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Thread: Gibson Falcon output transformer

  1. #1
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    Gibson Falcon output transformer

    I found out the output transformer looking a little blackened. I checked the resistance of it, got ~1440 ohms on the primary, and .7 on the secondary..which I know is too low. Does anyone have the specs on what a proper output tranny should measure? I looked at Mercury's site, and they make one, but is there an alternative that is at least in the ballpark of wattage output, and resistance to keep the amp as true as possible, and slightly cheaper? Any help is greatly appreciated.

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    Output transformers are impedance matching devices and winding resistance has little to do with the specs that are important to know.

    If in fact your transformer is bad, then start by listing the important details of the amp. What design type output is the amp? What output tube does it use? What is the secondary speaker load?

    If keeping the amp "as true as possible" is the important factor here, then search the web for an original part, or order a Mercury clone. If getting the amp up and running is the main factor, then search for a similar transformer from another supplier.

  3. #3
    Senior Member Daver's Avatar
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    I may have an output tranny for a Falcon. What year is yours? The one I have here is a '63 if I remember correctly.
    Dave

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    I'm not entirely sure what year mine is. It's an earlier tweed one, though. As far as I can tell, it's either '61 or '62. The cabinet looks like the same shape as a GA-8. So it has the controls in the top rear. I can take a few pics of the amp if necessary. The speaker is a 6.7 ohm (technically 8) Jensen Vibranto 12" LMI 220 model (replacement speaker). That's why I was asking about the transformer specs: I've never seen a transformer have that low of secondary resistance (.7 ohms), yet call for an 8 ohm speaker load. Tube compliment is as follows from left to right, looking at the back of the amp:
    V1: 6EU7 (preamp)
    V2: 7199 (Reverb tube)
    V3: 6EU7 (preamp)
    V4: 6EU7 (preamp)
    V5: 6V6GTA (power)
    V6: 6V6GTA (power)
    V7: 5Y3GT (rectifier)

    I would use a generic output tranny, but the third wire on the primary leading from the power tranny is what is making me wonder. I'm guessing it has to do with the tremolo effect (I'm just starting to learn about basic electronics, so anyone can expect a lot of stupid questions from me). I would like to preserve the sound of this amp, as it's pretty unique sounding compared to the other amps I have around here. If I do buy a Mercury, has anyone had experiences with them? Are the replacement outputs any good, do they have the same wiring setup as stock? All help thus far has been appreciated.

  5. #5
    Senior Member Enzo's Avatar
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    The higher power an output transformer is, the lower will be the resistance of its secondary winding. This is because the wires will be heavier gauge. The heavier the wire the lower the resistance. It has little to do with the impedance it serves. In fact the transformer has no inherent impedance, all it has is a ratio.

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    I understand about the wire gauge size and resistance per foot, and whatnot. I figured measuring the two ends of each winding would result in a resistance. I also thought the secondary winding of the output would match the speaker resistance at least a little closer. Time for me to open up the other amps and see what's going on. This also brings out another question:
    How can a replacement Fender transformer claim 2/4/8 ohm stability when the windings and taps are not changed on either primary or secondary? Or is it not that big of a difference to begin with? Yeah, I have lots of questions.

    Oh, this output transformer is for an amp rated at 14 watts...not exactly a killer.

    Just checked my Jackson JG2. It has a 85 watt Fender replacement output. Measures .5 ohms on secondary. Primary is like 80 ohms. I guess I'm fine. Thanks for the ratio info, Enzo. I'll now smack my forehead and yell "idiot" to myself for not checking other stuff sooner.
    Last edited by UnexplodedCow; 02-02-2008 at 07:00 AM.

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    I have a Falcon transformer also. The turns ratio is about 50:1, meaning 10K for a 4 ohm load, however my Falcon has an 8 ohm speaker, so 20K is the order of the day. I've long since taken mine out and replaced it with a custom-made (not for me) Hammond with a primary of 6K for 8 ohms and replaced the 6V6's with Tung Sol 5881's. As I've mentioned every chance I get, this amp is killer. You're welcome to this giant (2"x1.6") piece of iron if you need it.

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    Thanks for the info, Clyde. What made you switch to 5881's vs. the 6v6's? I imagine there were a few minor circuit changes needed.

    The whole reason this is brought up is due to the amp crapping out on me, and I've been trying to read up on this amp, and tube amps in general to familiarize myself enough to do a rebuild of it, or at least a cap/resistor/pot job.

    So a 50:1 ratio is what it's supposed to be. Somehow that math doesn't jive with my output, as primary is ~1440 ohms (give or take about 3 ohms on my meter).

    What's the math behind coming up with turns ratio and resistance? Did you measure your tranny's resisance to come up with it, or some other method (someone rebuild a tranny for that amp)?

    Sorry all I've got are more questions, but thanks for the patience, and not flaming the new guy.
    Last edited by UnexplodedCow; 02-02-2008 at 07:52 AM.

  9. #9
    Senior Member Enzo's Avatar
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    as primary is ~1440 ohms (give or take about 3 ohms on my meter).

    What's the math behind coming up with turns ratio and resistance? Did you measure your tranny's resisance to come up with it, or some other method (someone rebuild a tranny for that amp)?
    The resistance of the winding does not enter into the impedances coming or going. You measured 1440 ohms on your transformer. If they had wound that transformer exactly the same, but used heavier wire, you would have measured a lower resistance. But that would have zero effect on the turns ratio, and thus no effect on the impedance an 8 ohm load (or whatever) reflects back to the tubes. SO the resistance reading is totaly irrelevant as to whether the transformer meets your impedance needs.

    Having said that, while your secondary will have relatively few turns of relatively heavy wire, and will therefore have a very low resistance, it still does have resistance. Just not much. But if you wind it with lighter wire, that resustance goes up, and it saps some of the power that would have gone on to the speaker. Might as well take a heavier transformer and add a resistor after it. SO low resistance is better for the amp, but doesn't enter into the impedance calculations.

    AN example is the typical output transformer for a MArshall 100 watt amp. The OT primary measures about 15-16 ohms on each side of that primary - or about 30-35 ohms total. SOme other similar transformer might measure 80 ohms per side or 160 across.

    You can apply an AC signal voltage to one winding, and then measure the resulting voltage on the other winding, and the voltage ration will tell you the turns ratios of the windings. From that you calculate impedances based on the squares and what impedance the load is intended to be. No resistance.

    Resistance in the wires affects efficiency but not impedance.

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    Like I said, I understand that much about wire gauge and length affecting resistance.
    I understand about the ratios making a difference. I also understand that less resistance is more efficient (lower impedance creates less voltage drop across a given point)

    What I'm trying to figure out is if the resistance the tubes "see" is harmful or not. I guess, if lower resistance is better, then wouldn't even lower resistances (lower than the marshall amp mentioned) be beneficial? If that's the case, why do so many replacement trannys list as higher impedance. And if impedance doesn't matter at all in regards to functionality, why list it at all in a replacement?
    I guess, what I'm thinking based on what I'm being told, is that I could, in theory, take 50 winds of smaller gauge wire for one side of the tranny, then give it 1 wind of larger gauge wire on the other side, and that should equal out to the 50:1 ratio mentioned earlier. That would seem to be the most efficient method.

    And the resistance I measured was from one end of the primary winding to the other. Same with secondary. I wasn't measuring between primary and secondary coils, if that's what it sounded like.

  11. #11
    Senior Member Enzo's Avatar
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    Lower resistance is good, but is not the main thing. The transformer still has to be a transformer. Your one turn to 50 turns would technically work. In fact on some TV sets, the heater winding for the picture tube is ONE turn of wire around the core of the flyback transformer. But the point of the transformer is to convey the power through the tubes to the speakers. There have to be enough turns on the core to drive flux through the laminations. You need to be able to generate a certain level of voltage across the speaker load AND at certain levels of current. Your one turn would not be able to induce that much current into the wire.

    Your primary winding might be a 3000 ohm impedance and have a DC resistance of 30 ohms. If we had a perfect 3000 ohm impedance transformer, we could add a 30 ohm resistor in series with it on one end and have the same thing as my "real world" transformer. That 30 ohms is invisible to the tube. Now that imaginary 3000 ohms is only 3000 ohms IF the appropriate speaker load is present across the secondary. The transformer has no inherent impedance.

    why do so many replacement trannys list as higher impedance. And if impedance doesn't matter at all in regards to functionality, why list it at all in a replacement?
    I have to say I am not sure what you are saying.

    Why do replacement transformers list higher impedance? What impedance? If they give winding resistance, that is separate from impedance. If you actually mean impedance, well transformers are made to match certain tube impedances to certain speaker impedances. If we start with an 8 ohm speaker load, we then design a transformer with turns ratios that result in a reflected impadance of whatever tube you plan to use needs. EL34, 6L6, etc each expect a certain impedance for best operation, so a transformer is wound to match one tube to one speaker impedance. SO if the primary should be 3000 ohms for a certain tube, I would not expect them to make a 4000 ohm transformer for the application.

    The transformer is an electrical equivalent to gears. gears can turn high speed low torque into low speed high torque. A gear has no inherent speed, the speed of one gear is proportional to the ratio of the size of it to another gear. By determining the speed of one gear, we can determione by ratios what the speed of the other gear will be. Likewise, if we know the input speed, and the desired output speed, we can calculate the ratio we need in gear size.

    Impedance not mattering at all? I certainly am lost as to your point there, please restate it. If i have made confusing statements, please point them out so I might try to clarify. After power handling capability, impedance is the whole point of the transformer - it TRANSFORMS the impedance of the tubes into the impedance of the speaker.

    I also thought the secondary winding of the output would match the speaker resistance at least a little closer.
    You say you understand the resistance thing, but when you say something like this it leads me to think you really don't have it yet. The resistance - not impedance - of the speaker and the transformer windings have nothing to do with each other. it is the impedances that need to match, not the resistances.
    Last edited by Enzo; 02-02-2008 at 11:24 AM.

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    The way I measure turns ratio is using a signal generator, I put a 1 volt sine wave into the secondary of the transformer and measure the voltage on the primary, ie your 2 plate leads, leaving the CT unconnected. This voltage divided by your input voltage (1 in my case) gives you your turns ratio-50:1 for my Falcon TX. Squaring this # and multiplying by your expected secondary load, 8 ohms also in my case, gives you your primary impedance,
    50 x 50 x 8 = 20,000. No, no circuit changes for the 5881's not even to the power transformer, tiny little overworked thing that it is. I gigged for 10 years this way, no problems. YMMV.

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    Quote Originally Posted by Enzo View Post
    Lower resistance is good, but is not the main thing. The transformer still has to be a transformer. Your one turn to 50 turns would technically work. In fact on some TV sets, the heater winding for the picture tube is ONE turn of wire around the core of the flyback transformer. But the point of the transformer is to convey the power through the tubes to the speakers. There have to be enough turns on the core to drive flux through the laminations. You need to be able to generate a certain level of voltage across the speaker load AND at certain levels of current. Your one turn would not be able to induce that much current into the wire.

    Your primary winding might be a 3000 ohm impedance and have a DC resistance of 30 ohms. If we had a perfect 3000 ohm impedance transformer, we could add a 30 ohm resistor in series with it on one end and have the same thing as my "real world" transformer. That 30 ohms is invisible to the tube. Now that imaginary 3000 ohms is only 3000 ohms IF the appropriate speaker load is present across the secondary. The transformer has no inherent impedance.



    I have to say I am not sure what you are saying.

    Why do replacement transformers list higher impedance? What impedance? If they give winding resistance, that is separate from impedance. If you actually mean impedance, well transformers are made to match certain tube impedances to certain speaker impedances. If we start with an 8 ohm speaker load, we then design a transformer with turns ratios that result in a reflected impadance of whatever tube you plan to use needs. EL34, 6L6, etc each expect a certain impedance for best operation, so a transformer is wound to match one tube to one speaker impedance. SO if the primary should be 3000 ohms for a certain tube, I would not expect them to make a 4000 ohm transformer for the application.

    The transformer is an electrical equivalent to gears. gears can turn high speed low torque into low speed high torque. A gear has no inherent speed, the speed of one gear is proportional to the ratio of the size of it to another gear. By determining the speed of one gear, we can determione by ratios what the speed of the other gear will be. Likewise, if we know the input speed, and the desired output speed, we can calculate the ratio we need in gear size.

    Impedance not mattering at all? I certainly am lost as to your point there, please restate it. If i have made confusing statements, please point them out so I might try to clarify. After power handling capability, impedance is the whole point of the transformer - it TRANSFORMS the impedance of the tubes into the impedance of the speaker.



    You say you understand the resistance thing, but when you say something like this it leads me to think you really don't have it yet. The resistance - not impedance - of the speaker and the transformer windings have nothing to do with each other. it is the impedances that need to match, not the resistances.
    I did word some of that badly....no sleep for three days does this. What I mean to say, why are the primary and secondary winding impedances mentioned at all in replacement transformers. I also meant, why do I read replacement transformers having primary and secondary resistance well above what was mentioned.
    Example: Replacement Fend Blues Jr. output tranny. Primary impedance is 1650 ohms. Secondary impedance is 8. Is this simply a mathematical guess using a combination of ohm's law, and a given turns ratio, or is the wire wrapped a specific number of times to achieve the required length and have primary and secondary winding impedances of the specification listed?

    And when I say I understand resistance, I did mention that I understand it on a wire gauge and length term, not in regards to any kind of transformers.

    Good analogy on relating a transformer to gears, though. I kinda figured them to be as such considering I've dealt with basic step up and down things, for making basic unregulated DC power supplies. But this is all relatively new to me, and I'm jumping to electronics from mechanics and engine building; quite a different duck. But thanks for the long and detailed answers, they've quelled my questions pretty much.

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    Wire size will determine the current handling capabilities of the transformer. Larger gauge wire will handle larger current loads.

  15. #15
    Senior Member Enzo's Avatar
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    Yes, turns are counted precisely. So they will have the proper number of turns of appropriate wire size to reflect that 8 ohms back to the tube as 1650 ohms. Transformers are like any other component, they are designed to meet certain specs. They don't just wrap wire around a core and hope for the best. So that same transformer would not reflect 4 ohms back to a tube expecting say 10,000 ohms at its plate correctly.

    it is not the wire length, it is the number of turns. More specifically it is the ratio of numbers of turns between the windings

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