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Discussion in 'DIY Amp Forum' started by sumran, Jan 18, 2018.

  1. sumran

    sumran Fan of Leo

    Mar 7, 2010
    Gainesville, FL
    After listening to the various samples I will be going with the Dirty Shirley as the third amp. Perfect compliment for my other amps. Lack of reverb can be nicely solved with the effects loop. The power transformers on the AO-29 are robust. Using 5881 tubes is a good option. I will be doing some tests today on the output transformer to see what those will provide.
     
    Robins likes this.

  2. Robins

    Robins Dr. von Loudster Strat-Talk Supporter

    Dec 22, 2010
    Germany
    Use the Sovteks 5881 WXT they are sturdy and even pushing them way above 500V they keep on rocking forever.
    Great tubes with big tone.

    All the best,
    Robin
     

  3. sumran

    sumran Fan of Leo

    Mar 7, 2010
    Gainesville, FL
    I don’t know that the first output transformer I tested on the Hammond is usable. The primary side is not balanced very well. 517 ohms when I read the full winding. 242 between center abc one end. 275 between center and the other end. Perhaps not enough to matter. The secondary is unusual. One lead was grounded there are two leads that went to the speaker connection. Not sure if this was made for a field coil speaker of if it drove two speakers. The secondary is balanced. I have not checked yet to see a number of turns.
     

  4. RJ Squirrel

    RJ Squirrel Strat-Talker

    Age:
    64
    287
    Jan 28, 2018
    Frostbite Falls
    The DC resistance of the output windings will not match because one side of the primary winding is wound over the top of the other. As a result, the outside winding will have a longer length of wire resulting in more resistance. The output connector has one connection for the output signal and a common ground connection. The OT was designed for 6V6 tubes. The OT is probably robust enough for 5881 tubes, but would not be optimal. If you want to use 5881's, they would probably work best in cathode bias mode with this OT. The PT is probably stout enough as well for 5881's.

    There are several interstage transformers. There is one push/pull connected to both triodes in a 12AU7. This looks like it might work for a headphone amp or maybe an amp in a box effect similar to the Herzog.

    There are a bunch of inductors and capacitors that are used for phase shift in the vibrato channel. It might be fun to play with this circuit.

    Here is a link to the schematic.

    http://www.captain-foldback.com/Hammond_sub/hammond_schematics.htm
     
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  5. sumran

    sumran Fan of Leo

    Mar 7, 2010
    Gainesville, FL
    Thanks RJ. I won’t say I fully understand the Hammond circuit, although I have it and am studying it as time allows. While I agree that OT could be interesting to experiment with I don’t think it is well suited to the amps I want to build. There is actually a different transformer in the amps that my be even more suited to a headphone amp build. But that is for another day.

    I have other output transformers on hand. I want to get the first of these amps underway soon.

    I will say that I am very impressed by the craftsmanship of these amps. They were excessively well made and the pride of the builders is evident in the components, lead dress, parts identification, and circuit design. They clearly expected these thing to function without problems for decades. And they wanted to make a good impression on the tech that followed them, even when service was needed. They could have been fully functional with far less effort and expense.
     
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  6. sumran

    sumran Fan of Leo

    Mar 7, 2010
    Gainesville, FL
    Trying to get the output transformers settled. I have a Hammond 1750e on hand. I think that should take care of the Tweed Deluxe. There are some others that people like but I would have to buy them.

    I have a Classic Tone 40-18013 that I got in trade. I doubt I will be building a Twin do I think I will use that in the DS style amp.

    Still need to search the drawer for the Deluxe Reverb OT.
     
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  7. sumran

    sumran Fan of Leo

    Mar 7, 2010
    Gainesville, FL
    I have decided to build the 5E3 first. It is the most straightforward build. I believe I have everything on hand. It will be a nonstandard configuration because of the chassis configuration. I will try to make it sound right and have enough familiar visual cues connect if to the original.
     
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  8. sumran

    sumran Fan of Leo

    Mar 7, 2010
    Gainesville, FL
    The Hammond chassis had vertically mounted turret/eyelet boards. This is helpful because the chassis is quite narrow. So I decided to incorporate that in the build. The organ amp used two mounted end to end but I wanted to use just one of them for the 5E3. There was not enough room for the components on one side. However both sides are accessible with the vertical mount. Just for fun, I put all the capacitors on one side and the resistors on the other. I have to order the 250 ohm, 5-watt cathode resistor. Everything else is soldered and ready. IMG_1097.JPG IMG_1098.JPG
     
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  9. sumran

    sumran Fan of Leo

    Mar 7, 2010
    Gainesville, FL
    Sticking with my “parts-on-hand” theme I decided to use some 500 ohm resistors I had in the drawer. Wired in parallel to get the 250 value. More surface area for heat dissipation! IMG_1099.JPG
     
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  10. sumran

    sumran Fan of Leo

    Mar 7, 2010
    Gainesville, FL
    The real challenge of remaking this amp is the chassis. Because it had a very specific and involved design, it is full of holes. Many of these are in the wrong places. It was not designed for control pots or guitar amp jacks. I can either live with a bunch of holes in my chassis or I can put in patch panels. I can’t live with holes, so I need to fab patch panels.
     
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  11. sumran

    sumran Fan of Leo

    Mar 7, 2010
    Gainesville, FL
    I have been rooting through boxes of tubes and testing them like a mad man for two weeks. Have sorted almost all of them. Threw out the bad and got test data on the good. I am well-stocked on tube for a good while. Lots of treasures discovered, including some very nice RCA 6L6 black plates that will be used in another amp.

    Picked up a small Lincoln MIG/FC wire welder to do my patch panels. Ordered some welding magnets to keep things in place while tacking. Fair warning: I am not an expert welder! I have marked up the portions that will need to be removed and patched. We will see what the weekend brings. The rest of the amp build should be fairly quick once the chassis is done.
     
    Last edited: Mar 6, 2018
    Robins likes this.

  12. sumran

    sumran Fan of Leo

    Mar 7, 2010
    Gainesville, FL
    Ugh! I have been working in the garage for the last two weekends. Had to draw a line and stop all work until that gets finished. The garage is where cabinet work, welding, painting, tolex, etc. gets done. I’ll will spare you my weak excuses, but it has become an obstacle to completing any project. I probably have another week until order is restored. Once it is done, possibilities are exciting!