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Blonde Fender Bassman - Mismatched Impedance

Discussion in 'Glowing Bottle Tube Amp Forum' started by DannyStereo, Apr 10, 2018.

  1. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    See, there ya go. People think nothing of toting a Marshall type of 4 x 12...really heavy plywood in those cabs... but they think a Fender 2 x 12/15 is too big..even though the Fender is lighter than the Marshall type...and in many case less cumbersome. ???? LOL....

    Here is a picture of such a Fender cab....the speaker cab is 39" tall.
    upload_2018-4-26_11-22-1.jpeg



    and here is a picture of the Ampeg....and the Ampeg is supposed to have a built in dolly underneath it. The Ampeg cab is 45" with the dolly underneath it.



    upload_2018-4-26_11-21-2.jpeg


    If I had a blonde 6G6B without the cab, I would contact J.D. Newell and have him build me a blonde 2 x 12" cab to match. ommv.....but that is the Brian Setzer amp and I would want...and so does the market....it to look 'correct'...and sound as close to 'correct' as possible. again..ommv...
     

  2. DannyStereo

    DannyStereo Poster Extraordinaire

    Aug 13, 2014
    Kelso, Washington
    I wouldn't mind hauling the 2x15". I have a truck with a cover on it, and my cabs go back there, heads on the seat next to me.

    I'm not so much a Setzer fan, but I believe Mike Ness of Social Distortion has used Bassman heads for a long time. His are modded to be more Marshall-y. Though I have to admit my buddy's Irish Falcon sounds DEAD ON Setzer through that amp.

    Eventually, I will have a correct cab for it. Actually, I'd be really keen on a 1x15" cab. I love 15"s for guitar. For now, I'll try and baby this thing as much as I can.

    And yes, it sounds beautiful and nasty in the Normal channel. I've ALWAYS wanted an old Bassman, and when I saw this one locally I had to jump on it. Some caps have been replaced, so it's not all "original", so more of a player than a collector.
     
    Wally and telemnemonics like this.

  3. Jammin'John

    Jammin'John Tele-Afflicted

    Mar 20, 2003
    Tug Hill Plateau
    "higher impedsimp is better than lower."

    NOT true.

    JJ
     
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  4. DannyStereo

    DannyStereo Poster Extraordinaire

    Aug 13, 2014
    Kelso, Washington
    Elaborate?
     

  5. Jammin'John

    Jammin'John Tele-Afflicted

    Mar 20, 2003
    Tug Hill Plateau
    Actually a greater load is bad for a tube amp.
    The reason is called reflected impedance and it's bad news.
    If you are going to mismatch VALVE amps it is actually less bad, (for the amp or more specifically, the Output Transformer), to mismatch to a lower impedance, (16 ohm into 8 ohm cab), rather then higher. Unlike solid-state amps, valve amps are basically self limiting current wise (the valves!) into a lower impedance, though the valves will take more wear. Into a too high impedance the risk is different - potential very high flyback voltages can fry the OT. But most valve amps with strong output transformers will take a 1/2 to 2x mismatch without complaining.

    JJ
     
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  6. radiocaster

    radiocaster Friend of Leo's

    Aug 18, 2015
    europe
    I don't think this question will ever be answered. You might have more luck with the meaning of life.

    I asked a similar question, true I was mostly dealing with 1/4 to 5 W amps. I don't know if that has anything to do with it, in particular that they are most often cranked, and the thread had several cases of high mismatch, 4x or 5x.
    http://www.tdpri.com/threads/output-transformer-question.779974/

    And then you have people like Fender, who put "8 ohm min" on the back of the Greta, which would imply 16 ohms is o.k. I also read on a forum that someone emailed Fender and they replied something like "do not connect a 16 ohm speaker under any circumstances". I used a 16 ohm speaker with it for quite a while, it still works.
     

  7. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    I have witnessed amps that had OT’s that ‘worked’ in that there was signal produced and sent to the speaker but that did not mean that the OT was doing what it should do and once did. One such amp was a ‘59 Bandmaster that sounded terrible and was making all of 8 watts. The other one was a BFDR That again sounded terrible and was making 15 watts. Without a doubt, both of those amps had suffered flyback voltage which pierced the insulation on some of the windings and compromised the integrity of the transformers...and the performance of both OT’s was unacceptable.
    The best answer to this impedance matching question is that a load that matches the specified load requirement of the OT yields the best soundand most output in the safest and most efficient manner possible.
    What people do is a totally different question, and whether or not their OT’s or power tubes suffer from that mismatch is in many cases not noticed by the users, Ime.
    The final arbiter of what one can do is one’s self. The results are determined by the electrons flowing through the circuit and their reactions to the equations they encounter.

    Free world.....
     

  8. DannyStereo

    DannyStereo Poster Extraordinaire

    Aug 13, 2014
    Kelso, Washington
    The issue is I definitely don't want to harm the amp in any way. It's too cool for me to #@$& it up by doing something risky to it.
     

  9. Dacious

    Dacious Poster Extraordinaire

    Mar 16, 2003
    Godzone
    Then given it's a bit special, don't run it mismatched. Fender said 100% over or under is OK - but that's when new, before decades of use and abuse. Apart from anything else you'll affect the tonaility as Wally said.

    I have seen amps run hard into low impedances which have melted wax out of the transformer, and old Fenders of the 6L6 variety are still running. But it's not what you'd want to do.

    I'd not do it with a Vox, and definitely not with new production stuff.

    Doing it occasionally at low volume probably won't hurt - but drive it with a square wave generator all bets are off. Given the amp's sixty years old almost, treating the old girl with respect is wise.

    Problem is, things have probably drifted meaning popping something is a possibility, then you won't know what went first and what caused it.
     

  10. DannyStereo

    DannyStereo Poster Extraordinaire

    Aug 13, 2014
    Kelso, Washington
    The beauty of old amps huh? According to the gentleman I bought it from, he'd been running it around 3 on the dial, pushing a single 8 ohm Jensen for a few years. Then he "retired" it from live use, had it serviced, and then used it sparingly since. Hence the "not all original" parts of the amp.
     

  11. DannyStereo

    DannyStereo Poster Extraordinaire

    Aug 13, 2014
    Kelso, Washington
    1523541571598.jpg 1523541580044.jpg 1523541591374.jpg 1523541601359.jpg 1523541609387.jpg

    Here's some inside shots for your viewing
     
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  12. Paul in Colorado

    Paul in Colorado Telefied Ad Free Member

    Mar 17, 2003
    Fort Collins, CO
    It's a '64 Bassman. How many times has it been run with impedance mismatches over the years by ignorant teenagers who thought running a bunch of cabinets would make them rock stars? It's still running, right? Run it at 8 ohms and don't worry about a thing. And if you're really concerned, build/get a cab with two 8 ohm speakers of your liking and be done with it.

    And welcome back, Danny!
     
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  13. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Danny, that OT is not an original transformer....the fourth picture above with the code 1052 9542....If my old eyes are reading what s there, that OT was built in the 42nd week of 1995. Pertinent to the point of the thread here, it would be of interest to know what that OT was built to do. It seems that something took out the original OT....could have been any number of things including mismatching the load to the original OT.

    The PT and choke are original...from 1961.
     
    Wyatt likes this.

  14. Wyatt

    Wyatt Tele-Holic

    996
    Nov 3, 2004
    Good catch by @Wally . Without knowing the OT specs/ratio, we have no clue what the optimum speaker load is.
     
    Wally likes this.

  15. schmee

    schmee Friend of Leo's

    Jun 2, 2003
    northwest
    One thing I have noticed regarding mismatch. The more powerful amps seems to sound fine mismatched. Like a Bassman or Twin etc. But you add an extension speaker to a low wattage Deluxe or etc and they seem to be much nastier.
     

  16. DannyStereo

    DannyStereo Poster Extraordinaire

    Aug 13, 2014
    Kelso, Washington
    Wyatt and Wally, how would I go about measuring the impedance of the new Tranny? Can it be done from the jack?
     

  17. DannyStereo

    DannyStereo Poster Extraordinaire

    Aug 13, 2014
    Kelso, Washington
    A quick Google search and it seems to be one of these: http://shop.magicparts.com/TF125

    Description: "Fender Super Reverb, Bassman General Repacement Mounting Centers : 3 1/4" ×2 1/16" 2×6L6GC Output Transfrmer 2,4&8ohm output"

    Does this mean it will "tolerate" 8ohm AND 4ohm loads?
     

  18. DannyStereo

    DannyStereo Poster Extraordinaire

    Aug 13, 2014
    Kelso, Washington
    By the way, you guys are the most helpful, nicest bunch of pluckers on God's green earth. Needs to be acknowledged!!!
     

  19. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Danny, in your first picture above, we can see those two OT secondary wires coming to the output jacks...one yellow and one black. What we cannot see is if there are two more secondary leads that are taped off on the outside of that chassis. If there are only the yellow and black secondary wires, then the OT you have is different from the one you found despite that TF125 code. If there are two other leads, then you have that OT. Now one can figure out from the spec sheet what secondary lead is which load. That multisection it-tap OT you show us in that ad has a green lead, a green yellow lead, a white lead and the black lead. Or....ammultimeter resistance test from the black to each of the other leads will tell you which is which. Those resistances are small...and will have only an ohm or so of difference usually. The lowest resistance would be the 2 ohm lead...and the highest resistance is the largest load.
    If you have a single secondary, then there is a test and math that will tell you what you have.
     

  20. DannyStereo

    DannyStereo Poster Extraordinaire

    Aug 13, 2014
    Kelso, Washington
    Got it. I will open her up when I get off work!
     

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