back again with the old tube amp!

Discussion in 'Mixing' started by drumist69, Oct 3, 2005.

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  1. drumist69

    drumist69 Active Member

    Ok. I've posted about this before, but haven't done anything yet, other than buy this old tube amp. The unit was pulled from a Zenith mono record player cabinet (circa 1956!). The guy I got it from re-capped it, replaced the weak tubes, and converted the ins and outs to 1/4" jacks. The amp is 15 watts. There is a 6J5 tube in the preamp stage, a 12AX7 (it says AF Amp-Phase Inverter in the specs...is this for the tone controls?), a 5y3gt rectifier tube, and a pair of 6v6gt for output tubes. First thing to do is replace the old two prong cord for a grounded cord! I'm thinking this can be used as a nice small guitar amp pretty much as is. I'd have to move a few things around to get it in a cabinet, but no biggie. The one thing I was wondering about was the possibility of using this as a mic pre. I know I don't want 15 watts going into my PC, so I was thinking the way to go was to use an attenuator to reduce the output. Today, I was reading about removing an output tube from a guitar amp to reduce the power for lower volume playing. I got to thinking, would it be possible to pull both output tubes and just use the preamp stage? This is my first exploration into tube electronics, and I haven't found any info regarding this idea yet. I know from reading in this forum that Kev would be one guy to talk to about this, so c'mon Kev, tell me what a stupid idea this is! If I pull both output tubes, what will happen? I have a schematic, but I'd have to scan it at work tomorrow to post it. Peace!
     
  2. MilesAway

    MilesAway Guest

    You can remove 1 tube in Class A/B amps ONLY to cut the power in half... there are impedance issues involved with this that i can't remember so you'd be better off looking this up. Regardless though, i *really* doubt an amp that old (and that low-power) is running in Class-A/B operation so chances are, that's not going to be an option for you.

    As for "pulling both tubes" and running it as a preamp... DON'T! If you just want the preamp functions, find out where the preamp goes into the poweramp in the schematics and wire up a jack there, in the same way an "FX-Send" would be wired in a modern amp.
     
  3. MilesAway

    MilesAway Guest

    sorry - just clarifying the first part: You can remove one tube in EACH PAIR for Class A/B amps...
     
  4. CoyoteTrax

    CoyoteTrax Well-Known Member

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    At 15 watts output you're probably talking 8 Ohms...mayyyyyyybe 16. As a guitar amp I'm sure it will sound very cool, you just need a speaker enclosure to connect to, which can be bought cheap on ebay usually. Impedence is the next question though. What's the output impedence? Personally I've purchased a few on ebay for different tones. The last one I bought was just a late 50's, early 60's Viking enclosure loaded with it's original 8 in. speaker. Ya gotta love the sound of those old magnets. Mic'ing an 8 in. enclosure works for guitar AND bass. Paid like $15 or something like that :lol:

    Miles has the right idea about adding an output jack where the preamp section ends. Then you can use it as a pre-amp or instrument amp, which is an advantage of using antique RTR's for the same purpose.

    An attenuator will work as well to convert this unit in a nice DI when you want.
     
  5. drumist69

    drumist69 Active Member

    thanks!

    Thanks for the input, guys! Lets see, the load is 8 ohms. I have a speaker I will use until I score a cooler one. I've got a lead on a pair of 1950-1960 era Jensens ( I think they're 12's)...the guy will sell me the pair for $50!!! I'm going to check those out soon. As for the pre-amp jack...duh! That's a great idea! I should have thought of that! It looks like this amp will be my project for this winter. So now I have to move the in and out jacks, add a jack in the pre-amp stage, build a cabinet for the whole thing, and one for the Jensens if I get them. I will just build a single enclosure, and probably hold on to the other speaker, or sell it for way more than he's selling them to me for! If and when I get this project off the ground I'll post some audio clips of what it sounds like, and maybe pics. Thanks again! ANDY
     

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