What you heard is completely consistent with that wiring arrangement, BTW.


    ---------you are right agan. Two switching jacks.





    you have been most helfull, thanks a lot!
     
  11. Passinwind

    Passinwind I Know Nothing Supporting Member

    So, bottomline is, i'm gonna offer the guy 100 bucks or so to "clean" his warehouse. What king of tubes should I be on the lookout for? Please include brands and , if available, pics.

    Start here: Triode Electronics Tube Index

    Grab pretty much anything listed on that site, for starters, if you have time to go for a bunch of stuff. Don't sweat brands too much, lots of them were rebranded major manufacturers' production, since there never were all that many tube makers. GE, RCA, Sylvania, Philips, Mullard, and Amperex generate a lot of lust though. Pictures aren't that helpful either, especially for preamp tubes, which look pretty similar until you get into esoteric details. Expect to spend lots of hours trying to read faded numbers on old tubes, especially if they are used. :cool:

    Take a look at the Angela Instruments website for some insight too: http://www.angela.com/ .

    Someone bought me a big box of old tubes for 5 bucks. The very first preamp tube I checked out was worth ~$15, even used, and there were a dozen more just like it in there. Most of 'em work fine too. I culled out most of the audio ones, and gave away the rest, which were mostly radio tubes. I'm not selling anything, in case anyone is wondering.

    If the present owner, or you, are sharp, you can make quite a bit reselling on eBay. Best of luck!
     
  12. elgranluis

    elgranluis

    Feb 14, 2003
    El paso, TX
    btw, about the speaker wiring. Do i want to keep it that way (i have 2 8 ohm cabinets), or should i redo the output wiring? Ive read that, in tube amps, if an impedance match is not available, it is better to "aim" towards lower impedance than higher. If an amp is designed for 4 ohms, and i put a 2 ohm load, then it is prefferable than putting a 16 ohm load on the same amp. Thanks!
     
  13. Passinwind

    Passinwind I Know Nothing Supporting Member

    That's correct, but with a cool amp like that, I'd check out those extra taps and see if you can get the correct match, and hence full clean power output. Be careful, meter the extra taps and be sure they're not on the primary side, which would be really bad juju if you hooked a speaker or dummy load up to it.

    -----yep, i found the trace. There is a reverb transformer hooked to the 12at7. there is also another identical transformer hooked to what seems to be a rectifier section. Any info on that?


    Filter choke (inductor) for the power supply. A lot of times the screen voltage is derived right after the choke. It looks the same as the 'verb transformer, but probably isn't, actually. Don't mess with it, you want it there. :cool:

    ----------CE

    PS: you can PM me if you want to get a little deeper into your amp, but try posting at Ampage too, you'll learn a ton there.
     
  14. elgranluis

    elgranluis

    Feb 14, 2003
    El paso, TX
    thanks a lot again!
     
  15. Passinwind

    Passinwind I Know Nothing Supporting Member

    No problem, I live to serve and confuse. :cool:

    you have been most helfull

    Have you been talking to my wife? :eyebrow:
     
  16. elgranluis

    elgranluis

    Feb 14, 2003
    El paso, TX
    the p and the s not always work on this keyboard, and it makes for some wonderfull word combinations ;)
     
  17. Rockbobmel

    Rockbobmel Supporting Member

    PLEASE, Please, email me if you have some 6L6/KT66 and 6550/KT88 tubes. Thanks, Bob
     
  18. DubDubs

    DubDubs

    Aug 23, 2004
    Los Angeles
    Do you have any pics of this crazy amp? For those of us that don't understand the tech talk in this thread we need pretty pictures to look at :D
     
  19. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    Maybe you should just list all the tubes (brand and type) you find in this warehouse on this thread so people would quit bugging you about it...
     
  20. DEVILMAN

    DEVILMAN

    Nov 24, 2001
    New York,NY
    ...LMAO...

    ~S~