Sad. I thought this would have some type of wedding crasher like story. :-)
Motorboating after tube change
I posted this on Audioasylum tubes, but I'd like to increase the knowledge base, so here I am.
I own an Aikido preamp that was built for me in 2007. Since I don't use it that much, I haven't replace the tubes till now. After I changed them out, there was clearly audible motorboating emanating from both speakers. I returned each old tube to the unit but the motorboating didn't stop. The only screwup was that when initially replacing the tubes, I accidentally installed a 5751 into the spot for a 5755.
Any ideas?
Thx,
GP
I own an Aikido preamp that was built for me in 2007. Since I don't use it that much, I haven't replace the tubes till now. After I changed them out, there was clearly audible motorboating emanating from both speakers. I returned each old tube to the unit but the motorboating didn't stop. The only screwup was that when initially replacing the tubes, I accidentally installed a 5751 into the spot for a 5755.
Any ideas?
Thx,
GP
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- 16 posts total
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Jim, :-) I suspect that you looked at the tube datasheets either with an iPad or some such device having a very small screen, or without putting your glasses on :-) The two tube types have identical pinouts for their filaments (pins 4 and 5, with the center tap on pin 9). Also, note that while he said that he "installed a 5751 into the spot for a 5755," he did NOT say that he also did the opposite, as your last post seems to suggest. The differences between the two pin-outs are: For the triode section on the left (lower pin numbers): 1)Grid and cathode are interchanged between pins 2 and 3. For the triode section on the right (higher pin numbers): 1)The connection on pin 6 that is intended for the grid of the 5755 would have been connected to the plate of the 5751. 2)The connection on pin 7 that is intended for the cathode of the 5755 would have been connected to the grid of the 5751. 3)The connection on pin 8 that is intended for the plate of the 5755 would have been connected to the cathode of the 5751. I suppose that various damage scenarios could conceivably have resulted from those differences, and it's hard to be more specific without a schematic. But I would feel pretty certain that the problem wasn't a coincidence. My speculation would be that an electrolytic capacitor was damaged. It might pay to look under the chassis to see if any capacitors appear to be bulging, leaking, etc. Of course, be careful not to touch any circuit points where a residual high voltage charge might exist. Good luck. Regards, -- Al |
Al, You are absolutely correct, my bad. LOL, I wish I could blame my mistake on looking at a small screen but I cannot. I am dumbfounded for an explanation. I will just have to blame it on a brain fart moment. 5751 Pin 1: Plate (Section no. 2) Pin 2: Grid (Section no. 2) Pin 3: Cathode (section no. 2) Pin 4: Heater Pin 5: Heater Pin 6: Plate (Section no. 1) Pin 7: Grid (Section no. 1) Pin 8: Cathode (Section no. 1) Pin 9: Heater Center-Tap 5755 Pin 1 Plate, unit 2 Pin 2 Cathode, unit 2 Pin 3 Grid, unit 2 Pin 4 Heater Pin 5 Heater Pin 6 Grid, unit 1 Pin 7 Cathode, unit 1 Pin 8 Plate, unit 1 Pin 9 Heater center-Tap Jim |
- 16 posts total