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Hiwatt output weak

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  • Hiwatt output weak

    The preamp is fine, I added two tubes 12DW7, but I'm not getting much volume like about 1/4 of what there should be through the speaker. Voltages seem good. Tubes are good too. I've changed alot of things and've hit an impass. Could be the PI...
    Another case of "Worked great before I modded it!"

  • #2
    Don't know what you did, but you do realize that a 12DW7 has one side with substabtially lower gain than the other. So if it replaces a 12AX7, I don'r doubt you lost level.

    otherwise, apply a steady signal at the input and trace it through the amp with a scope or an AC meter and see where it goes away.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      OK, thanks. I did trace it (guitar cord into another amp) and things seem fine even into those two caps at the bias stage. May be PI. I don't know why but I nearly always have problems when I build one of those. I may just settle on the simple Ampeg design which I've always liked. For now I have a concertina (I think that's what ye call it- alike the Peavey20/Orange) into cathode follower which forcefeed the EL34s. I still have the original PC output board in there but launched the preboard in favour of 3 channels. If I bypass the CF tube driver it the same diff- low output. It's all alike the Holdon/Marshall Major approach. A bloated amp sounds bad to me.
      Our drummer is a big man and freaken loud! I'm trying to have an alternative to the 500 watt/side SS amp that I', using now. I figure the DR50 should work. I'd also like to get individual bias so I could try a NOS KT88 with a EL34 or whatever. Do you think that may work sound wise?
      I called a guy who's an hour from here, Mark Stevenson, but he's pretty busy these days. The normal tech would have a freakin' flip out if he looked at my build techniques!
      Also, Enzo I have to thank you for your help a while back with my buddy's Blues Deluxe (the Q1 thing) as after the fat cats did their repairs it now WORKS and is reliable.

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