making a cheap amp better

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by reachjkh, Apr 27, 2004.


  1. reachjkh

    reachjkh Member

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    Along with window shopping for a new amp head, I'm thinking about how I can fix up my little Crate combo as a backup amp.

    I've been wanting to make a head out of it. I think I'll have someone build the box for me, but while that's being done, I'd like to add a few other features if I can.

    I'd like to mount tube sockets to the chassis and remove the sockets that are soldered into the PCB, add a fuse holder(I think the fuse is soldered in currently), add a receptacle for a removeable power cord, put a speaker jack where the wires currently hang out for the speaker, and maybe add an input on the rear panel for when it's rack mounted.

    This should make it a little more useful to me.

    The only problem is that I don't have any experience buying tubes. Unfortunately, there are no markings on my tiny little power tubes, so I'm getting the schematics from Crate 'cause I can't buy new ones if I don't know what type they are.

    I'd like to add a standby switch too, but I don't know quite how to do that yet.

    (I have an electronics background, so I know enough to not get myself killed while poking around)

    Anyone ever do something like this? Seems like most folks here are into much nicer gear than what I currently play.
     
  2. aleclee

    aleclee TGP Tech Wrangler Staff Member

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    Dunno if a lot of the stuff you're thinking about is worth the effort. Of the mods you describe, installing an IEC power connector is probably the only one I'd even consider.
    1. None of the mods you're proposing is gonna change the tone of the amp, except perhaps the speaker out which facilitates mixing/matching speaker cabs. How happy are you with the way the amp sounds? Do you anticipate holding on to the amp long enough and using it enough to make a lot of these changes (e.g., fuse socket) worthwhile?
    2. A decent head cab is probably a significant portion of the value of the amp...unless your friend is really hooking you up. ;)
    3. Is there a place on the chassis to mount the tubes? I dunno if an improvised chassis-mounting is gonna give you better reliability (assuming that's what you're after).[/list=1]My $0.02, IMHO, FWIW, YMMV, etc.

      Since you describe the power tubes as "little", they're probably EL-84s. What model Crate is it?
     
  3. reachjkh

    reachjkh Member

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    It's a Vintage Club 20 watt combo (VC2112RB). I'm just putting it in a simple hardwood box with metal grill to keep hands out, nothing extravagant.

    I was under the impression that PCB mounted sockets could be a problem due to heat and flexing over time(I'll probably never sell this since it has no resale value)? Maybe you're right about that not being necessary. I could do that in the future if needed.

    The fuse holder does seems pretty imperative to me though if I want to use the amp for gigging even as a backup. I'd hate to loose a gig's pay over a fuse. And the rack ears and power cord sockets are being recycled from some old Compaq servers.

    Thanks for the reply, if you know what power tubes this thing takes, it would save me some turn around time waiting for the schematics to arrive.
     
  4. aleclee

    aleclee TGP Tech Wrangler Staff Member

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    It seems somewhat improbable to me that you'd blow a fuse in a backup amp (assuming you have reasonable power to the amp). If your #1 is adequately reliable, it seems to me that you wouldn't have to get the backup out often enough to worry about it blowing a fuse on the gig.

    That's just my opinion but it's your amp and your time.

    I found several references indicating that it uses a pair of EL84s.
     
  5. John Phillips

    John Phillips Member

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    I actually think all those changes are fairly worthwhile except for chassis-mounting the tube sockets. That is A - a lot of work; and B - could just possibly cause trouble since you'll change various internal capacitances between lead wires to the tubes, which might be used deliberately to control gain at high frequencies - and you'd only find out afterwards, if the amp became unstable (or may just sound bad),

    The speaker jack, fuse holder, power socket and standby switch (which is used to disconnect the B+ feed, usually just after the rectifier) are pretty easy to do and shouldn't change the way the amp works.
     
  6. reachjkh

    reachjkh Member

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    You're probably right, but it's a simple fix. Actually, if I don't sell some gear soon, it may be my main amp until we get a few weddings under our belt(just joined a band).

    This must be the paranoid side of me coming out. I carry around more odds and ends "just in case" when I play. I actually carry drumsticks in my bag just in case the drummer forgets his.

    Thanks for the info on the tubes.
     
  7. reachjkh

    reachjkh Member

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    Ok, nix changing the sockets. Bad idea on my part.

    Thanks for the info on the standby switch.
     

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