Peavey AlphaBass plate voltage?

Discussion in 'Amps and Cabs [BG]' started by Mika, Oct 20, 2005.

  1. Mika

    Mika Guest

    Nov 29, 2002
    What's the plate voltage of the power tubes of your AlphaBass head? Mine runs at a surprisingly low 330 V at the plates and 320 V at the screens.

    I was expecting something around 450 V at the plates, so I thought I'd check if someone else has measured the plate voltage of their AlphaBass.
  2. What does it matter? Seriously I don't know, but want to.

    I also have an alphabass, sweet tube amp that can even get a good slap sound. Can't get a slap tone out of a tube amp, pfffftt :rolleyes: I noticed the biggest difference in this after I got a pair of cxl-112. Funny thing is I used to hate slapping, but now it's not repulsive, it's fun. :D
  3. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I do a lot of repairs, and the power supply voltages are generally the first thing I measure whenever I open up any device. Also, the plate voltage dramatically impacts the performance of the tube with respect to output power rating and possibly distortion.

    Nonetheless, the metal plate on the bottom of my amplifier is at zero Volts ;)
  4. A9X


    Dec 27, 2003
    Sinny, Oztraya
    Email Peavey and ask. I've found their customer service to be very good.
  5. Hey Mika

    If you let me know where the plate and screens are then I could measure then and let you know. Also do you know if there are any other tubes other than a 6l6 that can be used in the alphabass.
  6. Mika

    Mika Guest

    Nov 29, 2002
    The easiest place to measure the plate and screen voltages is the ribbon cable connector on the power tube board. Looking at the amp from the front, the rightmost two pins of the connector are the plate and screen supply pins, so connect the "positive" probe tip of your multimeter there and the "negative" probe tip to ground (a screw hole in the chassis will do nicely).

    You could use 6550s/KT88s in the AlphaBass if the power transformer could handle the extra filament (heater) current drawn by the beefier tubes, but the problem is that the power tube sockets are quite tightly spaced and therefore at least KT88s simply won't fit. Another thing is that there's no bias adjustment for the power tubes, and adjustments would most probably be required if 6550s/KT88s were used.

    I emailed Peavey's tech support about the plate voltage.
  7. so what your telling me then is no.
    That the transformer would probably burn out and that there's no easy way to bias the tubes if you could even get them in there.

    I'll check my plate voltage for ya when I get a chance, I'll bet it'd be a couple of days, because when I get spare time with my gear I usually play it. But I'll try to beat peavey's response :hyper:
  8. Mika

    Mika Guest

    Nov 29, 2002
    In the stock configuration there's no way to adjust the bias. I did a simple global bias adjustment mod to my AlphaBass though. :) One per side of the OT would be better, but the single adjustment seems to be quite good enough with the matched JJ 6L6GC set I got from Eurotubes.

    Peavey hasn't responded yet, so you probably have until Monday. :D
  9. Mika

    Mika Guest

    Nov 29, 2002
    Bump for Scutterflux! Nothing from Peavey tech support yet...
  10. It might not be worth it for you, but I've found that calling Peavey is the easiest way to get ahold of them.