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Post by DonaldDemon on Mar 17, 2010 18:51:46 GMT -5
I'm about to install my new tubes and do the bias.
Which preamp tube is the phase inverter? I think it is V3 but where is that in relation to the amp? I have the 3-preamp model.
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Post by MetalHeart on Mar 17, 2010 19:46:33 GMT -5
your right  |
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Post by brocksamson on Mar 17, 2010 19:48:07 GMT -5
It is the preamp tube closest to the power tubes. I double checked on the Eurotubes website and he said 99% of the time that is where it is located. Hope that helps. Still haven't tried tackling biasing my amp on my own. Good luck.
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Post by DonaldDemon on Mar 17, 2010 20:23:19 GMT -5
That's what I figured and you're right, most amps are like that. I just wanted to make sure. I checked the manual online and it said the same thing though that was for the 4-preamp version. I assume it's the same for the 3-pre version as well. Ok....on to my first bias. I'll go say a prayer or two.  |
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Post by MetalHeart on Mar 17, 2010 20:43:08 GMT -5
oh sh1t ,sorry for my incomplete anwser ,duh  |
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Post by DonaldDemon on Mar 17, 2010 20:45:49 GMT -5
oh sh1t ,sorry for my incomplete anwser ,duh haha! it's cool brutha |
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Post by DonaldDemon on Mar 17, 2010 21:55:45 GMT -5
Ok, here's a dumb question. No matter which way I turn the bias screw, the mA go up.  They started off at 39 and now are at 44 mA. No matter which I turn the screw it goes up! I'm sure the bum power in this crappy house is not helping me out here.  |
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Post by DonaldDemon on Mar 17, 2010 22:26:38 GMT -5
Ok WTF is going on here? I just measured plate voltage at 30 VOLTS! That can't be good. IS that because I was tweaking the hell out of the screw? Do I even need the plate voltage reading? I thought all I had to do was adust the screw until it read 32 mA on the amp.
FFFFFck it, I give up. I need to go to bed, lol.
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Post by sasquatch on Mar 18, 2010 16:32:52 GMT -5
Are you sure you're turning the bias adjustment? I believe there is a similar looking pot with an adjustment screw that is actually a hum canceler. There's no way the mA should go up no matter which way you turn the bias adjustment screw. I wouldn't get too caught up in the plate voltage at this point. If you're not sure what to bias to, then you can calculate as a percentage of plate voltage. But you already know you want to be around 32mA.
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Post by DonaldDemon on Mar 19, 2010 7:26:13 GMT -5
Are you sure you're turning the bias adjustment? I believe there is a similar looking pot with an adjustment screw that is actually a hum canceler. There's no way the mA should go up no matter which way you turn the bias adjustment screw. I wouldn't get too caught up in the plate voltage at this point. If you're not sure what to bias to, then you can calculate as a percentage of plate voltage. But you already know you want to be around 32mA. Yeah I was turning the right screw. The problem was, which I figured out at 1:30 in the morning is that the QR is biased at 32ma. The Pro Mod should be around 42-45ma because of the higher wattage tube. I called Josh at Splawn and they said I got it right. I didn’t have a chance to test it so I will find out tonight at the gig! |
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Post by philm on Mar 19, 2010 8:43:32 GMT -5
...I was gonna ask this but I wasn't sure. I knew EL34s in the QRs are around 32 but I didn't think that was the case for KT88s or 6550s. Glad you figured it out.
Where'd you get your replacement Tung Sol 6550s from?
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Post by DonaldDemon on Mar 20, 2010 10:24:16 GMT -5
...I was gonna ask this but I wasn't sure. I knew EL34s in the QRs are around 32 but I didn't think that was the case for KT88s or 6550s. Glad you figured it out. Where'd you get your replacement Tung Sol 6550s from? I got them from Doug's tubes. I have dealt with them in the past and they are helpful. Real fast service and good prices. Well, I played the gig last night. Everything worked fine but I did notice the amp seemed a little muddy on the dirty channel. Does that mean I need to bias it even colder? |
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