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Question to Fender Dual Sowman users

Discussion in 'Amps and Cabs [BG]' started by OldogNewTrick, Apr 21, 2006.

  1. OldogNewTrick


    Dec 28, 2004
    Germany, EU
    I am running my '75 Dual Showman into an Aguilar GS210 cab.
    As I originaly planned to get a GS115 or GS212 at a later stage, I bought the GS210 as 8 Ohm cab. Now it appears that the 2nd cab wont be coming anytime soon.

    As the Dual Showman has only a 4 Ohm tap, I am wondering if adding an impedance transformer 4:8 Ohms is worthwhile.

    I have found 2 sources for them
    (sorry, page only available in German)
    or from the Tubeampdoctor

    So far so good, both will work, but where I get conflicting opinions - is it worth it ?

    Pro: extend tube life, increase power to full 100W, lower frequency bandwidth back to original level
    Con: some say I wont be able to hear the difference in sound and, as long as I dont play really loud, I wont strain the tubes, resp. need the full power and the transformer is bloody heavy...

    Is there anybody out there who has used such a transformer?
    Anybody with a similiar problem?

    Waste of money or great idea ?
    Any advise is greatly appreciated !

    a pic of my setup:
  2. OldogNewTrick


    Dec 28, 2004
    Germany, EU
    bllody typo !
  3. Passinwind

    Passinwind I am Passinwind and some of you are not. Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Dual Sowman? That's a real pig of an amp, bro.:cool:

    I'd recommend you just get a multi-tap replacement output transformer. They're readily available (at least in the US) and are not hard for a tech to install fairly quickly. You don't have to hack the chassis or drill new holes, even. Then you can run whatever load you want to with no worries.

    In the meantime, be aware that running an 8 ohm load on a 4 ohm tap is not such a great idea. You will likely get better (as in "safer", plus maybe slightly higher power) results just pulling two output tubes for now if you're stuck with the wrong load impedance. Pull either the two adjacent ones, or the two furthest apart from each other. Now you'll have a heavy Bassman 50 that wants an 8 ohm load, essentially, but at least it won't want to eat the transformer or burn tube sockets. You should still ideally get a tech to check B+ voltage and bias when you do this, by the way.
  4. jz0h4d


    Apr 26, 2005
    Passingwind is quite correct about pulling the tubes and how it changes the output impedance of the amp.

    I have to take exception though to the ideal that running an 8 ohm load will hurt anything, it won't.

    Best ideal, add another 8 ohm speaker.
  5. Passinwind

    Passinwind I am Passinwind and some of you are not. Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    I assume you're probably aware that this subject is somewhat controversial? :cool: With old Fenders, I tend to agree with you, but I'd amend that to "probably won't".

    I'll stand by my advice though. I've repaired a number of Twin Reverb amps with arc'ed-over tube sockets that were the result of the owners deciding that one 8 ohm speaker was a "better" load than two in those amps. If we start discussing other amp makes, there's less ambiguity in some cases, IMHO. A Marshall Major or many Ampegs often will not tolerate upward mismatches gracefully, in my experience.

    To the orignal poster: by all means do your own research on this, and draw your own conclusions. Even the engineers and techs at the Fender factory didn't all agree one way or the other when I was working there. But I'd bet most everyone would agree that the best long term solution is to get a cab setup that matches what your amp is spec'd for.
  6. OldogNewTrick


    Dec 28, 2004
    Germany, EU
    where can I find a multi tap transformer? PM, if posting rules dont allow a straight reply.

    The ideal scenario is clear.... But:
    - 2nd cab is out for now
    - trade-in the 8Ohm for a 4Ohm GS210 close to impossible in Germany
    - selling and buying something else -it'll be cheaper to get the transformer...
    (and I really like the sound of the combo)

    Somehow I dont like the idea of tube pulling, getting the amp re-biased will cost me nearly the same as the transformer.

    So basically, that leaves the impedance transformer...
    Are there any quality/sound differences ?
    What is "good" / "bad" ?
    Multi-tap or 4:8 straight ?

    Your input is greatly appreciated !

  7. +1...Good advice!! I fried mine with a mislabeled cabinet running at 8 ohms (labled 4!!) about 12 years ago and will say this...it WILL run for a while at 8 OHMS but eventually it WILL fry!! I used mine primarily in the studio without really driving it too hard and after about 3 or 4 months (if I remeber correctly) it finally just gave up in the middle of a session....



    edit - I should have read the whole thread before I replied...I disagree that it won't hurt it to run an 8 ohm load....I do agree that it won't hurt it to do it once or twice but in the long run I am convinced that was what fried the amp.....I sent it to Fender to have it reapired and when I told them what happened, the tech said the same thing, that "Should not" have caused the problem...After I insisted that it HAD to be the problem he talked to several other techs and a repair supervisor called me back and said that after checking the amp himself he was pretty sure the load was the problem. I told him that I had used it daily at that load and he agreed that the damage caused was most likely caused by the load....YMMV, I have heard the same thing both ways but I know it cost me about $350 in tubes, 1 or 2 boards (I can't remember if it was 1 or 2, but the heat burned through the mounting) to have mine repaired...beware!
  8. Trevorus


    Oct 18, 2002
    Urbana, IL
  9. OldogNewTrick


    Dec 28, 2004
    Germany, EU
    checking various transformers out, I've come across two basic types:

    single winding transformer (Peavey Auto-match)
    Pro: smaller, lighter, cheaper, very good frequency response
    Con: inability to provide isolation of grounds between input and output signal.

    conventional transformer (e.g. Glockenklang, built-in Fender)
    Pro: complete isolation of input and output signal
    Con: larger, heavier, more expensive.

    Since I'm no electrical engineer (obviously, otherwise I wouldn't bother people with my stupid questions :D ) I've no idea of how important it is to isolate the input and output signals.
    The output transformer of the amp is also of conventional design.
    Also Glockenklang -like or dislike their sound- who make arguably some of the highest quality equipment, have chosen this design.

    Anybody there who can explain what it all means ???
  10. Passinwind

    Passinwind I am Passinwind and some of you are not. Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Here's a $90 multi-tap Fender replacement : http://www.mojomusicalsupply.com/cgi-bin/mojotone/MOJO775.htm
    If you shop around you might find a little bit better deal on this, but I have no idea on European vendors or pricing. Double check the mounting center dimensions too.

    Here's a $40 external converter: https://weberspeakerscom.secure.powweb.com/store/magnetic.htm
    (WZC-100). You might want to post your same question on the Weber forums, since lots of Fender techs reside there. Weber's products are generally top shelf stuff, in my experience.

    Ground isolation is pretty much moot in your case, since the internal output transformer already provides it. The Glock transformer probably sounds great, but I've neither seen nor heard one. On general principles I would try to avoid adding a second transformer to the equation though.
  11. OldogNewTrick


    Dec 28, 2004
    Germany, EU
    Much appreciated !!!

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