motorboating

[FuzzFreak]

i am building a dlite amp and fired it up with signal but some noise. so i tried to clean up my ground and switch the OT taps to the power tubes, GOT A LOT OF NOISE, high pitch squeals. so when i switched them back the noise was quieter but now i am getting this motor boat sound whenever the master is not all the way on or all the way off. does anyone have any suggestions on what might be the culprit?

[Colossal]

i am building a dlite amp and fired it up with signal but some noise. so i tried to clean up my ground and switch the OT taps to the power tubes, GOT A LOT OF NOISE, high pitch squeals. so when i switched them back the noise was quieter but now i am getting this motor boat sound whenever the master is not all the way on or all the way off. does anyone have any suggestions on what might be the culprit?

If you are getting squealing sounds or motorboating, you may have the leads on your output transformer reversed on the anodes (plates) of your power tubes. It's a 50/50 shot that you'll get it right the first time. This is a common occurrence with ampbuilding. I usually do not cut the output transformer's leads to fit until I am sure I've gotten it right after startup, then I will go back and dress them a bit.

[FuzzFreak]

Like I said, I tried that already. When I reversed the leads the first time it just squealed really loud.

[ER]

is your speaker common grounded?

[Colossal]

Like I said, I tried that already. When I reversed the leads the first time it just squealed really loud.

Sorry Fuzz, it would have helped if I had read your post carefully.

[SoundPerf]

Motorboating can happen for a couple reasons. Since this is the first start up. I would go through all your components (caps) and make sure you have good strong solder connections. Also make sure your grounds are secure. Take some voltage measurements and see if there are any oddities.

[BobW]

Using too high a value of coupling caps or cathode caps can also cause motorboating. Recheck your values.

[heisthl]

ground the preamp side of the PI input cap and see if it persists, divide and conquer.