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SVT motorboat

10/18/1999 7:51 PM
Marc	SVT motorboat Help! I have a problem wit a '73 SVT that I'm not sure where to go next.... I have just recapped this SVT with 100/100 LCR's(against psycho bass guy's advice) for the original (c12 & c9(100/40 cans and I stacked 100/350V IC's for the (c11)30/600V cap and used 220K bleeder resistors. I used 100/450V for c10 and a 100/250V for c8. This SVT most closely resembles the schematic on p. 351 in Pittman's book. I also replaced two of the 5 ohm plate resistors, one was open the other read 3 ohms. I carefully diagramed all of the cap connections and replaced the caps securely. When I turned the amp on and biased it it was fine. But after playing about 4 notes on a bass it went into a mean motor boat that only stopped when I cut the standby switch. I nearly wet my pants from the vision of speaker cones flying through the grill cloth and red lining my income for the month. It didn't motorboat right off the bat, so I'm stumped. Could the stacked caps be a problem? or the increased capacitance in the second 100mfd sections of the LCR compared to the original 40mfd? Could it be just a poor ground? Any help will be greatly appreciated! Thanks, Marc

10/18/1999 7:51 PM

Marc

SVT motorboat

Help!
I have a problem wit a '73 SVT that I'm not sure where to go next....
I have just recapped this SVT with 100/100 LCR's(against psycho bass guy's advice) for the original (c12 & c9(100/40 cans and I stacked 100/350V IC's for the (c11)30/600V cap and used 220K bleeder resistors. I used 100/450V for c10 and a 100/250V for c8. This SVT most closely resembles the schematic on p. 351 in Pittman's book. I also replaced two of the 5 ohm plate resistors, one was open the other read 3 ohms.
I carefully diagramed all of the cap connections and replaced the caps securely. When I turned the amp on and biased it it was fine. But after playing about 4 notes on a bass it went into a mean motor boat that only stopped when I cut the standby switch. I nearly wet my pants from the vision of speaker cones flying through the grill cloth and red lining my income for the month. It didn't motorboat right off the bat, so I'm stumped. Could the stacked caps be a problem? or the increased capacitance in the second 100mfd sections of the LCR compared to the original 40mfd? Could it be just a poor ground?
Any help will be greatly appreciated!

Thanks,
Marc

Replies:

Marc simpler question -- 10/19/1999 3:39 AM