Marshall Amp Forum - View Single Post - Preamp Tubes?

RiverRatt · 07-02-2009, 05:25 AM

OK, bear with me if this rambles. I just put in 19 hours at the office staring at a computer monitor, then I come home and sit in front of this one. Thank God for cheap beer and benzodiazepam. I can't remember the last time I drank Pabst Blue Ribbon, but it has to have been in college. Anyway, since I'll probably be out of it in a half hour or so, I thought I'd share the latest roll. Since I got my newly tested tubes back from Marty, my good ol' RCA side-getters are back in V1 and V2. I've been trying to get V3 and V4 dialed in, but everything I put in there sounded like crap. I had ended up with a Tung-Sol RI 12AX7 in V3 (living on the edge), and some form of Russian 7025 in V4 and I knew the amp should be sounding a lot better than it did - the tone was dominated by this harsh treble sound. Finally it dawned on me... with all this preamp rolling, I'd been neglecting the big boys. I hooked my Sperry up to the test points, and one of my fairly new GTEL34M's was cruising at around 32mV and the other was up around 39mV. I got them back to around 36.5 each, which seems to be the sweet spot, and the magic was back! I'm always telling people if their DSL isn't sounding right, check the bias, and here I go like an idiot, swapping preamp tubes every 5 minutes and wondering why it ain't happening for me. Now I'm good to go until that Tung-Sol craps out, but I think I have 2 or 3 others lying around somewhere. See you guys in a day or two.

07-02-2009, 05:25 AM	#544 (permalink)
RiverRatt Senior Member Join Date: May 2008 Location: Between Memphis and Nashville Posts: 517	Re: Preamp Tubes? - Who, What, When, Where, Why, and How? OK, bear with me if this rambles. I just put in 19 hours at the office staring at a computer monitor, then I come home and sit in front of this one. Thank God for cheap beer and benzodiazepam. I can't remember the last time I drank Pabst Blue Ribbon, but it has to have been in college. Anyway, since I'll probably be out of it in a half hour or so, I thought I'd share the latest roll. Since I got my newly tested tubes back from Marty, my good ol' RCA side-getters are back in V1 and V2. I've been trying to get V3 and V4 dialed in, but everything I put in there sounded like crap. I had ended up with a Tung-Sol RI 12AX7 in V3 (living on the edge), and some form of Russian 7025 in V4 and I knew the amp should be sounding a lot better than it did - the tone was dominated by this harsh treble sound. Finally it dawned on me... with all this preamp rolling, I'd been neglecting the big boys. I hooked my Sperry up to the test points, and one of my fairly new GTEL34M's was cruising at around 32mV and the other was up around 39mV. I got them back to around 36.5 each, which seems to be the sweet spot, and the magic was back! I'm always telling people if their DSL isn't sounding right, check the bias, and here I go like an idiot, swapping preamp tubes every 5 minutes and wondering why it ain't happening for me. Now I'm good to go until that Tung-Sol craps out, but I think I have 2 or 3 others lying around somewhere. See you guys in a day or two.