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Tweed Transformer info

Discussion in 'Shock Brother's DIY Amps' started by jsnwhite619, Dec 27, 2020.

  1. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I started this thread due to a couple OT posts lately that had me spending a lot of time researching this today and would like some feedback/conversation on the topic. Please chime in on anything that doesn't look right.

    For the PP 6v6 Tweed amps - Harvard, Vibrolux, Deluxe, Tremolux - I'm seeing that they ALL used the same OT, either the Triad 108, then to the Schumacher 125A1A in the late Tweed amps. The difference in output between the model lines is dependent on the choice of PT with them all - current rating & voltage. So, the 10W Harvard and 18W Tremolux used two 6v6 power tubes and the same OT, but the power transformer obviously made the difference, and rectifier in the Tremolux.

    The next stop is that the Triad 108 was an 8k primary, the 125A1A was a 6.6k primary, the 6.6k giving more clean headroom and higher output. Both appear to be similar size and bolt spacing. ClassicTone lists both their models for these as 20W transformers, practically the same dimensions, but the respective primary differences - 8k vs 6.6k.

    What was eye-opening to me was that the Hammond 1750E (listed as 8.5k) I've always used in any of these situations that they list as a Tweed Deluxe or Princeton Reverb OT appears to be a copy of the later Princeton 125A10B OT. It's smaller than a vintage 108 by a 1/2" in some places, and the bolt spacing matches the PR, but not the Deluxe. It is certainly smaller than their 1750H which is their 125A1A model replacement, and it is a 6.6k primary. So, it would appear that all of my builds using the 1750E OT - including my 5e3 - are essentially using a Princeton Reverb OT, not the Deluxe OT I thought it was.

    That being said, I don't think I've never finished one that I wished was louder, cleaner, or that it had more bass response. And it looks like Hammond needs to design an 8k version of the 1750H DR transformer if they want to really offer an authentic Triad 108 replacement.
     
    Last edited: Dec 27, 2020
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  2. dankilling

    dankilling Tele-Afflicted Silver Supporter

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  3. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I noticed the 1750E was 8K and is now 8K5.
     
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  4. jsnwhite619

    jsnwhite619 Friend of Leo's

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    You are correct. I emailed them about it a while back when I noticed it, and they said "In further review of the design we noticed it was actually closer to 8500." I don't know if that means what they were producing was actually closer to 8.5k and they relabeled it, or if the transformer they were basing it on was actually closer to 8.5k. If the former, then nothing should be any different in performance, just the specs.

    I'll edit the original post to 8.5k.
     
  5. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    You're exactly right. And I say you're right that the Triad was 8K while the later Schumacher was 6.6K; at least that's what I found when I was researching my 5G9 build. And so my 5E3 and my 5G9 have exactly the same Classictone 40-18022, which should be similar to the Triad. And of course the two amps share the same input and EQ circuits.

    But the two amps sound *very* different, no doubt due to the factors you mention and the choke, fixed bias, LTP, and bigger cab.

    I know OT character is correlated with physical size and mass. But when you mention the 5E3 has a bigger OT than a PR, (and I see it does) I start to get confused about how OT size affects sound in those two amps. More headroom? Cleaner bass? Hmm. Is it fair to say an OT is sorta like the differential in a car -- it helps get the power and torque to the road, and beefier can be better, but a lot of other factors determine overall driving style and performance?
     
  6. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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  7. NTC

    NTC Tele-Holic

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    As stated in another thread, I built my 5E3 about 20 years ago and used a "Deluxe Reverb" OT. I was going to replace it with the Hammond but balked at it's size. When I found the specs for the OT I used originally, it turned out to be 8.5k. Not quite right, but it is staying.

    Odd that a Deluxe Reverb OT replacement would be 8.5k.
     
  8. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I have to wonder if the 125A10B on the Princeton was intentionally designed as a "step down" from the Triad 108. After the switch to the 125A1A with a 6.6k, how much difference would there have been if the Princeton had gotten a bigger 108-sized OT with an 8k? Or, since the Princeton was designed for "student and home use", if it was deliberately designed smaller so that it would knock some bass & output off as the end result? From this thread https://www.tdpri.com/threads/fender-amps-1965-price-vs-today-by-model.792688/ it looks like the price difference in a PR and DR in 1965 was 40% more for the Deluxe. Today's cash value would be nearly $600 difference. I'm betting that they had to make sure that everyone didn't play a Princeton and say, "Well, there's no way I'm paying that much more for a Deluxe!"

    Regarding the sum of the parts determining things - how's this sound? Apparently, my 5E3 has a 138mA Deluxe Reverb PT (660v) (which I already knew) and a Princeton Reverb OT (which I just learned). So, I'm running a higher rated PT than stock (138ma 660v vs 100mA 710v) at lower voltage into a smaller OT...how does that compare to stock? I have no idea, but I like it. ;-)

    Here's that transformer combo with the rest of the circuit being stock from a Mojo small parts kit.

     
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  9. Nickfl

    Nickfl Friend of Leo's

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    I would assume that it means they realized they were winding it to 8.5k and relabeled it. I think we are generally giving these manufacturers way too much credit when we picture them "cloning" some old magic transformer they keep in a vault somewhere and loosing sleep about getting it exactly right. I think there is a lot of "close enough" involved. Especially when you look at how they tend to recommend the same transformer for several different amps that all used different OEM parts. For instance, how many transformers are sold as being appropriate for a 5e3 and a Deluxe Reverb? If they are comfortable saying that, why would they change their winding specs over a 0.5k variance? Thats only a 6% discrepancy, to put it in perspective.

    I think this is a useful discussion that will be helpful to a lot of people. Transformer specs and the why and how of them were something that I had a lot of trouble finding good information on when I was first learning about amps. I think that the fact that Fender and others didn't list transformer specs on their schematics or layouts leads a lot of new builders to treat them as a blank spot on the map, which in turn leads to a lot of the voodoo recommendations and assumptions floating around on forums.

    These recent threads discussing actual transformer specifications and their consequences are a good resource.
     
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  10. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Totally agree^^^. On one hand, for sure a DR OT will *work* in a 5E3, and may sound great to many players. On the other hand, 'perfect clones' that are 'built exactly to vintage specs' seem like marketing hype, sometimes expensive hype, sometimes actually undesirable if true -- who wants a perfect recreation of a PT that ran on 110VAC or less when it now has to run on 120VAC or more?

    And yet it's not academic. We see folks here everyday who've already bought their transformers and realize they got a totally bad match to their amp, or already built their amp and find their B+ is *way* off from a reasonable target, or they didn't even get the right rectifier amperage, or...

    Without 'which transformer' planning threads and 'wrong transformer' build threads, this forum would be about half its current size. :D
     
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  11. Muzzy

    Muzzy TDPRI Member

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    Hey, if anyone's interested, there are a few Classictone 40-18022 tweed deluxe OT's available on ebay. I bought one yesterday.
     
  12. Nickfl

    Nickfl Friend of Leo's

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    I think the smaller output transformer is one of the factors, but there is a lot going into making the Princeton reverb seem "smaller" than the Deluxe reverb. The cathodyne PI is going to factor into that and of course, the smaller speaker. And don't forget the notoriously underpowered PT...

    I just recently swapped out a Classic Tone 40-18002 (6.6K, 20W DR transformer) for a Hammond 1750-E in a 5D3 circuit. Definitely changed the tone (for the better IMO) but there was basically no difference in output in this case, the amp seems equally loud to me as it did with the larger DR transformer. So in this case I seem to hear a difference from the change in impedance value but no significant effect from the change in wattage rating.

    Perhaps there would have been more of a difference (in volume) in a 5e3 circuit, I suspect there definitely would be in a LTP driven circuit like a 6g3. The speaker could be a limiting factor as well, it certainly has to be considered as a major variable in overall sound.

    In any case, I think this illustrates the fact that a tube amp is an interdependent set of variables and we have to be careful about "rules of thumb" that may apply to one specification in one circuit but may not behave the same way in a different amp.
     
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  13. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    I'm having a nice easy "what Nick said" day. :) But I'll note again that the LTP, fixed bias, big PT, choke, much bigger reservoir cap, and big cab make my 5G9 worlds different from my 5E3 despite having the same exact OT.
     
  14. jsnwhite619

    jsnwhite619 Friend of Leo's

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    You have to wonder how accurate the vintage tolerances were on these things as well - how accurate were those counts and windings, and how close was "close enough" back in 1957? The schematics have a +/-20% that seems to usually get blamed on resistor values & tolerances and tubes, but who's to say the transformer variances weren't a large portion of that as well?

    So, here's where the historical "fun" part comes in -- if it's a late-model Tweed that got a 125A1A from the factory, it would be suitable for a 5E3 or Deluxe Reverb. ;-)

    My 5881 Tweed Princeton build this year let me play with 5k & 8K primaries on the same OT. Miles of difference in punch and headroom there. The 8k was much fatter and softer sounding, but much lower headroom. As you said, I don't know that there was much volume difference. I should have measured it with my dB meter, but I didn't think about it. That being said, there are situations that I could have used it to design around a particular sound/tone and it would have been fantastic.
     
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  15. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I have learned something here. I thought the Princeton Reverb had a 6K6 primary.

    So Hammond recommends the 1750E for a 5E3 but bolt spacing is not correct?:rolleyes:
    The dimensions of the 1750E are smaller so it follows there would be less or thinner wire. I would assume the 1750E would give the 5E3 more compression.

    The Classictone 40-18022 bolt spacing of 3 1/8" is correct for the 5E3 chassis. It is a shame Magnetic Components Inc. is no longer viable.

    Here is some info on the last three Classictone 40-18022 I received.
    Resistance on primaries (cold). Red is the CT.
    Green to Red = 301, 306, 310 ohms
    Yellow to Red = 342, 346, 347 ohms

    Mojotone 5E3 OT. Mojo768
    Resistance on primaries (cold). Red is the CT.
    Brown to Red = 294 ohms
    Blue to Red = 330 ohms

    It would be nice to know the primary DC resistance of other manufactures to compare.
     
  16. jsnwhite619

    jsnwhite619 Friend of Leo's

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    The Hammond 1750E sitting here measures
    Brown to Red = 150 ohms
    Blue to Red = 156 ohms
     
  17. dwindover

    dwindover TDPRI Member

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    Hello All,

    I"ve been nerding out on this very question over the last couple of weeks myself. From what I've read, there seems to be three OT's used in the 5e3, 5e9a, 5g9, etc:

    8k/8ohm - 50246 - paper-wound (what the Classictone 18022 was modelled after.) Hammond also references the 50246 part number for their 5e3 OT clones (8.5k/8ohm, both plastic bobbin and paper wound versions (new). The mounting spacing is slightly smaller than the rest of the clones out there. The Mojotone one is paper-wound like the 50246 (8k/8ohm).

    8k/8ohm - 108 - plastic-wound (Mercury Magnetics and Soursound seem to make copies of these). There's a great explanation about this OT on the Soursound site: https://soursound.com/collections/transformers/products/5e3-deluxe-triad-108-output-transformer

    6.6k/8ohm - 125A1A - paper-wound - the Schumacher OT that was used in the Brown Deluxe, and on a bunch of the '59 and '60 Deluxes and Tremoluxes.

    I have a Mercury Magnetics copy of the 108, as well as the Classic Tone 50246 copy and the Classictone 125A1A copy (made for Clark amps for their 5E3 amps). The paper-wound Classictones are much larger than the plastic-wound Mercury Magnetics - 2" thick vs. 1.5". The frame is exactly the same size.

    I wonder if there are numbers on how many of each were used on the originals. Also, the OT's on the pre-5e3 Deluxes (1839) seem to be more in line with the 60's Princeton OT's.

    I wonder why each manufacturer decided to go with the models they did. I suspect it's based on what original examples they had at their disposal to reverse-engineer.

    None of the original OT's were considered high quality at the time of manufacture. Leo was likely thinking of two things:
    1. Expense
    2. Keeping the fidelity low, with a sonic emphasis where he could maximize output without blowing the fragile Jensen speakers. It seems that the only interleaved transformers were the Bassman and Twin ones.
     
  18. NTC

    NTC Tele-Holic

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    I know this is a big ask, but since uou have measured some of these, can you post the dimensions?

    Thank you for sharing all of this info.
     
  19. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Thanks for the info!
     
  20. dwindover

    dwindover TDPRI Member

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    Mercury Magnetics FTDO-59
    Frame - 2.75" x 2.25" tall
    Bobbin - 1.7" x 1.7" x 1.25" tall
    Windings on Bobbin - 1.5" - 1.7" thick x 1.5" wide

    Classic Tone
    Frame - 2.75" x 2.25" tall
    Windings - 2" - 2.10" thick by 1.35" tall x 1.65" wide


    I would imagine that paper windings add more bulk than the plastic bobbin style? Perhaps a transformer expert out there can answer that question.

    I'm not sure what effect, if any, plastic vs. paper would have on the quality of the sound, though many have debated this. Science says that those materials are non-magnetic and thus should not have any impact on the sound. According to Soursound, the 108 was the ONLY plastic bobbin OT that Fender used in the 1950's. I would imagine the way that the wire and metal are wound, and spaced according to the bobbin/paper will have an effect.

    Does anyone have any pictures/dimensions of the original OT's?
     
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