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Two transformers: Which would you pick? (Or, my build blog)

Discussion in 'Amp Tech Center' started by gabasa, Nov 17, 2020.

  1. gabasa

    gabasa Tele-Meister

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    I'm thinking of building another amp and it may be a 5E3 or a Harvard. If it's a 5E3, there are two power transformers I've been looking at and I'm not sure which to pick:
    • Hammond 290BX
    • Hammond 290BBX
    As you can tell, I'm a big Hammond fan. I played with '60s Traynors a lot in the old days and I've always loved Hammonds because of how good those amps sounded.

    Both of these transformers would work just fine. Which would you pick? Why? I've attached pdfs here of their schematics for easy reference.

    Btw, I added the, "build blog," thing into the title. I figured I'd turn this into a journal/blog; it would be fun!

    Thanks for any suggestions in advance.
     

    Attached Files:

  2. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    The BBX will deliver too high of a voltage. The BX will come in around 370B+.
     
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  3. gabasa

    gabasa Tele-Meister

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    Thanks, that was my thinking too, but the Hammond page recommends the BBX for the 5E3 so I thought I'd ask the opinions here. I'll definitely get the BX.

    I have two Jupiter 10LA speakers in boxes, begging to go into amps. I was thinking of a portable, 1x10 5E3 and if budget permits, a second one; perhaps a Harvard, a 1x10 5E3 with a bunch of Harvard-ish mods or a tweed Vibrolux. I'm still mulling it over, but option #2 sounds like fun because it would be unique.

    This reminds me of the Daffy Duck line, "You need a house to go with this doorknob..."
     
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  4. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    +1 on the 290BX!

    That said, a 5E3 doesn't use anywhere close to 138mA, so don't be surprised if your secondaries show a little higher than 330VAC in action.
     
  5. gabasa

    gabasa Tele-Meister

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    Thanks. This is the idea for these builds this morning, it's evolved a hair further:
    • 1st amp: 5E3: 1x10, 16"x18" cabinet (blonde tolex & wheat grille), Jupiter 10LA, with a Hammond 194A 4H choke
    • 2nd amp: Exactly the same as above with the following changes: 0.02uf input caps, no bypass cap on V2, 56k NFB resistor. This will bring it closer to the voicing and gain of a Harvard, but it'll be two channels and cathode biased. Different color tolex that the other one so I can tell which is which. I just like this idea overall because it's unique.
    I can't tell whether or not Hammond's 1750E output transformer is paper or plastic bobbin. On their current website it says paper, on the old website (which is still up) it says plastic. I've emailed them for clarification on this. If it's plastic, I'll get Classictone OTs.
     
  6. theprofessor

    theprofessor Poster Extraordinaire

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    As others have said, I'd stay away from that BBX! Even the BX is a 330V transformer, and I'd think that could still be too high. @jsnwhite619 is a fellow Hammond lover, and he's built loads of tweed with them. I'd see if he pitches in with his personal favorite.

    In my opinion, lower voltages are better on these tweeds. They won't sound right if the voltages are too high. I'd be shooting for between 340-360V at B+1
     
  7. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Agree with theprofessor. The 330-0-330 PT is the max you can get away with. If you can find a PT with less go for it.
    Since you like Hammond... If you can stand a little larger bolt spacing, the 1750PA is Hammond's Marshall 18W suggestion. Paper. 8k4 primary. 4,8,16 secondary. (Mouser had them for a lower price). I have used it in a 5E3 and I recommend.

    I have no affiliation with the above mentioned companies.

    LLC
     
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  8. Nickfl

    Nickfl Friend of Leo's

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    What are your goals with this build or builds? I don't think any of your ideas sound bad but I think it's helpful to actually come up with a sort of mission statement for your amp sometimes because if you let specific technical details of the circuit lead the way sometimes that can take you off course from where you would be headed if you had a sound in mind as your goal.

    Right now you're talking about building a 5e3 with a 10-in speaker and a very slightly modified 5e3 with a 10-inch speaker. Are those what you want? Are those different enough from each other to be worth building both?
     
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  9. trancedental

    trancedental Tele-Meister

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  10. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I have the 290BX on my 5e3 and JJ's come in at 370v B+ with a 270R cathode resistor. I've only gotten to check out one original 5e3 and the vintage tubes on it measured around 396v B+ I think. So, the BBX is probably more correct for how a vintage measures today, but the BX is probably closer to how the original measured back then?

    Since you are wanting a possible Harvard out of it too, but using a 5e3 chassis, I would get the 290BX with a bias tap. Check out Rob's great site on mods and consider the following:
    • switchable fixed/cathode bias
    • switchable NFB
    • .022uf coupling caps on the Bright channel
    You'll darn near have a 5e3 and a Harvard that will measure out closer to Vibrolux voltages than Harvard voltages. There will be a few differences that will separate it from being truly one or the other, but pretty close either way.

    For the OT, I use that 1750E on anything using 6v6's and smaller than a Deluxe Reverb. If you want the vintage overdrive and saturation, you need the 8k primary.

    If you end up with a modded 5f2 chassis, the 290AX will do what you want for the Harvard.
     
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  11. gabasa

    gabasa Tele-Meister

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    That's a good question. I feel like I'm good with amps, I don't feel the need to get any for myself. I have a Champ, Deluxe and Bassman that I built and they keep me pretty happy! My kids also play guitar and they're putting together a music playing/practicing/recording area in the house. I always try to do things to encourage them to play together, so I thought to build two amps around these awesome Jupiter 10LA speakers I have lying around. Even though one 5E3 would be slightly modified, I feel those mods would drastically alter the tone and gain characteristics of the amp towards the Harvard end of the spectrum. If I fixed-bias it, the only difference to a real Harvard would be the second channel.
     
  12. gabasa

    gabasa Tele-Meister

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    Thanks so much for the info. I'll take a look at all that and the 290HAX mentioned above as well; it looks like it might be a great choice too.
    I feel the same though ... it could make darn near a Harvard, but with two channels and interactive volume controls.

    Isn't the Harvard input wired like the bright channel of a 5E3, with the only change being the 0.02uf coupling cap?
     
  13. gabasa

    gabasa Tele-Meister

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    I was just looking at the 290AX, the 550V secondary looks interesting.
     
  14. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Nope, reversed on the input/output. I had a thread several months ago now where I was playing with some mods on my 5e3 and swapped the input wiring on it & my Harvard just to see how they responded. Both of them reversed how they performed. The 5e3 cleaned up and had a much slower taper - actually increased the overall headroom - and the Harvard went the other way. It got louder and dirtier.
     
  15. gabasa

    gabasa Tele-Meister

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    You're right. I didn't see this earlier and it makes this idea problematic now, lol. I don't think that Harvard volume/tone wiring would work well at all in a two-channel configuration.
    Nobody sells a Harvard chassis/eyelet board kit anywhere. Maybe I can see if anyone is willing to make up a batch, like Boothill or Marsh. I just don't feel like punching holes and making up customized boards, even though I know it's doable.
     
  16. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    The Harvard could probably get by with a 5E3 eyelet board with a little finagling. The 68k could hang on the input jacks or not. All in all, very doable IMO.
     
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  17. gabasa

    gabasa Tele-Meister

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    Ok...based on all the updates here, I'm going to try to figure out how to get a straight-up Harvard together as one of the amps, and a 1x10 5E3 as the second.
    No Deluxe/Harvard hybrids. Thanks.
     
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  18. zook

    zook Friend of Leo's

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    For the Harvard/Vibrolux I like to use the Hammond 290CAX and the 315 Volt taps. Don't forget, these amps use a 5Y3, Not a 5AR4.
     
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  19. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    The schematics show a B+ of 305v for the Harvard and 340v for the vibrolux 5f11. I guesstimate the 315v tap with 5Y3 would deliver around 350v. For the 5F11 that is close enough.

    zook, from your experience with a Harvard, wouldn't the ~45v higher B+ take away some of the woolly character one might want?
    I have not built a 6V6 amp with a 305v B+ yet. I guess what I'd like to know is whether the low B+ is driving that smokey character of the Harvard I like so well.
     
  20. jsnwhite619

    jsnwhite619 Friend of Leo's

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    The times I've used the 290CAX & 315v tap, JJ's always biased between 370v & 380v I think. I know the plate to cathode was 370v+. I tried it both ways with the 275v & 315v options. The 275v will nail the 5f10 schematic voltages. The lower level has a great, warm, vintage clean tone. If you wanted to play T-Bone Walker type stuff, the old Harvard voltages sound great. For the firmer bass and hard-hitting overdrive, I had to get the voltages back up in the 370v+ range.

    275v secondary, dirtiest parts used a Blues Driver


    315v, straight into the amp.
     
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