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Junkyard Parallel Single-Ended Combo with Two OTs and Two Speakers?

Discussion in 'Shock Brother's DIY Amps' started by SerpentRuss, Feb 23, 2021.

  1. SerpentRuss

    SerpentRuss TDPRI Member Ad Free Member

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    My first amp build was a funny yet ingenious hybrid that used LND150 Depletion MOSFETs in the pre-amp section and a single-ended 6CL6 for the output. I got the idea and schematic from eBay user "videosync". It actually sounds pretty awesome except the PS is starving when it's driven. A 6Cl6 is not a current sipper for the sound it puts out.

    When I purchased the 6CL6 tubes, I bought a 5-tube lot of them on Ebay. I might possibly build the six-shooter, but I'll still have two tubes leftover.

    I also have two more of the Dukane 25/70 volt OT transformers that were used for the hybrid and probably will not work with a project much bigger than that. They were like $3 each.

    Keeping with the Junkyard theme, I have in my personal stash of things I could not throw out in good conscience, a 480/220 to 120-volt 150 VA tranny that will give me 60 volts when 110 is hooked up to the 220 primary taps. I have loads of 820 uF/400volt caps and plenty of 1000 volt diodes so that 60 volts could easily be doubled or tripled. The original hybrid design is running at less than 120 volts DC.

    For heater voltage supply, I have a 480 to 24 volt, 50 VA control tranny that puts out 6.45 volts when the 480-volt primary is energized with 120 volts. BTW, I have like 4 of these.

    Note: I need to do an as-built on this schematic, I added a tone pot, a bright cap, high-frequency shunt caps, and a cathode bypass cap, none of which are shown. The original project cost is about $30 before you start buying a speaker (if wanted) and building an enclosure.

    So my question is not should I build it, for I know I shouldn't, but rather what design modifications would be necessary coming off the last stage of the preamp to feed two parallel power tubes?

    Is there any strange interaction that might happen with two OTs connected to the same DC power?

    Does this concept spark any ideas about tweaking the outputs separately for some type of tonal goulash?

    I know it's going to be underpowered and heavy and strange. I think I have to do it. 6CL6_Stub_Amp.jpg
     
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  2. gigante

    gigante Tele-Meister

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    If it were me, I'd just go ahead and go stereo. I have a couple pedals that would like a stereo amp.
     
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  3. SerpentRuss

    SerpentRuss TDPRI Member Ad Free Member

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    Hmm, I have enough pieces and parts to do that. I'd want a provision to feed both sides monaurally from one jack. I guess I could work that out.
     
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  4. printer2

    printer2 Poster Extraordinaire

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    What is the lowest wattage tap on the transformers. It would be interesting to have a stereo P-P amp. You should not have a problem with two amps on a power supply. Plenty of tube stereos back in the day.
     
  5. NTC

    NTC Tele-Holic

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    How about a bias-modulation tremolo that drives the two halves out of phase so that you get a stereo panning effect. Should be simple and easy using the transistors.
     
  6. SerpentRuss

    SerpentRuss TDPRI Member Ad Free Member

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    OK, so here is a photo of the OT and some readings.
    Parts Express has a bunch of them for $3 each.

    https://www.parts-express.com/Dukan...xCGCNHIsgeyJwhBGHP5Swt0IZNrkGrpEaAprGEALw_wcB

    The secondary has a DC resistance of 0.75 Ohms. On the original build, I used the 75 volt .5 watt tap (Red) on the primary side which has a DC resistance of around 212 Ohms

    The rest of the DC resistances are as follows

    75 volt, 1 watt = 133 ohms (blue)
    75 volt, 2 watt = 82 ohms (Yellow)
    75 volt, 4 watt (white) and 25 volt .5 watt (orange) are both 45 ohms but have separate leads, probably for clarity's sake.
    25 volt, 1 watt = 18 ohms (green)
    and 25 volt 2 watt = 15 ohms. (purple)

    I'm assuming that you could possibly use the green or purple for common on the primary side and give any of the 70-volt settings a boost, kind of reading between the lines. For the record, these things are voodoo to me, and I'm not sure how you would calculate impedance for the primary taps.



    20210223_222947.jpg
     
  7. SerpentRuss

    SerpentRuss TDPRI Member Ad Free Member

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    Here is the junkyard PT - I think it's OK, if not, I may be able to find another one. It came out of an MCC bucket at work, that was being tossed in the scrap steel bin till I saved it. I might power it with a power resistor load and drive the moisture out of it and see if it makes noise. Nice built-in fuse clips on the primary. I'm looking to feed 120 to the 220 primary taps and run the output through a tripler to get around 145 volts.


    20210223_223031.jpg
     
  8. SerpentRuss

    SerpentRuss TDPRI Member Ad Free Member

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    This is the heater transformer - a 50 VA 24 volt secondary with multi-voltage primaries. I took out a cabinet years ago that had a dozen of these. It was a 208-volt panel. About half of them had 480 taps and built-in circuit breakers like this one. They make good paperweights. Today I hooked up a the 120 to the 480 primary and got 6.45 volts driving a light resistive load. It should work fine for two 6CL6 heaters.

    20210223_222958.jpg
     
  9. SerpentRuss

    SerpentRuss TDPRI Member Ad Free Member

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    Here is a stash of 400-volt capacitors taken from two junked variable speed drives. Normally these drives fail in the rectifier or switching section and the caps are still good. We used to send them out to be repaired, but now they just get tossed, of course, 10 to 100 HP drives used to cost a lot more than they do now. At any rate, every cap I've taken off the board has been good so far. These are all listed as 820 uF, but they test at about 760 uF. I don't know if that's because my meter is inaccurate with caps this big, or if it's because they have a lot of miles on them. They've been energized recently, both drives were replaced in the last few months. I have 37 of them. Here's a picture of 20.

    All of the cap tops were glued to a neighbor so some of these are skinned up. Any suggestions on what to coat them with. I also have to figure out a good way to attach and insulate leads. If I attached wires and then dipped them in polyurethane, would that make them run significantly hotter?

    20210223_232306.jpg
     
  10. drewg

    drewg Tele-Meister

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    View attachment 824645 View attachment 824643
    [Edit- I was feeling guilty about the glossy-eyed Homer Simpson picture I put up, so I took it down. I was just joking, but didn't want anyone to interpret it as mocking. I'm interested in trying to learn to build an amp someday but I've got a long ways to go. I admire you all for your knowledge and ability and apologize if it came across as mocking knowledge. It's over my head.]
     
    Last edited: Feb 24, 2021
  11. SerpentRuss

    SerpentRuss TDPRI Member Ad Free Member

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    Absolutely no worries! Stay on forums long enough and you will post something you have second thoughts about or more often, something that is misinterpreted. Look, I know people are going to roll their eyes at this project because frankly it's not serious. I mean, I am going to build something, but if it comes out sounding like the junk that it is, I will consider it cheap fun. Any speakers I buy or find can be used for something else.

    My present inclination is not to try to make two duplicate amp sections, but to use two different power tubes, both low watt and be able to run each one independently or together and to put as man tonal tweaks for each section on the front panel. The PS is going to be relatively large, I may put the power switch and the power supplies in the bottom of the cabinet, and use shielded cable and connectors to bring the power to the top section of the amp.
     
    Last edited: Feb 24, 2021
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  12. drewg

    drewg Tele-Meister

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    Thanks, SerpentRuss. To me, any amp building sounds like a serious project. I really like the idea of using different parts from here and there– junkyard, as you say. To me it's recycling and repurposing and full of creativity! That's why I was interested in the thread, but I have a lot to learn before I can hope to do something like that!
     
  13. 2L man

    2L man Tele-Meister

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    I think your meter cause the difference especially if all of them show about the same capacitance.

    They also look like their housing is not part of capacitor and insulation function is to show polarity and data. Measure ohms between housing and electrodes and if there is almost infinite then housing is just aluminium can where capacotor is.

    If you mount them using mounting bands you can remove some of the insulation what comes under the band and then it comes a part of chassis and makes chassis better shield against electromagnetic noise. Then also possible noise what capacitor greate to its housing goes to earth thru mains cable eart wire.
     
  14. SerpentRuss

    SerpentRuss TDPRI Member Ad Free Member

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    I did get a chance to check this just now on one of the skinned-up caps. The negative terminal and aluminum case are tied together.
     
  15. 2L man

    2L man Tele-Meister

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    Majority of can electrolytucs are like that obviously because they are cheaper to make. Then you need to isolate them from chassis to avoid ground loop. Plastic tape between band and can should be enough when most likely on circuit the can potential is zero when negative electrode is connected to zero so there is no danger of electricity although some of the insulation is not intact.

    I also take components from scrab electronics. My best recent find was an UPS driver card which had many quality brand 2200uF 450V electrolyts and 68uF 200V and 15uF 630V poly caps and many more smaller.
     
  16. 2L man

    2L man Tele-Meister

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    I think that "line transformer" does not work as an output transformer too well. Its impedance ratio is too small. Connect heater supply to primary and measure it and what comes out. 100V standard line transformer input impedance is about 600 ohms when it drives a loudspeaker. That is 75V standard and it has less.
     
    Last edited: Feb 26, 2021
  17. SerpentRuss

    SerpentRuss TDPRI Member Ad Free Member

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    It's a line transformer, but in the sub-1-watt design I first shared, it does a fine job driving an 8-ohm speaker. Excuse the messy wiring job

    20210207_153315_LR.JPG

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