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5E4A vs. 5F4 decision when buying a clone

Discussion in 'Glowing Bottle Tube Amp Forum' started by archetype, Dec 16, 2020.

  1. archetype

    archetype Fiend of Leo's

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    No worries @ThermionicScott This is a wide-ranging discussion, but informative. In the end, I'll have clarity on the original questions.
     
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  2. theprofessor

    theprofessor Poster Extraordinaire

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    That's fantastic! I really like those coin-base Sylvanias with the big black plates. They look like 6V6GTA's. If so, I believe those are the ones Jim Kelley liked to put ~500V on.
     
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  3. archetype

    archetype Fiend of Leo's

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    That was kind of my reaction. If I wanted to roll tubes to get a tweed a bit brighter or defined I'd try the Sylvania (and the Philips).
     
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  4. telemnemonics

    telemnemonics Telefied Ad Free Member

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    Yeah and two of those are actually the same exact construction as the pair of Philips, while there is another single Philips with the same plate/ getter/ rods etc. A bit odd given production dates but those coin base are some of the later last improvements of 6v6.
    Two of the coin base though are a different internal build and may not be Sylvania but I'm not sure.
    I also have a pair of those somewhere that appear to be same production yet one is gray and the other black plate.
    I think by then the demand for tubes was way down but so many factories closed, and it seems Philips with the ECG was when several factories were bought by the bigger Philips parent company and some "golden '80s era" tubes like the really rugged STR 415 and 417 dual getter Sylvania continued, but with crimped rather than welded plates.

    My sense is that the holy grail '50s power tubes are not better made than the best of the end of the good tube production, just a more vintage/ sweet/ fat/ soft/ dirty sound rather than the last Sylvania power tubes that seem to deliver a harder cleaner sound, which amps like the Boogie depended on as the dirt and fat came from the preamp.
    Peavey and Fender along with Mesa was the force behind the last best power tubes AFAIK, requesting more rugged build and upside down optimized. Though upside down might really not have been a design factor as much as a selling point.
     
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  5. theprofessor

    theprofessor Poster Extraordinaire

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    As I attempt to re-narrate some of this in my own words, is it safe to say this? ...

    The output transformer is essentially working to build a bridge between your output tubes (in this case, 6L6/5881's) and your speaker (of variable nominal impedance). So if a pair of 6L6's in a class AB1 push-pull amplifier do best (according to the data-sheets) with 6k6 load resistance, plate to plate, and you're wanting them to pair with a 4-ohm speaker load (say, 2x10/ 8-ohm speakers wired in parallel), you'd get an OT with a ca. 6k primary and a 4R secondary. HOWEVER, the stated specs are simply nominal, and the impedance "bridge" between the tubes and the speaker is actually relative and also fluctuating. So if the primary actually reflects the secondary, you'd have a 4R primary when you have a 4R secondary.

    Then what it looks like you've done in the first batch where we assume an 8R secondary is to take the stated OT primary impedance (~6k) and divide it by the actual primary impedance, as that primary reflects the load, with the Bandmaster, Super, and Pro respectively. Then you're multiplying the load as reflected by the number of speakers in each, relative to the stated 8R secondary speaker impedance, and then multiplying that by the ratio from the actual primary impedance 750/1 in each case, to get the "true" primary impedance: highest in the tweed Pro and lowest in the tweed Bandmaster.

    When we assume an OT with a ~6k primary impedance and a 4R secondary, the numbers change, as in your second batch....

    Does that sound close so far?

    As for what OT was used in each of those amps, the Vintage Guitar article states this, for example: "Tweed aficionados have long assumed Bandmasters were built with OTs with a secondary impedance of 2.67 ohms to match the load of three 8-ohm speakers wired in parallel." Here is one thing I really do like about the Mercury Magnetics Tone Clone stuff: if it is a Tone Clone, it existed at some point in a Fender amp (right?) And MM offers the FTWBN-OM, which has a 2.6R secondary. So at least some 5E7 amp out there did, in fact, have a 2.6R secondary tap.

    I went back and looked at the one I used -- the FTWBN-O -- which is supposed to be a clone of the 1848. It has a 4R secondary.


    Well I'll buy you one if I ever get through Augusta again...
     
    Last edited: Dec 18, 2020
  6. archetype

    archetype Fiend of Leo's

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    Hmmm. I wouldn't take their Tone Clone designation as evidence that Fender used an OT with 2.6R secondary in Bandmasters.

    What's the Triad number for such a thing and has it ever been found in a Bandmaster?
     
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  7. theprofessor

    theprofessor Poster Extraordinaire

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    Fair enough. I thought that's what it meant, though, when they're offering a clone. I believe I asked Paul at MM this very question, and I thought he said that there must have been at least one of the transformers that did have a 2.6R secondary. I think the Triad number is the same for several variations -- the 1848 -- and that the Vintage Guitar magazine article may overgeneralize. I do not doubt that the particular 5e7 Bandmaster in question had a 4R secondary; I think there may have been some variation in specs, even under the umbrella of a certain part number. That is, unless I'm misunderstanding what MM is doing when they create these clones.
     
  8. archetype

    archetype Fiend of Leo's

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    Agreed, they're offering clones of original transformers. IMO I just don't take 'original' as an absolute, despite the "clone" designation.

    I think the 5E7 OT is one of the bigger mysteries. Coming from the world of manufacturing, long ago, I have a hard time thinking that Triad would vary the secondary resistance for a given transformer with a cataloged part number. A part number has specifications that designers used for incorporation into products. Did Fender say ship us (50) Triad 1848, but with 2.6R?

    I don't know. I'm not challenging you on this, please understand, but it doesn't make sense to me. Then again, a lot of odd stuff happened, didn't it? o_O
     
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  9. jsnwhite619

    jsnwhite619 Friend of Leo's

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    For a disclaimer, my opening statement was directed toward myself - as in, "I think this is correct, but I may be wrong."

    I'm going to borrow from Rob's 5e3 Mods page for using 6v6 tubes in a 6L6 amp --

    If your output transformer is made for 6L6 or EL34 power tubes you would do the opposite. When using 6V6 tubes and a 16 ohm speaker you would use the 8 ohm speaker tap. When using an 8 ohm speaker you would need to use a 4 ohm speaker tap.

    So, if you have a 6L6 amp with a 4k primary and 8 ohm secondary, to use 6v6 tubes you could use a 16 ohm speaker. Doubling the speaker impedance doubles the primary impedance, so the 16 ohm speaker would now see the recommended 8k primary for the 6v6's.
     
  10. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Yeah, that calculator factors in an extra 10% I think and is for absolute worst case scenario maybe.
     
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  11. theprofessor

    theprofessor Poster Extraordinaire

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    Hey, no sweat. Even if you were challenging me, it's clear that I need challenging at points. I'm no expert! And it's not like this is some kind of cutthroat debate. We're just trying to sort stuff out as best we can -- thinking out loud. :)

    Thanks, Jason. And no problem. I assumed that was directed at me, and I was totally cool with it. Because I did misunderstand. Thanks for your help.
     
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  12. High Head Brad

    High Head Brad Tele-Meister

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    I dont have any experience with a 5E4 and have nothing to add about the circuit designs.

    My only contribution is to add that my 5F4 clone (made by Headstrong) is one of the best amps I have ever played or heard in person (including an original). If you are looking at getting a Tweed Super made then i would highly recommend contacting Wayne.
     
  13. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    I have trouble believing Leo Fender would have gone to the effort (and expense) to have custom OTs made with an oddball 2.67Ω secondary. Consider that he offered most of these amps with an external speaker jack that would cause up to a 2:1 impedance mismatch when it was used, and he was evidently fine with that. My understanding (unless someone has evidence otherwise) is that the 2.67Ω secondary taps are a recent addition to replacement OTs for us obsessive types that want everything to match. :)
     
  14. theprofessor

    theprofessor Poster Extraordinaire

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    I totally get it, and I don't disagree with that reasoning. But then I'd like to know what MM is doing if they are "cloning" a 5e7 tweed Bandmaster OT, and said OT has a 2.67R secondary. I can't figure out what else MM would be claiming when they call something a "clone," other than that they found one with such a secondary, and they copied it.
     
  15. NTC

    NTC Tele-Holic

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    Lots of places to look this up on line - I went to Wikipedia. Ideal transformer equations:

    Np = number of primary turns
    Ns = Number of secondary turns
    Vp = Primary voltage (Volts RMS - it has to be AC)
    Vs = Secondary Voltage
    Ip = Primary Current
    Is = secondary current

    The turns ration is Np/Ns. Np/Ns = Vp/Vs = Is/Ip

    Now, Zp = Primary impedance and Zs = Secondary Impedance

    Zp = Vp/Ip; Zs = Vs/Is (from Ohm's Law)

    But Zp/Zs = (Vp/Ip) / (Vs/Is) = VpIs/VsIp = (Np/Ns)^2 (Np/Ns squared)

    Now we can work backward:

    6000 ohms/4 ohms = 1500 (our Super)
    1500*2.6667 = 4000. (Our Bandmaster)
    By the way, the turns ratio == Square root (1500) = 38.7. There are 38.7 primary turns to every secondary turn. Start winding, folks.

    Of course, in my case, my Bandmaster has a nominal 4K:4ohm transformer, so the nominal primary impedance is 2667 ohms. (I am tempted to start a different thread about this).

    Yes, the derivation above is probably unnecessary here, but it helps to illustrate the relationships. It also illustrates what we need someone to do - take their Original 5E7 and 5F4 and go put a voltage into it and see what voltage comes out across a suitable resistor - 8 ohms, 4 ohms, whatever. That way, we can find the turns ration and figure all of this out.

    Agreed. A change to the specification would have resulted in a new part number.

    Also Agreed. You certainly didn't see 2.67 ohm output impedances 20 years ago when I started doing this (and 15 years ago when I stopped).

    Now that we have COMPLETELY obscured the original posters post with some (admittedly very good) tangential information, I suggest he get the 5E4A with the 6V6's built. Lacking any better information (I don't think anyone here knows the real turns ratios of the transformers we seek), an 8K primary to 4 ohm secondary is PROBABLY what you want. If you can get it. I like weird, and this amp is - I didn't know this one existed. Of course, I would go even weirder and get the 3 x 10". You can always disconnect one, and that added low end is great.

    Many of the differences between the 5E7 and 5F4 were mentioned, but don't' forget the different feedback resistor around the second stage gain and Cathode Follower (probaly a subtle difference, but I don't really know) and the 12AX7 there in the 5E7. BIG difference, that, though it is easy to try.

    Sorry for the long post. I had to go to the computer for this.
     
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  16. theprofessor

    theprofessor Poster Extraordinaire

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    Thanks very much for this, NTC -- especially for setting the terms right at the beginning. I have to work harder at this, as I see abstract equations and my eyes kind of glaze over. But I'll see if I can get a hold of some of it. It's the part of amp stuff that I'll have to force myself to learn.
     
  17. telemnemonics

    telemnemonics Telefied Ad Free Member

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    Well maybe 17 years ago I wanted a specific year Plexi 100 OT and called MM for info.
    Took a couple of reps then an engineer then a call back from another engineer.
    Turned out their clone was more of a generalization, and in fact was the same OT they sold for the metal panel amps.
    There were at least three different OTs in just the '66- '68 Plexi 100 production.
    But they really didn't even know which OT they "cloned", while my guess was the really cloned a '70s metal panel version.
     
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  18. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    To wit, Mercury Magnetics sells "tweed Bandmaster" OTs with: an 8Ω tap, 2/4/8Ω taps, 4/8/16Ω taps, a "#1848" with a 4Ω tap, another "#1848" with 4/8Ω taps, and finally a couple with 2.6Ω taps. I'll grant that the one with the 8Ω tap is what you want for the earliest 1x15" Bandmasters, but the rest can't all be exact clones of the same part. ;)
     
  19. NTC

    NTC Tele-Holic

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    I wonder what the primary impedance was?

    Regarding those transformer equations - they are the "ideal" transformer equations. Real transformers end up a bit different due to winding losses, mutual inductance, and losses in the core. Those things are where the art of transformer making come in.
     
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  20. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    Back when I built my 5E7 from a Weber kit ~15 years ago, they shipped it with a "universal" 4K:2/4/8Ω output transformer, and I didn't learn until much later that the real ones might not have been 4K. I think 6K makes a lot of sense for the cathode-biased ones, but I've never been sure about the fixed-bias tweed ones. 4K looks really good when you have 6L6s at about 400 plate and screen volts, so the OCD part of me kind of wants to buy a 6K:4Ω unit so that the mismatch would bring the primary closer to that ideal 4K. :lol:

    Back to the OP's quest... we tend to look at the 5E4A Super as one of those Leo Fender experiments that didn't work out well enough to keep (like the 6BQ5-powered Tremolux), but I wonder sometimes if it taught them a lot about what they could do with 6V6s. Fixed-bias, B+ up closer to 400V, and if they used the same 6K output transformers that they had lying around, that's starting to look a lot like the operating conditions inside a Brown and Blackface Deluxe (6.6K primary)! That's pure speculation on my part, but I'd like to think that in addition to not letting any hardware components go to waste, Leo held on to good ideas, to try again later. :)

    So if I were to do a purpose-built 5E4A, a Deluxe Reverb type OT with a 4Ω secondary would be on my list to consider...
     
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