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Thread: building 6aq5 based harp amp 6x4 rectifier12ax7 preamp

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    building 6aq5 based harp amp 6x4 rectifier12ax7 preamp

    Hi does anyone know of a schematic I could use that would use these tubes. I have a chassis with these tubes and transformers that look good they are labeled C-9.281 (515 613) and C-9 264-E(515 623) The amp was one I bought as parts had a 6at6 wired in as well outputting to a 4 ohm speaker. I would like to built something like a champ or a kalamazoo model 1. My problem is I am a complete novice so need something I do not have to know how to adapt values etc. I am learning as I go here is a pic.Click image for larger version. 

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    Senior Member booj's Avatar
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    Just go to google images and type in "50's amplifier schematics" or whatever gets you some scats. Get the diagrams of the tubes. The 6AQ5 will give you a solid 2 watts output.

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    Don't forget the joker g1's Avatar
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    The Kalamazoo used a 6BQ5 Kalamazoo Amp Field Guide: Model 1 Schematic
    This amp uses a 6AQ5 but with 5Y3 rectifier http://www.angelfire.com/vt/audio/se6aq5schem.gif

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    Supporting Member loudthud's Avatar
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    The Kalamazoo Model 1 needs a dual triode (12AX7) as a preamp tube which requires a 9 pin socket. A 6AT6 won't have enough gain, you will just barely be able to overdrive the 6AQ6. If you don't want to modify the chassis to install a 9 pin socket, one option would be to use a 6AU6 pentode as the preamp tube. There was a Silvertone amp that used that tube, I'll look for the schematic.

    Link to Kalamazoo schematic, the one above is blocked: http://www.el34world.com/charts/Sche...oo_model-1.pdf

    The following thread uses a 6AU6, 6AQ5 and 6X4. But, it is unproven and it would probably need to be tweeked to your power transformer. One thing I don't like about it is the volume control before the 6AU6. What you would really like for a harp amp is volume and tone between the 6AU6 and 6AQ6. Link: http://music-electronics-forum.com/t26033/

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    Last edited by loudthud; 02-23-2012 at 04:32 AM.
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    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Possibly over your head right now but... think to the future.
    I would dump the 6X4 in that socket rewire it and use two power tubes with a solid state rectifier and a little 12 watt push pull output tranny... then you could use that 12ax7 and the 6at6 as a cathodyne driver... what you think?
    I bet you could easily get 7 to 10 watts out of what you'd have.

    I added a lousy, mouse drawn schemntaic so you can see what I mean....
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by Bruce / Mission Amps; 02-24-2012 at 06:49 PM. Reason: add scribble
    Bruce

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    Supporting Member Zer09's Avatar
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    Quote Originally Posted by terryepayne View Post
    Hi does anyone know of a schematic I could use that would use these tubes. I have a chassis with these tubes and transformers that look good they are labeled C-9.281 (515 613) and C-9 264-E(515 623) The amp was one I bought as parts had a 6at6 wired in as well outputting to a 4 ohm speaker. I would like to built something like a champ or a kalamazoo model 1. My problem is I am a complete novice so need something I do not have to know how to adapt values etc. I am learning as I go here is a pic.Click image for larger version. 

Name:	P1030840.JPG 
Views:	188 
Size:	2.88 MB 
ID:	13416
    Look at the Gibson Crestline GA-5 Skylark (around 1963-64). It had 2 6AQ5's, 6x4 rectifier, and 6c4 phase inverter (for your 7 pin socket) and 6eu7 preamp (which you can easily rewire the 12ax7 socket for or just use a 12ax7). They make great harp amps. Sold mine to a harp player who was starting up a recording studio here in NJ a few years back and he loved it. Figure 5 in this link. I may still have a copy of the schematic. http://www.angelfire.com/blues/rocki...lark_ga_5.html

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    Last edited by Zer09; 02-25-2012 at 03:59 PM. Reason: forgot link

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    I'm with Bruce. I like the Tweed tone control though. Did these a while back and might use a couple of different values now. Basically a Fender Harvard.




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    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    Very nice.... what preamp tubes did you use?
    I think your amp, with 6AQ5s power tubes and the two preamp section's cathodes bypassed, will probably have too much gain for him.
    Remember, he said "harp amp" with 6AQ5s.
    Also, in my opinion (which isn't worth that much, ha ha)... the classic Fender, tweed tone control is not quite as good for a quick and dirty Chicago Blues harp amp either.
    Actually, the Fender tone control might be better, but that would be better for guitar players, not electrified harp players.
    The two component, "High-Cut Tone" I drew seems to really work well with most harp players wanting a very simple circuit.
    Easy to try them both though.

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    Bruce

    Mission Amps
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    www.missionamps.com
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    Thanks, have not built this one yet, it is basically a stripped down version of an amp I built. It was for guitar, I just showed it because I already had it drawn up and the layout matches the schematic close so someone new to amp building can relate the two.

    Dropping a cathode capacitor would be a good move as it had plenty of gain, the amp I built to experiment with has switches for the cathode caps in all positions and has a BF tone stack that can also be switched in and out. Probably enough gain for harp with the tone stack, also switched NFB. I was new to tube amps and I wanted to see what effect the different elements had on the amp. I used a 70V line transformer for the OT but it is currently running Class A, need to jack up the voltage to get into AB, lent it out and have not got it back yet to do it though. Not a friendly build I crammed it into an odd space.






    Used 12AT6/12AV6's for the first position and a 12AX7 along with 12AQ5's. 12V wall wart transformer for the heaters and an isolation transformer with 240V primary windings that I am using as a secondary (end up with 205V on the diodes). Next one will use the 120V secondary going into a voltage doubler. Just wanted to show that if there is a will there is a way even if the money is tight and a person is handy. Had the above amp at 270V using a variac,, like to hit the 300V range though. I would think the simple cut control should be fine, mainly use my SE amp Tweed tone control with some roll of more than as a treble boost. Mind you I am new to guitar so I am just happy getting the notes right.

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