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Ivy League Transfer: Princeton -> Harvard

Discussion in 'Shock Brother's DIY Amps' started by FiddlinJim, Aug 28, 2010.

  1. FiddlinJim

    FiddlinJim Tele-Holic

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    I built a tweed Princeton (5F2-A) from a Marsh kit some years ago as my first amp build. A while ago, I decided I wanted something a little more, but cleaner, brighter, and more controlled than my Deluxe (5E3). So, I decided to modify the chassis for a Harvard. It was already the big-box 5F2-A with a 10" Weber Alnico speaker in it.

    For a circuit board, I got a Mojo tweed Vibrolux board and chopped out the section of the board with all the 'vibe stuff in it. When that was done, the only difference is that the V1 plate resistor angles in from the left instead of the right (looking from the bottom of the chassis). I stapled and taped the two pieces of the circuit board back together and, although a little ugly, seems to be stable.

    I used an overbuilt PT from Allen (TP-25) and an Allen OT (TO-20), F&T filter caps, Mojo "Blue Molded" coupling caps and made an adjustable fixed-bias circuit. I used metal film plate resistors to minimize hiss in the preamp, metal oxide for high voltage resistors, carbon comp otherwise.

    I had to punch a 2nd octal hole for the 2nd power tube and a hole for the 6AT6 preamp plus I went with the 3-input scheme so I had to put a 3rd hole between the existing input jacks.

    On fire-up I had problems getting the bias voltage in range, but got the right resistor and pot in series to get that fixed. I got the high-freq squeal that a simple switch of the OT leads easily fixed. It's nice and quiet; I think my grounding scheme seemed to work.

    It sounds just like I had hoped. It's almost as loud as the Deluxe, but brighter and cleaner. I'll probably mess with speakers a little (I have 2 Jensen P10Rs from a CVR), but I'm happy with 'er as is. I've got 2 6AT6 and 2 6AV6 tubes to compare in V1. I like the RCA 6AT6 best so far.

    B+ is about 390 V (305 is on the Fender schematic) and all other voltages seem to have scaled up as expected. I'm running the 6V6s at 25ma.

    Here's a few pix... With this amp, I used black for grounds, red for grids, green for filaments, yellow for everything else.
     

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  2. TNO

    TNO Friend of Leo's

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    Very nice! I'd like one just like it except cathode biased. I think it would be a popular kit...
     
  3. M Fowler

    M Fowler TDPRI Member

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    I always wonder why people just don't build a completely new amp, keep the old one, it is a heck of alot easier to start with a fresh chassis. A blank one from Turretboards.com or even a Weber chassis.

    Anyway your amp looks good!
     
  4. FiddlinJim

    FiddlinJim Tele-Holic

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    Well, nobody makes a Harvard chassis for starters... I could have bought a new Princeton chassis for $100 and done the same modifications to it. Then there's a cab for $200, a speaker for $170. So, there's almost $500 worth of reasons for me. No regrets from me!

    I can use the old Princeton parts for something else in the future.
     
  5. M Fowler

    M Fowler TDPRI Member

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    I know what you mean using what you have is good. I just can't get myself to stip my amps apart and just keep accumlating more amps. Its a disease I'm sure.
     
  6. FiddlinJim

    FiddlinJim Tele-Holic

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    Oh, I'm sure this won't keep me from accumulating more amps!!!
     
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