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Output Transformer Danelectro Leader.

Discussion in 'Amp Tech Center' started by Stringbender58, Mar 8, 2021.

  1. Stringbender58

    Stringbender58 TDPRI Member

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    I have a Danelectro Leader amp that was the first amp my Dad gave me as a boy. Trying to find and or calculate appropriate output transformer replacement. This amp seems to differ from the only schematic available online. Differences are no isolation or step up tranny on the 115v in. Just a 60 ohm ballast resistor. Power Filter caps were three Planet 80-150 vdc not the 100 uF and one 22uF on schematic. Power tube grid resistors are 390k not 39k as schematic and cathode resistor is 82 ohm not 56 ohm as schematic. Tried to calculate for OT but have less experience than most. 25L6GT has two columns in general characteristics. Is the first column foe single ended and second column for push-pull? Finding others saying B+ is 180v. And output 10 watts for these amps? Original OT has 285308 on frame. Think found the code is Rola 53 8th week? I will be adding the isolation transformer soon as I know which one is big enough. Heard people say N-51 and others say they used N68 and got little hot. One more question I have is can the ballast resistor on the wall voltage in 115v be increased to offset todays 120v into help keep plate and grid voltages as designed. Thanks in advance for any help. I would love to get this running again after making it safe. I know I will come up with many more questions that I haven't gotten to. Thanks again.
     
  2. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    DanelectroLeader.jpg

    For a standard OT probably a 6k to 8k primary would suffice. The 8k would be more woolly, so maybe the 6k would be more suited to a Danelectro.

    Found this schematic over at EL34 world.
     
  3. Stringbender58

    Stringbender58 TDPRI Member

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    I can find OT of 6k and choose my choice of secondary? No idea if original ran 4 ohm or 8 with those old rola speakers either. Will probably try to acquire an original speaker but isn't top priority. I know these aren't valuable enough to warrant going overboard on originality but is valuable to me. I have the same schematic but mine doesn't gave the transformer at beginning of power supply. Is that an iso or a step up? Circuit component difference dictate slightly different circuit and schematic or that idea they used whatever parts they had available any given day? Any other values I have to consider on that OT? Thanks so much for your help.
     
  4. goldguitarguy

    goldguitarguy Tele-Meister

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    It’s a push pull amp for sure with the power going to the center tap of the OT. I would look at the output transformers for the AC15. Would be around the 6000ohm mark and have a center tap.
     
  5. goldguitarguy

    goldguitarguy Tele-Meister

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    Here’s the schematic that would have come with your amp on the back panel. I found this on Reverb. It’s hard to read though and the listing has sold. I thought it was available at first.

    4F556D3E-570C-4C59-9539-BC3180659453.jpeg
     
    Last edited: Mar 8, 2021
  6. Stringbender58

    Stringbender58 TDPRI Member

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  7. Stringbender58

    Stringbender58 TDPRI Member

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    20210308_181429.jpg The output transformer I am finding for AC15 are big compared to this one. Only have a small area to mount it. The schematic picture you sent off back of amp is is what I bet this circuit is. Agree it's a little struggle to read. Will have my wife do her magic with image in photoshop hopefully. New my back panel is missing with that schematic for info. Thank you guys for all your help. Know being an beginner and no electronics background is still making me miss things. Was under the impression that I would need more exact values besides just primary impedance to choose OT. Like Volts and/ mA chooses.
     
  8. Dacious

    Dacious Poster Extraordinaire

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    Try a Princeton Reverb or Deluxe 5E3 transformer. They are relatively tiny and some vendors have them as uncovered wire wound.

    Look for a shop that renovates old stereogram radios. They usually have connection to someone who can rewind your original while maintaining its appearance. Also they often have small OTs for p-p stereos. You can also find good transformers on eBay. Triode electronics sometimes has blowouts and oddballs.
     
  9. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Give the dimensions for the OT. Especially the mounting hole spacing.
     
  10. Stringbender58

    Stringbender58 TDPRI Member

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    Hole centers are 2-13/16" about 2" tall, 1-7/8" wide across windings. Top of frame is about 2-1/4". Have kept a spec sheet that I found on Hammond universal output transformer 125D. Am curious if these will work push-pull. My old one has 3 leads primary and 3 leads secondary. Centertapped both? Don't know if that is accomplishable with all the voice coil lead configuration?
     
  11. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Hammond 1750F or 1760F has the right spacing.

    The 1750F is 6k9 primary, 8 Ohm secondary. The 1760 is 4/8/16 Ohm secondaries.

    mouser lists them for $39 and $42.
     
  12. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Hah! I think that is the size of the Blues Jr OT. You could go on the cheap and get pull from the bay or reverb.
     
  13. Stringbender58

    Stringbender58 TDPRI Member

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    Is there anything with the 125D makes it unsuitable? Thank you lowerleftcoast.
     
  14. Stringbender58

    Stringbender58 TDPRI Member

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    Just realized the third wire of secondary goes to unused pin 1 of 25L6GT. Meaning it's not even being used?
     
  15. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    The 125D would work just fine.

    The third wire... Maybe a ground??? Maybe a convenient place to terminate an unused wire???
     
  16. Stringbender58

    Stringbender58 TDPRI Member

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    Yes LLC seen both were for blues junior. May be good choice. Have heard about an upgraded OT for those amps and some were slightly less reliable or life span? Thanks again LLC. Kind of a big deal for me to have someone to ask my stupid questions to.
     
  17. Stringbender58

    Stringbender58 TDPRI Member

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    Awesome. Thank you LLC. The 125D is nearly exact same size as original and only 10 watt. Yeah that's my guess on third wire since nothing is joining there just using that pin 1 which the 25L6GT doesn't use. 125D are very reasonably priced too. Liking the 1750F and 1760F as well.
     
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  18. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    The BJr OT doesn't seem to have reliability issues. The main complaint is it lacks bass. Iirc Heyboer made a replacement with more bottom end and maybe better fidelity.
     
  19. Stringbender58

    Stringbender58 TDPRI Member

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    That sounds more familiar. Knew had heard discussion about it but wrong in issue. Knowing that third wire isn't an issue may be several options. Was looking at some classic tones but only had two secondary wires and not sure about availability.
     
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