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Scratch Build, -from the beginning...

Discussion in 'Shock Brother's DIY Amps' started by Jewellworks, Sep 24, 2020.

  1. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Yes two 6L6G or GA would be in the ballpark. The only concern for the OT is if it could handle the added current but from what you have described of the original amp, the OT was probably handling a high-ish current anyway.
    That is correct.
    It seems the 5Z4 from different sources say similar but different max ratings. I think the 5Z4 can take it but... I bet you will install rectifier backup diodes (recommended for most of our amps). The backup diodes would allow much higher current without issue.
    40uF is the max suggested cap for the 5Z4. No problem using less.
    My opinion: the tube datasheet is usually very conservative and the tube can take it. As mentioned just use the backup diodes. Win win.:cool:

    I have found this tube reference handy. Quick and easy compared to individual tube datasheets. For the 5Z4 it is right with the purple line 125mA.
    https://frank.pocnet.net/other/docs/MK-RT.pdf

    The PT you choose may need to have a higher current rating to handle the two 6L6 and the ebay find will probably get you there.
     
  2. Jewellworks

    Jewellworks Tele-Meister

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    not to get nitpicky, but this isnt the same OT that came from the Ampro with the 3, 6V6's ect... but it IS the same OT weve been talking about w/ the 3.3/8ohm, 6.6k/16ohm ratings. that OT came from a small 10W PA amp with a single 6L6GC, and had taps for 8ohms, 70v and 25v. i can use the Ampro OT if its more appropriate. that Ampro OT was discussed in this thread, https://www.tdpri.com/threads/output-transformer-taps.1046923/page-2 and we discovered what the various Taps came out to be. but Plan A was using the 10W OT. -we still good?
    backup diodes? mmmm... so its... double-rectified? whats the schematic for that?

    thanks for the help on this, and the MK-RT.pdf link.
    and i just bought that PT
     
  3. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Rob has a description and layout on several of his sites. I know you can find it on his 5E3 mods page under rectifier backup diodes.
    I would hope if the OT was used for a 6L6GC it will not be too far off for this build. OT size can be a little small and add some nice compression to a build. Worst case scenario is to find it too small and you end up having to replace it which you have already considered.
    Physically, how big is this OT? If it is dinky this may not be the project it wants to see.
     
  4. Jewellworks

    Jewellworks Tele-Meister

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    physical measurements are about 2 1/2 x 1 3/4. weighs a pound maybe?
    20201001_202643.jpg
     
  5. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I would run with it.
     
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  6. printer2

    printer2 Poster Extraordinaire

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    Run at a lower voltage and current will keep the transformer happy and make the 6L6's last a long time.

    http://www.r-type.org/pdfs/6l6g.pdf

    page 3, 240-250 in Class A looks good.
     
  7. Jewellworks

    Jewellworks Tele-Meister

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    something that has been a big roadblock in my brain, is what CHANGES if i use the 10W OT (with the impedance ratio of 414:1 -that reflects a Load Resistance of 3.3k@8ohms, and 6.6k@16ohms back to the primary) with a Single 6L6G? the plate voltage? the Current draw on the PT? something else??
    im planning on using this 320-0-320 PT (with enough ma available to run a Hammond M3, and 10 tubes) i just bought on ebay. i think its overkill, but the price was nice. i shouldnt be taxing the current draw at all, and therefore the voltage should stay constant.
    adjusting my calculations with this PT, my peak voltage will be 452V
    with that in mind, and a previously calculated draw of around 70ma, ohms law says the load resistance will be 6457 ohms. -which again, looks close enough to the 6.6 reflected by the OT if i use a 16 ohm speaker.
    where im getting lost is, what CHANGES if i use the 3.3k coming from the 8ohm speaker? the plate voltage? the Current draw on the PT? the operating point? all of it?

    ((BTW im still confused as to why this OT has the ratio and LR values we calculated, when it came from an amp with a single 6L6GC and was labeled as 8ohms. -was it labeled wrong? the 6L6GC data sheet wants to see a LR of 4300. so 3300 was close enough? the data sheet for a 6L6G is 5k. what happens/changes if i use 3.3k, and what numbers do i plug into the ohms law calculator?))
     
  8. printer2

    printer2 Poster Extraordinaire

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  9. Jewellworks

    Jewellworks Tele-Meister

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    .
     
    Last edited: Oct 4, 2020
  10. juliusaurus

    juliusaurus TDPRI Member

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    Probably would help, in this video, the OT also have 25V and 70V output.
     
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