Peavey jsx 6550

Discussion in 'The Workbench' started by vscrl1, Apr 11, 2021.

  1. vscrl1

    vscrl1 Member

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    Is it possible to put 6550’s in my jsx head? They physically fit and the amp can run el34 or 6l6 but didn’t know if 6550’s would damage it or not. I’m gonna guess it can’t but thought I’d ask. Thanks
     
  2. pedecamp

    pedecamp Well-Known Member

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    Ask Peavey :shrug:
     
  3. vscrl1

    vscrl1 Member

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    Anyone?
     
  4. XTRXTR

    XTRXTR Active Member

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    https://drtube.com/datasheets/6550a-ge1972.pdf
    page 6 of 8

    If you keep your bias no higher than around -29V (better to be lower like -30V or -31V) and assuming you have around 450 Plate voltage you shouldn't overload your current on the HT (B+) winding. 6550 run heaters at 1.6 amps vs the el34 at 1.5 amps so you will have about 200mA more current draw on the heater winding. If there are fuses on the heater it will blow 1st to protect your PT.

    I don't know the specs of your PT but it is likely it is able to handle 200mA more current on the heaters if a 50 watt, 400mA 100watt. In general most PTs are spec'd a bit higher current than what is needed for the amp as designed

    I would run them as cold as possible unless you determine the specs or as has been suggested call Peavey to be certain.
     
    Last edited: Apr 15, 2021
  5. XTRXTR

    XTRXTR Active Member

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    What exact model do you have?
     
  6. vscrl1

    vscrl1 Member

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    There’s only the 100 watt head and combo and a tiny little studio combo if I remember right. The 50 was never released.
     
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  7. XTRXTR

    XTRXTR Active Member

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    I can't find a schematic that matches what you told me. I also can't find 6550 brands that are consistent with Plate dissipation, Plate current, grid bias neg voltage, filament current from brand to brand. Given that, I am retracting what I said before. It may be due to these inconsistencies that Peavey didn't want to design for the 6550 or at least does not state it can be used in the JSX manual. Without a clear answer from Peavey I would not attempt this.

    I did try for several hours to research so I apologize for leading you on but after careful consideration I would not want to see you blow your PT or OT. 6550s are high watt output some say 26, 36, even 45 and 60 watt Max output.

    This leads me to a question. Why do you want to do this? EL34s run at 25 Watts Max. x 4 is rather loud output. Try setting the bias for your EL34s at 70%, 17.5 Watts Plate dissipation which is the idle Max, once the signal is added it gets up to 25 Watts per tube so that is going deaf loud with 4 tubes.

    I hope you find the tone you are looking for.
     
  8. vscrl1

    vscrl1 Member

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    Hey no worries man I appreciate you looking into it. The jsx can run el34 or 6l6 tubes. Has a bias switch in the back for it. I’ve read some have used 6550’s but didn’t know if it was a safe thing to do. I tried to email peavey with no luck. Guess I’ll have to call and get a tech on the phone lol. Thanks again!
     
  9. vscrl1

    vscrl1 Member

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    So I contacted peavey and they said that the transformers and everything can handle the 6550, but they said the ribbon cable for the heater supply is what worries them. A tech actually contacted an engineer there and that’s what they came up with. They said the ribbon cable might handle the voltage and it might not. They said I could try it but no guarantees. But everything else would for sure be fine. I asked about kt66’s instead and he said those should actually be fine. Suggested I try those instead of the 6550’s for sure, but he also said a pair of 6550’s instead of a quad should be ok also, so basically running the head at 50 watts with a pair. So guess I need to open the thing up and watch the connector. Maybe I need to remove the ribbon cable and hardwire? Any suggestions on gauge of wire to accommodate the extra current?
     

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