6550 in marshall...what to get?

Discussion in 'Amps and Cabs' started by joolzriff, Oct 3, 2004.

  1. joolzriff

    joolzriff Member

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    i need to buy a quad for a marshall jmp and these 6550's are ''Pricy''!!....
    could anyone reccomend me a good quad for a good price...
    i couldnt believe the prices of 6550 compare to 6L6'S and EL34's that i have bought in the past in other amps.
    is a 6L6 in the same family as 6550?? if it is maybe that would be a cheaper route in the future..
    cheers
    j
     
  2. Steve Snider

    Steve Snider Silver Supporting Member

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    I just put a quad in my Herbert of the imposter Tung Sol 6550s being offered by new sensor . They sound great to me. Not too expensive.
     
  3. StonerTone

    StonerTone Guest

    Where did you get them ? I want to try these and compare to my real Tung-Sols.
     
  4. Roccaforte Amps

    Roccaforte Amps Member

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    For NOS, GE 6550's always sounded best in Marshalls.
    However, I've used Sovteck (Reflector) made 6550's
    in many different amplifiers with great results,
    same goes for the EH KT88, great tube too.
    The new TungSol 6550 sounds real good,
    I can't comment on reliability yet, but
    its built well.
    All of these tubes are very reasonable,
    you just have to try them.
     
  5. Steve Snider

    Steve Snider Silver Supporting Member

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    I got them from New Sensor. They should be available soon if not already.
     
  6. John Phillips

    John Phillips Member

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    I'd convert the amp to run EL34s like it was designed to :).

    Standard 50 and 100W Marshalls were never originally intended to run on 6550s - there's no need at all for a tube of that power capability. They were only fitted for the US market at the request of the US distributor at the time, because of some 'reliability' problems with EL34s. This was most likely unneccessary, since those same Marshalls in most other parts of the world have always used EL34s.

    6550s change the sound a lot - much harder, with more clean headroom and a sharper transition to distortion when it does eventually occur. You'll hear much more preamp distortion and less power amp distortion with them. Good if you want a really big metal tone (eg Zakk Wylde), but not if you want a more 'classic' Marshall rock tone.

    Changing to EL34s will need a resistor in the bias supply circuit replacing (the rebias is outside the range of the trimmer), but that's all.


    You could also convert to 6L6s/5881s. I'm not actually certain whether you'd need to change the resistor or not - I've never done this particular conversion (6550 Marshalls are virtually unknown over here), but the bias requirement is somewhere in between the EL34 and 6550. That will give a different tone again, but it's worth considering. Marshall did in fact use 5881s for a time in the mid-90s when good EL34s were not available in the sort of quantities they needed.

    6CA7s are an option too - they're essentially a US equivalent to the EL34, and will need the same kind of rebias, but the tone is bigger and more 'American' - Van Halen used them in his Super Lead, FWIW ;) - and they have better life expectancy than EL34s if long-term cost is a consideration.
     
  7. Greazygeo

    Greazygeo Member

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    Not everyone prefers EL34's....I change all my marshall's over to 6550's right away and I don't play metal....the tone is much nicer IMO....

    George
     
  8. Roccaforte Amps

    Roccaforte Amps Member

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    You'll also want to change the feedback loop
    over to 8 ohms.
    Marshall used the 4 ohm tap with 6550's,
    they have a higher drive requirement.

    While you're in there, it wouldn't hurt
    to also change the bias feed resistors
    to 220K, EL34s don't sound good
    with the 82K-150K bias feed resistors
    used on 6550 equipped models.


    6550's do sound good in Marshalls,
    especially the 2 12" combos,
    makes them fuller sounding.
    Just FYI. Doug
     
  9. joolzriff

    joolzriff Member

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    ok....ive been doing some research and the EH 6550/KT88 is roughly $100 for a quartet thats in my price range...
    they have a 6550 and a KT88....what is the difference in these 2 tubes?
    ive never owned a 6550 pwrd amp b4 so i'm totaly dumb to this...
    if u ask what tone i'm looking for its just a good rock tone not super heavy music....
    and thanx to all who have reply'd to my thread
    cheers
    j
     
  10. 85db

    85db Member

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    I'm looking at the JCM800 schematics right now. Here are the resistor values:

    For 6550: bias feed = 150k, bias supply in series with the pot = 47k
    For EL34: bias feed = 220k, bias supply in series with the pot = 56k

    Now, the conversion instructions I found on voodooamps.com say:

    "1.) Locate the 47K resistor above the bias pot and solder another 47K in parallel."

    Two 47k in parallel is 23.5k... Does this shortcut create an equivalent bias voltage? Are there any cons to doing it this way vs implementing exactly per Marshall schematics?
     
  11. QRSS

    QRSS brutalist

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    great question! maybe get better results as a seperate thread in the "amp technical info" section?

    i'm very interested as i need to convert one of mine for this very pricey reason(el34s~half price of 6550/kt88).
     
  12. drbob1

    drbob1 Silver Supporting Member

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    Has anyone used the new KT77s in a 6550 Marshall? From the sound of things they should give a more EL34 tone without the hassles of rebuilding the bias?
     
  13. QRSS

    QRSS brutalist

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    it's my understanding kt77s are a drop-in replacement for el34s. kt88s for 6550s. i'm runnin' 2 kt88s in my '80 2203 with no bias section mods. will kt77s bias in the stock range?
     
  14. stump

    stump Member

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    I put KT 77s in my friend's 1983 50 watter and they sound great. They biased up about 35mv and sound fine... better than the 6550s.
     
  15. Lou Brush

    Lou Brush Member

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    The new Tung-Sol 6550s are a good choice, and not too pricey. If you want to spend a little more, get the NOS GE 6550's as previously suggested.

    I prefer 6550s over EL34s in Marshall amps. To my ear, they sound "bigger". The 6550s also perform better than EL34s if you use the Marshall low input jack, imho.
     
  16. kurtsstuff

    kurtsstuff Member

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    I'm currently using JJ 6L6's in one of my 1980 JMP 2203's with great success!
     
  17. 908SSP

    908SSP Supporting Member

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    To my ears EL34s are the sound of Marshalls. But my ears are tuned to the late 60s early 70s and to English rather then American bands.
     
  18. 85db

    85db Member

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    bump on the resistor values.
     
  19. TAVD

    TAVD Guitar Player Gold Supporting Member

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    My 2203 has SED 6550's per Pete Cage's recommendation. The amp sounds great once the master volume is opened up but it's not what you'd call a bedroom amp.:)
     
  20. keano

    keano Member

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    What does it mean to bias the amp hotter? I have heard this but don't understand it?

    Also I heard from Myles rose at Groove Tube he prefers KT88 to 6550 as they are simialr but distortion ins't as harsh as 6550s?

    and who is Pete Cage?
     

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